The fishery of the Ea Kao reservoir, southern Vietnam: a fishery based on a combination of stock and recapture, and self-recruiting populations

The present paper describes the fishery of the Ea Kao reservoir in south Vi etnam. Historical data on the total production and total numbers of fish st ocked were available from 1983 to 1996, and this information, together with the results of monthly monitoring of the fishery from June 1996 to Decembe r 1998, was used in the present study. A number of gears are used in the Ea Kao fishery, the most important being gill, lift and integrated nets, and beach seines. The fishery of Ea Kao is based on the annual stocking of adva nced fry/early fingerlings of 0.3-1.0-g bighead carp, Hypophthalmichthys no bilis (Richardson), silver carp, Hypophthalmichthys molitrix (Cuvier & Vale nciennes) and rohu, Labeo rohita Hamilton, as well as the self-recruiting i ndigenous species Toxabramis houdemeri Pellegrin and two exotic species, i. e. Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carp io L. On average, the regularly stocked species contribute to 78% of total production, which has been around 400-450 kg ha(-1) in the last few years. The monthly peak catches of stocked species tend to coincide with the rainy season from May to October and the catches of self-recruiting species peak between February and April. A significant relationship (P < 0.001) exists between the stocking density in year n (SD, n ha(-1)) and the yield of stoc ked fish in year n + 1 (Y, kg ha(-1)): Y = -0.0006SD(2) + 0.097SD-45.50 (r(2) = 0.85, P < 0.001) Stocking efficiency (SE, based on number stocked per hectare versus yield o f stocked species, i.e. n ha(-1) versus kg ha(-1)) was computed for all sto cked species combined because the landings prior to 1997 did not distinguis h between bighead carp, silver carp and rohu. The relationship between SE i n year n + 1 to SD in year n was: Y = 0.05SD(2) + 0.07SD + 60.49 (r(2) = 0.33, P < 0.05).