EFFECTS OF POND PREPARATION AND FEEDING RATE ON PRODUCTION OF PENAEUS-MONODON FABRICIUS, WATER-QUALITY, BACTERIA AND BENTHOS IN MODEL FARMING PONDS

Fibreglass pools with sediment were used as model farming ponds to investigate the interactive effects of pond preparation and feeding rate on prawn production, water quality, bacterial dynamics, abundance of benthos and prawn feeding behaviour, Pools were either fertilised 1 month (prepared) or 2 days (unprepared) prior to stocking and either 'high' or 'low' feeding rates were used. The 'high' rate was 5.0% (range 4-8%) wet prawn biomass/day and was similar to that recommended for commercial farms. The 'low' rate was 2.5% (range 2-4%) wet prawn biomass/day. Juvenile Penaeus monodon (2.0-7.5 g) were stocked at 15 prawns/m(2) and were cultured for 71 days. With the exception of one prepared, high feeding-rate pool where mass mortality (>80%) of prawns occurred following an interruption to aeration, prawn survival was high (>86%) and was unaffected by preparation, feeding rate or their interaction. Pond preparation improved growth and biomass gain by about 20%. Growth was 4% higher with the higher feeding rate but biomass gain was not affected and, as food conversion ratio was much worse, use of the lower feeding rate offers considerable scope to reduce production costs, especially during cooler periods. There was no interaction in relation to growth between pond preparation and feeding rate. Meiofauna were more abundant, and prawns grew faster, in prepared pools than unprepared pools at the start of the experiment, However, changes in bacterial dynamics or meiofauna abundance over time did not explain reductions in prawn growth over time. In general, water quality was reduced in pools receiving the high feeding rate compared with low feeding rate pools. Other interactive effects of pond preparation and feeding rate on water quality, bacteria, benthos and prawn feeding behaviour are discussed.