A technique using sequential feedings of different coloured foods to determine food intake by individual rainbow trout, Oncorhynchus mykiss: effect of feeding level

Sequential meals do not mix to any extent in the stomach of rainbow trout. This observation was used to develop a technique to measure food intake by individual fish based on the consumption of sequential meals consisting of different coloured foods [brown (natural coloured food), red (carmine added) or green (chromic oxide added)]. The method was evaluated by examining the effect of underfeeding, feeding to satiety or overfeeding on food intake by individual rainbow trout, Oncorhynchus mykiss, raised in groups. Fish were fasted overnight and fed the test meal at 50, 75, 100 or 133% of predicted satiety for the group as a whole. Following feeding, fish were killed and stomach contents were separated by colour and quantitated by weighing. In fish fasted for 16 h prior to consuming the test meal, almost 1 3 of the total stomach contents were residual contents. Increasing the amount of food provided in the test meal increased the level of consumption, but did not alter the variability between fish within the tank. There was no apparent relationship between body weight and food consumption. This method provides an easy and objective means to quantitate intake of several sequential meals by individual fish.