Compensatory growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually

Abstract

The effect of feed cycling on compensatory growth was examined in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually at 15 °C. Fish were fasted for 2, 4, 8, or 14 days and then refed until either their relative feed intake differed by less than 10% of fed controls, or the duration of the refeeding period was four times the fasting period. After 80 days, fish fasted for 8 days at a time were smaller than controls, or fish experiencing 2 or 4 days of fasting, while fish fasted for 14 days did not differ from other groups. There were no differences in visceral fat or hepatosomatic indices, but within-treatment variation was high. Fish subjected to fasting displayed compensatory growth, and high growth rate during the recovery phase was achieved by hyperphagia, rather than improved feed conversion. There was a highly significant relationship ( R 2=0.951) between feed intake and weight gain, and feed conversion did not differ between fish subjected to the different treatments. The results indicate that rainbow trout can be subjected to short periods of fasting without significant effects on growth, but no improvement in feed utilization was obtained during the refeeding period.