Prawn (chingri) crustaceans related to crabs and lobsters, of the order Decapoda, found in all types of waterbody throughout the world. Some species live near the shore, hiding in mud or sand, or in crevices of the stones; some others swim about in groups in deep, cold water. They are of grey, brown, white or pink coloured. Some have bands over the body, some have spots.
Some prawns are red, yellow, green or blue in colour. Some species can change colour to match the surroundings. Many deep sea species are luminescent (light producers). The size ranges from 2.5 to 30 cm.
The prawn body divided into cephalothorax and abdomen is covered by a chitinous exoskeleton, normally consisting of 19 segments. Each body segment bears a pair of jointed biramous appendages, which are modified in structure according to their functions, eg, antennae, antennule, various types of mouth parts, long walking legs with chela (periopods), paddle-shaped swimming appendages (swimmerets/ pleopods), and fan-shaped uropod. Most of the prawns have stalked compound eyes.
Prawns are omnivores and essentially scavengers. Some are planktivores and vegetarians. Others feed on aquatic small insects and other animals. The type of food varies according to the developmental stage and species of the prawn. Some females carry fertilized eggs under their abdomen with the pleopods until they hatch, others shed the fertilized eggs in water. Eggs of most species usually hatch as a nauplius larva and pass few larval stages, similar in appearance with the primitive crustacean groups. Bangladesh has very rich source of prawns in the Bay of Bengal, estuaries and freshwater. A total of 56 species is reported, of which 37 are salt water, 12 are brackish water, and 7 are freshwater in habitats. However, some species migrate in between lower and higher saline zones. The prawns are classified under six families, Palaemonidae, Penaeidae, Pandalidae, Alpheidae, Hippolylidae, and Sergestidae. The freshwater species are included in the family Palaemonidae.
Prawn is a popular food throughout the world, having good markets at home and abroad. It occupies a major portion of the export item of Bangladesh, earning a considerable amount in foreign exchange each year. Bangladesh Fisheries Development Corporation (BFDC), Bangladesh Jatiya Matsayjibi Samabay Samiti (BJMS), Bangladesh Sugar and Food Industries Corporation (FSFIC), and some private companies collect, process and export prwans and shrimps. A number of prawn processing industries have been developed in khulna, chittagong, and dhaka. [Selina Parween]
Prawn culture' Raising, processing and marketing of prawns/shrimps as a source of protein food. The most widely cultured fast growing species in the globe as well as in Bangladesh are the giant black tiger shrimp Penaeus monodon and the giant prawn Macrobrachium rosenbergii. Their culture techniques are traditional, extensive, improved extensive, semi-intensive, intensive and super intensive, named mainly based on the stocking density of post larvae (pl) and management techniques of the culture ponds. Both monoculture, polyculture and integrated culture with paddy (rotational and concurrent) and with fin fish (mullets, carps and tilapia) are the common systems practiced. But shrimp culture starts in saline water and prawn culture mainly in freshwater though they all need saline water for hatching of eggs in the hatchery. In Bangladesh ecosystem and socio-economic conditions, extensive and improved extensive systems are being successfully practiced. Semi-intensive culture during 1993-1995 in cox's bazar area failed due to poor management and outbreak of bacterial and viral diseases. In brief, the extensive/improved extensive culture technique involves gher/pond preparation during December-February, stocking in February-March with wild as well as hatchery produced fry (pl), post stocking management including water exchange, liming, manuring etc. whenever necessary, harvesting and restocking from June to November. Macrobrachium prawn culture is low density, long duration (5-8 month cycle), mono, poly or integrated paddy cum prawn-fish mixed culture, commonly practiced in ponds as well as in paddy fields. Shrimps and prawns are omnivorous and accept natural as well as artificial feed.
Table Size, habitats and breeding period of some commercially important prawns.
|Species||Average size (cm)||Habitat||Breeding period|
|Macrobrachium rosenbergii||Male: 34.00; Female: 26.70||Rivers, tributaries, canals and river mouths||
|M. malcolmsonii||Male: 16.60; Female: 12.80||Rivers, tributaries, canals, river mouths and floodplains||Throughout the year|
|M. rude||Male: 12.00; Female: 10.50||River mouths and tidal rivers||July-November|
|Penaeus monodon||Male: 29.80; Female: 30.00||Bay of Bengal and estuaries||November-March|
|P. semisulcatus||Male: 20.40; Female: 23.00||Bay of Bengal and estuaries||January-April|
|P. indicus||Male: 15.00; Female: 23.00||Bay of Bengal and estuaries||October-November, May-June|
|P. japonicus||Male: 16.00||River mouths of Banshkhali and Satkhira||January-April|
|P. merguiensis||Male: 15.50; Female: 20.00||River mouths and estuaries of Khulna and Patuakhali||October-January|
|P. penicillatus||Male: 14.50; Female: 16.60||Bay of Bengal, the Sundarbans and back waters of Patuakhali||January-March|
|P. orientalis||Male: 12.20; Female: 19.00||Bay of Bengal and the Sundarbans||November-March|
|Metapenaeus monoceros||Male: 12.50; Female: 15.50||Bay of Bengal, the Sundarbans and river mouths||Throughout the year peaks: July-August and November-December|
At present tiger shrimp (Bagda) is being cultivated in about 145,000 ha of coastal and tidal lands in ghers and ponds (in 25-30 thousand farms) at satkhira, Khulna, bagerhat and Cox's Bazar (including Chakoria and Teknaf) area under both monoculture, polyculture and integrated with paddy in Khulna area and salt in Chakoria area. Prawn (Galda) culture in about 30,000 ha in about 60,000 ponds and paddy fields is being practiced mainly in Bagerhat, Khulna, jessore, patuakhali, barisal, Chittagong, lakshmipur, feni, gopalganj, madaripur, faridpur, kishoreganj, rajbari and Dhaka. Annual farmed shrimp and prawn production is about 28,514 m tons (headless) which bring about 16,150 Tk million as foreign exchange. About 60% of the total export product comes from culture source and the rest from capture sources. In 1999 farmed Bagda and Galda production was 63,164 m tons (head-on) of which contribution of shrimp was 65%, prawn 20% and others 15%. The major input in shrimp and prawn culture is the fry (pl). It is now being produced in hatcheries; about 48 tiger shrimp hatcheries are located in Cox's Bazar and teknaf area producing about 4 billion tiger shrimp fry annually. Earlier in the 1980s and 1990s main source was wild fry collected from coastal and tidal waters. About 440,000 people mostly the women, children and landless are engaged in this profession.
Main problems in the shrimp/prawn culture are the outbreak of diseases mostly due to poor pond management, and lack of adequate technical knowledge, extension and institutional credit facilities. The major diseases causing mass mortality are white spot syndrome virus (WSV), vibriosis (Vibrio bacterial diseases), soft shell, black gill, muscle necrosis, fungal and protozoan infections. Metamorphosis molt mortality syndrome, bacterial necrosis, larval mid-cycle disease, and white prawn disease are specific for the prawn.
Poor management of pond bottom and water quality, recycling etc leading to pond environmental degradation, are other factors responsible for disease outbreak and mass mortality. For sustainable and environment friendly shrimp/prawn culture, integrated polyculture with paddy and fish has recently been proven to be successful technique as paddy recycle the bottom nitrogenous wastes and fish as an ally control bacteria and other shrimp/prawn pathogens to tolerable level. To prevent viral infection, screening of spawners and fry at the hatchery has been very effective. Balanced planning and management strategies based on clear understanding of the interactions between shrimp culture and environment are the best way to prevent disease problems. [Abu Tweb Abu Ahmed]
Impact Export of frozen shrimp has become an important foreign exchange earner of this country in the recent years. The greater part of this commodity originates from the coastal aquaculture sector. It has created employment opportunities for thousands of people both in shrimp fishery (culture and capture) sector itself as well as in the backward (wild shrimp fry fishing and hatcheries), and forward linkage (frozen shrimp) industries.
In absence of any code of conduct or national strategy for aquaculture in Bangladesh the coastal shrimp farming expanded very rapidly in an uncontrolled, uncoordinated and unplanned manner. In the recent past this expansion has been very remarkable, from less than, 20,000 ha of brackishwater ponds in 1980, the area was increased to about 70,000 ha in 1985, 115,000 ha in 1989 and now it is about 145,000 ha. Shrimp farms are primarily located at the south-western part of the country in the districts of Khulna (29%), Satkhira (19%), and Bagerhat (29%), and at the south-eastern part mainly in the Cox's Bazar district (31%), the rest are in other coastal districts.
Destruction of mangroves and associated impacts Like some Southeast Asian countries rapid destruction of mangroves was done in Bangladesh for expansion of coastal aquaculture. In the southeastern part of the coastal zone of this country majority of the shrimp farms were developed at the cost of valuable mangroves. Once the entire chakaria sundarbans area was occupied by dense mangroves, and had the status of the forest reserve with an area of about 18,200 ha. Following introduction of shrimp farming most of the mangroves (more than 50%) were rapidly cleared for preparation of shrimp ponds. Leaseholders ruthlessly cleared the forest in their leased land.
The impact of shrimp farming on mangroves through habitat conversion has been the concern of many. How many species of fish and shrimp have been extinct, or endangered or migrated elsewhere leading to destruction of mangroves in Bangladesh has not yet been recorded. However, functionally mangroves are important in nutrient cycling, as a source of organic matter to increase coastal productivity, and as breeding grounds, nursery areas or general habitats for many commercially important finfishes, crustaceans, and molluscs. Mangroves can support various forms of fish, mollusc, crab, and crustacean aquaculture. Opportunities may be lost if mangroves are destroyed or degraded.
Besides ecological impacts, inhabitants in the vicinity of Chakaria Sundarbans used to earn their livelihood through collection of fuel wood, thatching materials, timber, various foodstuffs such as honey, fish etc. Consequently with the removal of mangroves people of this area have been deprived of this benefits.
Impact on human habitation In the southeastern part of this country alternate fish culture and rice cultivation during dry season (March-June) and monsoon (July-November) respectively in the same land was a traditional practice. After rapid development of shrimp farming by influential and well-to-do people, serious and strong objections were raised by local residents, peasants, leaders of grass root organisations, NGOs operating in the area, and local elected representatives to highlight the deleterious effects of shrimp farming.
The majority of conflicts arose following construction of shrimp 'ghers' (areas impounded by dykes), covering generally 40-66 ha of land. Peasants are often compelled to lease out their land to shrimp farming entrepreneurs. When a peasant opposes establishment of a gher that encompasses his land he is intimidated and threatened and has to ultimately yield. There are middlemen through which the entrepreneurs (often outsiders), are buying up the local lands. This is leading to growing land-less peasants in the region.
The ghers are controlled by entrepreneurs and larger land owning shrimp farmers; poor small land owning peasants receive an insignificant amount of money (called hari) for leasing out his land to the entrepreneurs. The entrepreneurs arbitrarily fix the amount of the lease money, which is only a small proportion of the income the peasants used to earn from the traditional rice cultivation in this land. There are many absentee landlords who do not care about hari and this facilitates non-payment of hari by the entrepreneurs to local peasants. Lease of government land (Khas land) is done in a non-transparent way and only the wealthy, mighty and influential persons can afford to get lease of such land. In some instances, influential people invite owners of small lands to form co-operative bodies for developing larger ghers, but there is a constant complaint that the owners of small lands neither get right share of profit, nor they can participate in gher management.
Once an area comes under shrimp farming, the gher owners inundate this large area adjacent to small rice fields with saline water when the productivity of lands (both inside and outside the gher in the whole area) declines drastically. Eventually, owners of these lands are compelled to either convert their lands into gher by themselves or lease out to the owners of the adjacent larger gher. Thus, in a vast area, rice cultivation is gradually being replaced by shrimp farming. A number of traditional rice varieties (valuable genetic resources) suitable for the locality (eg gunshi, kalshi etc) are gradually disappearing. Once the Satkhira district was a rice surplus area but now there is an inflow of rice from outside.
Crop diversification has been severely undermined because of shrimp farming. In such area production of non-rice crops, fodder for livestock, vegetables, etc can no longer be grown. Thus, there is an acute shortage of these crops in areas under shrimp farming and their prices have gone up significantly in recent years.
The law and order situation in the gher areas has deteriorated drastically over the years. Violence between the people of shrimp farms and those who oppose shrimp farming is a common occurrence. The result is that a large number of poor families have been forced to leave their homes for unknown destinations. A recent study conducted by a non-government organisation (NGO) on the impact of commercial shrimp cultivation on the socio-economic and ecological conditions in the three coastal districts of Khulna, Satkhira and Bagerhat, revealed that the socio-economic and family status of the people living outside the shrimp cultivation area was higher than those living in the shrimp cultivation belt. Before the onset of shrimp farming, the people of this region worked 10 hours a day, but after the expansion of shrimp cultivation their working hours are now hardly two to three on average. This has affected their earning ability by, in some cases, as much as 75 percent.
Due to the adverse effects of shrimp cultivation, people's earning from extra agricultural activities like vegetable production, farming, the rearing of domestic animals fell by 30 to 50 percent. All kinds of trees, including fruit trees, have declined by 10 to 30 percent due to increasing salinity. Consequently shrimp cultivation has forced many marginal farmers to abandon their homesteads and small croplands, and migrate to nearby towns or in the city's slums. [Nuruddin Mahmood]