Complete energy budgets were constructed for 19 grass carp, Ctenupharyngudon idella (Val.), held individually in a respirometer for a month. The fish were fed one of four diets or starved. Diets varying in the proportions of protein, lipid and carbohydrate were described as high protein (HP), high carbohydrate (HC) or high lipid (HL). A fourth diet (LM) was made from dried duckweed, Lemna spp., to provide a more natural diet. Fish were fed and faeces collected daily and oxygen consumption was measured continuously over the month that each experiment lasted. Excretion of ammonia and urea was measured on several days. The total energy lost via nitrogenous waste was calculated using an average daily ammonia quotient (AQ).For growing fish between SO and 61 YO of consumed energy was lost via respiration. Energetic losses via nitrogenous wastes were highest on the HP diet (4.7%) and lowest on the HC diet (3.1%). FaecallosswashighestontheHLdiet(19~4%)andloweston theHPdiet(l0.2%). Overa month of starvation, 32.5% ofenergy requirement was met by the respiration ofprotein and 3.2% of the total energy lost was via nitrogenous waste. Fish fed zero or sub-maintenance rations tended to respire lipid in preference to protein whereas fish fed super-maintenance rations accumulated lipid. Protein retention was proportionally highest on HP (48% of total energy retained as growth) and lowest on HC (32%) and HL (30%). This reflected the accumulation of lipid on both the high carbohydrate and high lipid diets. The partitioning of metabolizable energy (ME) was investigated and 0.45 (HL), 0.59 (HP) and 0-67 (HC) kJ ME.kJ-' retained were lost via respiration.

Individual grass carp, Ctenopharyngodon idellu, were maintained in a respirometer for a month and fed pelleted diets containing various proportions of carbohydrate, fat and protein at different ration levels. Oxygen consumption was measured continuously, allowing the effects of consecutive daily feeding on respiration to be studied. The relationships established between daily food intake and oxygen consumption showed that, on average, 23.3% (high protein diet), 15.3% (high carbohydrate diet), 20.7% (high lipid diet) and 7.0% (Lemnu diet) of the absorbed energy was partitioned into specific dynamic action (SDA). (Here the term SDA is used to describe the oxygen consumption of a feeding fish in excess of the routine metabolic rate.) In terms of the overall energy budgets of growing fish, SDA represented between 12and 58% of the total heat lost over the experimental period and was equivalent to between 14 and 33% of the consumed energy. Ration was positively correlated with heat loss due to total respiration (r=0.881) and with heat loss due to SDA (r=0.762). As ration increased, the size of SDA relative to total respiration increased. Significant positive correlations were found between oxygenconsumption (total or due to SDA) and specific growth rate, and between oxygen consumption and the deposition of protein and energy. However, growth rate had a minimal influence on daily oxygen consumption when compared with food intake.

Nitrogenous excretion by grass carp, Crmopharyngodon idella (Val.), was measured in the form of ammonia and urea. Endogenous nitrogen excretion (ENE) was estimated as the daily rate of excretion by grass carp which had been starved for 2 days. ENE was scaled allometrically with body weight with weight exponents of 0.75 for ammonia, 0.63 for total nitrogen and 0.63 for the energy lost. The proportion ofnitrogen attributable to urea was smaller than that attributable to ammonia and decreased from 25 to 12% as fish weight increased from 2 to over 10 g.Linear relationships were found between daily rates of ammonia, total nitrogen and energy loss and daily rates of food intake. High carbohydrate and high lipid diets were not shown to have a protein-sparing action compared to a high protein diet. Differences in the amount of nitrogen excreted were explained by the differing nitrogen contents of the diets. Nitrogen budgets were erected and their implications discussed.