COST OF GROWTH IN LARVAL AND JUVENILE AFRICAN CATFISH (CLARIAS-GARIEPINUS) IN RELATION TO GROWTH-RATE, FOOD-INTAKE AND OXYGEN-CONSUMPTION

The effect of fish size on the cost of growth, growth rates, food inta ke and oxygen consumption was studied in Clarias gariepinus, Measureme nts were performed on larvae reared at 28 degrees C, and results compa red to those for juveniles (recalculated from literature). As C. garie pinus grows (0.07 mg to 38 g BDW (body dry weight)), the cost of growt h increases from 64 to 149 mmol ATP g(-1) DW (dry weight) deposited. A higher cost of growth is associated with reduced growth rates (from 1 41 to 2.48 BDW day(-1)), and is also reflected in lower gross food con version efficiencies (93 to 24%). Decreasing growth rates are a result of reductions in relative rates of food intake (152 to 6.2% BDW day(- 1)) and are accompanied by a reduction in oxygen consumption (1.0 to 0 .033 mu mol O-2 mg(-1) DW h(-1)). Fish size was allometrically related to growth rate, food intake and oxygen consumption. The absence of an y distinct breakpoint in these relations suggests a gradual transition from the larval to the juvenile pattern of fish growth and metabolism . Providing that optimal conditions are met (e.g., temperature, oxygen availability and feeding), the pattern of fast growth at low cost mig ht be extended for a longer time span during the transition period fro m the larval to the juvenile stage, resulting in improved growth and f ood conversion efficiency. (C) 1998 Elsevier Science B.V.