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Hilsa (ilish) any of the members of the genus Tenualosa of the family Clupeidae, order Clupeiformes. Locally known as Ilish, the fish has been designated as the national fish of Bangladesh. The body is strongly compressed and moderately deep with dorsal and ventral profile equally convex. The upper jaw has a distinct median notch. Regularly arranged medium-sized scales cover the metallic silver-coloured body. Body length may reach up to 60 cm, but commonly found specimens measure 35 to 40 cm. A large-sized hilsa weighs about 2.5 kg. Females grow faster, and are usually larger than males. The hilsa is known to be a fast swimmer, and attains maturity in one to two years.

Hilsa has a wide range of distribution and occurs in marine, estuarine and riverine environments. The fish is found in the Persian Gulf, Red Sea, Arabian Sea, Bay of Bengal, Vietnam Sea and China Sea. The riverine habitat covers the Satil Arab, and the Tigris and Euphrates of Iran and Iraq, the Indus of Pakistan, the rivers of Eastern and Western India, the Irrawaddy of Myanmar, and the Padma, Jamuna, Meghna, Karnafully and other coastal rivers of Bangladesh.

Hilsa, Tenualosa ilisha

The fish is anadromous, with a life cycle that follows the general pattern of breeding upstream in fresh water and the larvae hatching from the free-floating eggs. The immature young stages grow in river channels and then descend to the sea for a period of feeding and growth before returning to the rivers as mature breeding adults to complete the cycle. The hilsa is a highly fecund fish. A large-sized female may produce up to 2 million eggs. Although hilsas spawn more or less throughout the year, they have a minor spawning season during February-March and a major season in September-October. Immature hilsa fish (6-10 cm), known as jatka, are extensively caught during their seaward migration in some of the major rivers of the country.

Hilsa is primarily a plankton feeder and its food includes blue-green algae, diatoms, desmids, copepods, cladocera, rotifers, etc. The feeding habit may vary according to the season and age of the fish.

Hilsa fishery The fish is exploited by intensive fishery for the mature migrating adults in the estuaries and river channels, and to a lesser extent by the capture of the jatka in the river. Nearly 16.4% of the country's total fish production is contributed by this fishery. In terms of production and quantity exported, hilsa has played a significant role in the economy of Bangladesh in recent years. An amount of Tk 1,34,79 million was earned by the fish and fisheries commodities in 1996-97, with hilsa alone contributing about Tk 4,88 million. It is estimated that about 2 million fishermen and traders are engaged in hilsa fishing in the country.

Scientific interest in the fish and its exploitation became evident in the late 1940s when attempts were made to define the major biological parameters of the species. Little attention, however, was paid to the fisheries. The shortage of information necessary for fisheries evaluation and management and lack of any programme of fisheries investigation led to the establishment of the Hilsa Fisheries Investigation and Management Unit to provide necessary information for optimum utilization of this important national resource.

Present status Until about 1972 the hilsa fishery was restricted to the upstream rivers, mainly in the rivers Padma, Meghna, Karatoya, Rupsa, Shibsa and Payra. At present, the fishery has severely declined in the upstream areas and is mainly concentrated in the downstream rivers, estuaries, coastal areas and the sea.

Since the construction of the farakka barrage in India to divert water from the Ganges, the fish are being caught in the coastal and estuarine waters before they can migrate upstream for spawning. Local fishermen catch migrating adults from May to October, and the juveniles from February to May. During the dry winter months from October to February hilsa are also caught by the coastal fishermen. The adult hilsa are caught using fixed or drifting gillnets (chandi jal) and lesser quantities are caught in berjal and lift nets (shangla jal). In the river these fishing units usually consist of non-mechanized single or two-boat teams, whilst at sea the fishing is done with mechanized 10-13m boats or trawlers. A system of collector boats, wholesale markets and transporter-traders supplies the inland markets with this prized fish.

During 1980s hilsa production was fairly stable. In recent years, however, the production has shown a downward trend, particularly in the inland fishery. In 1999 the production was significantly low and in 2000 the fishery continued to decline steeply.

Causes of depletion A number of factors are thought to be responsible for the decline of the hilsa fishery in Bangladesh. Low water discharge from the Ganges due to construction of the Farakka Barrage and consequent heavy siltation, indiscriminate exploitation of juveniles (jatka), disruption of migration routes, loss of spawning, feeding and nursing grounds, and increased river pollution are considered to be some causes of this decline. Moreover, uncontrolled use of mechanized hilsa fishing boats in coastal areas is preventing upward spawning migration of the fish.

Water resources development activities such as the Flood Control Drainage (FCD), and Flood Control Drainage and Irrigation (FCDI) projects have also adversely affected the aquatic ecosystem and hilsa fishery. The closure of the Kumar has cut off hilsa migration from the sea via Nabaganga to the Padma. The Chandpur Irrigation and Flood Control Project and the Meghna-Dhanagoda Irrigation and Flood Control Project have also exerted similar negative effects on the hilsa fishery through destruction of nursery grounds of the juvenile hilsa.

Jatka the local name for the young or juvenile stage of hilsa. Migrating adult females release eggs upstream in major rivers, including the Padma, Jamuna and Meghna. After hatching from free-floating eggs, the larvae remain in their nursery grounds for some time where they feed and grow. In about six to ten weeks they grow to about 12-20 cm and become known as jatka. At this stage they start descending to the sea for further growth and maturity. A survey conducted by the Bangladesh Fisheries Research Institute in 1992-94 estimated that every year in the fishing season from January to April, about 3,500-4,000 m tons of jatka are caught by using different types of gears such as jagat berjal, current jal and behundi jal. More than 50% of the total jatka are caught in the Meghna. Although fishing regulations do not permit catching jatka, since it is very damaging to the hilsa fishery, the practice continues unabated. [SM Humayun Kabir]

See also fish; fisheries.