FAST GROWTH, PROTEIN-TURNOVER AND COSTS OF PROTEIN-METABOLISM IN YOLK-SAC LARVAE OF THE AFRICAN CATFISH (CLARIAS-GARIEPINUS)

In fish larvae the costs of rapid growth may be accommodated by a decr ease in the rate of protein turnover or by a reduction in the costs of protein synthesis. Protein growth, synthesis and degradation were mea sured in yolk-sac larvae of Clarias gariepinus and the costs of protei n synthesis and protein growth were estimated. Growth rates were over 100% protein weight day(-1). Protein synthesis retention efficiency (r etained protein per unit of synthesis) was estimated to be 69.6%, a va lue comparable to that of larger fish. The larvae used 43% of their ox ygen consumption for protein synthesis. Nevertheless, protein synthesi s costs were close to theoretical minima. Therefore, the high growth r ates of catfish yolk-sac larvae seem to be possible through minimisati on of the costs of protein synthesis. These low costs are associated w ith high rates of protein synthesis (138% protein weight day(-1)), and elevated RNA concentrations (107 mu g RNA mg(-1)protein), which toget her suggest very high RNA efficiencies (12.9 g protein synthesized g(- 1)RNA day(-1)).