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:

History

Fish habitats

Fisheries resource

Fish biodiversity

Fish cooperatives

Fish farm management

Fish parasites and diseases

Fish marketing

Fisheries administration

Fish laws

Fisheries education and research

Fish culture

Beel, Baor and Haor fishery

Kaptai Lake fishery

Marine 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.

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 under different types of waterbodies

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.

Table 2 Production (m tons) of different species of fish, shrimp and prawn in various types of inland waters, 1987-88

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:

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 upzilla 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]

Bibliography  F Day, The Fisheries of India, William Dowson and Sons, London, 1878; M Shafi & MMA Quddus, Bangladesher Matshya Sampad (in Bangla), Bangla Academy, Dhaka, 1982; BFRSS (Bangladesh Fisheries Resources Survey System), Department of Fisheries, Dhaka, 1986; M Lamboeuf, Demersal fish resources of the continental shelf of Bangladesh, FAO, Rome, 1986; AKA Rahman, Freshwater Fishes of Bangladesh, Zoological Society of Bangladesh, Dhaka, 1989; WB (World Bank), Bangladesh Fisheries Sector Review, Report No 8830-BD, Dhaka, 1991; MMA Quddus & M Shafi, Bangopasagarer Mastsy Sampad (in Bangla), Bangla Academy, Dhaka, 1993; FAP (Flood Action Plan), Fisheries Study and Pilot Projects, Interim Report, Dhaka, 1995.

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.

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 Upazilla 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]

Fish culture

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 h