Capture-based aquaculture of wild-caught Indian major carps in the Ganges Region of Bangladesh

Mhd Mokhlesur Rahman
Center for Natural Resource Studies
Dhaka, Bangladesh
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Rahman, M.M. 2008. Capture-based aquaculture of wild-caught Indian major carps in the Ganges Region of Bangladesh. In A. Lovatelli and P.F. Holthus (eds). Capture based aquaculture. Global overview. FAO Fisheries Technical Paper. No. 508. Rome, FAO. pp. 127–140.

INTRODUCTION

Background and country context

Bangladesh is a riverine floodplain country with over 700 small, medium and large rivers and three major river systems (the Ganges, Brahmapura and Meghna) that originate from the Himalayan chain, cross the country and then join before emptying into the Bay of Bengal. The rivers cover over 24 000 km which constitutes approximately 6 percent of the total area of the country. Apart from rivers, there are numerous natural wetlands in the form of canals, beels, haors, baors1, mangrove swamps and lands which flood seasonally for 5–6 months of the year. The wetlands range from 7.5 to 7.8 million hectares (Table 1) (Nishat, 1993). The floodplains are very rich in natural productivity and support a diverse flora and fauna, among which fish is considered the most important natural resource, as it supports the livelihoods of millions of inhabitants, including many of the rural poor.

Bangladesh has a humid climate with three broad seasons: warm summer (March to May), wet monsoon (June to October) and cooler winter (November to February). Rainfall is abundant and ranges annually from 140–400 cm, with over 80 percent received during the monsoon months. The temperature during the summer varies from 35.0–37.5 ?C, reaching 43 ?C at times, while in winter the temperature ranges from 17.5–24.0 ?C, falling as low as 4.5 ?C in some locations.
Monsoon flooding strongly influences the biophysical and socio-economic functions of the country. With the onset of rains in April–May,

TABLE 1
Area of seven types of water bodies in Bangladesh
Types of water bodies Area (ha)
Large reservoirs 90 000
Coastal shrimp farms 141 000
Permanent rivers and streams 480 000
Estuaries and mangrove swamps 610 000
Shallow lakes and marshes 120 000–290 000
Ponds and ditches 300 000–400 000
Seasonally flooded lands 5 770 000
Total 7 511 000–7 801 000

Source: Nishat, 1993.

1 Beels are floodplain lakes, which may hold water permanently or dry up during the winter season; haors are depressions in floodplains located between two or more rivers, which function as internal drainage basins; and baors are oxbow lakes (Hasan and Ahmed, 2002).
128 Capture-based aquaculture: global overview
the water level in the river systems start to rise, and gradually overflows the river banks and inundates nearly one third of the country for 5–6 months. The river water starts rising even before the monsoon, because of the rise of temperature that causes snow melt in the Himalayas.
The warm temperatures and high rainfall, coupled with numerous rivers and wetlands that are rich in nutrients, have endowed the country with rich fisheries resources. The wetlands in Bangladesh support around 265 species of freshwater bony fishes representing 154 genera and 55 families. There are also more than 30 species of prawns and shrimps in freshwater systems and coastal waters. Of the 265 freshwater fish species, four species of Indian major carps are commercially important, and make up a significant proportion of both the inland capture and culture fisheries production.

Information availability on capture-based aquaculture

Although there is an established practice of collecting major carp spawn from rivers to supply seeds to the carp aquaculture industry, this aspect of the fishery has not been well documented. However, studies have been conducted on some of the main aspects of carp stocks in the wild, and on breeding behaviors and spawn collection, by different research projects and by the Bangladesh Fisheries Resources Survey Systems (BFRSS) of the Department of Fisheries (DoF).
Most of the available information is focused on the biological aspects of carp, their migration and breeding behaviors, spawning times and grounds, and on spawn collection and nursery rearing. Since 1984, the BFRRS have been collecting data on major carp spawn collection from the main river sources. This database includes spawn collection centers by river systems, number of nets used, collecting period (season), quantity caught, price, and the number of people engaged. However, there is no mention of the socioeconomic aspects of the people engaged in the wild-caught spawn fishery, nor of the marketing and distribution systems for the wild-caught spawn. The environmental implications of collection of major carp spawn from the wild are poorly documented.
Some literature highlights the stock of major carps and spawning-related information, indicating concern over declining carp stocks in the wild and making recommendations. Tsai and Ali (1985) analysed the BFRSS data, and found no significant adverse impact of carp spawn collection from the wild on the natural stock of major carps in Bangladesh.
There has been extensive work on the Halda River stock of carp in southeast Bangladesh, the only main carp spawning grounds in the country, and from which fertilized eggs are collected. Changes in the course of rivers made by the Bangladesh Water Development Board (BWDB) resulted in negative impacts on carp spawning grounds. The harvest of broodstock fish from Halda River, especially while they migrating to their spawning grounds, has negative impact on the wild stock. The other stock of major carp spawn is in the upper reaches of the rivers outside Bangladesh, a location from which spawn, rather than fertilized eggs, are collected.