EFFECTS OF STOCKING DENSITY ON PRODUCTION OF PENAEUS-MONODON FABRICIUS IN MODEL FARMING PONDS

Sixteen 3.5-m diameter, 1.2-m high fibreglass pools with sediment were used as model prawn-farming ponds to investigate the effects of four stocking densities (5, 15, 25, and 40 prawns M-2) on prawn survival, growth and biomass gain, water quality, natural food resources, prawn feeding behaviour and economic return. Prawn survival was high ( > 88%) and unaffected (P > 0.05) by density and there was a significant (P < 0.05) decreasing exponential relationship between weight gain and density (y=9.177e-0.0103x.; r=-0.88) and a significant (P < 0.001) increasing linear relationship between final total biomass (g m-2) and density (y=21.044+8.348x; r=0.99). Biomass gain, apparent food consumption (feed input) and food conversion ratio increased (P < 0.001) as density increased. A simple economic analysis indicated that returns were affected by density (P < 0.01), but differences among more profitable treatments (15, 25 and 40 prawns m-2) were not significant (P > 0.05). Dissolved oxygen and concentration of algal pigments were affected by density (P < 0.001), although density-related effects on water quality did not explain reductions in prawn growth with increased density. The population density of macrobenthos, but not of meiobenthos, within the sediment layer in each pool declined with increasing stocking density. However, the decline in growth of prawns at higher densities may have been due to decreased grazing activity as indicated by the number of stomachs containing neither natural nor supplementary feed.