PREDICTING THE PRODUCTION OF WASTE PRODUCTS IN THE HIGH-DENSITY CULTURE OF SHARPTOOTH CATFISH (CLARIAS-GARIEPINUS)

The production of waste products by the sharptooth catfish (Clarias ga riepinus) was measured under high density controlled laboratory condit ions. The waste products that were investigated were ammonia nitrogen, nitrite nitrogen, nitrate nitrogen and suspended solids. A flow-throu gh system with a 360 l tank was used to keep 67 catfish (average mass = 550 g). Water temperature was kept constant at 24 degrees C. The sys tem was subjected to a continuous light cycle and the feeding level wa s 20 g . kg(-1). d(-1). Water samples were taken at regular intervals throughout the feeding cycle and analysed for the above-mentioned meta bolic wastes. The measured concentrations were transformed mathematica lly into metabolic waste production per unit biomass. The resulting da ta compare favourably with similar data for other species published el sewhere. It was found, however, that the production was somewhat prolo nged. The size distribution of the suspended solids (SS) was investiga ted to facilitate easier removal of this metabolic waste from systems. The results were that 52% of the SS did not pass a 300 mu m sieve whi le 17% passed through a 100 mu m sieve. The balance of the SS fell bet ween these two sizes. This investigation also showed that there were t wo types of SS that had to be removed; the first type had a fine granu lar appearance while the second was mucoid. No attempt was made to dif ferentiate between these two types during this investigation. A model calculation illustrates the prediction of the accumulation of wastes i n high-density aquaculture systems.