THE RELATIONSHIPS BETWEEN PROTEIN-INTAKE AND PROTEIN ACCRETION, SYNTHESIS, AND RETENTION EFFICIENCY FOR INDIVIDUAL GRASS CARP, CTENOPHARYNGODON-IDELLA (VALENCIENNES)

The aim of this study was to investigate the influences of diet, ration, and individual variation on protein-nitrogen flux in the grass carp, Ctenopharyngodon idella (Valenciennes). Grass carp were fed either lettuce or a pelleted diet or were starved. Fish fed lettuce had lower rates of protein accretion than those fed the pelleted diet and some lost body protein. Rates of whole-animal protein synthesis were ranked as follows: pellet-fed fish > lettuce-fed fish > starved fish. Productive protein value was negatively correlated with rate of protein degradation and positively correlated with the efficiency of retention of synthesized protein. Rates of protein synthesis were not correlated with productive protein value and these data suggest that ultimately it is the rate at which proteins are degraded that determines efficiency of growth. Comparison of pairs of fish eating the same diet and amounts of food but having different growth rates demonstrated that the faster growing fish had lower rates of protein degradation, higher retention of synthesized protein, higher RNA activity, a lower capacity for synthesis, and variable rates of protein synthesis.