Bangladesh Fisheries Research Institute
Mymensingh-2201, Bangladesh
Mazid, M.A., and A.N.H. Banu. 2002. An overview of the social and economic
impact and management of fish and shrimp disease in Bangladesh, with an emphasis
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In Bangladesh, increasing population pressure, with increased demand for fish, has made fisheries a lucrative sector for the present generation. Fish culture in the country has been progressing towards semi-intensive culture, while shrimp culture moves towards an improved traditional system. However, indiscriminate and unplanned use of feed and fertiliser, with subsequent effects on water quality in pond ecosystems correspondingly increases stress on fish and accelerates susceptibility to pathogens. The effects of disease in improved culture systems are significant; however, proper systematic information on disease outbreaks is not yet available. The most obvious effect of the occurrence of disease is mortality, followed by economic losses. Mass mortalities of carp fry and fingerlings due to protozoan and metazoan parasites are frequently reported. A small initial infection gradually leads to a serious outbreak of disease, resulting in large mortalities and great economic loss for small-scale farmers. The most common disease problem in the country is epizootic ulcerative syndrome (EUS). There is a lack of technical knowledge in the management of shrimp farming. In Bangladesh, outbreaks of disease in shrimp caused by white spot syndrome virus (WSSV) (reported as systemic epidermal and mesodermal baculovirus -SEMBV) alone caused a 44.4% production loss in 1996; although the incidence of outbreaks has reduced considerably since then. It has been estimated that the shrimp culture industry provides direct employment to some 350,000 persons, who are engaged in fry collection and transportation, nursery and grow-out operations, and handling and processing. It is obvious that disease outbreaks in fish and shrimp culture systems have a great impact on low-income groups.
Aquaculture production continues to expand in an attempt to meet the needs of developing countries like Bangladesh. However, population pressure and a shortage of alternative employment opportunities in the country increase the attraction of fisheries as a form of employment. Bangladesh faces many challenges and constraints in the sustainable management of aquatic resources. Aquaculture production in the country has been facing problems from outbreaks of disease, lack of up-to-date management practices, and lack of awareness on the part of fish growers. Information on emerging problems needs to be communicated to the aquaculture and fisheries sector.
There is widespread agreement that there is a need to enhance the contribution that fisheries makes to national economic, social and nutritional goals. Fish culture in Bangladesh has been progressing towards semi-intensive culture, and inland fisheries, especially freshwater fish, are exploited for local consumption. Some 43 million ha is used for inland fisheries, of which ponds and tanks cover an area of 147,000 ha. Indiscriminate and unplanned use of feed and fertiliser and overstocking increase stress on fish and increase their susceptibility to pathogens. The effects of disease on improved culture systems are significant, however, outbreaks of disease are poorly reported and documented. The most obvious effect of disease is mortalities in the fish population, followed by economic losses. Although the country is facing serious problems in fish production due to disease outbreaks, production has still slowly increased (Table 1).
It has been estimated that more than 380,000 people are directly or indirectly involved in the shrimp culture industry. They are engaged in shrimp fry collection, nursery operation, fry transportation and depot operations, such as de-heading shrimp before sending them to processors. Before December 1993, there were no reports of mass mortalities due to disease in semi-intensive or traditional shrimp farming. During the past four years, however, the shrimp farming industry in Bangladesh has suffered severe problems, mainly due to disease outbreaks caused by white spot syndrome virus (WWSV, often reported as systemic ectodermal and mesodermal baculovirus, SEMBV).
Three different systems of shrimp culture are practised in the country. These are traditional or extensive, improved extensive and semi-intensive culture systems. The extensive system operates with minimal inputs and depends on tidal rise and fall for the intake and discharge of water. In traditional systems, a single canal is used for the supply of water. Because the farmers typically lack knowledge about the disease risks posed by the introduction of potential disease carriers, there is no screening at the inlet and outlet points, and thus predatory fish and potential carriers of pathogens can freely enter the system. The improved extensive system is similar to the above, however, inputs such as lime, fertiliser and feed are used. Semi-intensive systems operate with higher inputs than those of traditional and improved extensive systems, and they have separate inlet and outlet canals. Disease outbreaks occur in all three farming systems.
Apart from white spot syndrome, a number of other problems occur. These include the occurrence of significant mortalities at low temperature and low salinity, especially during the rainy season; black gill and red gill disease; black spot disease and necrosis; soft-shelling and parasitic infections.
Given the importance of foreign exchange earnings, the Government of Bangladesh has made extending the area of shrimp culture to increase shrimp production a priority. The problems faced by the shrimp farmers are as follows:
Land leasing is one of the major social problems in shrimp culture in Bangladesh. In most cases, land for shrimp culture is leased from small farmers who are unable to bargain and do not have the capital to set up a shrimp farm for themselves. Fry collection became an occupation for a large number of people only after the culture of penaeid shrimp (Penaeus monodon, known locally as "bagda") proved profitable as an export commodity. Fry are sold mainly to fry traders on the shore. About 60% of survey respondents (Hoq et al. 1995) sold their fry to traders, while 37.7% sold directly to shrimp farms and 2.7% to the markets. The price of shrimp fry fluctuates with demand from farms.
In Bangladesh, almost 80% of the population is poor, and a great number are landless. The life of the landless people is uncertain, and they are always on the move in search of better living conditions, often migrating to the urban areas where there are better economic opportunities. Some rural people settle in uninhabited lands, called char lands. Fishing is one of the main sources of income of people living in char areas, and it is seasonal. During the fish-breeding season (February-July), they set traps in rivers to catch fingerlings of carp species, such as catla (Catla catla) and mrigal (Cirrhinus cirrhosis). The catch is usually sold to pond owners on the mainland. Fishing in canals and open waters is also carried out by landless people during the flood season.
Fishery-dependent communities live on boats or floating houses or on the banks of rivers. They rely exclusively on fishing and fishing-related activities, such as fish growing, processing, gear manufacture and fishing boat construction. The socio-economic circumstances of these communities are very poor.
Aquaculture development in the country has intensified recently through increased stocking densities and artificial feeding and fertilisation. Intensification is increasing fish production but may lead to deterioration of water quality and increased susceptibility to infections.
Fish disease in carp farms has been reported in up to 31% of extensive farms and 24% of semi-intensive farms (Chowdhury 1997). The most common disease problem in freshwater fish is epizootic ulcerative syndrome (EUS). Common diseases of freshwater fish in Bangladesh are as follows:
The occurrence of disease in farmers' ponds and related problems are recorded regularly at the Bangladesh Fisheries Research Institute (BFRI), where necessary suggestions and advice are given. After receiving samples, water quality is tested and specimens are examined in the laboratory.
The success of shrimp farming is measured by its rate of return on investment, which mainly depends on the yield, capital investment, international demand and market price, and the production cost. This, in turn, is affected by a number of factors, the most important of which are farm operation and management. Disease is one of the major factors affecting productivity. Damage caused by disease was estimated to affect 50-60% of the semi-intensive shrimp farms in Cox's Bazar in 1994, and monetary losses were estimated to be Tk 50 crore (US$10 million) (M.S. Islam, unpublished data). According to the Department of Fisheries (DOF), Bangladesh suffered a 44.3% production loss in 1996, leading to a reduction in foreign income of 42.3% from shrimp exports (Siriwardena 1997). Disease is a major concern, and was reported in 13% of extensive shrimp farms and 74% of semi-extensive farms. In another report, the estimated average financial loss per affected farm was estimated to be as high as US$832/yr for extensive and US$3,928/yr for semi-intensive farms (Chowdhury 1997). Illiterate, and even literate, shrimp farmers are unable to point out the real cause of shrimp diseases. However, nowadays, they are more aware of shrimp diseases and take precautionary measures whenever possible.
The socio-economic circumstances of small-scale aquaculture holders are poor. Moreover, they have no chance to set up farms, especially shrimp farms, as rich and influential local person(s) control the industry in their locality. Disease is one of the major constraints of fish and shrimp farming in the country. Considering the above, the following recommendations are made:
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