Appropriate Technologies for Sustainable and Environmentally Compatible Aquaculture Development in Bangladesh

pp. 95-105 in Traditional Technology for Environmental Conservation and Sustainable Development in the Asian-Pacific Region

Proceedings of the UNESCO - University of Tsukuba International Seminar on Traditional Technology for Environmental Conservation and Sustainable Development in the Asian-Pacific Region, held in Tsukuba Science City, Japan, 11-14 December, 1995.

Editors: Kozo Ishizuka, D. Sc. , Shigeru Hisajima, D. Sc. , Darryl R.J. Macer, Ph.D.


Copyright 1996 Masters Program in Environmental Sciences, University of Tsukuba. Commercial rights are reserved, but this book may be reproduced for limited educational purposes. Published by the Master's Program in Environmental Science and Master's Program in Biosystem Studies, University of Tsukuba, 1996.

Dr. M.A. Mazid
Director, Fisheries Research Institute, Mymensingh-2201, Bangladesh
Fax : 880 91 4874

and Mr. M.G.M. Alam
Research Student, Tsukuba University, Japan


Abstract

In the agro-based economy of Bangladesh, fisheries play an important role in nutrition, employment and foreign exchange earning, contributing 4% to GDP, 10% to export earning, 73% to animal protein intake, in addition to providing 1.4 m people full time and 11 m part time employment. The vast water resources covering 4.3 m ha of inland water and 480 km coast line with sub-tropical climate, and suitable soil and water conditions offer a very high potential for fisheries and aquaculture development. Out of total fish production of 1.08 m tons, inland open water capture fisheries generate 51%, inland fresh and brackish water aquaculture 25% and marine capture 24%.

Production from inland open water capture fisheries is being depleted due to over-exploitation and habitat degradation. However, aquaculture production both from fresh water and brackish water which mostly follows traditional and improved traditional practices has been steadily increasing. Semi-intensive shrimp farming in a limited scale is a recent development where production of 3-5 ton/ha is being obtained. Production from improved traditional practices which comprises over 95% of the total shrimp farming is as low as 300-500 kg/ha. Aquaculture technologies so far developed and practiced in Bangladesh include polyculture of carps, integrated aquaculture, culture of tilapia and silver barb in seasonal water bodies, breeding and culture of various catfishes, culture of fish in pens, brood stock improvement and nursery management etc. These are very low input environment friendly sustainable technologies being able to produce 2-6 ton/ha or more depending on the management and culture practices with assurance of good quality produce.

Key Words: Aquaculture technology, Sustainable development, Fish, Shrimp.

Introduction

Bangladesh is located in South-Asia between 20 34" and 26 38" north latitude and 88 01" and 92 41" east longitude (Fig. 1, Map of Bangladesh) and is surrounded by the Bay of Bengal, the Gangetic plains of India and the forest of Myanmar. It is primarily a low lying plain of about 148,000 sq. km criss-crossed by innumerable water courses including the mighty rivers, the Padma, Jamuna, Meghna and Karnophuli. It is a fertile, deltaic land mostly flat except for a range of hills in the southeast. And much of the land is characterized by wooded marsh land and Jungle.

In the agro-based economy of Bangladesh, fish and fisheries play an important role in nutrition, income, employment and foreign exchange earnings. It contributes 73% to national animal protein intake, 4% to GDP and 10% to export earnings, in addition to providing full time employment to 1.4 m people and part time employment to another 11 m. An estimated 73% of rural households are involved in rural fishing.

The production of fish in 1993-94 has been estimated to be about 1.08 m tons. Inland open water capture fisheries contributes to 51%, inland fresh and brackish water aquaculture 25% and marine capture fisheries 24%. Current per capita fish consumption is about 25.0 g up from 20.5 g in 1989-90. However, to achieve recommended consumption rate of 38 g/capita/day, the country needs to produce about 1.9 m tons of fish. Vast potential exists to achieve this production through sustainable development of aquaculture and resource management. The role of fisheries in nutrition and economy of Bangladesh is shown in Table 1.

During 1994-95, export earnings from fish and fishery products increased considerably to Tk. 13,000 m (US$ 325 m; Tk. 40=US$ 1) in foreign exchange of which the export of shrimp alone contributed to Tk. 10,400 m (US$ 260 m) (DOF, 1994). The production of shrimp in 1992-93 from the sea was 23,233 tons, from rivers and inland water bodies 53,520 tons and from coastal shrimp farms about 23,530 tons, the country total being 101,025 tons (Hussain and Uddin, 1995).


Table 1: Statement showing the role of fisheries in nutrition and economy of Bangladesh

Fisheries contribute: : 4.0% of GDP
(1993-94) 10.0% of export earnings
(Tk. 13,000 m=US$ 325 m in 94-95)
6.0% of total protein intake
73.0% of animal protein intake
Employment : 7.0% of total employment
Population engaged in fisheries activities : 1.4 m (full time), 11.0 m (part-time)
Recommended daily fish intake : 38.0 g/cap/day
Average daily fish intake : 25.0 g/cap/day
Average yearly intake : 9.13 kg/cap/yr
Recommended protein intake : 45.0 g/cap/day
Recommended animal protein intake : 15.0 g/cap/day
Average animal protein intake : 11.0 g/cap/day
Average fish protein intake : 7.56 g/cap/day


Fishery resources

Bangladesh is bestowed with vast and highly diverse aquatic resources which can be categorized as (a) Inland capture fisheries (b) Freshwater and brackish water aquaculture, and (c) Marine fisheries. The inland fisheries are constituted by rivers, estuaries, canals, flood plains, reservoirs and inundated paddy fields and ponds covering an area of 4.3 m ha. The culture fisheries include freshwater ponds 0.15 m ha, oxbow lakes 0.005 m ha and coastal shrimp farms about 0.125 m ha. The country has a coast line of 480 km along the Bay of Bengal with an area of 64,000 sq. km. These vast and varied aquatic resources support artisanal and commercial fisheries as well as offer opportunities for aquaculture development. The inland, coastal and marine water resources along with their productions are shown in Table 2. The trend in growth between different sub-sectors of agriculture over the last five years (DAE, 1995) is shown in Table 3.

Aquaculture

Through out the world, aquaculture is being looked upon as a panacea for meeting the increasing demand for fish, as catches from open waters are declining due to over exploitation and degradation of fish habitats, in which Bangladesh is no different. Fish production from inland open waters of Bangladesh declined due to massive construction of flood control structures, over exploitation, abstraction of water for irrigation, intensive agriculture and industrial development, erosion and siltation, reclamation of land for human settlement, pollution, destruction of mangrove forests, etc. On the other hand, there are 146,890 ha of ponds, 5,488 ha of ox-bow lakes and 140,000 ha of brackish water areas, where aquaculture can be undertaken. Also there are large number of beels (natural depressions) which were much abundant in fish earlier have now silted up and being used for growing paddy have become fishless due to twin problems of water shortfall and pesticides use in such shallow water. This calls for undertaking enhanced aquaculture both in depressions and oxbows and to upgrade and maintain the resource base properly for such use. In addition, there are some 8 million ha of rice fields, where aquaculture can be integrated with rice farming. These water resources offer excellent opportunities for culture of various species: carps, tilapia, catfish, various species of prawn and shrimp, etc. Though aquaculture is still in its infancy, it has shown an average annual growth of 16.8% in the last ten years and contributed 36.7% to the inland fish production and 25.3% to the total fish production during 1993-'94 (Mazid and Gupta, 1995). Productions obtained from these aquaculture resources are still below optimum levels, being on an average 1700 kg/ha in case of carp culture in freshwater ponds (1992-`93) and 250 kg/ha in case of shrimp in brackish water enclosures locally called ghers.
Table 2: Area of different fisheries resources with production in 1993-94.

Source Water area Production % contribution to
(ha) (tons) total production
A. Inland fisheries
a. Inland open water capture
Rivers and estuaries 1,031,563 137,000 12.6
Flood plains 2,832,079 353,000 32.5
Beels & Haors 114,161 57,000 5.2
Reservoir 68,800 5,150 0.5
Total capture 4,046,800 552,150 50.8

b. Inland closed water culture
Ponds 146,890 231,000 21.2
Oxbow lakes (Baors) 5,488 2,000 0.2
Brackish water farms 125,000 42,000 3.9
Total culture 254,678 275,000 25.3
Total Inland (a+b) 4,301,281 827,150 76.1

B. Marine fisheries
Industrial 15,000 1.4
Artisanal 245,000 22.5
Total 260,000 23.9

GRAND TOTAL (A+B) 1,087,150 100

Table 3: Data showing the progress of growth between different agriculture sub-sectors during 1990-95 (%s)

1990-91 1991-92 1992-93 1993-94 1994-95
Agriculture 1.6 2.2 1.8 1.8 0.2
a) Crop 1.2 1.7 0.8 0.5 -2.0
b) Forestry 2.1 2.4 3.0 3.0 4.5
c) Livestock 2.2 3.6 6.2 6.2 9.0
d) Fisheries 5.8 6.5 6.6 8.7 8.5

Source: Department of Agriculture Extension


Aquaculture technologies

Scientific aquaculture in Bangladesh was actually initiated in mid 1980's when Fisheries Research Institute (FRI) was established in 1984 and started developing improved aquaculture technologies through research. The Institute in the mean time has developed a number of improved aquaculture and management technologies (FRI, 1993) aimed at increasing fish production among which those found viable in farmer's field are being disseminated throughout the country. These include: (i) culture of tilapia (Oreochromis niloticus ) and (ii) culture of Silver barb (Puntius gonionotus ) in seasonal water bodies, (iii) polyculture of carps, (iv) integrated poultry/duck- fish farming, (v) paddy-cum-fish/shrimp farming, (vi) culture and breeding of catfishes (Ompok , Mystus , Pangasius , Clarias spp.), (vii) culture of fish in pens, (viii) genetic approaches to the stock improvement of some commercially important fishes, (ix) fish feeding and nutrition, (x) hatchery and nursery development, (xi) culture of freshwater giant prawn (Macrobrachium rosenbergii ), and (xii) culture of penaid shrimp. The impact of these technologies is discussed in some details below:

Culture of tilapia

Tilapia (O. mossambicus ) was first introduced in Bangladesh in 1954 which was not succeeded at that time. Later in 1974, UNICEF again introduced O. niloticus from Thailand. This attempt for tilapia culture also did not flourish as its biology, behaviour and culture technology were not known.

FRI then in 1987 and 1988 imported black and red tilapia, carried out investigation on their biology and behaviour and successfully developed culture technologies through research. As a short-cycled quick growing fish, O. niloticus has proved as a worthy fish for culture in seasonal ponds and ditches in the rural areas of the country which retain water for 4-6 months. The culture technology is so simple that by stocking at a density of 20,000/ha and by using 60% rice bran and 40% mustard oil cake as feed, a production of 3.5 tons/ha was possible to obtain in 6 months with a net profit of Tk. 65,000. Under intensive system, net yield of 6.6 tons/ha/6 months was obtained in monosex culture which makes aquaculture of tilapia competitive than any other trade.

In case of red tilapia, a production of over 5.5 tons/ha/yr was achieved applying the same management practices. In such culture practices the fish farmers could get a net profit of Tk. 0.19 m/ha/yr. This low-input technology is suitable for rural women's participation in the context of socio-religious point of view where women can not get out of home for work. Culture of tilapia even in seasonal ponds and ditches would substantially increase the country's total production of fish.

Culture of Silver barb (Puntius gonionotus )

This is also known to be a short cycled fish with faster growth which attain marketable size in 4-6 months was introduced to Bangladesh in 1977 from Thailand. FRI has developed viable technology of induced spawning for commercial seed production and semi-intensive low-input culture technology. The large group of marginal fish farmers can easily have a good crop even within 3 months from their homestead mini-ponds and small ditches like seasonal water bodies by culturing this fish. After preparation of ponds as an essential step in all aquaculture operations, fingerlings of 8.0-10.0 g size of silver barb have to be stocked at a density of 15,000-16,000/ha. The culture technology is so simple that by feeding only rice bran at the rate of 5-6% of standing crop, the fish attains harvestable size of 100-150 g within 3-5 months. A minimum production of 1.4 tons/ha in 3 months or 2.5 tons/ha in 5 months is presently being obtained by the farmers with a net benefit of Tk. 57,000/ha/3 months.

Figure 1: Map of Bangladesh

Taking into account of the potential and prospect of tilapia and silver barb culture in large number of country's existing seasonal ponds and ditches, the successful transfer of the technology to the farmers would certainly bring a revolutionary change in aquaculture production, public nutrition and economy of Bangladesh.

Polyculture of carps

By the age-old traditional carp culture practice in perennial waters, farmers used to get very low production. Culture of different species of carps together is known as polyculture or mixed culture of carps. In polyculture system, fast growing compatible fish species of different feeding habits are stocked in different proportions in the same pond, so that all the ecological niches in the pond are proportionately occupied. A stocking density of 6,000-9,500/ha with 6.0-9.0 cm size fingerlings usually gives better production. Based on feeding habit, a suggested ratio of different species for polyculture system is surface feeders 40% (Catla catla 10% and Hypophthalmichthys molitrix 30% or Catla catla 30% and Hypophthalmichthys molitrix 10%), column feeder 20% (Labeo rohita and Puntius gonionotus ), bottom feeders 30% (Cirrhina mrigala and Cyprinus carpio ) and macrovegetation feeder 10% (Ctenopharyngodon idella ). In polyculture system, an average production of 4.0-5.0 tons/ha/yr is obtained by using simply rice bran as feed and fertilizing water with cow-dung and inorganic fertilizers (urea and triple super phosphate), as a low capital input technology. This sort of operations provide a farmer a net profit of Tk. 0.16 m/ha/yr.

In case of medium and large farmers who have some financial resources, integration of polyculture with poultry has been found to be highly profitable. It is evident that through aquaculture practice, a farmer can increase his income 5-7 times more than from agriculture, thus offering an excellent opportunities for generation of employment and alleviation of poverty.

Integrated poultry/duck fish farming

The increasing demand for food to support world population and continuing blockade of land or other production bases call for integrated production approach to improve the efficiency of utilization of limited resource base of small farmers. So, from the farming system point of view, farmer's activities in a farm, such as, crop production, homestead vegetable production, raising livestock and poultry, fish culture, etc. have to be viewed not as separately but as totality of all such activities which are very much interlinked. The interlinking mechanism operates in such a way that crop residues and wastes are used for feeding livestock and fish, again livestock wastes are used in agriculture and aquaculture operation and livestock is used in agriculture as draft power.

In integrated poultry/duck fish farming, droppings of birds and feed wastes are recycled in ponds for production of fish. Only by raising 500 ducks or chickens in a poultry shed over per hectare pond, production of 4.0-6.0 tons/ha/yr of fish in the case of duck-fish and 4.0 tons/ha/yr in the case of chicken-fish was obtained. In addition, up to 240 eggs were obtained per bird per year (Latif et al., 1993). Broiler/fish is more profitable than layer/ fish farming as the broilers grow fast and become sellable within 6-8 weeks thus ensuring quick cash return for the poor farmers. Use of 500 birds/ha has been found a standard density which keeps water quality good for domestic purposes except for drinking. Here, except feeding the birds, the fish do not require any supplementary feed or fertilizer in order to grow.

In such an integrated system, poultry excreta acts as manure in the pond and enter into the food-chain in the pond ecosystem. Economic analysis of operations proved the system to be highly remunerative providing a net profit of up to Tk. 0.16-0.18 m/ha/yr thereby enhancing productivity of land many-folds.

Paddy-cum-fish/shrimp farming

In the past, plenty of fish was available in the rice field during monsoon which used to form natural rice-field fisheries. However, increasing cultivation of HYV paddies with subsequent increase in application of pesticides has severely affected the natural rice-field fisheries of the country. As mentioned in page 3, the country's 8 m ha rice fields have great potential for developing rice fish farming system. Considering the input cost, multi-commodity farming system is more economical than monocropping system.

In the context of present rice cultivation method, two crops of paddy (long-stem transplanted Aman in Kharif and HYV in Rabi season) and a single crop of fish rearing through both the seasons can be obtained. In Bangladesh, short-cycled fish like, Silver barb (P. gonionotus ), Tilapia (O. niloticus ), Common carp (C. carpio ) and shrimp (M. rosenbergii ) in freshwater paddy fields, P. monodon in coastal paddy fields have been found to grow well in rice-fields.

In rice-fish farming experiments of FRI, production of T. Aman ranged from 0.6-3.0 tons/ha and that of second crop of boro ranged from 4.5-5.0 tons/ha. Production of fish (major carps, common carp and silver barb) stocked at a density of 6,000-9,000/ha ranged from 0.70-0.80 tons/ha. Net benefit from concurrent rice-fish culture would stand around Tk. 41,208.0/ha/6 months. Freshwater giant prawn (M. rosenbergii ) when cultured with rice at 16,000-17,000 stocking density/ha, produced 0.30-0.40 tons/ha (Haroon, 1989). Both fish and shrimp culture with rice do not require any feed or any extra fertilizer other than those that are normally applied for rice.

In rice-fish integration as shown in Figure 2, crop residues (brans and straw) can be used as feed to fish (bran) and livestock (bran and straw); pond mud can be used as manure in rice fields and vegetable plots and livestock manure can be used for fertilizing fish ponds and rice fields.

Coastal saline soils occupy an estimated 2.8 m ha in southern part of the country which receive tidal saline water and hold for few months. Kharif paddy varieties are widely cultivated in these areas. After the tidal water enters in March, tiger shrimp (P. monodon ) and mullet (Liza parsia ) are stocked at a density of 100,000/ha and cultured up to June and harvested. Subsequently, saline water is drained off before monsoon and after washing out the land with monsoon water, kharif paddy cultivation with freshwater fish is undertaken. The fish cultivation for 3 months gives an yield of 0.25-0.30 tons/ha of which 40% is contributed by M. rosenbergii and the rest by carps.


Figure 2: Material flows in rice-fish farming system


Culture and breeding of catfishes (Ompok , Mystus , Pangasius , Clarias spp.)

In Bangladesh, both native and exotic catfishes are popular to the farmers. Among them Ompok pabda , Mystus cavasius , Clarias batrachus , Pangasius pangasius are native and C. gariepinus and P. sutchi are exotic. Breeding and culture techniques of all of them have been developed.

Hybrids have been produced through cross breeding between native female C. batrachus and male African C. gariepinus . The F1 hybrid showed better growth and survival than the parental stocks and proved to be a maternal heterosis. This hybrids attain a size of 200-300 g within 2-3 months, where it needs about one year for C. batrachus to grow to this size. Fingerlings of 5-10 g in size are stocked at a density of 50,000 - 400,000/ha depending on the culture and management practices. Feeding is applied daily at 4-5% of body weight. Formulated diet containing either fish meal (40%), rice bran (20%), wheat bran (15%), oil cake (20%), molasses (4%) and vit. premix (1%) or fish meal (2%), blood meal (22.5%), sesame oil cake (23%), rice bran (43.5%), flour (4.5%), vit. premix (0.5%), salt (1%), soybean oil (1%) and oyster shell (2%) is used as feed. Fish production ranges between 49.0 and 50.0 tons/ha and net profit is around Tk. 1.70 m/ha.

Polyculture of Pangasius spp. with major carps at a stocking density of Pangasius 8,000/ha, Catla 1,000/ha and Labeo 500/ha produced an yield of 4.0-4.5 tons/ha/yr and net benefit was at the tune of Tk. 0.194 m/ha/yr. In contrast, monoculture of Pangasius produced only 2.0-2.5 tons/ha/yr. In 1990, P. sutchi was introduced to Bangladesh from Thailand. Subsequently its breeding and larval rearing techniques have been developed in 1993. By now it became one of the popular species for closed water aquaculture.

Culture of fish in pens

Bangladesh has got numerous tributaries, irrigation canals, ox-bows, haors and depressions where potential exists for pen culture. FRI initiated experimental fish culture in pens within the irrigation canal and Flood Control Project at Chandpur in 1990. During the last 3 years the Institute has standardized stocking density, selection of species and the ratio and succeeded in developing appropriate technology for culture of fish in pens. Results so far obtained is quite promising. A production of 2.7 tons/ha/6 months was obtained by stocking 20,000/ha of major carps following a ratio of L. rohita 30%, C. mrigala 20%, C. catla 10%, H. molitrix 10% and C. carpio 30% . Economic analysis of the operation shows a net profit of Tk. 0.13 m/ha.

Genetic approaches to the stock improvement of some commercially important fishes

Genetic improvement of catfish, carps and tilapias was undertaken with a view to develop triploidy in hybrid Clarias sp., L. rohita and C. mrigala and mitotic gynogenesis in L. rohita leading to the production of genetic clones in F2 generation by heat shock treatment. Sex reversal technique was used to develop all male progeny of O. niloticus and subsequently, a true breeding population of red tilapia was produced through the test cross and body colour inheritance studies.

Improvement of stocks of P. gonionotus , C. catla and L. rohita through selective breeding and line crossing techniques is in progress.

Fish feeding and nutrition

Balanced supplemental feed plays a key role in increasing aquaculture production. Development of balanced feed again depends on the knowledge of the exact nutritional requirements of fish. The nutritional requirements of fish also varies with species or even within the individuals of the same species. Therefore, feeding strategy must be economic and satisfy all nutritional needs of the fish to be cultured. The natural food available in the water are not sufficient to maximise growth and production of fish. Shortage of natural food in the pond still remains even after application of fertilizers which affects normal growth. Therefore, supplemental feeding is necessary to increase the per unit area production.

Initially a nationwide survey was undertaken to identify potential fish feed ingredients based on their availability, price and primary nutritional value (FRI, 1989). Eighty three different types of ingredients, both of plant and animal origin, have been studied. The survey covered materials that are being traditionally used and also non-conventional items such as, kitchen waste, processed waste from the food/fish industry, aquatic weed, etc. On the basis of the results, 35 out of 83 ingredients were found suitable as fish feed. Most important ones are : rice bran, wheat bran, mustard oil cake, sesame oil cake, fish meal, animal blood meal and viscera, silk worm pupae and aquatic plants like, water hyacinth, duck weed, azolla, etc.

The use of animal protein source in the supplemental feed is most important for growth. The institute from an investigation determined that the requirement of protein in the diet for various species of major carps remain between 35% and 45% depending on the type of species (Akhter et al, 1993). Keeping in view the socio-economic aspects of rural poor fish farmers, the Institute has developed low-cost but high quality supplementary feed for carp polyculture and nursery. The formula of two such supplementary feed are given in Table 4.


Table 4: Composition of feed for nursery and grow-out of carps

Ingredients % used % protein

a. Nursery feed for carps (Feed price Tk. 12.82/kg)

Fish meal 21.0 12.13
Mustard oil cake 45.0 13.65
Rice bran 28.0 3.33
Flour 5.0 0.89
Vitamin & mineral mix. 1.0 -
Total 100 30

b. Grow-out feed for polyculture of carps (Feed price Tk. 8.80/kg)

Fish meal 10.0 4.24
Mustard oil cake 30.5 9.19
Rice bran 53.0 6.30
Vitamin & mineral mix. 0.5 -
Waste molasses 6.0 0.27
Total 100 20


Hatchery and nursery development

Aquaculture for its high potential is expanding at a faster rate because of development of improved technology. However, the shortage of fish seed is a major constraint. This problem can be reduced to an extent if the hatchlings produced in the hatchery are raised properly in nursery pond. To meet the increased demand for fish seed for large-scale aquaculture extension, the Institute conducted a series of experiments for the development of nursery technique to increase the growth and survival through improved pond preparation and optimizing stocking density, feeding and fertilization. A flow diagram of improved nursery management operation of carp is in Figure 3.


Figure 3: A flow diagram of improved nursery management operation of carp.

Improved nursery management practice follows a double stage rearing technique. In the first stage nursery, fries are stocked at a density as high as 8.0 m/ha and reared for up to 21 days to attain 2.5 cm size survival rate being obtained as 70%. In the second stage nursery, stocking density is reduced to 10% (0.8 m/ha) and reared for 60 days to get fingerlings of 5.0-7.5 cm size which are suitable for stocking in the ponds (Haque et al, 1993, 1994). The net income derived from nursery operation of a 10 decimal pond was estimated to be Tk. 0.16-0.19 m.

Pond culture of freshwater giant prawn

(Macrobrachium rosenbergii )

From economic point of view, shrimp is a high value commodity in the world market. In Bangladesh, a large quantum of foreign exchange earnings (9% of total export earnings) is being generated from the export of both freshwater and marine shrimps and is continuously increasing year by year. This has given a big push in rapid expansion of brackish water shrimp farming in the coastal areas. However, freshwater shrimp farming did not progress significantly compared to the brackish water shrimp culture, although favourable climatic conditions prevail.

Freshwater giant prawn (M. rosenbergii ) is the major freshwater shrimp in respect of production and demand. Keeping this in view, FRI gave a major thrust for the development of a viable technology for commercial culture of Macrobrachium in freshwater ponds and achieved significant success. Monoculture of Macrobrachium at a density of 15,000/ha yields 0.277-0.322 tons/ha/6 months (Mahmud et al, 1991, 1993) which is quite satisfactory compared to the present level of production of 0.15-0.20 tons/ha from extensive culture practice.

Polyculture of Macrobrachium with fish is more profitable than its monoculture. A production of 3.0 tons/ha of fish and 0.20 tons/ha of prawn is obtained when juveniles of shrimp are stocked at a density of 10,000/ha and fish at 5,000/ha (following recommended ratios for various carp species) and cultured for 8-10 months in perennial waters. Macrobrachium has also been found suitable for concurrent culture with rice and a production of about 0.30-0.40 tons/ha/6 months is obtained in such operation.

Macrobrachium constitutes about 70% of the total freshwater prawn production. So, culture of Macrobrachium in ponds with fish would not only increase total pond production but would also raise the economic return of the farmer in view of the high price it commands in the market. However, the constraints in expanding Macrobrachium culture is the non-availability of seed to the farmers. The Government has put top priority to encourage establishment of Macrobrachium hatchery for large scale production of seed. FRI has recently developed a prototype backyard prawn (freshwater) hatchery which already has become extremely popular to the progressive prawn seed producers.

Culture of penaeid shrimp (Penaeus monodon )

Shrimp culture in large inundated tidal flats in the coastal districts of Bangladesh is primarily the culture of penaeid shrimp (P. monodon ) which is generally called brackish water aquaculture. The culture system is by and large traditional. Under the traditional system, tidal water carrying shrimp juveniles and fin fish are allowed to enter during February to April through sluice gates of the embankment originally constructed to prevent saline water intrusion into the tidal flats for crop protection. The trapped young are allowed for about four months to grow before harvest.

With the increase in demand and price in the international market, shrimp culture started expanding since 1970's. According to a survey conducted in 1982-83, the area under shrimp culture was 52,000 ha (Mazid, 1994). Presently land under shrimp culture has increased to about 0.125 m ha. About 75% of this land is located in the Khulna, Bagerhat and Satkhira districts in the south-west and the rest in the Cox's Bazar district in the south-eastern region of the country. The area suitable for penaeid shrimp culture in the country is about 0.20 m ha. In Khulna areas, penaeid shrimp is cultured in the dry season followed by paddy cultivation in the rainy season often with freshwater prawn and in Cox's Bazar area, shrimp and salt are produced alternatively.

The average production of shrimp under traditional culture system as mentioned in the previous section is about 0.20 tons/ha. Some of the private farms initiated semi-intensive shrimp culture in Cox's Bazar area in 1993 and achieved a production of 3-5 tons/ha which opened a new era in shrimp culture (Hussain, 1995). However, the semi-intensive shrimp culture requires high investment in the form of seed, feed and other appliances (aerator, pump, soil/water quality checker, etc.). The greatest problem affecting semi-intensive shrimp culture is the shortage of seeds. Presently, monodon culture almost entirely depends on the collection of wilds seeds. Over-exploitation of shrimp seeds in the natural water is not only causing ecological imbalance but also resulting in severe scarcity. Therefore, in order to sustain the penaeid shrimp culture, establishment of monodon hatchery is an urgent need. Foreign collaboration is very much encouraged for this purpose. However, experiences from other countries show that semi-intensive shrimp culture has a high risk of disease which need highly improved management in respect of water quality management, stocking density, feeding, aeration, water exchange, sludge removal, etc.

In Bangladesh, penaeid shrimp is cultured mostly by extensive, improved extensive and in a very limited scale by semi-intensive method. Under the improved extensive method as developed by FRI, 2-3 juveniles are stocked per m2 in ponds of a few to 50 ha size. With little pond preparation, soil and water quality management, manuring, fertilization and occasional feeding with some water exchange, a production of 500-800 kg/ha is being obtained. This is sustainable and environmentally compatible having no risk of disease.

Conclusions

Although resources for fish production are vast, there are many constraints: biological, social and economical, where research needs to be strengthened to harness this potential. Fisheries and aquaculture research support in Bangladesh are still in its early stages and investments made in this sector in the past were negligible. To conserve and manage fishery resources for the benefit of the present and future generations, the resources need to be managed and exploited on a sustainable basis. Keeping this in view, aquaculture research so far carried out was primarily directed towards improving the age old traditional culture practices so that the rural poor farmers can really afford those to increase their aquaculture productivity with little scientific intervention. The farmers could increase fish and shrimp production by 3-5 times following the improved aquaculture management practices. While developing improved aquaculture technologies, proper consideration was given to sustainability, environmental protection, social acceptability and economic viability. The aquaculture technologies discussed in this paper are appropriate, sustainable and environmentally compatible in the context of Bangladesh.

Fisheries Research Institute is the nodal institution in the public sector and is responsible for conducting and coordinating all fisheries research in Bangladesh and advising the Government in all matters relating to fisheries research and development. The institute practically functioning from 1986 is still in its infancy. In order to carry out its mandated responsibility, the capability of the institute needs to be strengthened in respect of physical research facility creation, procurement of equipment, manpower development and research planning. So, the institute would appreciate any Japanese technical cooperation for its development. It is worthy to mention that many Bangladeshi Scientists have persuade higher studies in the field of fisheries from Japanese Universities but they are not in a position to fully utilize their knowledge and expertise that they have gained during their higher studies in Japan because of inadequate and inappropriate research facilities at home. Presently about 20 FRI Scientists are pursuing higher studies in different Japanese Universities.


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