1. Aquaculture extension services: Review

1.1 Introduction
1.2 Capture fisheries
1.3 Aquaculture

1.1 Introduction

Agro-demographic features
Economic indicators
Social indicators

Agro-demographic features

Location. Bangladesh lies in the northeastern part of South Asia. It is bordered by India on the west, north, and northeast; by Burma on the southeast, and the Bay of Bengal on the south. Its area is 143,999 km². Its territorial waters extend up to 12 nautical miles (19.2 km) and EEZ up to 200 nautical miles (320 km) from the coastline.

Physiography. The country consists of low and flat land except in the northeast and northwest which are strewn with small hillocks. The north and northwest are slightly undulated. A network of 230 rivers with tributaries more than 24,000 km long traverses the country, particularly its southern half, flowing down to the Bay of Bengal. The main rivers include the Padma, Jamuna, Teesta, Brahmaputra, Meghna, Surma, Karnaphuli, Sibsa, and Pussu. The sun- and wind-eroded particles of mineral-rich rocks of the Himalayan region are washed by rains into the rivers which transport the silts and deposit them on either sides of the river banks during the annual floods. This continuously enriches the soil and water.

Climate. The country has a sub-tropical monsoon climate. The beginning and the end of the six seasons (summer, monsoon, early autumn, late autumn, winter and spring) are often difficult to distinguish, there being three main seasons: summer (March-June), monsoon (July-October) and winter (November-February). The average maximum and minimum summer temperatures are respectively 34°C and 21°C, and during the winter season 29°C and 11°C. The maximum temperature in summer is 36.6°C but this occasionally rises to 41°C. The minimum winter temperature sometimes decreases to 6°C in scattered places. The average monsoon rainfall of the country varies from 1,194 mm to 3,454 mm. The hilly districts of Chittagong and Sylhet which fringe the eastern border receive the maximum rainfall, while the western and northern parts of the country are relatively dry.

Table 1. Fisheries and livestock contribution to GDP (at constant 1984-85 prices), 1989/90-93/94 (in %)

Sub-sector	1989-90	1990-91	1991-92	1992-93	1993-94
Fisheries	2.8	2.8	2.7	2.8	2.9
Livestock	2.7	2.7	2.8	2.8	2.9

Demography. The 1991 census indicated the population at 111.4 million, with a density of 755 per km². The urban sector accounted for 20 percent of the population and the rural, 80 percent. The population growth rate between 1981 and 1991 was 2.17 percent. There were 106 males per 100 females. The life expectancy at birth was 58.1 years in 1994, and the literacy rate, 37 percent in 1991. The Muslim population was dominant (88.3 percent); the rest consisted of Hindus, Buddhists and Christians. More than 47 percent of the population lived below the poverty line (calorie intake below 2122 kcal) and 28 percent below the absolute poverty line (below 1805 kcal)

Economic indicators

GDP. The country’s GDP (1993-94) at current price is Tk.1030 billion and at 1984-85 constant price, Tk.583.80 billion. The agriculture sector and its four sub-sectors (crops, forestry, livestock and fisheries) are the largest contributor (34.6 percent in 1993-94) to GDP (Table 1).

The crop sub-sector constitutes the biggest component of agriculture, but its contribution has been declining; in 1994-95, its GDP growth rate was negative. However, the overall GDP growth rate for the agriculture sector was positive as a result of the significant growth of non-crop sub-sectors (forest, fisheries and livestock).

Table 2. GDP growth rates at constant price (1984-85=100), selected sub-sectors, 1990-95.

Sector		1990-91	1992-93	1994-95
1. Agriculture		1.6	1.8	0.2
	1.1 Crop	1.2	0.8	-2.0
	1.2 Forestry	2.1	3.0	4.5
	1.3 Livestock	2.2	6.2	9.0
	1.4 Fisheries	5.8	6.6	8.5
2. Minerals and quarrying		21.2	13.8	13.1
3. Industries		2.4	9.1	10.1
Total GDP		3.4	4.5	5.1

Source: BBS and Planning Commission

Social indicators

Employment. Bangladesh is a country of rapid population growth and its labour force has correspondingly increased at a fast rate (from 16.9 million in 1961 to 30.9 million in 1985-86 and to 50.7 million in 1989). The significant increase in the size of the labour force (about 20 million over a three-year period) is due to the sharp increase of the female labour force from 3.2 million in 1985-86 to 21 million in 1989. It should be noted that recognition of female involvement in economic activities on-farm started only with the 1989 Labour Force Survey (LFS). The Bureau of Statistics and DOF report 1.3 million fisherpersons, of whom 0.8 million are engaged in inland and 0.5 million in marine waters. Statistics on employment in the aquaculture sub-sector are not available, but preliminary estimates on aquaculture and related activities are shown in section 5.1.

Fisheries activities, like those of other subsectors, are male-dominated. But some departures from the general pattern can be seen in shrimp fry collection and shrimp processing activities. In the case of aquaculture in small domestic fishponds, and Galda Ghers, women have been observed to play a significant role.

Administrative units. The country is divided into 6 administrative divisions, 64 districts, 490 thanas, 4,451 unions, 59,990 mouzas (revenue villages) and 19,979,932 households (BBS, 1995).

Health. In 1994, the country had 919 hospitals of which the Thana and Rural Health Complexes made up 396; 35,795 hospital beds and 24,911 registered physicians (BBS, 1995). There was only one bed for every 3,288 persons, and one physician for every 4,725 persons representing 802 households.

Education. The 1994 enrolment at the primary education level (5-9 years) was 16.7 million; secondary level (10-14), 4.1 million; college level, 0.9 million and university level, 0.12 million. Per capita, total public sector expenditure was Tk.235 in 1994 (BBS, 1995). The literacy rate (7 years and above as per 1991 figures) was 32.4 percent.

1.2 Capture fisheries

Inland fisheries
Marine fisheries

Inland fisheries

Bangladesh fisheries consists of inland capture, marine capture and inland aquaculture. The major portion of the country’s fish production is of inland capture fisheries origin, consisting of freshwater and brackishwater rivers and their tributaries, beels, Kaptai lake and floodplains. Data on fish production by source are shown in Tables 3 and 4.

Table 3. Annual production of inland and marine fish, 1970/71-1982/83

Year	Inland	Marine	Country Total
1970-71	729	85	814
1971-72	729	85	814
1972-73	731	87	818
1973-74	732	88	820
1974-75	533	89	822
1975-76	745	95	640
1976-77	541	100	641
1977-78	533	110	643
1978-79	527	118	645
1979-80	524	112	636
1980-81	524	125	649
1981-82	556	130	686
1982-83	584	144	728

Source: Department of Fisheries

Source/Areas (ha)	84-85	85-86	86-87	87-88	88-89	89-90	90-91	91-92	92-93	93-94
Rivers and Tributaries 1,031,563	219882	206712	201152	191883	187556	174803	142006	131140	145,685	150,552
Beel 114,161	45898	45258	42077	45610	47019	46594	47923	49201	53,019	55,592
Kaptai lake 68,800	2700	2433	3981	4068	3439	3713	4392	4216	4,142	6,635
Floodplains 2,832,792	194130	187396	183796	182037	186126	193762	249083	295185	329,573	360,597
Total 4,047,316	462606	441799	431006	423598	424140	423872	443404	479742	532,419	573,376

Source: DOF, 1993-94. Fish Catch Statistics of Bangladesh, 1993-94.

An analysis of fish production statistics indicates the following major points:

• Inland capture fisheries has always been the largest important contributor to total fish production.
• During the 60s and 70s, both culture fisheries and marine fisheries were poorly developed.
• As detailed statistics of fish production by various sources during the 60s and 70s are not available, the relative contribution of each type of water body cannot be gauged. But taking into consideration the fact that culture fisheries in the early 70s was poorly developed, it could not have contributed more than 10 percent to the total catch of inland origin.
• Consequent upon the implementation of a fishery resources survey system (FRSS) project, fish production statistics by source and by year can be compared starting 1983-84. Between 1983-84 (471,595 mt) and 1987-88, inland capture fisheries production registered a decline of 10.2 percent. Its contribution to the total catch in 1983-84 was 62.6 percent, and subsequently declined to 51.2 percent in 1987-88. Production in rivers and floodplains, the two largest sources of inland open water fish production has registered a steady decline for several years since 1983-84. A combination of factors mostly man-made or -induced apparently affected inland capture fisheries. Most of these factors are associated with resource use conflicts.
• Since 1988-89, overall production from inland capture fisheries has improved and shown a steady upward trend. However, the riverine fish catch continued to decline until 1992-93.
• Since 1992-93, riverine production (145,685 mt) has shown an upward trend, reaching 150,552 mt in 1993-94; this level is below the 1983-84 level (219,882 mt). Floodplains production declined from 201,000 mt in 1983-84; 194,130 mt in 1984-85; and down to 186,126 mt in 1988-89. Since this period, production has improved, increasing to 360,597 mt in 1993-94. Statistics suggest that the declining trend in the production from inland open water fisheries has not only been halted, but reversed. This reversal reflects the large-scale artificial stocking of the open water systems and concurrent Government action to conserve fisheries resources.

Catch from inland open waters, 1993-94

Percentage of catch by water type. The percentage contribution of various types of inland open waters to the total catch from open water fisheries are as follows: rivers and estuaries 26.2 percent, beel 9.7 percent, Kaptai lake 1.2 percent and floodlands 62.9 percent. The Meghna river alone contributed 47 percent to the total fish catch.

Catch by major species group and water types. Inland capture fisheries produced 573,376 mt of fish in 1993-94 (Table 5). Various species of carp combined constitutes 8.2 percent, and hilsa, 12.4 percent. The airbreathers (snakehead, climbing perch, Heteropneustes and Clarias species) consist of 20.3 percent and catfish (Wallago attu, Mystusaor, Rita rita, Pangasius, etc) 4.7 percent.

Table 5. Catch (in mt) by species groups and water types, inland capture fisheries, 1993-94.

	Rivers, estuaries, Sundarbans	Beel	Kaptai lake	Flood lands	Total	% of total production
All Carps	3,285	18,401	345	25,169	47,200	8.2
Hilsa	71,370	-	-	-	71,370	12.4
Catfish	5,347	16,066	315	5,337	27,065	4.7
Airbreathers	639	4,531	62	111,244	116,476	20.4
Big shrimp	1,012	-	-	2,885	3,897	0.7
Small shrimp	21,571	1,751	-	22,177	45,499	7.9
Others	47,328	14,843	5,913	193,785	261,869	45.7
Total	150,552	55,592	6,635	360,597	573,376	100.0

Contribution of various fish groups by water types

The percentage contribution of various fish groups to overall production, by different categories of open water bodies, is shown in Table 6.

Table 6: Percent contribution to the total catch of fish groups by category of inland open water bodies.

	Rivers, tributaries	Beel	Kaptai lake	Flood lands
Carps	1.3	33.1	5.2	7.0
Hilsa	49.5	-	-	-
Catfish	3.7	28.9	4.7	1.5
Airbreathers	0.4	8.2	0.9	30.8
Big shrimp	0.5	-	-	0.8
Small shrimp	15.0	3.0	-	6.2
Miscellaneous	29.6	26.8	89.2	53.7
Total percent	100	100	100	100

Table 6 shows that in the riverine sector, hilsa is by far the most important (49.5 percent) species. In beels, carp and catfish species together constitute 62 percent. In Kaptai lake, the most important species by tonnage is chapila (Gadusia chapra) constituting 19 percent of the lake fisheries. Carp and catfish in this lake respectively account for 5.3 percent and 4.7 percent. In the floodland fishery the airbreathers form the dominant group (30.8 percent) and carp accounts for only 7 percent.

Principal brackishwater species. The principal brackishwater finfish species are mullets (Mugil cephalus, Liza tade, L. parsia), Lates calcarifer, Glossogobius giuris, Eleutheronema polydactylus. The important shrimp species that spend a part of their life cycles in the inland brackishwater regions include several species of penaeid, metapenaeid, and palaemonid shrimp.

Spawn and fry collection from the open waters. Nearly 4,000 million Penaeus monodon and Macrobrachium rosenbergii fry are currently collected from the open surf and the estuarine rivers for stocking about 140,000 ha of shrimp farms.

Until the 1970s the major share of the carp spawn used for aquaculture came from open waters. Dependence on wild fry gradually decreased with the development of carp hatcheries in several places. About 92.5 percent of the total carp spawn (78,407 kg) used in aquaculture are from hatcheries while only 7.5 percent (5,872 kg) are from riverine sources.

Marine fisheries

Unlike in most maritime nations, marine fisheries in Bangladesh does not constitute the major share of total fish production; its contribution is not very significant. In 1973-74, the share of marine fisheries (88,000 mt) in the national catch (820,000) was 10.7 percent. By 1993-94, marine catch increased to 253,044 mt accounting for 23.2 percent of the national total catch (1,090,596 mt).

Table 7. Areas by depth zone, Bangladesh shelf

Depth zones	Area (km2)
<10	24,000
10-24	8,400
25-49	4,800
50-74	5,580
75-99	13,410
100-199	10,250
Total	66,440

Source: BOBP, 1985

Of the total marine catch, the artisanal fisherpersons account for 95 percent, and industrial trawlers for 5 percent. But the discards of industrial trawlers (some 30,000-40,000 mt of low-value fish or trash fish) are not included in their reported total catch. The artisanal fishing fleet, composed of some 11,000 non-motorised and 6,000 motorised boats are operated within the 40-m depth line. The industrial fishing fleet consisting of 43 shrimp and 11 fish trawlers operate between 40 and 100 m depth zones. There are about 0.5 million fisherpersons engaged in marine fishing (BSS, 1995).

Artisanal fishing is done by using gill net, set bag net, longline, trammel net, beach seine, and cast net. The gill net and set bag net are the two most important fishing gears, accounting, in 1993-94, for 86 percent of the total marine catch. The entire marine hilsa catch is effected by gill net alone.

In 1993-94, hilsa accounted for close to 48 percent (121,161 mt) of the total marine landings (253,044 mt). Shrimp of various species combined constituted 8.5 percent, bombay duck 7.9 percent, jew fish 4.9 percent, catfish 4.5 percent. A large number of other species which individually occur in small quantities, form the rest of the catch.

Fishlandings together with discarded catch could be possibly close to the maximum allowable harvest limit. However, some data indicate an unexploited stock of Indian mackerel (Rastrelliger) and scad (Decapterus) at 60-80 m depth range (Sivasubramaniam, 1985). These two species are pelagic but are constrained to migrate to the high saline deeper layers during the wet season when the surface layers become diluted. Occurrence of small quantities of tuna and large species of mackerel in the catch, gives rise to speculation on large schools of these two fish in the offshore areas of Bangladesh.

Problems in marine fisheries

1. Past surveys (15 so far) were mostly short-term, fragmentary and not comprehensive. The surveys were also mainly concerned with industrial fishing and shrimping, and provided little technical information for the artisanal sector which is the main producer of marine fish.

2. Lack of expertise in management, conservation and utilisation of marine fisheries resources.

1.3 Aquaculture

Freshwater fish culture
Freshwater shrimp culture
Brackishwater aquaculture and shrimp culture

Potential. Aquaculture has high potentials for increasing production of selected species of fish and shrimp for domestic consumption and export. It also generates employment, creates opportunities for local ancillary industries, utilises local resources and improves the environment. It is a good source for generating additional family income. Aquaculture in Bangladesh is undertaken in freshwater and brackishwater.

Production. Culture fisheries production in 1993-94 consisted of 264,190 mt fish and shrimp, accounting for 24.2 percent of total production (1,090,610 mt) from all sources and 31.5 percent of the total inland production (837,566 mt). Out of the total aquaculture production of 264,190 mt, brackishwater aquaculture produced 39,447 mt. Between 1983-84 and 1993-94, total fish production increased by 44.7 percent and aquaculture production by 125.6 percent. Culture areas included 1.3 million ponds covering 147,000 ha, 5,500 ha of oxbow lakes and 138,000 ha of shrimp farms.

Freshwater fish culture

Of the total production of 264,190 mt in 1993-94, Indian major carps constituted 57.2 percent, and other carps (including silver carp, grass carp, mirror carp and common carp), 18.3 percent. Tilapia, Magur, Rajpunti, and others constituted 5 percent, while miscellaneous other fish including predator fish species e.g., Chana, Notopterus, Wallago, Mystus, Anabas, Heteropneustes which were actually intruders, made up 20 percent of the production.

A. Pond culture

Potential. Freshwater aquaculture is mostly undertaken in excavated ponds covering about 147,000 ha in area. Pond sizes vary from less than one ha to as big as 37 ha, with average size at 0.1 ha. Only 46 percent of the total number of ponds (representing 52.2 percent of the area) are under culture and produced 168,000 mt in 1993-94 (Table 8).

From the pond culture point of view, the important districts are Comilla, Chittagong and Chittagong hilltracts, Rajshahi, Jessore, Noakhali, Mymensingh, Dinajpur, Barisal and Khulna. Each of the above areas produces at least 10,000 mt fish through pond culture.

Table 8. Number, area and production, by category of ponds 1993-94

Item	Total	Cultured	%	Culturable	%	Derelict	%
Pond number (‘000’)	1,300	600	46.0	390	30.0	310	24.0
Pond area (‘000’) ha	147	77	52.2	45	31.0	25	17.0
Production (‘000’mt)	222.54	168	75.4	41.6	18.7	13	5.8

Culturable: Where the ponds are suitable but fish are not cultured.
Derelict: Where ponds are not suitable for culturing fish.
Sources: Water Area Statistics of Bangladesh, DOF; Fish Catch Statistics of Bangladesh 1993-94, DOF.

• Lack of adequate finance for pond repair and purchase of production inputs.
• Multiple use of ponds including for domestic purposes, thereby not permitting the application of lime, manure and fertilisers.
• Joint ownership of ponds, making investment decisions difficult.
• Lack of adequate technical knowhow on pest control, liming, fertilisation, nursery rearing, growout techniques.
• Lack of effective extension service in aquaculture.
• Insufficient supply of fingerling of appropriate sizes (10-15 cm) and of required species combinations.
• Loss of fish due to poaching.
• Non-retention of adequate water in many ponds, enabling only seasonal but not year-round culture operations possible.
• Overflooding of ponds in many areas, causing the escape of stocked fish and resulting in financial loss to the farmers.

According to the DOF (1984), the most important factors that hinder pond development are the following: lack of funds (68%), joint ownership (18%), non-profitability (7%) and other reasons (7%).

B. Baors (oxbow lakes)

Potential. Baors (oxbow lakes) covering nearly 5,500 ha produced 2,201 mt of fish in 1993-94, representing a yield of only 400 kg/ha/year. This yield is very low, compared to their production potential. Nearly 50 percent of the area covered under oxbow lakes is in the greater Jessore district, and the rest scattered in Faridpur, Khulna and Kushtia. The distribution of oxbow lakes is given in Table 9.

Table 9. Distribution of oxbow lakes, by district

District	Area (Ha)	% of total area
Jessore	2,734	49.8
Kushtia	1,458	26.6
Faridpur	965	17.6
Khulna	331	6.0
Total	5,488	100.0

Problems. There are a number of problems in oxbow lake culture.

• Short-term lease which discourage any meaningful development-oriented investment; this results in the absence of efforts to maintain minimum water level, control overflooding, and install screen in the mouth of the lake to prevent aquatic weeds from entering the lake.
• Leaseholders’ general lack of technical knowhow of the basic principles of fish culture.
• Lack of capital for development.
• Free access of flood or tidal water accelerating siltation.
• Conflicts with agriculture with regard to the use of land and water within and in the neighborhood of the baor.
• Slackness of law-enforcing agencies, thus encouraging unauthorised fishing.

C. Pen and cage culture

Potential. Considerable hopes have been placed on intensified pond fish culture to enhance fish production and generate employment. Although these efforts would help increase fish production and family income of pond owners, the impact on rural employment is limited as the ponds generally belong to families with other assets and therefore not of the poorest sector. The most needy people are those with no land or other assets, and who need employment immediately. There are excellent opportunities in Bangladesh for employing thousands of rural people on long-term basis in developing aquaculture in several promising waterbodies which are now neglected. There is an urgent need to introduce new culture techniques to make use of these water bodies.

Applying pen culture techniques can turn seasonal or perennial water bodies into productive units. Examples of these are the following.

• Slow flowing rivers or canals perennially retaining adequate depth of water (year-round);
• Irrigation canals e.g., Chandpur irrigation canal, DND canal (10-12 months);
• Roadside and along the railways, canals (5-8 months);
• Monsoon-flooded lowland (5-6 months), including haors (5-8 months), baors, oxbow lakes (year round), shrimp polders (6-8 months), and selected creeks in Kaptai lake particularly for nursery rearing (3-6 months).

Problems. Some poorly planned pen and cage culture operations under an ADB assisted fisheries project were implemented in 1980-86, and the results were not successful (Karim 1988). The failures were attributed to faulty site selection, unwise choice of pen materials, culture species and feed. Faulty implementation thus led to the failure of pen and cage culture technologies in Bangladesh, although these were successful in many countries. For the culture technologies to be successfully applied, it may be necessary to establish pilot projects in various prospective water bodies to develop appropriate models for commercial application of the technologies.

Freshwater shrimp culture

Galda (M. rosenbergii) is the target species of freshwater shrimp for culture. It has emerged as a significant economic activity during the last 4-5 years. From less than 890 ha in 1991, galda culture is now reported on over 11,000 ha (Table 10).

Table 10. Statistics on Galda farms by districts 1994[1]

District	No. of farmers	% of total number	Area of farm (acres)	% of total area	Ave. size (acre)
Bagerhat	18,105	81.2	12,803	46.2	0.7
Khulna	2,047	9.2	4,047	14.6	2.0
Jessore	299	1.3	2,211	8.0	7.4
Narail	474	2.1	617	2.2	1.3
Gopalganj	350	1.6	350	1.3	1.0
Pirojpur	669	3.0	5,665	20.5	8.5
Other1 districts	350	1.6	2,000	7.2	5.7
Total	22,294	100.0	27,693	100	1.2

Note: The statistics are based on field estimates of the DOF field officers and figures given by the Galda Farmers’ Association of Fakirhat, Mollhat and Chitalmari, Bagerhat. Area is in acres.

¹ Barisal, Barguna, Patuakhali, Jhalakati, Satkhira, Madaripur etc.

Most of the farms are located in the lowlying beel areas where at best one crop of low-yielding paddy could be grown. The low productive agricultural lands now find a very good alternative utilisation through the production of high priced shrimp for export and of food fish for local consumption. Production in the Khulna and Bagerhat districts is around 350-500 kg/ha. Significant quantities of carp are also produced simultaneously with shrimp.

Advantages

Galda farming has many socio-economic advantages. There are no apparent conflicts between the present system of Galda culture and agriculture, as landowners are Galda farmers. The culture integrates well with fish culture and paddy production. Farms are far from the sea and therefore not vulnerable to tidal bores as is frequently the case with the Bagda farming areas, and the farmland is safe from saltwater intrusion. The potential for expanding Galda farming is great, with its ability to grow equally well both in freshwater and in brackishwater with salinity up to 10 ppt.

Some constraints to Galda farming

a) The culture period is limited because of dependence on the monsoon for water supply. The inadequacy of stocking materials in February or March, which is the beginning of good growth season for shrimp and fish, is another problem. There are very few operational hatcheries and their total output is insufficient to meet the demand for seed.

b) Snail meat is the main growth-promoting component in the feed supplied to the Galda farms. Snails are in short supply and are only seasonal. The demand far exceeds the supply and the snail price is sharply increasing. The situation leads to more excessive exploitation of snails with the possibility of their extinction, thus causing environmental imbalance.

c) Farmers do not have sufficient knowledge on the following:

• Pond engineering and environmental requirements of Galda and fish.
• Pre-stocking pond preparations including complete drainage of water, eradication and prevention of pest animals, pond drying, liming and fertilisation, etc.
• Selection of healthy seed and their acclimatisation with growout pond water.
• Management of pond water to maintain essential environmental parameters within ideal range and sustain natural pond productivity.
• Appropriate feeds and feeding techniques; excessive feeding is a normal practice.
• Recording and analysis of pond data.

d) Galda ponds have been established in a very crowded fashion without due consideration to the source of water supply and drainage network facilities. In such ponds, good water management and sanitation measures cannot be provided, and shrimp and fish stock remain vulnerable to environmental stresses and diseases. Disease is not yet a problem in Galda farms, but a potential threat does exist.

Brackishwater aquaculture and shrimp culture

Brackishwater aquaculture, also known as coastal aquaculture, is a rapidly expanding farming activity and is important in fisheries development in Bangladesh. Marine and estuarine shrimp, fish and crabs are the farm products. Bagda shrimp (black tiger shrimp, P. monodon) is the target culture species, while fish, heterogeneous shrimps and crabs are the by-products. Brackishwater aquaculture activities are most visible in the coastal districts of Satkhira, Khulna, Bagerhat, Cox’s Bazar and Chittagong. (Because of the turbulent nature of the Bay of Bengal, wide fluctuations of tide and salinity and the absence of sheltered places e.g., lagoons or backwaters adjoining the sea, mariculture has not developed in this country.)

Brackishwater aquaculture as an economic activity first appeared in the early 70s when Bangladesh started exporting shrimp. It now covers about 125,000 ha or 43 percent of the total aquaculture area, nearly 75 percent of the area under freshwater aquaculture. Statistics on brackishwater shrimp culture areas are shown in Table 11.

Table 11: Statistics of Bagda farms by districts.

District	1983-84 Survey1		1993 Survey2		1993 Survey3
	No.	Area (ha)	No.	Area (ha)	No.	Area (ha)
Satkhira	1,094	8,001	701	15,673		23,924
Khulna	1,051	12,817	835	20,523		30,187
Bagerhat	396	11,013	1,100	25,624		40,740
Cox’s Bazar	549	18,665	1,062	24,114		28,908
Chittagong	63	917	39	666		27,385
Others	3	43	5	26		3,000
Total						125,236	137,996

¹ DOF, 1986. Fisheries Information Bulletin, Vol. 3, No. 1. Department of Fisheries, Bangladesh.

² Authors estimate based on a field study undertaken by field officers in 1993.

³ Fish Catch Statistics of Bangladesh 1993-94, Department of Fisheries. The DOF data represent brackishwater and freshwater shrimp culture areas lumped together. Excluding the Galda area, thedata for Bagda area more or less tally with the author’s estimate.

Various culture practices

Based on species

Mixed culture of bagda with heterogeneous species. Screens are occasionally used. At times In this type of culture, the entry of non-predatory fish such as mullets, and species of exportable shrimp such as Penaeus indicus (white shrimp) and Metapenaeus monoceros (brown shrimp), is desired, but heterogeneous species of highly predator fish and crabs also enter the pond freely. Bagda fry are stocked separately.

Monoculture of bagda. For this type, the culture of bagda as the lone species is intended. But pure monoculture seldom exists because of the intrusion of pest animals through imperfect screening. As a result, most monoculture farms are degraded to mixed culture farms.

Based on crop rotation

Bagda-paddy. The rotation is bagda for the period February-mid August (normally with heterogeneous shrimp and fish which are either deliberately allowed entry or are intruders in the farms); and transplanted aman for the period from mid-August until December.

Rotation of aquaculture with agriculture is the most common farming system in the southwest brackishwater belt covering Bagerhat, Khulna and Satkhira districts. Marine and brackishwater shrimp and fish are cultured during the high salinity period (February-July), and a salt-resistant transplanted aman paddy in the elevated parts of the field during the low salinity period (August-December). Simultaneous with paddy, the leftover euryhaline shrimp and fish may continue to grow in the ditches or lowlying parts of the farm. Some farmers even combine freshwater shrimp (M. rosenbergii) and fish such as tilapia, carp, Thai sharpunti, with the euryhaline species.

However, prolonging the aquaculture process in the land beyond the optimum period for paddy transplantation often creates serious conflicts between aqua and crop farmers. Such conflicts are unfortunate but can be avoided. Crop rotation is not only good for both crops, but also helps sustain soil productivity.

Bagda-salt. Under this system, salt is produced in December-April and bagda (normally with intruder species) in May-November. In the eastern zone where salinity is much higher than in the western zone, shrimp culture and salt production in rotation is the usual practice. Shrimp is cultured during the wet season (mid-May to mid-October), while salt is produced during the dry and high saline period of December-April.

Based on seasonality of brackishwater

Seasonal culture. Aquaculture is undertaken in February-mid-August in most areas in the Khulna region and Cox’s Bazar; and in May-November in salt production areas in Chakoria, Moheshkhali and Teknaf.

Perennial culture. In some areas where river salinity is high all year round, shrimp is cultured throughout the year. Such farms are found in Syamnagar, Koira and Asssuni thana in the southwestern zone and Teknaf, Moheshkhali and Cox’s Bazar thanas in the southeastern zone.

Based on fry stocking and harvesting system

Continuous stocking and harvesting. Be it seasonal or perennial culture, this system features one-time pond preparation in the beginning and one-time complete harvesting at the end. Multiple stocking and harvesting are done in the entire culture period, a usual practice among the farmers.

One time stocking and periodic harvesting. This system is characterised by one-time stocking in the beginning, periodic harvesting during the culture season and complete harvesting at the end of culture. A new culture cycle is started every 4-5 months after pond drying, liming and fertilisation in double-crop areas with suitable salinity for at least 8 months. This type of culture is ideal, but not practised by most farmers.

Based on water source

Completely tide-dependent. This is by far the most common cultural practice. However, tidal inundation in most farming areas in February (which marks the beginning of culture season) is inadequate. The land elevation exceeds the tidal height. Most of the farming areas in Bagerhat, nearly 75 percent of the area in Cox’s Bazar, and more than 50 percent in Khulna and Satkhira cannot be tidally inundated under even 50 cm of water in the beginning of the culture season. Yet the farms depend upon tide alone. Chakoria and Rampal are two thanas with the largest bagda areas but are among the worst from the tidal inundation point of view. Supplemental pumping could significantly increase productivity of the land, but is not practised.

Completely pump dependent. Several hundred ponds in Kaliganj and Shyamnagar thanas of Satkhira are located in high lands not inundated by tide at all. These farms depend completely on pumps, mostly low-lift, some shallow.

Based on intensity of stocking and degree of management. Basically, three types of cultural practices exist: extensive, improved extensive and semi-intensive culture. A comparison of the three culture types is summarised below.

a. Extensive type. This type of culture is predominantly practised. An estimated 75 percent or over 93,000 ha of the brackishwater culture area (125,000 ha) is under extensive culture.

b. Improved extensive type. An approximate 25 percent or 28,000 ha of the culture area is under improved extensive type of culture or in a transitional state between extensive and improved extensive type. This category includes both completely tide-fed and completely pump-fed ponds.

c. Semi-intensive/Intensive culture which basically consists of high stocking rates (25-60/m²), heavy artificial feeding, pumping of water and use of aerators. Semi-intensive culture (which is actually intensive) sporadically demonstrated impressive production results exceeding 5 mt/ha in 4-5 months time in 1993. In 1994, about 36 farms covering an estimated area of 700 ha in the Cox’s Bazar started semi-intensive shrimp culture but mass mortalities occurred in most of the farms due to diseases. A similar disaster recurred in 1995 and 1996.

Table 12. Comparison of three culture types: extensive, improved extensive and semi-intensive.

Culture type	Artificial stock of Bagda per m2	Liming/ fertilisation	Artificial feeding	Screening	Aerator	Pumping	Shrimp prod’n (kg/ha/year)
Extensive	1-1.5	No	No	None, or imperfect	No	No, tide-fed	150-200
Imperfectly Improved extensive	1.5-3.0	Yes	No/Yes	Yes, but not perfect	No	No, or completely pump-fed	300-750
Semi-intensive/ Intensive	20-40	Yes	Yes	Yes; much better than in improved extensive	Yes	Partly tide-fed and partly pump-fed	3000-6000

Some constraints to brackishwater aquaculture

Some of the constraints faced in brackishwater aquaculture in Bangladesh are the following.

• Unmanageability of most of the ponds because of large size and inadequate supply and drainage network system in the farming areas.
• Short-term leasing system do not allow the leaseholders to make structural pond improvements.
• Land-use conflicts on the use of coastal land for paddy, shrimp, salt, mangrove plantation, cattle grazing, social afforestation, drinking water, etc.
• Dearth of culturable shrimp fry during the peak culture season.
• Wastage of valuable shrimp fry collected from the wild.
• Lack of efforts to conserve broodstock populations.
• Insufficient local supply of fishmeal to support feed industries.
• Inadequate physical infrastructure in the farming areas.
• Lack of well organised and sustained extension efforts at the farmers level.
• Recent occurrence of white spot viral disease.

Perceived needs

A policy for best economic utilisation of land in the brackishwater belt is urgently required to remove land-use conflicts and create opportunities for small farmers to benefit from shrimp culture.

Environment friendly improved extensive type of culture with various management options to suit different types of topographic and hydrological environment and farmers of varied background is the preferred culture technology. Brackishwater aquafarming alternating with paddy in low saline areas and with salt production in high saline areas suit the country’s socio-economic and environmental needs. In perennially saline areas, people tend to extend the culture season. The MFL (1994) has identified suitable areas where two crops of tiger shrimp can be raised using improved extensive or low level of semi-intensive culture techniques. Expansion efforts for semi-intensive culture could be undertaken after the fry and feed problems have been solved.