An introductory view on cage aquaculture, oxbow lakes and Bangladesh
With the rapid increase in population and development of world economy there is an increasing demand of fish protein and to meet the future demand at the present status of per capita consumption, world aquaculture production is to be doubled within 2010 AD. Culture based fisheries as well as different mode of aquaculture has given tremendous importance at this stagnant situation of world capture. In this aspect, cage aquaculture is coming up as a promising venture for optimum use of water resource without disturbing much the surrounding ecosystem. Despite conflicts in resource use, cage culture in lakes and reservoirs continues to expand and covers almost ten percent of world aquaculture production, but problems from waste production and questions regarding sustainability.
However, cage culture, an intensive operation by nature, has both detrimental and beneficial effect on the environment. Major problem areas in cage culture are-
1. environment - aquaculture interaction i.e. effluent from cage culture disposed throughout the water body and thus causes a depletion in the surrounding environmental quality as well as environmental degradation by other causes also affect cage production
2. Competition for resources - fisheries activity in the water body affected by the cage culture operation
3. Genetic improvement and biodiversity concern - where composition of indigenous fish may be affected by cage culture.
Though Bangladesh has a history of pond aquaculture of about 1000 years cage culture is a very recent introduction and started from early 80ís only on trial basis. Another experiment was also done in brackish water on nursery rearing of shrimp and prawn fry in cages in 1994.
Water bodies of Bangladesh can be divided into two categories- open and closed. Oxbow lakes may be defined as semi-closed water bodies formed by dead arms of rivers situated in the moribund delta of the Ganges in the southwestern part of the country (BCAS, 1994). Though there is more than five hundred oxbow lakes occupying total water area of 5488 ha, only 29 are being managed under some sort of culture practices initiated by the Directorate of Fisheries (DoF). Also very few of the rest are under management of true fisherís cooperatives or NGOs.
As Bangladesh is one of the most densely populated country of the world, natural resources of the country are under tremendous pressure. Thus to meet the present need and as well as for future generation there is a growing urge to manage and utilize the existing resources in a sustainable way. For the reason, there is a great possibility of future extension of such practice in oxbow lakes in the South-western region of Bangladesh as an alternative income generating activity (IGA) for resource poor fishers.
No study on suitability of cage culture has not yet been done which can help to formulate an institutional plan for sustainable expansion of cage aquaculture in oxbow lakes. Presently, cage aquaculture operation is going on as an experimental basis by Oxbow Lakes Small Scale Fishermen Project (OLP-II) in two baors (Konnadah and Bahadurpur) and by CAGES Project of CARE -Bangladesh in one lake (Baluhar). The ongoing research of OLP-II is especially on Clarius batrachus, Pangasius suchi and Cyprinus carpio in 20 different cages while CARE looks into the suitability of fish species like common cap (Cyprinus carpio) and silver barb (Puntius gonionotus) in eight cages.
However, depletion of oxygen caused by jute retting, cage fish have faced severe mortality. It was reported that the process of decomposition of jute plants in oxbow lakes produces deleterious effect on fish life (Ali, 1994). Hence, there is a growing need to formulate a plan for oxbow lake management in terms of productivity, suitability of cage culture for rural poor, income generation and cash flow.
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Some valuable information and links
AQUANIC - an interesting site for aquaculture
CENTRE FOR TROPICAL ECOSYSTEMS RESEARCH
Welcome to ICLARM, an international research organization
DIFTA - Danish Institute for Fisheries Technologyand Aquaculture