Fisheries the occupation or industry of catching fish or tapping other marine or freshwater resources. One of the major sectors of Bangladesh agriculture is represented by the fisheries sector. Being a deltaic land with numerous rivers and inland haors and beels (lakes and lowland areas of considerable size), and also ponds that are dug in populated areas for the purpose of bathing, washing and often as a source of drinking water, fish became an integral part of the food culture. In the past hardly any need was felt for fisheries education and research, because population was low and fish in plenty.
Fisheries now play a major role in nutrition, employment and foreign exchange earning. Fish alone supply about 60% of animal protein and about 1.4 million people are directly employed by the fisheries sector. About another 11 million people indirectly earn their livelihood out of activities related to fisheries. The production of fish was estimated to be about 13,73,000 m tons during 1996-97, of which inland fisheries contributed about 10,79,000 m tons and marine fisheries about 2,94,000 m tons. The growth rate of fish production during the last seven years averaged at 6.5% which fell short of increased demand; however, the present rate of fish production has increased to about 8 percent. A few articles related to fisheries have been presented below:
Fish farm management
Fish parasites and diseases
Fisheries education and research
Beel, Baor and Haor fishery
Kaptai Lake fishery
History Fish as a food item must have found favour with man at a very early stage of human history. The muscular tissue or flesh of a fish is made up of 60 to 82% water, about 13 to 20% protein and a greater or less amount of fat. This makes fish a food of choice not only to the Bangladeshi people but many other people of the world.
From time immemorial, people in Bengal have been harvesting this gift of nature for food. Fishing in the open waters here is a kind of hunting activity. Indeed, fishing is even older than agriculture itself and always has a major role to play in the supply of delicious and high quality protein food to people. It is because nature has had bestowed these items liberally on the land that the people of Bangladesh have traditionally been identified with fish and rice which constitute the major items of their daily diet.
Knowledge of the freshwater fish fauna of Bangladesh begins with the work of Francis Hamilton (Hamilton 1822). Francis Day published accounts of marine as well as freshwater fish fauna of the subcontinent in 1878. Subsequently numerous other works contributed to the knowledge of fish and fisheries of eastern Bengal, now Bangladesh.
In 1908, Sir KG Gupta, a member of the Revenue Board of Bengal, first investigated the possibilities of the fisheries sector in the province and as a result a Directorate of Fisheries was created and later merged with the Directorate of Agriculture in 1910. In 1917, the Directorate of Fisheries was separated but was abolished in 1923, following a recommendation of the Bengal Retrenchment Committee because of the non-availability of properly qualified persons. However, the Directorate was revived in 1941 following the recommendation of MR Naidu of the Madras province for the development of the fisheries resources of Bengal.
Shrimp cultivation has been in vogue since the 1940s in the south and southeastern coastal belt of Bengal. Calcutta was the principal consumer of most of the shrimps cultivated there. After the partition of India, the Bengal shrimp cultivators lost their Calcutta market and the practice of shrimp cultivation gradually disappeared. Thereafter, in the 1970s when the demand for shrimp grew in the world market, shrimp culture again started in the Khulna, Bagerhat, Satkhira and Cox's Bazar areas. Rearing of fish along with paddy is an age-old practice in Bengal. Use of pesticides in recent years, however, has greatly impeded fish culture in paddy fields.
Fishing from sea
Fish habitats As a result of the adaptation of fishes to definite habitats, the fishes have been divided into ecological groups of freshwater, brackish-water, marine and migratory fishes. The freshwater fishes always inhabit freshwater. Brackish-water fishes inhabit the less saline regions of the seas and estuaries. The marine fishes live in seawater and may be oceanic, living in the surface zone of open seas or neritic, inhabiting the coastal marine waters. Migratory fishes move for reproductive purposes either from the sea to freshwater (Hilsa, Tenualosa ilisha) or from freshwater to the sea (Bou Baim, Anguilla bengalensis).
The major river systems (the padma, brahmaputra and meghna) flow into the sea through Bangladesh. A fairly large number of big rivers with their tributaries and branches criss-cross the country. About 54 rivers are shared with India. According to the World Bank (1991) Bangladesh has the water resources (rivers, floodplains, ponds, beels, haors and a long coastline), diverse aquatic wealth and climate suitable for high yields and considerable increase in fish production. The low-lying, deltaic, alluvial land becomes submerged with rivers over-running their banks and with natural depressions and flats area virtually becoming broadly interconnected inland seas during monsoon. Again, during the dry season most of the rivers dry up or are greatly reduced in size and most ponds gradually disappear.
All these rivers have extensive floodplains along their course. In Bangladesh inland fisheries production is an integrated system in the rivers, floodplains and other natural depressions (beel and haor), all connected by khals (canals). The floodplains act as nutrient-rich nurseries for a large number of larval and juvenile fish species.
Bangladesh has carried out extensive water and land remodelling efforts for flood control, drainage and irrigation projects. This has drastically changed the country's water and landscape. It was necessary to mitigate the destructive forces of voluminous floodwater. But it has altered and modified the natural habitats and ecosystems of the aquatic fauna and flora of the land. These activities have already shown an adverse impact on the fishes and other living resources. In the sixties the total area of the floodplains was 6.3 million ha, which was reduced to 5.4 million ha in 1985 and to 2.8 million ha in the late eighties, thereby causing aquatic habitat obliteration, degradation and decreasing fish production (BBS 1989). The details of the impact of flood control projects on fisheries are as follows: loss of catch through loss of fish habitat, reduction in catch per unit area (CPUE), reduced fish density/abundance, increased fishing effort, reduced biodiversity, reduction in the number of migratory fish and number of migrations, disruption of fishermen's community structure, increased fish capture at regulators, reduced opportunity for mitigation measures, and reduced potential for stock enhancement (FAP 17, 1995).
Besides rivers, floodplains, beels and haors, a large number of waterbodies known as baors or oxbow lakes occur, particularly in the districts of Jessore and Khulna in the southwestern region of Bangladesh. These baors are the bends of the rivers, which were cut off from the main river courses and became isolated waterbodies.
A large reservoir, kaptai lake, with an area of about 68,800 ha of water surface, was created in the chittagong hill tracts by building a dam across the river karnafuli at Kaptai in the 1950s for generating hydro-electricity. This is the largest man-made freshwater body in Bangladesh, not connected with the open water system. It has a tremendous potentiality for fisheries development.
Besides, Bangladesh has about 12,88,222 ponds which provide a total water area of about 1,46,890 ha (BFRSS 1986) and the average pond size is 0.011 ha. These ponds are classified as small (less than 0.01 ha), medium (0.1-0.6 ha) and large (greater than 0.6 ha). Ponds are further classified as (a) cultured ponds where fish fry are released; (b) culturable ponds where fish fry are not released, and (c) derelict ponds that are not suitable for culturing fish. The distribution of ponds by category varies from one district to another. At national level, 46% of the ponds (covering 52% of the pond area) are cultured. The remaining ponds, either culturable or derelict, produce low fish yields. All the ponds have multiple uses: 63% are for washing, 25% mainly for fishing, 7% mainly for irrigation and 5% for other purposes (BFRSS 1986).
Bangladesh is bounded by the bay of bengal on its southern limit. The coastline of the country is about 480 km in length. The area of the sea that makes up the Bangladesh Exclusive Economic Zone (EEZ) is estimated to be about 1,25,000 sq km. The area is vast but the resources are limited and need proper exploration, exploitation, conservation and management for sustainable yields. Three major fishing grounds have been discovered in the Bay of Bengal (i) South Patches (6,200 sq km) lying between 20'50'N-21'40'N and 91'E-91'E; (ii) Middle Ground (4,600 sq km) lying between 20'50'N-21'20'N and 90'E-91'E; and (iii) Swatch of no Ground (3,800 sq km) lying between 21'N-21'40'N and 89'E-90'E. Of the three fishing grounds, the South Patches are found to be the most productive one, with an estimated standing stock of 11.4-16.0 m ton per sq km, followed by 10.2-14.4 m ton in the 'swatch of no ground' and 8.4-12.0 m ton in the Middle Ground. From Cox's Bazar most of the South Patches are located within a distance of 112 km and the 'Swatch of no Ground' about 19-24 km. The entire middle ground, half of South Patches and two-thirds of the Swatch of no Ground are encompassed within a radius of 129 km from Galachipa. Thus all the three fishing grounds, at least in parts are within the range of small-scale fishermen, operating 9-15 m long motorised boats fitted with 15-33 Hp engines. The potential of the Bay of Bengal in terms of fish and shrimp production is speculated to be more than 1,57,000 m ton per year.
Table 1 Area and Fish Production in different water bodies of Bangladesh (2007-08)
|Fish Source||Area of waterbody (hectare)||Production (metric ton)||Percentage (%)||Production/area (kg/hectares)|
|(I) Open waterbody|
|1. River and Estuary||853,863||136,812||160|
|4. Kaptai Lake||68,800||8,248||120|
|(II) Closed Waterbody|
|3. Shrimp Farm||217,877||134,715||618|
|Total Terrestrial Waterbody||4,575,706||2,065,723||80.59%|
|Total Marine Waterbody||497,573||19.41%|
Source National Weekly Fisheries 2009.
Fisheries resource Bangladesh possesses a wide range of fishes, prawns, lobsters and other crustaceans, molluscs, turtles and other fishery resources inhabiting its extensive marine and inland open waters. The total fish production of Bangladesh was estimated at 11,72,800 m tons (DOF 1995) in 1995. Inland openwater fisheries contributed 73 percent of the total fish production. In 1987, Bangladesh became third in world inland fish and shrimp production after China and India and produced 5,81,827 m tons of fish and shrimp (FAO 1987). Fisheries play an important role in the national economy and account for 4.7 percent of GDP, 9.1 percent of the export earnings (1995-96), 6 percent of the supply of protein and about 80 percent of the animal protein intake of its population. But the human population growth has resulted in a decline in per capita fish consumption from 36g per day in 1965-66 to the level of 20.5g per day in 1996 in place of the required 38g per capita consumption per day.
The fisheries sector provides full-time employment for about 2 million people, equivalent to 7 percent of total employment, of whom about 1.4 million people are engaged in fishing and fish farming while the rest work in fish transportation, packing and processing. Another 11 million people are involved in seasonal or part-time fishing or other ancillary activities.
Freshwater resource' In Bangladesh freshwater fish is preferred over marine species. The fish catch from the inland open water capture fishery is decreasing while the demand for fish is increasing. The fish yield from the rivers and estuaries except the sundarbans area has decreased from 207,766 m tons in 1983-84 to 173,410 m tons in 1989-90 and 138,746 m tons in 1992-93 (BFRSS, DOF). The Brahmaputra stock, Padma stock and upper Meghna stock of major carps (Rui, Catla and Mrigal) have apparently declined. At the same time, closed water culture-based fish and shrimp/prawn production has registered an increase from 117,025 m tons in 1983-84 to 192,592 m tons in 1989-90 and 237,743 m tons in 1992-93.
hilsa' is the largest single species fishery. The production of fish in ponds was 24.9% of the total catch in 1987-88. Indian and Chinese carps are the major fishes in pond culture. The fish productions from the beels and Kaptai Lake occupy 7.6% and 6.8% respectively. Catfishes are again the major fishes there, followed by the major and minor carps. Shrimp farms contributed about 4.2% of the total inland catch. Snakeheads (Taki, Shol, Gazar) and live (=jeole) fishes (Koi, Magur, Shing) are the fishes from the floodplains, followed by the major carps and catfishes. Hilsa is primarily caught from the rivers and estuaries, but small shrimps and prawns are caught from all types of water except Kaptai Lake.
The production of miscellaneous inland fishes in all types of freshwaters is significant, particularly in the floodplains, rivers and beels. Some of these fishes are Bata, Biam, Bele, Bashpata, Bacha, Bheda, Chewa, chanda, chapila, Chela, Chiring, Chital, Gutum, Kholisa, Kaikka, mola, Phasya, Pholi, Poa, Punti, Shilong, Tapashi, Tengra, etc. Many of these fishes are threatened.
There are scopes for further increase in freshwater aquaculture production through integrated farming system, fish feed development, improvement of breeding techniques and culture practices for indigenous and endangered fish species. Pen and cage culture, improved hatchery and culture system for golda, genetic improvement of cultured fish species and aquaculture development in derelict ponds, irrigation canals, borrow pits, roadside ditches and floodplains may further augment fish production.
Marine resource 'Of the three fishing grounds (South Patches, Middle Ground and Swatch of no Ground) occupying about 70,000 km of the Bay of Bengal, the South Patches are known to be the most productive. The fish stock and maximum harvestable stock in the Bay of Bengal are estimated to be as follows:
|Varieties||Standing stock (m tons)||Annual harvestable stock (m tons)|
|a. Demersal fish||200,000-250,000||100,000-125,000|
|b. Pelagic fish||160,000-200,000||30,000-60,000|
|a. Demersal fish||150,000-160,000||50,000-85,000|
|b. Pelagic fish||90,000-120,000||not estimated|
Lamboeuf (1986) estimated the biomass for the 19 major groups of marine fishes with the percentage of abundance in each depth zone of the Bay of Bengal. According to him, the shallow area between 10m and 20m is the most productive with 36% of the biomass and fish density of 8.1 m tons/km, followed by the 20-25m zone with 28% biomass and density of 6.5 m tons/km, 50-80m zone with 22% biomass and density of 4.1 m tons/km and finally 80-100m zone with 22% biomass and density of 2.9m tons/km. Thus, about 64% of the total resources are inside the 50m depth line. Lamboeuf's overall estimate in Bangladesh EEZ deeper than 10m is about 191,000 m tons of catches.
The major groups of species are Ariidae catfish 12.7%, Sciaenidae jawfish 11.4%, Nemipteridae threadfin bream 9.2%, Scombridae mackerel 6.2% and Mullidae goatfish 5.0%. These five groups account for about 44.5% of the total biomass. Similar data on commercial pelagic fish species are not available for lack of proper survey, although these are caught in large numbers.
Marine fish catches have increased from 164,882 m tons in 1983-84 to 264,650 m tons in 1994-95 and shrimp landings from 12,020 m tons in 1983-84 to 23,233 m tons in 1992-93. Fifty to 60% of the fish catch (30-40 thousand m tons) came from shrimp trawlers in 1983-84. The trawlers numbered 41 and 12 respectively for shrimp and fish in 1996-97. There were about 14,000 non-motorized boats and 3,347 motorized boats in 1983-84. The number of motorized boats increased to 8,000 in 1996-97. There were about 97 fish and shrimp processing plants in 1992-93. From the frozen seafood US$ 165.34 million (94.34%) and from other fishery products US$ 9.80 million (5.66%) was earned in 1992-93. Out of these, frozen shrimps accounted for US$ 155.48 million (90.1%) and frozen fish US$ 9.80 million (9.8%). The export of froglegs is banned since 1992-93. Dry salted and dehydrated fish, shark fins and fish maws are exported every year.
Estuarine resource The intricate canal system of tidal waterways in the estuaries of Bangladesh is rich in different aquatic species and the resource is exploited by small-scale or subsistence fishermen. The estuaries and the mangroves are the nursery grounds for the development of post-larvae of several marine shrimps where they feed and grow to juveniles before returning to deep waters of the sea for maturity and breeding. Macrobrachium rosenbergii, the freshwater giant prawn, spends life in freshwater but returns to the brackish-waters of the estuaries to hatch their eggs. So, favourable environmental conditions for brackish-water aquaculture, particularly for shrimps/prawns, are available in Bangladesh. Post-larvae of P. monodon and M. rosenbergii, locally known as Bagda and Golda respectively, are available almost round the year in the brackish-waters, providing work for thousands of larva collectors. The larvae and juveniles of fin-fishes are also available there.
At present, some 120,000 ha are under prawn/shrimp farming in Bagerhat (29%), Satkhira (19%), Khulna (19%), Cox's Bazar and Teknaf. Usually, monoculture of P. monodon in high saline waters and culture of M. rosenbergii in less saline waters are practiced. Mixed culture of Bagda with mullets (Mugil corsula and M. cascasia) or other shrimps is also in vogue. Sometimes, predator fishes (Lates calcarifer, Eleutheronema tetradactylus) and crabs enter the ponds freely. L. calcarifer, Mugil spp., Chanos chanos, etc are important fin-fish species for mariculture.
Rotation of aquaculture (shrimp, fin-fish) with agriculture (paddy) is practiced in the polders in the brackish-water tidal area in Bagerhat, Khulna and Satkhira and in mangrove areas of Chakoria and Teknaf. During high salinity period, marine and brachishwater shrimp and fin-fishes are cultured. During low salinity period, cultivation of 'aman' paddy is done. The practice is known as 'bheri/gher' culture. Some farmers even combine freshwater prawn (Golda) and other fishes (Tilapia, Carps, Thai Punti). Shrimp culture and salt production in rotation are practised in the Chittagong region.
Eleven species of crabs, belonging to the family Portunidae, Calapidae and Ocypodidae, are found in shallow coastal and brackish-waters. Of these, Scylla serrata is popular as human food. Fishing crabs by baited hooks by fishermen on boats is a common sight in the Sundarbans. Most catches are exported. In 1992-93, crabs worth US$ 3.78 million were exported.
Fish biodiversity fish and prawn/shrimp populations in the open waters (rivers, floodplains, haor, beel, lake, estuary and sea). Inland freshwaters are inhabited by over 266 species of finned fish. Shafi and Quddus (1982) recorded 148 species of fishes belonging to 36 families and 10 species of Palaemonid prawns from the freshwaters of Bangladesh, all of which are edible and popular as food. Prominent inland fish fauna include major carps (6 species including Rui, Catla and Mrigal) and minor carps and minnows (41 species including Punti, Chela, Mola and barbs), perches (31 species including Meni, Baila, Chew and Chanda), catfishes (29 species including Pangas, Boal, Magur, Shing, Air, Rita, Pabda and Bacha), shads (10 species including Hilsa representing 40 percent of the total inland catch, Chapila, Kachki and Phasya), snakeheads (5 species including Gazar, Taki and Shoal), loaches (7 species) and featherbacks (2 species including Chital). Rahman (1989) listed 260 species of freshwater fishes from Bangladesh. Bernascek et al. (1992) listed 137 species belonging to 31 families from the northeastern region of the country. Of the freshwater prawns, the genus Macrobrachium is represented by 9 species.
The rivers (Halda, Padma, Jamuna, Meghna and Brahmaputra) also support a major carp spawn fishery in which eggs, fry and fingerlings are collected to meet the demand for fish culture in ponds. Several exotic species of fin-fish, such as tilapia (2 species), Chinese silver carp, grass carp, big-head carp, black carp, common carps (all 4 varieties), Thai punti, Thai pangas, and African magur have been introduced in Bangladesh for augmenting fish production through culture in ponds and lakes.
Hussain (1969) listed 475 species of fishes belonging to 133 families from the marine and estuarine waters of Bangladesh. Quddus and Shafi (1983) identified 169 species of fishes from marine and brackish-waters, of which, 148 species belonging to 59 families are bony fishes and 21 species belonging to 10 families are cartilaginous. Major fishes are sea perches (63 species under 30 families) followed by herrings and shads (21 species under 3 families), catfishes (19 species under 3 families), and flatfishes (16 species under 5 families). Hilsa alone makes up about 60% of the total catch from the sea. Sharks are represented by 10 species. Only about 65% of the marine fishes are of commercial importance.
Marine shrimps are represented by 17 species, of which 6 belong to the genus Penaeus, 5 to Metapenaeus, 4 to Parapenaeopsis and 2 to Solenocera. However, only 5 species of shrimp, such as, Penaeus monodon, P. semisulcatus, P. indicus, Metapenaeus monoceros and M. brevicornis are commercially important. About 5 species of lobster occur in the Bay of Bengal but only two species, Panulirus polyphagus and Scyllarus nearctus are commonly found.
Fisheries cooperatives organisation of working fishermen where they pull their resources for more effective fishing and thereby better profit. Its activities include fishermen's purchasing, sale or insurance of fishing craft and gear. Fishermen belong to thousands of successful co-operatives in Japan, Norway and other countries, where the co-operative's activities include credit facilities, transport, marketing, processing of fish, etc. In Bangladesh the fishermen are mostly exploited by the middlemen in trade. Because of ready-money-lending facilities provided by these middlemen, particularly during periods of no-fishing, off-season or slack season, the fishermen hardly can get out of their clutches. The fisheries co-operatives guard the interest of poor fishermen and assist in promoting fish trade.
Fisheries cooperatives began to be formed with government support from 1960. The former Provincial Fishermen's Co-operative Society was renamed as the Bangladesh Jatio Matshyajibi Samabaya Samity (BJMSS). The objectives of the Samity are (a) to procure and supply fishing inputs to the fishermen at fair prices; (b) to issue loans to the affiliated societies for financing their members; (c) to introduce modern techniques of fishing; (d) to set up ice-plants, cold storage, net making machines, etc; (e) to arrange marketing of fish and set up processing units for exporting fish and fish products; and (f) to improve the socio-economic conditions of the fishermen.
The co-operative society (BJMSS) is organised in a traditional three-tier pyramidal structure, primary (bottom), central and apex (top). There is one national society (apex), 80 central societies and 4,300 primary societies, with the total number of members of the primary societies being about 5,00,000. Besides, there are 88 district and upzila societies with about 4,000 members. The total number of fishermen in Bangladesh was about 0.8 million in 1977. The number of the commercial fishermen increased to 1.1 million in 1988-89, of whom 60% were in inland fisheries (river, floodplain, haor, beel, baor, lake and pond) and 40% in marine fisheries. In the inland sector, the society, Bangladesh Jatio Matshyajibi Samity (BJMS) was formed after the implementation of the New Open Water Fisheries Management Policy by the government in 1986.
In Bangladesh mechanisation of fishing boats was first introduced by the Marine Fisheries Department along with introduction of nylon twine in 1957-58. Thereafter, mechanisation programme was enhanced through the Bangladesh Fisheries Development Corporation (BFDC) and the co-operative society.
At present, non-government organisations (NGOs) like grameen bank Fish Foundation, brac, caritas, and proshika are directly involved in the development of the fisher folk community. More women are now participating in fish production activities besides works like traditional net making and mending, drying of nets and fish, etc. [Mohammad Shafi]
Fish farm management the act or manner of managing, handling and controlling waterbodies devoted to the raising of fish. The principal aim of fish farm management is to achieve the maximum feed conversion ratio (FCR) and income with minimum investment of feed and care from a limited water area within the shortest possible time through proper managerial skill. The other management procedures include maintaining most favourable physico-chemical and environmental conditions of water, a well-lighted and aerated atmosphere, free from diseases, and a good soil bed, safe from inundation due to natural causes.
Fish farms in Bangladesh consist mostly of different sized ponds that can be categorized into nursery, rearing, and stocking ponds. Nursery ponds are usually less than 0.1 acre in size, rectangular, with depth 0.75 to lm. The sizes of rearing ponds vary from 0.1 to 0.66 acre, rectangular, and 1 to 1.5m deep. The stocking ponds may be 0.66 to 1.50 acres, rectangular, having depth 1.5 to 2 m.
Hatchling stocking Transported hatchlings after 15-20 minutes acclimatization are usually released at 6-8 g/decimal for single stage management, while for dual stage management 15-20 g/decimal is suggested. As management practices demand, netting should be done fortnightly for growth observation, fry exercise, feed assessment, bottom racking, and for other changes.
To maintain a constant growth of plankton as natural feed for the fish, regular water flashing with a small amount of fertiliser (urea 15g, TSP 25 g/decimal) is recommended as a daily manuring practice. Equal amounts of soaked oil cake and wheat or rice bran are suggested for broadcasting over the shore areas for morning and noon feeding. Such a daily feeding schedule should continue except on cloudy and rainy days until harvesting.
Harvesting For early crops (March-June) harvesting may be done by 4-5 weeks in case of single stage, while for dual stage the fry should be ready for thin out within two weeks of hatchlings release. An exception may be for late (July-September) crops.
Rearing pond Almost similar management practices except stocking density 1000 fry/decimal) and reduced feed intensity (5% of body weight) once daily are suggested.
Stocking pond Before stocking, the fish fingerlings need to be disinfected. The stocking rate must be related to pond size, topography, shore vegetation, bed soil category, and overall pond productivity.
Depending either on natural food or on supplemental feed the stocking composition shown in table, with respect to Bangladesh conditions, is suggested by fishery scientists. [Mohammad Sanaullah]
Fish parasites and diseases
Fish parasites Aquatic organisms living on or in the internal organs of the fishes and thriving at the expense of the host fishes. The parasites may be ecto-, endo-, pathogenic or nonpathogenic. Parasitic infections in fishes usually increase when reared in artificial conditions such as in ponds, tanks, and aquariums. High-density culture of one or a few species in artificial conditions usually results in increase of parasite population, which is seldom seen in natural system. That is why parasitic diseases are more serious in culture fisheries than in the wild fishes.
Parasites cause substantial reduction in fish production in the form of early mortality as well as nutritional loss to adult fishes. They infect almost all organs of the host with some organ specificity. The most common organs are the gills, skin, fin, intestine, stomach, kidney and muscles.
The parasites so far recorded from the Bangladesh fishes exceed 130 species. The most common and important groups are listed below:
Protozoan parasites Ichthyobodo necatrix, Ichthyophthirius multifiliis, Chilodonella cyprini, Trichodina species, Epistylis species, Zoothamnium species, Myxobolus cyprini, M. mrigala, Mitraspora cyprini, etc.
Metazoan parasites (a) Trematodes Dactylogyrus glossogobii, D. vastator, Gyrodactylus species, Neobucephalopsis species, Phyllodistomum species, Posthodiplostamum cuticola, P. minimum, Clinostomum complanatum, Opegaster species, Neopecoelina species, Genarchopsis species, Pleurogenes species, and Isoparorchis hypselobergi. (b) Cestodes Ligula intestinalis, Bothriocephalus opsarichthydis and Caryophyllids (Lytocestus species Bovienia serialis, Djombangia penetrans, and Pseudocaryophyllaeus species). (c) Nematodes Ascarididean larvae, Camallanus species, Zeylanema species, Spirocamallanus species, Procamallanus species, and Gnathostoma spinigerum. (d) Acanthocephalans Neoechinorhynchus species, Acanthogyrus acanthogysus, Acanthosentis species, Pallisentis species, and Heterosentis species (e) Crustacean parasites Ergasilus species, Lernaea cyprinacea., Argulus species, Bopyrus species, etc (f) Leech Piscicola geometra.
Fourteen parasites have been reported from the exotic fishes introduced in Bangladesh Ichthyophthirius multifiliis, Trichodina reticulata, Chilodonella cyprini, Balantidium ctenopharynogdonis, Eimeria sinensis, Mysobolus pavlovoski, Trichophrya sinensis, Dactylogyrus extensus, D. vastator, Gyrodactylus cyprini, Bothriocephalus opsarichthydis, Camallanus cotti, Argulus foliaceus and Lernaea cyprinacea.
Fish diseases Common protozoan diseases include (i) Ichthyobodiasis- caused by the flagellate Ichthyobodo (= Costia) necatrix damages skin and gills of fry and fingerling, can be prevented by pond disinfection, proper management and maintenance of same age groups of fish. Common therapy are baths in 5% NaCl for 5 minutes at intervals of 5-8 days or 200 ppm formalin solution for 1 hour; (ii) Ichthyophthiriasis 'Ich' or White spot- by Ichthyophthirius multifiliis. Common in aquarium and cultured fishes; white spots on the skin, fins and gills. The free swimming stage of the parasite can be killed by 160 ppm formalin for 1 hour, or 3% NaCl for 1 hour for 7 consecutive days. (iii) Chilodonelliasis- caused by Chilodonella cyprini attacking the skin, fins and gills causing excessive mucous secretion leading to suffocation, can be treated in the same way as 'Ich'. (iv) Trichodiniasis- by Trichodina spp. infests skin, fins and gills causing mass mortality to fry and fingerlings by severe gill damage. NaCl (15%), formalin (200 ppm) or KMnO4 (100 ppm) bath recommended. (v) Myxosporidiasis- by different genera (Myxobolus, Henneguya, Myxosoma, etc) of Myxosporidia. Gill, skin, kidney, muscle and some other internal organs are affected. Formation of white cysts is a common symptom. Pond disinfection, periodic liming and reduction of organic load are the control measures.
Common metazoan parasitic diseases are (vi) Dactylogyriasis caused by the gill fluke Dactylogyrus spp. induces gill damage. Dip in formalin (250 ppm), NaCl (3-5%), KMnO4 (50-100 ppm) or Dipterex (1.5 ppm) is effective. (vii) Gyrodactyliasis/'Gyros'- caused by Gyrodactylus spp.; the fluke attacks skin and fins causing lesions. Remedial measures are more or less similar to that of the gill flukes. (viii) Diplostomiasis/Black spot disease- caused by Posthodiplostomum cuticola, producing black spots on skin. The snail (Limnea) is the intermediate and heron (bird) is the final host. (ix) Clinostomiasis/yellow grub disease caused by the metacercariae of Clinostomum complanatum; mainly found on the skin, fins and gills, may migrate to the heart and muscles forming yellow or cream-coloured cysts. (x) Ligulosis caused by the large cestode Ligula intestinalis, induces internal organal atropy and belly rupture. (xi) Caryophyllidiasis- caused by Lytocestus indicus, L. parvulus, Bovienia serialis and Djombangia penetrans in the intestine of clarial catfish. (xii) Piscicolasis- caused by leech Piscicola geometra, affects the fish skin, fins, gill, mouth and eyes. Pond disinfection and dip in NaCl (2-3%), CuSo4 (0.5%) and acetic acid solution (1000 ppm) are the control measures. (xiii) Ergasiliasis- caused by Ergasilus spp. affecting gill tissue of carps and catfish, may result in the outbreak of epizootics. (xiv) Lernaeasis/Anchorworm infection by Lernaea cyprinacea. The female larva burrows into the fish body and grows out as a short splinter or bristle-like projections to the body surface, often penetrate the visceral cavity and damage internal organs. Weekly application of dipterex (0.25 ppm) or lindane (0.2 ppm) destroys the naupli of the parasite. (xv) Argulosis/Fish louse disease- the parasite (Argulus spp.) punctures the skin with proboscis and feeds on blood. Application of dipterex, lindane, or KMnO4 (100 ppm for 5-10 minutes) proved effective.
Non-parasitic fish diseases Fish being a poikilothermic aquatic animal easily get diseased, particularly in complex artificial environmental conditions. Disease initiates when the dynamics of equilibrium between the fish and the pathogens collapse and shifts in favour of the disease, primarily due to stress caused by environmental degradation.
The external and behavioural symptoms of fish diseases are fading of body colour and change in pigmentation, lethargy or erratic swimming and loss of balance, crowding and peeping at water surface and gulping abnormally; abdominal swelling or emaciation of body, anaemia, exophthalmia, enlarged heart, spots or lesions on skin, erosion of fin and skin and puffed and loose scales, excessive mucous secretion, loss of appetite, etc.
The internal symptoms of diseases include accumulation of opaque fluid in the body cavity, swelling or emaciation of viscera, lesions, deep ulceration, and heamorrhagic spots or cyst on internal organs.
The principal causes of fish diseases are the degradation of water quality and loss of environmental balance due to overstocking, overfeeding, water pollution, and poor pond management.
In addition to fish parasites, other fish disease producing agents/factors are microbial pathogens, environmental degradation, nutritional deficiencies and hereditary defects.
Some of the common and important nonparasitic fish diseases found in Bangladesh are 1. Viral disease- There is no report of fish viral disease in Bangladesh. 2. Bacterial disease- (i) Columnaris disease- caused by the bacterium Flexibacter columnaris which attacks the external organs like skin, gills, fins and body surface of almost all kind of freshwater fish, causing ulcerations and haemorrhages. Low O2 and accumulation of metabolic wastes are the main cause to induce this bacterial disease. (ii) Haemorrhagic septicaemia (Dropsy) caused by Aeromonas hydrophila and Pseudomonas florsescence. The common symptoms are external lesion, haemorrhage, and abdominal distension with accumulation of opaque fluid in intestine, liver, spleen and kidney. (iii) Scale protrusion is caused by a Pseudomonas bacteria. Rough and vertical scales resembling pinecones are due to the accumulation of exudate in the scale pockets. (iv) Bacterial gillrot disease- caused by the myxobacterial complex and is common among young carps. Gill hyperplasia leads to gill rots and the fish die of suffocation. Liming the pond may improve the situation. 3. Fungal disease-' (i) Saprolegniasis is caused by Saprolegnia sp. affecting freshwater fish, eggs, and hatchlings. Skin lesions lead to morbid muscle rot. (ii) Branchiomycosis- is caused by the Branchiomyces spp. Massive necrosis in the gill due to clotting in blood vessels induced by the fungal hyphae causes suffocation of the fish. 4. Nutritional disease- There are a number of nutrition deficiency diseases in fish of which vitamin C deficiency syndrome is common in carp and catfish. Fish usually obtain vitamin C from the macrophytes and algae consumed with the main food, but in intensive culture they usually develop spinal curvature- a disease usually found in carps with stunted growth and deformity; and cracked/broken head disease due to failure of ossification in head and necrosis of the skull. The disease may also cause haemorrhage beneath the chin and is common in African magur. 5. Environmental diseases- Environmental degradation may cause mass mortality and varieties of fish diseases of which Gas-bubble disease is associated with the super-saturation of nitrogen or oxygen. The gas bubbles are conspicuous in yolksac and skin, gills, mouth and even swim bladder of the fry and fingerlings and in visceral peritoneum of older fish. The affected fish turn darker in color, shows loss of balance in movement, and suffers from suffocation.
Epizootic Ulcerative Syndrome (EUS) an infectious disease characterised by large necrotising ulcers extending deep into the tissues on a wide variety of wild and farmed fish species leading almost invariably to death. It is a seasonal epizootic condition of freshwater and estuarine fish of complex infectious aetiology characterised by the presence of invasive Aphanomyces infection and necrotising ulcerative lesions typically leading to a granulomatous response. The disease outbreak is usually recorded after heavy rainfall or floods with subsequent reduction in alkalinity, chloride and salinity at the onset of the seasonal decrease of ambient temperature. In Bangladesh, the disease was first reported in February 1988 at Faridganj of Chandpur district, and in September 1988 in Faridpur. There was no known evidence of human health hazard associated with EUS. But wherever the disease occurred there was a great reduction in the fish population causing obvious nutrition effects.
Generally bottom dwelling carnivorous species are affected by EUS followed by middle layer species at the marginal water column. Many air breathing fishes (Channa punctatus, C. striatus, C. marulias, Anabas testudineus, Clarias batrachus, Heteropneustes fossilis) especially adapted to suboptimal water quality are more or less equally affected. Although the highest incidence (30%) was recorded in Channa spp.
followed by highly susceptible Puntius spp., the population of Nandus nandus and Monopterus cuchia being closely linked to muddy bottom habitat were found to have seriously declined in the most affected areas of Bangladesh. Perhaps, because of their resilient capacity, the Channa spp. can survive longer, often with striking and grotesque necrotic malformations, than the other species that succumb more readily. [Abu Tweb Abu Ahmed and Mohammad Sanaullah]
Fish marketing the act of buying or selling fish or fishery products. Preserving, transporting and marketing are three important links in the chain of fish production and consumption connecting the producer, broker, wholesaler, retailer and consumer. Fish harvesting and marketing become profitable only when the fishery products are delivered in a wholesome condition and at a price acceptable to the consumers.
Fish marketing is almost entirely a function of the private sector and operates through a complex system of village markets (hat), township markets (bazar), assembly centres, major urban wholesale and retail markets. There is a corresponding network of personnel, from buyers who may be hat traders or agents of bigger bazaar fish merchants (Bepari/Mahajan) to wholesale market commission agents (Adotdar/Paikar) who effectively control the whole system. The fishermen are compelled to hand over their catches to the trader/middleman (Adotdar/Paikar) at a price determined by the latter. The middleman is not just a trader in fish. He is often an owner of capital like boat, net, etc, which he leases out to fishermen. He may be a fisherman himself owning and operating boat, gear, employing fishermen on a fixed wage as hired labourers and enjoying unearned income depriving the actual fishermen of the benefit of their labour and production. The exploitation of the fishermen is mainly due to the monopolistic set up of the fish trade.
Despite many problems the fish marketing system in Bangladesh is quite efficient and enables fish to be moved as and when needed between market centres without excessive loss of quality. Boats are used to collect fish from the fishermen. The fishes are packed in baskets with ice. Trucks and buses are used to transport the fish to larger towns. The main problems, however are unavailability of ice, or inadequate supplies at most landing centres and the unsatisfactory state of fish market structures. Almost all markets are ill managed and unhygienic.
The Bangladesh Fisheries Development Corporation has constructed a modern fish harbour at Chittagong and fish landing centres at Cox's Bazar, Barisal, Khepupara, Patharghata and Khulna for marine catch and at Rangamati, Kaptai, Rajshahi and Dabor for freshwater catch. The harbour and all the centres are equipped with modern and hygienic facilities like berthing, auctioning, ice-plants, cold storage, freezer storage, fish vans, etc. But the traders are often less interested in using these facilities due to ignorance and self-interest. [Mohammad Shafi]
Fisheries administration In Bangladesh the term 'Fisheries Management' is commonly used to imply lease management of rivers or segments thereof, beels, baors, and other waterbodies under the ownership of the Ministry of Land for revenue (rent) earning of the government. This mode of management dates back to 1793 when Permanent Settlement Regulation I was proclaimed in India. Under this Regulation, large chunks of territories were given to landlords (zamindars) permanently. Such zamindaries or estates included not only land, but also portions of large rivers, their tributaries and distributories as well as their floodplains. Within the inundable floodplains also existed deep depressions popularly called beels. Baors or oxbow lakes are old river bends cut off from the main streams of the rivers. However, fisheries management, as understood elsewhere in the world, is the management of the populations of living aquatic resources inhabiting the waters in a manner that would sustain them perpetually after taking a harvest at a predetermined level year after year.
Portion(s) of large rivers like the Padma, Brahmaputra, Jamuna, Meghna, etc or portions of their branches as also the beels or baors falling within the territorial limits of a landlord became the private property of the concerned landlord. Each of such segments of rivers, beel or baor was termed as jalmohal or jalkor (water estate). The landlords leased out these jalmohals for maximising revenue earning. Lease periods varied from one year for a riverine jalmohal to three years for beels and baors. At present there exist about 10,000 jalmohals, which include household tanks and ponds of the erstwhile zamindars.
Administration and management by the government Through the State Acquisition and Tenancy Act, 1950 (East Bengal Act, XXVIII of 1951) the government of East Bengal (later, East Pakistan), acquired the rent receiving rights of zamindars. The Revenue Department of the provincial government thus became the owner of all jalmohals including homestead tanks and ponds of the zamindars. The Revenue Department of the erstwhile provincial government (now Ministry of Land) retained the system of administration and management of jalmohals practiced by the erstwhile landlords.
The only change that came into being was that the Department of Revenue and the attached Board of Revenue administered the leasing of jalmohals through District Collectors (now designated as Deputy Commissioner) of districts. Open auctions were held to grant lease of jalmohals to the highest bidders. Lease settlements of riverine jalmohals are given for a one-year term (one Bengali year) whereas the lease term for beels, baors and large ponds/reservoirs, is usually three years. Once the possession of the leased jalmohal is handed over to the lessee, the lessee treats the jalmohal as his private property and exploits the fish/prawn resources. Leasing of jalmohals (water states) is currently handled by the Ministry of Land (formerly Ministry of Land Administration and Land Reforms). Management of jalmohals like closed ponds of up to 20 acres in area was given to the Upazila Parishads with the provision that 1% of the income from such jahnohals is to be paid to the Ministry of Land by the Upazila Parishads. All the other open and closed jalmohals of more than 20 acres will be managed by the Ministry of Land. The leasing of riverine jalmohals was abolished in September 1995 by the Ministry of Land.
New fisheries management policy In early 1986, the Ministry of Fisheries and Livestock (MOFL) initiated a new fisheries management concept, called the New Fisheries Management Policy (NFMP). Objects of this policy were (a) to divert maximum gains from fish catching in the jalmohals to the genuine fishermen actually catching fish and thereby to eliminate middlemen lease-holders, and (b) to enforce measures to sustain fishery resources. To attain the objects, MOFL sought possession of some selected jalmohals from the Ministry of Land (MOL) on condition that the MOFL would reimburse the rent for the jalmohal to the MOL usually with an increase of 10% of the rent for each term. The new fisheries management policy envisaged the following (a) each fisherman living on the shores of each jalmohal would be given renewable licence to fish in the jalmohal in exchange for a licence fee, the amount of which will be determined by the size and capability of the fishing devices (fishing net or other gears) and number of fishermen in the fishing unit; (b) fishermen would be listed by the Upazila Fisheries Officer jointly with the representative of the National Fishermen Association. After approval by the district committee, the Upazila Fisheries Officer would issue renewable licenses to listed individual fishermen and fishing units. The Bangladesh Krishi (Agricultural) Bank was to supply credit to the listed fishermen.
Community based fisheries management (CBFM) The object of the project, initiated by the Department of Fisheries (DOF) in 1995, was to promote a more equitable distribution of benefits from fishery operations in a waterbody through the ecologically sustainable use of open water fisheries. DOF works in collaboration with large non-government organisations. The partner NGOs are to (i) develop and strengthen fishermen's organisations and develop appropriate institutions for co-management; and (ii) improve the livelihoods of poor fishermen including developing alternative income sources for them. At present, 20 waterbodies are being managed under CBFM.
Fisheries management by other owners Several other government agencies own waterbodies. Of such owners, the Department of Forests exercises ownership over large and small rivers, canals and creeks within the Sundarbans Reserve Forest. The administration and management of fishing in these waters are confined to collection of tolls, taxes and rents from fishermen and fishing boats entering and passing through the reserved forest area by the Forest Department. Fishermen and fish traders are to pay (i) a Boat Licence Certificate (BLC), (ii) a dry fuel consumption fee (DFC), and (iii) a levy on different varieties of fish, prawn and dry fish in their boats at different rates. The Forest Department thus earns a good amount of revenue from fishing and fish transportation activities. The bangladesh water development board and the Department of Roads and Highways (R&H) create waterbodies such as canals and ditches. Such waterbodies are leased out through open auction by the owner agencies mainly for fish culture. Bangladesh has yet to undertake fishery resources management on modern scientific principles to replace the fisheries management currently being practised. [M Youssouf Ali]
Fish laws After the partition of British India in 1947, the headquarters of the Directorate of Fisheries was shifted from Kolkata to Dhaka when the Directorate had to look after only fish marketing and fishermen's welfare. Since then the directorate started considering other aspects, such as conservation of fish, control of the fishing period, mesh size of the gears, etc and framed a set of laws which directly and positively influenced the development of the fisheries sector.
The East Bengal Protection and Conservation of Fish Act was passed in 1950 by the provincial legislative, with a view to conserving young and brood stocks of specific species of fish and restricting certain fishing activities. The Act, which is still in force, empowers the government to promulgate laws and regulations to ensure conservation of fishery resources. The Act was subsequently amended in 1963, 1970, 1982 and 1985-1988.
The salient features of the Act are as follows fish means all cartilaginous and bony fishes, prawns, shrimps and other edible crustaceans, amphibians, tortoises, turtles, molluscs, and echinoderms; capture of fish by fixed net, cage, traps, etc put across the river, canal and outlet khal or beel is prohibited; such fixed structures may be removed or seized; construction of temporary or permanent weir, dam, bund, embankment except for flood control, drainage and irrigation is prohibited; capture of fish by use of explosives, gun, bow and arrow in inland and coastal waters is prohibited; destruction of fish by poisoning water or by polluting water by industrial wastes or other means is prohibited; capture of shoals of fry of Shol, Gazar and Taki (snakheads) or their broods in the river, canal, khal and beel from 1st April to 31st August, except for the purpose of culture, is prohibited; for the purpose of culture Rui, Catla, Mrigal, Kalibaus and Ghonia of any size may be caught in 27 selected rivers and khals after obtaining a licence by the payment of prescribed fees to the District Fishery Officer; except for the purpose of culture, nobody is permitted to catch (i) Rui, Catla, Mrigal, Kalibaus and Ghonia below the size of 23 cm from July-December, Jatka (young Hilsa) and Pangas from November to April every year; and (ii) Shillong and Air below the size of 30 cm from February to June every year; fishing with the help of current net/mosquito net having mesh-size below 4.5 cm is prohibited; first-time violators are to be jailed for 6 months or fined Taka 500 or both; second-time violators are liable to be jailed for one year or fined Taka 1000 or both; violators may be arrested without warrant; all magistrates, sub-inspectors of police at upazila level, Deputy Rangers of the Sundarbans belonging to the Forest Department and Upazila Fishery Officer are empowered by the government to implement the Act. Nobody is permitted to appeal against a step taken under the Act.
The Marine Fisheries Ordinance, 1983 The ordinance is generally known as the Marine Fisheries Rules, 1983, which were amended in 1992. The salient features of the rules are as follows a Director, posted at Chittagong, shall be responsible for the survey, conservation, development and management of marine fisheries resources, enforcement of laws and licensing, etc; an annual fishing licence (January-December) is compulsory for every fishing trawler and mechanised boat and is obtainable after the payment of prescribed fees (Taka 200-1,800).
Non-mechanised boats were brought under licensing in 1995. Every licence-holder must furnish data on every catch and the sale of the fish to the Director at Chittagong. Entry of foreign trawlers in Bangladesh waters is banned. The government reserves the right of permitting to any trawler or person for scientific investigation in Bangladesh waters; an illegal trawler will be seized along with its crew.
The Tank Improvement Act, 1939 Generally, the act is known as the Pond Development Act, 1939, which was amended in 1986. Under the Act, any unused pond may be brought under fish culture by the upazila nirbahi officer (UNO) after issuing proper notice and time to the owner of the pond.
The Fish and Fish Products (Inspection and Quality Control) Ordinance, 1983 Generally, the ordinance is known as the Fish Quality Control Act, 1983, which was amended in 1989. The salient features of the ordinance are as follows Freshly caught fishes and shrimps may be processed in processing plants which fulfil the necessary terms and conditions and after payment of prescribed fees. During processing use of any element affecting the quality is prohibited. Export is allowed only after receiving a good condition certificate from the government.
Shrimp Culture Tax Act, 1992 According to this Act the government can impose tax on a shrimp culture area if anybody is benefited by the construction of an embankment and water control structures and the excavation of khals. [Mohammad Shafi]
Fisheries education and research
Education With the increase of population and depletion of fisheries resources due to loss of fish growing land to agriculture, siltation, etc it became necessary to develop an institutional set-up for fisheries education and research. In order to meet the demand for fisheries education and to translate the vast potential of fisheries in Bangladesh into real wealth, the Faculty of Fisheries was established as one of the six faculties of the bangladesh agricultural university, Mymensingh in 1967. The faculty of fisheries with its four constituent departments, a fish farm, and a field laboratory, is responsible for training, education and research in various aspects of fisheries. The rationale for setting up the faculty was to produce high quality fisheries graduates equipped with modern knowledge in different fields of fisheries science and to develop the country's fisheries sector through research and dissemination of technology. The Faculty of Fisheries confers the Bachelor's degree, BSc Fisheries (Honours) and has four departments-Fisheries Biology and Genetics, Aquaculture, Fisheries Management, and Fisheries Technology. These departments offer a wide range of courses covering all aspects of fisheries, both basic and applied.
In all the major state run general universities of the country, such as the university of dhaka, university of rajshahi, university of chittagong, and Jahangirnagar University, there are zoology departments where a major thrust area is fisheries. Recently, the University of Dhaka has established (1998) a separate department of Aquaculture and Fisheries. Chittagong University has a specialized institute called the Institute of Marine Sciences that emphasizes on marine fisheries. Khulna University has a separate discipline named Fisheries and Marine Resources Technology Discipline.
Research Basic research on fisheries is mainly carried out by the university departments. The Faculty of Fisheries at Bangladesh Agricultural University carries out research in various areas through its four constituent departments. The Department of Fisheries Biology and Genetics focuses on fish fauna, reproductive biology, conservation and management of brood stock, fish breeding, and chromosome and gene manipulation. The Department of Aquaculture deals with fish culture, nutrition and fish pathology; the Department of Fisheries Management offers studies on population dynamics, economics and marketing, biostatistics, and fish health. The Department of Technology deals with processing and preservation, pre- and post-capture technology, fish microbiology and quality of fish products. All the general universities have zoology departments with research programmes at MSc, MPhil, and PhD levels in fisheries subjects.
Applied research on fisheries is carried out in a number of R&D institutions, the foremost of which is the Bangladesh Fisheries Research Institute under the Ministry of Fisheries and Livestock. The Bangladesh Fisheries Research Institute was established in 1984 on the campus of the Bangladesh Agricultural University. The institute has several stations and units such as Freshwater Station on the Bangladesh Agricultural University campus, Riverine Station at Chandpur; Marine Fisheries Technology Station at Cox's Bazar; Brackish-water Station at Khulna; Marine Fisheries Survey and Management Unit at Chittagong; and Marine Fisheries Survey and Management Unit at Cox's Bazar. [Gulroo Begum Sufi]
Cage culture culture of aquatic organisms in cages. Generally carps, catfishes, murrels, etc are cultured in cages. Molluscs such as oysters and clams, and crustaceans such as prawns and shrimps are also cultured in cages. Cage culture is generally done in open waters like bays, rivers, canals, haors, and floodplains. The cage is made with nets in such a way that it looks like an inverted mosquito curtain. Normally nylon threads are used for making cages, which may be used for 2-3 years. The nets may also be made of iron wires, which may last 4-5 years. Sometimes cages are made with bamboo. The shape may be rectangular or square, and depends mainly on the place where the cage is to be set. Normally the cage is 1-2 metre long, 1-2 metre wide and about one metre deep. The cage is to be set in a place where there is water for at least 3-6 months.
In Bangladesh, species like Tilapia nilotica, Labeo rohita, Catla catla or Cirrhina mrigala are cultured as composite culture in cages. The other species, which are often cultured in cages, include Puntius spp., Anabas testudineus, Clarias batrachus, C. gariepinus, Channa striatus, Macrobrachium rosenbergii, and Penaeus monodon. CARE-Bangladesh has undertaken a project called CAGES (Cage Aquaculture for Greater Economic Security). This is a development project in the Agriculture and Natural Resources Sector of the government. CAGES is conducting experimental cage culture in the Meghna-Gomti River in Baushiaghat and Gojaria thana of Munshiganj district. Cage culture is being practiced in certain areas of Dhaka, Mymensingh, Comilla, Jessore, Sylhet and Barisal districts. [Abdus Salam Bhuiyan]
Mixed fish culture culturing together several different species of fast growing and compatible fish of different feeding habits, which usually take food at different strata of a waterbody. Mixed farming is also known as polyculture or composite culture. The basic principle of mixed fish farming is to stock and rear together some species of fish in the same waterbody like ponds, lakes, ditches, etc so that all the ecological niches are occupied by fish and make it possible to exploit all requisites of life available in the waterbody. Typical examples of mixed fish farming in Bangladesh are the culture of Indian major carps, viz, catla (Catla catla), rui (Labeo rohita) and mrigal (Cirrhinus mrigala); and the culture of indigenous small fish species like mola (Amblypharyngodon mola), punti (Puntius chola), kholisa (Colisa fasciatus), etc. Recently, some exotic carps like silver carp, common carp, grass carp, some catfishes, tilapias, prawns, etc are being cultured in ponds so as to obtain higher production per unit area of waterbody through mixed farming.
In mixed farming, the improvement of pond oxygen regime occurs due to the presence of silver carp, which consumes excess algae. Concentration of excess algae creates depletion of oxygen in the pond, but consumption of excess algae by silver carp helps improve the pond environment. Some bottom-feeders that feed on organic debris also improve the oxygen condition in the pond. Grass carp cleans the pond weeds and aquatic vegetation by consuming them. Besides, some fish feed on the excreta of other fish, eg, common carp feeds on the excreta of silver carp. Thus mixed farming of some fish has the added advantage of improving the aquatic ecosystem.
Before the practice of mixed fish farming, the food habits of the fish species to be stocked and the amount of the natural food available in the stocking pond must be assessed. The ratios among the different species of fish and their stocking densities are of great importance in polyculture. According to Fisheries Research Institute (FRI), Mymensingh, a seven-species mixed fish farming has recently proved successful. This includes silver carp, catla, rui, mrigal, grass carp, mirror carp, and sharpunti at the stocking rate of 1200, 300, 300, 300, 300, 400, and 1200 fish fry/acre respectively, with a size range of 5-7 cm.
For successful mixed fish farming, there are some pre-conditions, such as (i) selection of suitable and compatible species of fish, (ii) appropriate time of releasing fry, (iii) appropriate number and size of fry, (iv) adequate natural food, (v) supply of supplemental feed, (vi) supply of chemical and organic fertilisers, (vii) harvesting and marketing of fish, etc. The fish for which there is a demand in the market should be cultured. For mixed farming of large-sized fish like Indian major carps and Chinese carps, a minimum pond area of 0.2 acre has been found suitable. On the other hand, small waterbodies called 'miniponds' below 0.2 acre are suitable for the mixed culture of indigenous small fish like mola, punti, chapila, dhela, kholisa, etc.
Monoculture rearing of a single fish species in a waterbody through scientific management. Generally, herbivorous as well as carnivorous fish species such as catfishes, carps, tilapia are selected for monoculture through which there would be better utilization of primary production of the waterbody and the supplied supplemental feed.
There are innumerable seasonal impoundments such as small ponds, tanks, ditches, canals, depressions, etc in rural Bangladesh, which are not suitable for the polyculture of large-sized fishes and often retain water for 5-6 months, and are used for the monoculture of some small fish species of short life cycles like mola, dhela, chapila, kholisa, punti, tengra, pabda, etc. [Md. Golam Mustafa]
Paddy cum fish culture Paddy fields are exploited for fish culture in two ways-fields that are used as trap, no stocking is made here; it is a capture system; and those used as ponds where fish stocking is made deliberately; it is a culture system. On the other hand, in relation to paddy cultivation fish culture may be one crop of rice and a crop of fish being harvested every year; one intermediate crop of fish between planting and harvest of rice, and culture of rice and fish together. However, in all cases fish is the secondary crop. Penaeid shrimp farming following paddy cultivation in ghers is an old traditional practice in certain areas of Bangladesh. The word gher means enclosure or an enclosed area. Encirclement of land along the banks of tidal rivers with low earthen dikes called 'baandh' or 'bheri' to control the free entrance of brackish-waters was the usual traditional practice in the southwestern district, Satkhira, and the adjacent 24 Parganas of West Bengal (India). The flow of water into the ghers is controlled by small wooden sluice gates. From February till April, sluice gates are opened to allow entry of riverine brackish-waters carrying post larvae of different shrimp and finfish. The shrimp and finfish fries thus trapped inside ghers are allowed to grow until they attain harvestable size.
During monsoon (June-September), the rainwater dilutes brackish-water inside the ghers. Sluice gates are opened periodically to drain out water from ghers. The monsoon rains and successive draining of water leach out salinity and make the land inside the ghers fit for paddy cultivation. Farmers then raise a crop of paddy and fish between late July and December. Water in the deeper canals inside ghers is retained in order to allow stocks of wild finfish and shrimp fries to take shelter.
Thereafter, rainwater is allowed to accumulate and then drain out to gradually remove salinity in the field. In the process, water in the deep canals holding shrimp and finfish juveniles also loses salinity.
Simultaneously, the land is prepared for planting Aman paddy seedlings. Ploughing is not generally done in lands used for brackish-water shrimp farming. After the plantation of transplanted Aman seedlings, rainwater is allowed to accumulate inside the gher to flood the land to a depth of 60-100 cm. At this time, shrimps and finfishes retained in the deep canal feed and grow in the inundated land until harvested. At the same time, post larvae of giant freshwater prawn, fingerlings of common carps and tilapia are liberated in the inundated paddy fields. Thus, during the monsoon paddy-cum-fish culture is practised. The harvesting time of finfish is between September and early December; freshwater giant prawn (golda chindi), Macrobrachium rosenbergii, is harvested around October-November. Preparation of ghers for the next round of brackish-water shrimp farming is taken up again in December after the finfish and prawn have been harvested and the rice harvest is also completed by November. The practice of natural stocking in ghers has been gradually replaced by artificial stocking of desired bagda shrimp. [Nuruddin Mahmood]
Pen culture fish culture in small enclosures. In typical pen culture, the sides of the enclosure are constructed by mesh or netting fitted to wooden poles, the bottom being the natural beds (soil bed). Pen culture originated in the inland sea areas of Japan in the early 1920s. China adopted it in the 1950s for rearing carps in freshwater lakes and later it was introduced in the Philippines between 1968 and 1970 in order to rear milk fish (Chanos chanos). The commercial culture of fish in pens is a relatively new practice.
In Bangladesh the concept of pen and cage aquaculture for commercial fish production was included in the national development programme in 1977. During 1981-1984, experimental pen culture activities were undertaken in a few places, viz Bahadurpur baor, Nabaganga River and Saganna baor in Jhenidah, and Dhanmondi and Gulshan lake in Dhaka city. In Saganna baor, 1,890 kg of fish was produced from a 0.5 ha pen after 8 months of polyculture of carps with supplemental diet. Silver carp grew to 350 g; catla, rohu, and mrigal grew even less. In 1981, a 0.25 ha pen of 100' 25m size was installed in Dhamnondi lake and stocked with five species of carps viz silver carp, grass carp, catla, rohu and mrigal of 4.0-5.6g size at a density of 38,600 individuals/ha. The fish reached an average weight of 186g in 6 months, and a total of 15,195 kg fish was harvested.
Polyethylene knotless net, bamboo fence (bana), bamboo poles, tire cord, and nylon cord are considered suitable materials for pen construction. Polyculture of Indian major carps and Chinese carps at a stocking density of 20,000/ha was found suitable for culture in a profitable manner. Macrobrachium rosenbergii, Oreochromis spp., Pangasius sutchi and P. pangasius were also found suitable for culture with carps in pens. Fingerlings of 10 cm size and 3 months old are found optimum for stocking. Economic analysis reveals that a net profit of about Tk 70,000 (about US $1,300) is possible from an irrigation pen of 0. 50 ha within one cycle. [Khan Kamal Uddin Ahmed]
Artemia culture Artemia is a planktonic crustacean about 12 mm in length and adapted to living in highly saline waters. Its cysts have become the most widely used live food item in the shell and finfish hatcheries throughout the world, because its nauplii are readily taken by aquatic animals under nursery conditions without fouling the aquarium water. Artemia cysts can be kept stored on the shelf in an anaerobic condition for several years, and at the times of need the nauplii are easily obtained by hatching them in seawater. The cysts are commercially produced in certain countries and are marketed in sealed containers.
Artemia is found all over the world in a wide variety of hypersaline habitats, eg coastal salt pans, and inland salt lakes. Its distribution, however, is not continuous, it does not occur naturally in Bangladesh and in SE-Asia. The factors that limit its presence in Bangladesh are the salinity, which has to be sufficiently high (mostly above 100 ppt) to exclude the presence of predators, and the water temperature, that must allow development and reproduction. Indeed Artemia needs active or passive dispersion vectors for its cysts, such as wind, water birds, and man. In an optimal environment the habitat is colonised at an astonishing rate; mature females reproduce ovoviviparously, can produce 200-300 free-swimming nauplii at every four days' interval. These nauplii grow to adults in less than two weeks.
Since Artemia does not occur naturally in Bangladesh; its propagation through inoculation is the only answer to go for commercial production. There is a distinct dry season in Bangladesh for about five to six months (November-April); also there are about 17000 ha of temporal salt pans in this country, some of which may be modified for the integrated production of salt and the culture of Artemia. It can survive in the extreme saline conditions of earthen salt pans, it grazes on phytoplankton, detritus, and can take low cost feed such as rice bran, etc. After proper modification and biological management, the potential yields of Artemia from the modified pond integrated with salt production in Bangladesh are estimated to be satisfactory.
Workers at the Institute of Marine Sciences, University of Chittagong have been conducting experiments in Artemia culture since 1976, and the first successful inoculation of Artemia led to the production of biomass and cysts in the year 1989 in a coastal salt pan of Bangladesh. Subsequent attempts with different geographical strains offered encouraging results for Artemia culture in Bangladesh. [Nuruddin Mahmood]
Brackish-water aquaculture raising fish (including molluscs and crustaceans) in waters having low salt contents. Brackish-water aquaculture constitutes an expanding farming activity and playing an important role in the overall fisheries development efforts in Bangladesh. Marine and estuarine shrimp, fish, and crabs are the farm products. Penaeus monodon is the primary target culture species, while several fish species, heterogeneous shrimp, and crabs are the byproducts. Amongst the coastal districts, brackish-water aquaculture is practiced in Satkhira, Khulna, Bagerhat, Cox's Bazar and Chittagong. Because of the turbulent nature of the Bay of Bengal, the wide fluctuations of tide and salinity, and the absence of sheltered places, eg lagoons or brackish-waters adjoining the sea, mariculture has not so far developed in Bangladesh. Extensive areas in the coastal belt are, however, under brackish-water aquaculture, which is mainly shrimp based. In the seventies, when brackish-water aquaculture started as an important economic activity, the culture system was quite primitive.
From the early eighties, the government of Bangladesh has been endeavouring to improve the traditional culture practices. Brackish-water aquaculture is mostly practiced in low-lying tidal flats within polders of Water Development Board. The polders were originally constructed to protect the agricultural land from brackish-water. In many places, the farmers themselves have constructed dykes along the riverbanks for the dual purposes of agriculture and aquaculture. The total area under aquaculture is about 2,92,378 ha of which about 48% is under brackish-water aquaculture.
In 1993-94, the total fisheries production was 1.087 million m tons, of which about 24% was of aquaculture origin. Brackish-water farms produced 39,477 m tons of shrimp and fish, of which shrimp accounted for about 25,000 m tons (204 kg/ha). In the total aquaculture production, brackish-water farms contributed about 15% by weight and an estimated 38.5% by value. The total cultured shrimp, as brackish-water products accounted for about 80% by volume and about 84% by value. In all shrimp taken together (100,538 m tons), brackish-water farm-raised shrimp accounted for about 25% by weight and about 50% by value. In Bangladesh shrimp is the third-largest foreign exchange earning commodity, following garments and jute. It is estimated that about 2,200,000 ha of the tidal lands are suitable for brackish-water shrimp culture.
Although intensive brackish-water shrimp culture is not practiced in Bangladesh, there are extensive traditional culture practices in southwestern and the southeastern regions of the country. The farmers traditionally culture shrimp and fish by entrapping them in low-lying coastal areas with the construction of embankments.
Shrimp culture is generally practised in rotation with rice or salt in some areas, and also as a single crop in other areas. Crops of shrimp farming and cropping pattern are different in both the regions, since the southwestern districts have lower salinity round-the-year compared to the southeastern region. In the southeastern region, a single crop of shrimp/fish only or a double crop of shrimp/fish and salt is produced, while in the southwestern districts, two major cropping patterns are practised, eg, shrimp/fish and rice, and shrimp/fish alone. The major species of shrimp that are cultured are the Penaeus monodon in the southeastern region, and P. monodon and Macrobrachium rosenbergii in the southwestern region. [Yusuf Sharif Ahmed Khan]
Oyster fishery culture of edible bivalve molluscs, the oysters, in shallow warm waters. Besides oysters, the fishery includes other bivalves such as mussels, clams, and scallops. They are filter feeders and have a common life history pattern in which the early stages are planktonic. For culture, poles are planted in shallow coasts with a gentle slope. Oyster spats collected from the natural breeding grounds are transferred to the growing site where they are hung on the raft, and are marketed when they are 4-7 cm in size after 7-8 months of culture.
In Bangladesh, some species of Ostrea and Crassostrea are known to occur and may be utilized for culture. The coastal area with high tidal amplitude, sufficient tidal current, a plain low-lying tract of muddy loams, fringe of mangrove vegetation, pollution-free zone, suitable salinity range, and high plankton abundance seems to be suitable for their culture either using stakes, poles, racks, and trays in the shallow areas or floating rafts and long lines in deeper waters with a very low capital involvement. Although not scientifically cultured, pearl produced by freshwater clams are regularly collected in certain areas in Bangladesh. [Nani Gopal Das]
Beel fishery fish and other edible resources collected or harvested from the beel, a type of naturally formed wetland. Beels are the depressions with at least a part of the area permanently inundated by water. They mostly occur in between the rivers and canals. Beels are usually saucer-shaped depressions of marshy characters. In the rainy season they are full of water and resemble lakes. In other seasons the water level goes down and sedges make them look like marshes. Some smaller beels dry up completely in winter and the land is used for cultivation. Surface run-off and small channels or canals that connect them with rivers feed them all. Bangladesh has a total of about 4,500 beels covering an area of about 11,41,161 ha.
There are a large number of beels in the northern part of the country. Dinajpur district has no large beels. Rangpur district has three- Tagrai, west of Kurigram town; Lunipukur, west of Rangpur town; and Bad beel in Pirganj upazila. In Bogra district there are two large beels, the Nurail and the Keshpathar. Along the Mahananda River there are several beels, of which Baitia in Bholahat upazila is the largest. The chalan beel system is very large and consists of a number of beels connected by channels to form more or less one continuous sheet of water during the rainy season. The beel zone comprises areas covering Singra and Gurudaspur upazilas of Natore, Chatmohar, Bhangura, and Faridpur upazilas of Pabna, and Ullapara, Raiganj, and Tarash upazilas of Sirajganj districts. The present area of the beel is about 26,000 ha.
In the southern part of the country there are far more beels than in the northern part, and also a number of baors. The larger beels in this area are Kamladaha, Boyra, Boalia, Taleria, Dakatia, Pabla and many others. In the central part of the country larger beels are few in number. Mention however, may be made of the Hamil beel of Madhupur, and the Rajdhala beel of Netrokona district. Beels are also scanty in the greater Sylhet areas, where many haors exist, and only small seasonal beels are found with water in the rainy season. In the Chittagong region large beels are even fewer. The well-known Gumai beel has been drained but occasionally floods quite deeply.
The beels are generally richer in fishes than the rivers. These waterbodies provide nearly 6.88% of total inland fish production. The overall production of beels is rather low, only about 560 kg/ha, and therefore the contribution of beel fishery at the national level cannot be said to be significant (table). This is due to the fact that little or no attention has been paid towards the better management of the beel fishery system. Various methods and management systems were tried in the past to economically manage the beels. These included leasing fishing rights to co-operatives or leasing to fishermen through open auctions. These efforts were not proved to be very effective as they were exploited by non-fisher middlemen and other agents.
Many different freshwater fish species are available in the beels during the rainy season, while during the dry winter and summer, the central zone acts as a sanctuary for the fishes. Extensive fishing is done all the year round. The most common fish species found in different beels are as follows Mola (Amblypharyngodon mola), Koi (Anabas testudineus), Khoira (Badis badis), Sarpunti (Puntius sarana), Punti (Puntius sophora), Titpunti (Puntius ticto), Catla (Catla catla), Garua (Clupisoma garua), Bacha (Clupisoma murius), Magur (Clarias batrachus), Chela (Chela baciala), Khalisa (Colisa fasciata), Banspata (Danio devario), Bacha (Eutropiichthys vacha), Singi (Heteropneustes fossilis), Ayeer (Mystus aor), Sonatengra (Mystus vittatus), Tengra (Mystus tengara), Bansha Tengra (Mystus cavasius), Gochi (Mastacembelus pancalus), Baim (Mastacembelus armatus), Tara Baim (Mastacembelus aculeatus), Chital (Notopterus chitala), Pholi (Notoperus notopterus), Bheda (Nandus nandus), Pangus (Pangasius pangasius), Pabda (Ompok pabda), Kani Pabda (Ompok bimaculatus), Gojar (Channa marulius), Shoal (Channa striatus), Lata (Channa punctatus), Darkina (Rasbora daniconius), Chapila (Gudusia chapra), Phasa (Setipinna phasa), Boal (Wallago attu), Mrigal (Cirrhinus mrigala), Raik (Cirrhinus reba), Rui (Labeo rohita), and Kalbaus (Labeo calbasu).
In some beels fish culture is being practised by stocking the beels with fish fingerlings composed of silver carp, catla, rui, mrigal, grass carp, rajputi, and common carp. Although capture fishery is the common practice, in some beels isolated large and deep areas are separated by constructing high dikes around them and are used for intensive captive fishery. [SM Humayun Kabir]
Baor fishery fishery of the abandoned bow-shaped bend (channel) of rivers. Fish culture in baors is a practice by which an open water fishery is converted into culture fishery by screening the inlets and outlets. A number of baors from the capture fishery yield less than 200 kg/ha/year on an average in comparison to a culture based fishery raising more than 500 kg/ha/year. The capture fishery is entirely based on small indigenous fish whereas the culture fishery is stocked with 90% carp fingerlings. More than 50 species of indigenous fishes belonging to 31 genera, 20 families and 11 orders could be found in a boar.
All the baors are now under a constant fishing pressure. The construction of dams and other flood control structures have reduced the natural recruitment and contributed to stock depletion. Fishing gears which are used in the baors include gillnets, liftnets, longline, seine nets, cast nets and also various box-like fishing traps. In Bangladesh, baors are usually found in greater Jessore and Kurigram districts. Some of the important baors of the country are Bukbhara, Kannadah, Baluhar, Joydia, Sirisdia, Habullah Rustampur, Sonadia, and Bahadurpur. The total catch area in the baors is about 5488 ha and the annual production is about 2,460 m tons.
Haor fishery capture of fisheries items from haors, which are natural quarries, mostly encircled by highlands or hillocks, found in the northeastern part of Bangladesh. Haors are generally richer in fishes than the rivers. Generally these vast low-lying areas (haors) are inundated during the rainy season and become confluent with riverine floodwaters. Fishes are not found in high concentrations during the monsoon due to increase in water areas.
The haors serve as the natural brood stocks of many indigenous fishes including carps. With the advent of the dry season water recedes, the relatively elevated parts of haor area begin to dry when paddy, mostly the boro crop, is raised on the dried upland areas. The relatively depressed areas, however, remain under water where fishes take shelter. These submerged depressions are known as beels. Almost all the freshwater fishes are available in haors. In Bangladesh, haors are usually found in Sylhet area. [Md Altaf Hossain]
Kaptai Lake fishery The Karnafuli reservoir, popularly known as the Kaptai Lake, situated in the SE part of Bangladesh, is one of the largest man-made freshwater lakes in the world and the biggest in southeast Asia. Maximum and mean depths of the reservoir respectively are 35m and 9m with annual vertical water fluctuations of 8.14 m. The reservoir was formed through damming the main course of the river Karnafuli at the vicinity of Kaptai town in Rangamati Hill District in 1961. As a result of damming, the river Karnafuli and its four other tributaries (Chengi, Mynee and Kassalong in the North, and Ryangkong in the South) with their surroundings became submerged and formed the vast H-shaped water body having an water area of about 58,300 ha at mean supply level. The previous Karnafuli River is not easily traceable now.
Like most of the hydroelectric reservoirs of the world, fishery in the Karnafuli reservoir is a secondary enterprise. Most parts of the lake spread over the valleys of the hills which were once covered with patches of dense natural forests and were partially made clear before submergence. As a result, the shorelines and the basin of the lake are uneven due to hillocks and are strewn with remnants of teaks and other timber logs obviating easy fishing operations. Fishery in the reservoir is of the multi-species and multigear type and supports more than 4000 small-scale fishermen.
Inspite of some unfavourable physico-chemical conditions, such as higher and uncontrolled water depth, and wide variations in the vertical water temperatures, the reservoir is quite rich in indigenous diversified fish fauna. About 73 species of fish under 47 genera and 25 families, and 2 species of prawn have so far been recorded from this reservoir. Of the fish species 66 are indigenous and the remaining 7 are exotic. The population structure was different at the beginning, but due to change from a riverine to a lacustrine environment, a number of indigenous species disappeared or changed greatly in number and abundance. On the other hand, a number of exotic species have been introduced either accidentally, or for enhancing fish production. At present 31 species are commercially harvested and the rest do not have any commercial importance, but have other biological uses. Although some species like the major carps are confronting adverse situations, the reservoir is considered to be one of the important carp breeding habitats of Bangladesh in respect of its depth, current velocity, turbidity and the meanders of the river stretches. Intensive studies on natural spawning of major carps in the Karnafuli reservoir however, is scanty. The fish population of the lake is composed of major carps 21%, predators 15%, weed fish 44%, and others 20%.
The landing record shows that the major carp population is gradually declining (Table). To meet the situation considerable amounts of carp fries/fingerlings have been liberated regularly since 1980s. From the beginning of the 1980s, a number of exotic species including the Chinese carps are being introduced to properly use the reservoir's trophic levels through the control of macrophytes and green algae, in addition to enhancing fish production.
An average 275-day fishing is exercised in the reservoir every year. A closed season (mid May-mid July) is maintained to ensure normal breeding of the fishes. From 1964, the Bangladesh Fisheries Development Corporation has been entrusted with the management of Karnafuli reservoir fisheries aspects and since then the corporation has undertaken various programmes to ensure marketing and transportation facilities in different suitable places of the country. [M Abdul Hye and Abdullah-Al Mamun]
Brackish-water fisheries fish, fishing, and fish culture in the less salty areas of the sea (areas where salinity is between freshwater and seawater). Brackish-water fisheries are also known as estuarine fisheries. Being situated in the biggest delta of the world, the brackish-water area in Bangladesh is one of the biggest. Brackish-water fisheries are of two types, open water and cultured. While fisheries constitute a small part of the gross national product of Bangladesh, its role in national development, however, is of considerable significance in terms of employment, foreign exchange earnings, food supply, and socioeconomic stability in rural coastal areas. Vast portions of frozen food exports come from the brackish-water region.
The open brackish-water fish landing in Bangladesh are generally categorized together with marine landings. The brackish-water culture fisheries generally deal with black tiger shrimp, the main export commodity of frozen food from Bangladesh. Though brackish-water fisheries contribute a fraction of marine fish landing in Bangladesh, the area has importance as a breeding and nursing ground of many marine and freshwater species. A vast number of marine species utilizes the brackish-water region as nursing ground. The giant freshwater prawn, popularly known as Galda (Macrobrachium rosenbergii), migrates towards brackish-water from a freshwater habitat for breeding and returns when young individuals attain post-larval stages. Similarly many marine species spend part of their life in a brackish-water area and juveniles travel back to the open sea.
Roughly 25,000 sq km of coastal rivers, natural depression, mangroves, etc fall into the brackish-water category. Nearly 7,00,000 ha are at present occupied by mangroves, the rest are deliberately converted into agricultural lands surrounded generally by dikes and embankments. The open brackish-water areas are generally used for community fishing, but coastal brackish-water aquaculture is privately owned. The brackish-water estuary, river mouth, canals, etc are also used for community fishing.
It is estimated that about 29% of total fisheries production in Bangladesh comes from seawater. Further 10-15% of total marine production is from the brackish-water region. Total production of fisheries in Bangladesh during 1997-1998 was 1.21 million m ton. Besides, the brackish-water region also supplies roughly 3.0-3.5 billion post-larvae of the Black Tiger Shrimp, Penaeus monodon, annually. Bangladesh produces roughly 50,000 to 60,000 m tons of 'head on' brackish-water shrimps annually. It is estimated that 150,000 ha of coastal aquaculture produce approximately 70,000 m tons of mixed fishes, crabs, and small shrimp annually as non-target species.
Brackish-water organisms may be classified into 2 categories resident and migratory. Resident species include mullets, thread fins, saienidaes, perches, Ribbon fish, clupeids, Catfish, Bombay Duck, Camila, etc. Besides, many penaeid shrimps are also resident. Brackish-water aquaculture in Bangladesh however, has not yet developed as a total system dealing with production of finfish and shellfish for domestic consumption and for export maintaining a sound ecological balance. [Md Abul Hossain]
Marine fisheries collection, commercial exploitation or harvesting of fishes or other products of the sea. World fishery is essentially marine, which occupies more than 97% of the total fisheries; freshwater fisheries constitute only about 2.5%. However, in Bangladesh freshwater fisheries constitute around 70% and marine fisheries including brackish-water occupy the rest. Marine fishing industries though have undergone a period of changes in the past 40 years elsewhere but are still predominantly traditional in Bangladesh. Here during the last 40 years traditional fishing boats got only an engine fixed to gain more mobility. Otherwise, marine fishing essentially remains coastal fishing in Bangladesh where a few species are targeted and which often leads to over exploitation.
Bangladesh has a territorial water of about 20 nautical km from the coast, and again the exclusive economic zone extends about 320 nautical km from the territorial waters. Therefore, the marine fisheries zone of Bangladesh is roughly above 200,000 km2, which is larger than the total area of the country. Marine fisheries can be classified into 2 categories, pelagic, and demersal. Pelagic fisheries of Bangladesh involve mostly plankton eaters, ever-swimming fishes of the upper zone of water. These include Hilsa, Mackerel, pomfret, ribbon fish, Bombay Duck, Indian Salmon, Mullets, Oil Sardine, pelagic sharks, Sword Fish, Butter Fish, Pike, Bonito, Skipjack, Threadfin, Smelts, Indian Anchovy, Dorab Herring, Indian Scad, Bone Fish, etc, and a few other and related fishes which have commercial importance. Dogfish, a smaller variety of shark is also found in Bangladesh water.
Demersal fishes are those which live on the sea floor or near the bottom of seawater. Most of the demersal fishes are either carnivores or detritus feeders. Though the Bay of Bengal has about 442 species of marine fishes, only about 20 species are harvested commercially. Among the demersal fishes Jaw fish, croakers, catfishes, flatfishes, pike, sea breams, snappers, scavengers, eel, goatfish, crabeater, rabbit fish, rock fish, seabass, grouper, silver bream, ribbon fish, and demersal sharks are the most important. On the other hand, roughly 10 species of marine shrimps are included among demersal fish, together with some crabs. Though gastropods are considered seafood elsewhere, in Bangladesh these are considered non-edible and hence are not harvested commercially.
Annually 350,000 to 400,000 m tons of marine fish and shrimp are harvested in Bangladesh. Most of the fishes are caught by ordinary fishing boats or mechanized boats and are caught by fixed and drift gill nets, set bag net and long lines.
The Bay of Bengal falls in the sub-tropical zone and no oceanic current enters into this Bay which deprives it in nutrient recycling through upwelling. However, a great volume of freshwater is added to the Bay of Bengal through the combined flow of the Ganges, the Brahmaputra and the Meghna. These rivers carry land washout and a great mass of organic and inorganic nutrients and also help in mixing fresh and marine waters to create one of the world's biggest brackish-water zones. Further, the inflow of a vast amount of freshwater into the Bay of Bengal created one of the world's biggest anadromous fisheries. Hilsa, a marine fish, spends most of its lifetime in the Bay of Bengal then migrates to the river system for spawning. The young individuals return to the sea again. Productivity of the Bay of Bengal partially depends on land washing and freshwater inflow from the landmass. [Md Abul Hossain]
Marine shrimp fishery In Bangladesh about 1,25,000 hectares of coastal area are now under shrimp cultivation. The four fishing grounds viz South Patches, Middle Ground, Swatch of No Ground and South of South Patches between 10 and 100m depth in the exclusive economic zone (76,800 sq km) of the Bay of Bengal have high fishery potential (stock size of about 30,000-60,000 tons) for capture fisheries. There are about 19 species of shrimps in the marine environment of Bangladesh. Of these, 6 species viz Penaeus merguiensis (Banana Shrimp), P. monodon (Tiger Shrimp), P. indicus (White Shrimp), P. semisulcatus (Green Tiger Shrimp), Metapenaeus monoceros (Brown Shrimp) and M. brevicornis are of commercial importance. The aquaculture production of Penaeus species was about 34,000 m tons in 1995.
The commercial caridean shrimp Macrobrachium rosenbergii though a freshwater shrimp breeds in the estuary of the Bay of Bengal and passes its early life in the estuary. The warm tropical climate, nutrient-rich water with a salinity range from 12 to 39 ppt and oxygen range from 4.0 to 4.8 ppm are favourable for the rapid growth and development of the shrimps. Fleets of small-scale fishing crafts such as traditional boats (about 20,000) and motorized boats (about 12,700), engaged in the continental shelf (66,440 sq km) of Bangladesh, use set bag nets (behundies), trammel nets, beach seines, long lines, gill nets, etc. Shrimps along with fish are caught by these nets at a depth of 10-50 m. In the offshore waters at 10-100m depth commercial shrimping is undertaken in the four fishing grounds by a fleet of about 50 shrimp trawlers. Of the four fishing grounds, the South of South Patches (Southwest of st martin's island) is very important for tiger shrimp.
About six hatcheries are producing fries of giant tiger shrimp for culture purposes. A large number of natural giant tiger shrimp larvae are also caught along the coasts of Cox's Bazar and Khulna with the help of thousands of fine-meshed pushnets, fixed bagnets and dragnets. In such larvae collections of giant tiger shrimp, a large number of larvae of other shrimps and fish are destroyed. Marine shrimp fishery provides a livelihood to thousands of people; the country earns about 270 million US dollars a year from the shrimp export. [Md Abdul Kader]
Offshore trawler fishery catching fish or harvesting other products at a distance from the shore by using vessels with trawl nets. The trawl nets are used in deep sea fishing in the Bay of Bengal especially in the four fishing grounds about the Bangladesh coast. Commercial trawling with large vessels (21-41m length) commenced around 1978-79. Initially there were only four trawlers, but it increased to about 130 in 1981. By the late 1980s, 31 shrimp trawlers, 10 finfish trawlers and 8 combination trawlers were in operation. At present about 70 trawlers are engaged in offshore fishery.
About 50 species of fish and 15 species of shrimps are recorded in trawl net fisheries in the Bay of Bengal. The principal species caught in the trawl fishery are, among the shrimp, the Brown Shrimp (Metapenaeus monoceros) and Tiger Shrimp (Penaeus monodon). Major contributions to the finfish catches are silver and Black Pomfret (Pampus argenteus and Formio niger), Grunts (Pomadasys spp.), Indian Salmon (Polynemus spp.), Snapper (Lutjanus spp.), Goatfish, Croaker, Mackerel (Rastrelliger spp.), Lizardfish (Saurida spp.) and Hairtails/Ribbon fish (Trichiurus spp.).
Two types of trawl nets are used for fishing in the Bay of Bengal, the Shrimp Trawl Net and Finfish Trawl Net. The shrimp trawl catch includes Brown Shrimp, Tiger Shrimp, Indian White Shrimp and Banana Shrimp; finfish are Tigertooth Croaker, Blotched Croaker, Bombay Duck, Lizardfish, Goatfish and Hilsa shad. The finfish trawl catch includes 20 commercially important species; of these the Indian Salmon, Grouper, Grunt, Pomfret and Ribbon fish show a relatively high proportion even in shallow waters (<30m depth). At the 30-80m depth shrimps and some trash fish are also included in the finfish trawl catches. Smaller penaeid shrimps are caught in relatively high proportions at <30m. The shrimp catch was about 3,000 m tons in 1990; finfish landings were about 7,400 m tons in 1986-87. However, 50-65 percent of the small finfish caught are discarded at sea as trash fish. The standing stock sizes of the Bay of Bengal have been assessed by experts as follows:
|Variety||Standing stock (in 000 m tons)||Max. annual harvestable stock (in 000 m tons)|
|Demersal fish||200 - 250||100 - 125|
|Pelagic fish||160 - 200||30 - 60|
|Shrimp||30 - 60||2 – 6|
Shark fishery collecting or harvesting of members of various orders of cartilaginous fishes belonging to the class Chondrichthyes from the sea as one of the fishery items. In Bangladesh the shark is not a target species in marine fishing; it generally comes as by-catch. Bangladeshi tribal people eat shark meat and fin. At present shark skin is processed for export. Sometimes fishermen collect the powerful jaws, which are sold as ornaments. Sharks are generally caught by gill nets, trammel nets, set bag nets, long line, as well as trawl nets. Total landing of shark could not be estimated as the fishermen generally after cutting their fins throw the carcasses into the sea.
Bangladesh earns a considerable amount of foreign exchange by exporting dried shark fins. In 1994-95, the country exported about 212 m tons of shark fin and fish maws valued about Tk 166 million. Sixteen species of sharks are available in Bangladesh waters. Some sharks enter into the estuaries of southern Bangladesh; these are popularly known as 'Kamot'. [Md Abul Hossain]
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