Cage fish trials in Ea Soup Reservoir, Vietnam

摘要

Reservoirs in the Central Highlands of Vietnam are numerous and growing in number. Dak Lak Province has about 370 reservoirs of varying sizes with a total estimated area of 8500 ha. While constructed primarily for irrigation, these reservoirs have great potential for fish culture in the area. Ea Soup Reservoir lies in a remote district of Dak Lak. It covers an estimated 240 ha at upper storage level, and has a drawdown of about 2.5 m. Probably for this reason, there is an abundant supply of macrophytes in the reservoir. Compared to most reservoirs in the Central Highlands, Ea Soup has a relatively large catchment area (350 Km~2). While a number of species have cage culture potential, grass carp (Ctenopharyngodon idella) is popular in many parts of Vietnam. The species feeds almost entirely on macrophytes, so cash requirements for feed are minimal. This is suitable for most poor farmers in the area. The market price of this species, about 0.65 dollar/kg, is higher than that for many species. In Ea Soup Reservoir, cage culture of grass carp commenced in 1993, and rapidly expanded. By 1996, there were about 157 cages. Stocks were hit by disease, and were decimated late in the year. Many owners suffered heavy financial losses. Pollution, poor circulation in the cages, high stocking density and overcrowding of cages may have contributed to the disease problem. From June 1998, the project, jointly with three fishers, has tested culture of grass carp combined with small numbers of tilapia and common Carp in cages with new materials, somewhat larger mesh size, and lower stocking density. The economic viability of this modified technology will depend mainly on the lifetime of the cages. Nevertheless. fishers are continuing to culture at their own expense. This suggests that the technology has some sustainability in the reservoir. The extent to which cage culture can be practised remains to be seen. but any expansion must be cautious.