1Department of Fisheries
8th Floor, Matsya Bhaban
Shaheed Capt. Mansur Ali Saroni
Ramna, Dhaka, Bangladesh
National Aquatic Resources and Development Agency
Crow Island, Mattakkuliya
Colombo-15, Sri Lanka
Rahman, M., S.C. Paul and P.P.G.S.N. Siriwardena. 2002. Farmer training and extension: the key to health management in extensive brackishwater shrimp aquaculture in Bangladesh. p. 313-321. In: J.R. Arthur, M.J. Phillips, R.P. Subasinghe, M.B. Reantaso and I.H. MacRae. (eds.) Primary Aquatic Animal Health Care in Rural, Small-scale, Aquaculture Development. FAO Fish. Tech. Pap. No. 406.
The shrimp aquaculture industry in Bangladesh has gained an important place in the national economy and is the third highest foreign income earner. Of the Taka (TK) 13,400 million (US$335 million) earned as export earnings from the fisheries sector in 1996 to 1997, TK 11,880 million (US$297 million) came from the exportation of 25,742 mt of shrimp. There are a total of 13,076 extensive and improved-extensive shrimp farms, covering an area of 134,488 ha, and 72 semi-intensive shrimp farms, covering an area of 995 ha. Since 1994, shrimp farming in Bangladesh has suffered from viral epidemics and other disease conditions. Lost production due to diseases valued at TK 4,688 million (US$117.2 million) was recorded in financial year 1996-97.
The techniques developed for semi-intensive and intensive shrimp farming in
other countries cannot be applied to low-input/low-output shrimp farming systems.
Awareness of the major contributing factors to the poor health of shrimp and
the low production levels in these extensive culture systems has not reached
the farmer. Hence, an extension programme was developed to educate farmers about
health management aspects of shrimp culture applicable to extensive systems.
The methodology adopted in this training programme was farm-site training and
establishment of demonstration farms. Much emphasis was placed on educating
the farmers about problems relating to low production and health management
in the extensive systems, and on low-technology (low-tech), low-cost management
measures to improve health and productivity. Remedial measures involving high-tech,
high-cost or major engineering modifications were considered as "beyond
the farmers' capabilities." This paper discusses the five management measures,
based on low-tech and low-cost techniques, that were disseminated and demonstrated.
Shrimp aquaculture in Bangladesh has gained an important place in the national economy and is the third highest foreign income earner. Of the Taka (TK) 13,400 million (US$335 million) export earnings from the fisheries sector in financial year 1996-97, TK 11,880 million (US$297 million) came from the exportation of 25,742 mt of shrimp. This figure includes both cultured and captured shrimp, as no reliable figure is available solely for cultured shrimp production. A total of 13,148 shrimp farms, consisting of traditional or extensive, improved-extensive and semi-intensive farms, cover an area of 134,560 ha, providing an estimated 380,000 employment opportunities, of which 350,000 are direct employment.
Since 1994, shrimp farming in Bangladesh has suffered from repeated viral epidemics and other disease conditions. Various management strategies to address health management problems and low yields, particularly in extensive and improved-extensive shrimp farming in Bangladesh, have been described (Karim and Stellwagen 1998); however, there appears to be a reluctance or inability to implement these strategies (Karim and Stellwagen 1998). In 1996, the Government of Bangladesh requested assistance from the Food and Agriculture Organization of the United Nations (FAO) to address the health management problems in coastal shrimp culture. This paper presents the management problems and inadequacies in extensive and improved-extensive systems that lead to health management problems and low yields, and also presents the five management measures disseminated to farmers in 1997 under the FAO-assisted project. This paper also reports some of the statistical information resulting from a linked survey of 8,600 shrimp farms in Bangladesh.
According to the terminology used for shrimp farming in Bangladesh, three different types of culture system are practised: traditional or extensive, improved-extensive and semi-intensive shrimp culture. Semi-intensive farms represent a small proportion in number (0.54%) and production area (0.74%). The extensive system operates with minimal inputs and depends on the tidal amplitude for both water intake and discharge. Some farmers culture what is naturally recruited with incoming water, while others stock additional postlarvae. The extent of a single extensive shrimp-culture pond varies from 4 to 200 ha, with an average water depth of 60 cm. Most of these ponds are irregular in shape and bottom morphometry, and have only a single canal for both intake and discharge of water. Some of these ponds have one or more nursery compartments with or without a gate connection to the main grow-out pond. The extent of the nursery compartments varies from 0.5% to 20% of the total pond area.
Improved-extensive shrimp culture is basically similar to the extensive system, except for the use of certain inputs such as lime, fertilisers, and in some cases, feed. Extensive and improved-extensive shrimp culture systems sometimes include crop rotation with either salt production or rice cultivation. These classifications of culture practice are based solely on the degree of management intervention and do not relate to the productivity or the health of the shrimp cultured in the system concerned. This is an important point, since yields from both extensive and improved-extensive systems are often similar. The only difference between these two systems is that the production cost in the improved extensive system is slightly higher.
Semi-intensive farms are not currently in production. This is considered to be principally due to repeated production losses between 1994 to 1997 which have been attributed to white spot syndrome virus (WSSV), also known as systemic ectodermal and mesodermal baculovirus (SEMBV), and this has been confirmed in some cases (Funge-Smith 1997). The route of infection is thought to be via importation of infected postlarvae from other countries. Since the first outbreak of WSSV in semi-intensive farms, it has occurred in all the other farming systems. Significant production losses are often observed during the rainy season (June to September) and cold months (December to January).
According to an estimation made by the Department of Fisheries (DOF), 13,284 mt of cultured shrimp valued at TK 4,688 million (US$117.2 million) was lost due to disease in 1996. This amounts to a loss of 42.3% when compared to the foreign income generated from export of shrimp in 1995.
It is worth noting that there is a tendency to blame shrimp mortality and production losses in extensive and improved-extensive farms on WSSV, although the descriptions of the condition of the shrimp and the manner in which they were affected are not always consistent with what is known about this viral disease (Siriwardena 1997). Bacterial infections appear to be a significant contributory factor to these mortalities. It was observed that 80% of the farms had shrimp with pale and red discoloration on the body and tails with rotten, broken or swollen edges, indicating deterioration of pond environment and pond bottom.
Viable training and extension strategies to improve the health of shrimp and increase the yield from extensive and improved-extensive shrimp-culture systems must take into consideration the environmental and socio-economic constraints. In this regard, the following strategy was adopted to design the training and extension programme:
In a broad sense, environmental problems are site specific and also relate to larval quality and pond environment conditions. Most of the site-specific problems are caused by the fact that farms are built where there is land available, and not necessarily in sites suitable for shrimp farming. The following have been recognised as site-specific problems (Siriwardena 1997):
In Bangladesh, extensive and improved-extensive shrimp farming is largely dependent on wild seed collection for stocking (BOBP 1993). The method of handling during collection and the conditions used for holding and transport stress the postlarvae. Hence, the postlarvae may be in poor condition when they reach the farmer. Exposure of postlarvae to stressful conditions can cause an increase in the occurrence of disease and low survival at stocking, and this immediately limits the potential yield of the pond. Neither quality assurance nor acclimation of postlarvae to the pond environment is being carried out before stocking. Thus, the health management of shrimp under culture should begin with postlarval collection and holding.
Shallow water in ponds in many shrimp farms (74% of ponds are around 60 cm in depth) causes problems due to fluctuations in water quality parameters, such as temperature, salinity, dissolved oxygen and pH, and possibly, toxic compounds such as ammonia and hydrogen sulphide. The salinity of the ponds in many farms is low (63.6% of farms have a maximum salinity below 10 ppt). Low salinity, together with shallow depth, causes sudden drops in salinity to fresh water, which severely stresses the shrimp.
Shrimp-only culture is carried out by a small percentage of farmers (2.5%). The majority practice shrimp-fish polyculture. By-catch of shrimp other than Penaeus monodon ("bagda"), and of fish, plays an important role in the shrimp farmers' lifestyle by providing alternate income and species diversity. Should production of P. monodon fail, there is always the by-catch to provide food security. Hence, suggesting management measures to enhance production of P. monodon at the expense of fish and other shrimp species would not be acceptable to the farmers. Shifting the composition of the shrimp species in the pond towards P. monodon to enhance its yield would be acceptable, as this would increase the income from the pond. Thus, the management measures suggested for extensive and improved-extensive shrimp culture in Bangladesh should suit a shrimp-fish polyculture situation more than a shrimp monoculture situation. Recommendations to correct site-specific environmental problems would not be acceptable to the farmer, as they involve high-cost engineering modifications, which he could not afford. Moreover, most farmers are lessees (15.5%) or sub-lessees (53.5%) and will not invest in improvements to land for which they do not have long-term tenure. Therefore, the training and extension strategy took into consideration that low technology, low-cost management measures should be used to improve the environment for P. monodon. The criteria used to identify the five management measures recommended for dissemination included (i) management within farmer capability, and (ii) the acceptability of the recommended management measures to the farmer.
Dissemination of the recommended management measures was carried out by conducting 120, one-day farm-site trainings for groups of 30 to 40 farmers, fry collectors and fry holders. This training was conducted during the period December 1997 to December 1998 in the districts of Cox's Bazar, Satkhira, Khulna and Bagherhat at the union level. A total of 3,459 shrimp farmers, fry collectors and fry holders and 113 officials, including Thana Fisheries Officers and Assistant Thana Fisheries Officers from the DOF and Scientific Officers from the Fisheries Research Institute (FRI), received field training in the recommended management measures. In addition to these training sessions, three Experimental Demonstration Farms (EDUs) were established to demonstrate the recommended management measures. These EDUs were selected from among the operational farms in Teknaf (Cox's Bazar District), Botiaghata (Khulna District) and in Tala (Satkhira District). It is expected that these 113 officials, and the demonstration farmers, will serve as "master trainers" for further training of farmers, fry collectors and fry holders.
The training programme aimed to improve the environment for P. monodon culture in ponds and to improve the quality of postlarvae at stocking by minimising the stress caused during collection and holding (Siriwardena 1998].
Grow-out farmers were made aware of the following management measures:
When P. monodon culture is carried out alternately with rice production (46.7% of farmers), the stocking of postlarvae is carried out in February. If culture is carried out alternately with salt production (5.6% of farmers), stocking is carried out from June to September, which is the rainy season. When crop rotation is not practised, stocking is carried out throughout the year, whenever the postlarvae are available (45.1% farmers stock throughout the year). The cold months, December to January, which have significant diurnal temperature fluctuations (around 5 to 10 0C) and rainy months, when sudden salinity drops lead to completely fresh water in the ponds and heavy loading of silt, create an unfavourable pond environment for postlarvae. Stocking postlarvae during these unfavourable months increases their susceptibility to disease and may result in mass mortalities soon after stocking. Thus, timing of stocking plays and important role in minimising production losses and avoiding health-related problems.
February to March, which is the peak season of availability of natural postlarvae, appears to be the correct time for stocking, as this will allow harvesting of the crop at the onset of the rainy season in June to July. Therefore, salt-shrimp culture is not a recommended type of crop rotation. Culture of shrimp-rice or shrimp-freshwater fish would be a more suitable crop rotation to reduce health management problems and to enhance production. It is evident that Bangladeshi farmers should culture shrimp for only one cycle a year.
1 In Bangladesh, each district is subdivided into thanas, and each thana into unions.
Some farmers prefer multiple stocking and multiple harvesting without an adequate fallow period to allow the pond bottom to dry (39.2% of farmers do not dry the pond bottom). In order to maintain a healthy pond bottom, it is essential to clean it before filling with water and stocking with postlarvae. As shrimp spend most of their time foraging for food on the bottom, it is important to promote a healthy pond bottom during the culture cycle, since accumulated sediments consume more oxygen and produce higher levels of toxic gases, such as ammonia and hydrogen sulphide. Such conditions can stress shrimp and increase the likelihood of disease (Chanratchakool et. al. 1995).
Farmers also lack knowledge on the type and quantity of lime and fertiliser to be used in pond preparation (62.9% and 77.0% of the farmers do not use any lime or fertiliser, respectively). The quantity and type of lime is selected arbitrarily and not based on the soil pH. Due to the use of inappropriate quantities and types of lime and fertiliser and their incorrect application, maintenance of a healthy plankton bloom is not possible (77.2% of the farms had transparent to very light green water throughout the culture cycle). In many instances, favouring of benthic algal growths was observed. Farmers were, therefore, made aware of the importance of a fallow period during which the pond could be dried, and taught the importance of proper selection and use of lime and fertilisers.
The importance of maintaining a healthy plankton bloom at stocking and during rearing was emphasised. It was also emphasised that proper pond preparation should be carried out, at least in the nursery area, even though farmers may not be able to do so for the grow-out pond, due to the large area and high costs involved.
Maintenance of the nursery
According to the recent survey, 74.3% of the farmers do not maintain a nursery for stocking and rearing of postlarval P. monodon. The nursery provides an area in which a predator-free environment can be easily maintained and where postlarvae are able to grow in better conditions than in the main pond. This enhances survival prior to release into the main pond. It also concentrates the postlarvae, allowing them to be more carefully monitored and fed than in the main pond (Chanratchakool et. al. 1995). Use of a supplementary feed in the nursery will be more effective than in the main pond. Hence, the training and extension programme included nursery maintenance to provide a predator-free environment for rearing postlarvae as the third essential management measure to enhance production and to minimise health management problems.
The training and extension programme advocated the use of a 0.4 ha nursery for a 6 ha pond. Larger ponds should include more than one 0.4 ha nursery for better management. Recommended stocking densities are 20 to 25 postlarvae/m2 in order to release one juvenile shrimp/m2 into the main pond, based on an assumed survival rate in the nursery area of 60%. Prior to stocking, acclimation of postlarvae is recommended. To avoid predators and competitors and enhance survival in the nursery area, it was emphasised that proper water control, including the installation of net screens (89 holes/cm2) on water inlets, be maintained.
Most farms have problems changing adequate amounts of water, maintaining sufficient water depth and draining the pond completely. Most farmers (88.3%) depend on full moon and new moon days to change water in their ponds, restricting the frequency of water exchange to twice a month. In order to overcome this problem to some extent, and to prevent the entry of predators and competitors, it is necessary to design and install the water control structures (gates) properly, so that animals cannot enter around the gate. It was advised that the floor of the gate should be installed lower than the lowest pond bottom, preferably lower than the lowest tide at the site, and should rest on a foundation to enhance water exchange and drainage. The height of the gate should be as high as the main dike, and the sides should be sealed properly into the dikes to prevent seepage.
Supplementary feeding in the nursery is recommended in order to enhance survival and grow P. monodon to healthy, large juveniles for release into the main pond. Large, healthy juveniles will have the ability to avoid predation and will be less susceptible to disease. Whole wet fish (50 to 60%), rice bran (20%) and cooked rice or potato (20 to 30%) should be prepared as a feed. Inclusion of other shrimp, mussel, cockle or clam should be avoided, as these may transmit shrimp viruses (Funge-Smith 1997).
Early detection of clinical signs of a disease is essential in order to save the crop or to decide if an emergency harvest is required. The shrimp should thus be examined at regular intervals for any signs of disease. Farmers were trained to assess shrimp health by visual checks. The nine visual checks that should be carried out are examination of the carapace and head region, body colour, gill colour, appendages, tail region, gut, muscle, cleanliness of the body and gills and behaviour (Siriwardena 1998). Farmers were provided with a range of possible observations and causes.
The estimated costs involved in implementing the improvements are presented in Table 1.
Table 1. Estimated costs involved in implementing the recommended improvements for a farm of 6 ha area.
There is a heavy dependence on wild seed for postlarval supply, as extensive and improved-extensive farmers believe that the route of infection for many viral epidemics is via stocking of hatchery-bred postlarvae and that wild postlarvae are free from viral infections as they have been subject to natural selection. Most of the surveyed farms (79.7%) stocked postlarvae collected from the wild, while another 17.2% depended on both wild and hatchery-bred postlarvae. Only 3.1% of the farms stocked only hatchery-bred postlarvae. The methods of collection, holding and transport are severely stressful to wild postlarvae. Postlarvae are held for long periods in the collecting gear, transfer from collecting gear to the sorting containers is carried out without adequate care, sorting water is often in poor condition and sorting is carried out in direct sunlight. The holding conditions involve very high stocking densities (1,000 PL/L without aeration), inadequate water depths (10-15 cm) in the holding facilities, use of water with high silt loads, holding for long periods without feeding and vigorous scooping to collect larvae. The following were recommended as immediate measures to reduce stress on the postlarvae:
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