The Culture of Tilapia Nigra (Gunther) in Ponds V - The Effect of Progressive Alterations in Stocking Density on the Growth of Male T. Nigra

Abstract

Experiments have shown that depression of growth always results with unfed fish in untreated ponds when the population density is increased, whether the density is increased at one time, or successively increased at short term intervals. The limiting factors are probably food supply available in the first place, but behaviour patterns of shoaling in themselves probably also introduce growth limitation by competition for feeding space. When, however, several different size groups of fish are stocked simultaneously, they do not affect each other's growth rate, and when two size groups of fish are stocked successively at much longer term intervals again depression of growth is not so marked. Generally, however, growth of male T. nigra shows great plasticity, and even at large sizes and long after maturity, such males can respond by increased growth to decrease in stock density, though there is an increasing limit to length increment possible as the fish grows larger; but this is offset by the fact that in larger fish small length increments correspond to considerable weight increase. The fattening of runted fish from overstocked conditions is entirely practicable when these can be given improved growth conditions by stock reduction.