EFFECT OF RATION SIZE ON THE GROWTH AND ENERGY BUDGET OF THE GRASS CARP, CTENOPHARYNGODON-IDELLA VAL

Young grass carp (12-13 g) were kept at five ration levels ranging fro m starvation to ad libitum feeding at 30-degrees-C. They were fed duck weed. Food consumption, absorption efficiency and growth were determin ed directly, and metabolism and nitrogenous excretion calculated indir ectly from energy and nitrogen budgets, respectively. The relationship between specific growth rate and ration size was linear. Absorption e fficiency for energy was not affected by ration size and averaged 50.6 +/- 0.57% (mean +/- s.e.). Depending on ration size, energy lost in e xcretion accounted for 4.5-5.9% of the food energy, energy channelled to metabolism accounted for 34.4-48.3% of the food energy, and energy retained as growth accounted for 6.7-11.9% of the food energy. Regardl ess of ration, a constant proportion of food energy (30.7%) was accoun ted for by feeding metabolism (total metabolism minus fasting metaboli sm). The energy budget at the maximum ration was: 100 C = 49.1F + 4.5U + 3.6R(fa) + 30.9R(fe) + 11.9G, where C, F, U, R(fa), R(fe) and G rep resent food consumption, faecal production, excretion, fasting metabol ism, feeding metabolism and growth, respectively.