Growth, carcass composition, and plasma growth hormone levels in cyclically fed rainbow trout, Oncorhynchus mykiss microform

The compensatory growth response (C.G.R.), a phase of rapid growth following a period of feeding restriction, is investigated in rainbow trout (Oncorhynchus mykiss). Underyearling rainbow trout were individually identified using coded tags and placed on either a cyclic feeding regime of 3 weeks of starvation followed by 3 weeks of refeeding (to elicit a G.C.R.) or a daily feeding regime. The effects of this feeding regime on growth, body composition, and plasma growth hormone levels were recorded weekly for 24 weeks to include 4 feeding cycles. Fish that were placed on a cyclic feeding regime exhibited higher specific growth rates, protein levels and lower fat content than fish that were fed daily. The condition factor, which is an index of the fatness or leanness of a fish, was slightly lower than that of the control groups at the end of the experiment as a leaner fish was produced. The response to the starvation phase of the feeding cycle (as far as weight and fat loss were concerned) decreased in intensity with subsequent feeding cycles, indicating that the fish were acclimating to the feeding regime. There was a significant increase in variability of both the weight and length data within the cyclically fed population as the experiment progressed and they showed increased sensitivity to water quality. No "inphase" cycling of plasma growth hormone levels was observed for the cyclically fed fish. The implications of these findings in the use of cyclic feeding regimes in fish culture are discussed.Science, Faculty ofZoology, Department ofGraduat