FOOD RATIONS AND RATE OF GASTRIC EVACUATION IN BROWN TROUT FED PELLETS

The size of food rations and rate of gastric evacuation by brown trout (Salmo trutta) were studied at five different temperatures in brown t rout weighing 6.8-23.8 g. After preexperimental starvation and surplus feeding on pellets, groups of 20 trout were slaughtered at intervals that decreased in duration as experimental temperatures increased. The ash-free dry weights of the stomach contents of the sampled fish were recalculated to be representative of 10-g trout. The size of the food rations decreased relative to fish size and increased with temperatur e. The food rations greatly exceeded the limits expressed by a model o f maximum food rations established for brown trout, especially at low temperatures. The stomach contents decreased exponentially with time a t all temperatures and their weight distributions became increasingly skewed to the right. The rate of gastric evacuation increased exponent ially with temperature. The obtained rates were among the lowest recor ded for salmonids; the commercial, pelleted food we used was not easil y digestible. The fastest-growing half of the cohort evacuated faster than the slowest-growing half.