Effects of handling, discrete meals and body weight on the individual variation of gastric emptying parameters

Individual feeding and gastric emptying was estimated for two salmonid species, brown trout (bt), Salmo trutta (L.), and rainbow trout (rt), Oncorhynchus mykiss (Walbaum), fed extruded feed with glass beads, and exposed to repetitive handling, anaesthetizing and X-raying. No significant effect was found to be caused by the handling and experimental procedures. Huge inter-individual (bt: CV_g= 52-104%; rt: CV_g= 19-33%) differences in discrete meal size were caused by interspecific differences in feeding behavior. An exponential model was fitted to the X-ray time series data for each individual for a computation of the initial (Ri) and fractional (R) gastric emptying rates. The individual variations in meal size had no significant effect on the rates. The meal frequency [two meals per day versus postprandial starvation (PS)] significantly affected the fractional gastric emptying rate. The rate decreased significantly for the PS groups while the inter-individual variation increased. Body weight (10-2500 g) significantly affected the fractional gastric emptying rates, which increased by up to 600 g and then decreased. The coefficient of variation for R increased with body weight. An equation for calculation of weight specific food processing rate (FP) is proposed. The FP decreased significantly with body weight. A maximum estimate of FP_i= 2.3 mg g^?1 h^?1 at 12°C for an individual was obtained with a 13.7-g trout. An increased weight-specific consumption (per cent body weight) for the smallest fish demonstrated that FP_g was 5.4 times higher than for the biggest fish, but after normalization with a body weight exponent of 0.75, an estimate of 1.7-2.3 was obtained.