Growth and production of the African catfish, Clarias lazera (C. & V.) : II. Effects of body weight, temperature and feeding level in intensive tank culture

An experiment including 273 separate trials was carried out in densely stocked 150-l aquaria to study the growth response of C. lazera (C. & V.) weighing about 0.5, 5, 25 and 125 g to five different feeding levels from feed deprivation to satiation at 20, 25, 27.5, 30, 32.5 and 35°C. Analyses of dry matter, energy and nitrogen content were made in samples of the feed and of the fish to determine the feed utilization. It was found that C. lazera is highly suitable for high density, intensive aquaculture, because of its rapid growth and efficient feed utilization. The specific growth rate decreased from a maximum of 11% per day for small fish at 30°C to a maximum of 2% per day for the largest size group at 25°C. The corresponding maximum feed conversion efficiency decreased from 170 to 100%. A model was developed to describe the feed utilization for growth on a dry and on a fresh weight basis. Winberg's balanced energy equation: dW dt = p·R−H and Pütter's original growth concept equating growth to the difference between anabolic and catabolic activities both related to the body weight already achieved: dW dt = k 1W m-k 2W n , were used as a basis for the model. It was found that the feed utilization was independent of feeding level and temperature. It was also independent of body weight in the case of the dry weight feed utilization. For the fresh weight, the feed utilization decreased exponentially with increasing body weight, probably because the dry matter content of the fish increased allometrically with body weight. Temperature optima were found for k 1 and m while k 2 increased not quite exponentially with temperature and n was constant. These findings complied with or supported related findings in the literature and could be interpreted biologically. The model was used to predict the growth of C. lazera as a response to the feed ration in relation to temperature and body weight. A table of recommended feeding levels for C. lazera was established.