TEMPORAL EFFECTS OF RESTRICTED DIET AND COMPENSATORY INCREASED DIETARY-INTAKE ON THYROID-FUNCTION, PLASMA GROWTH-HORMONE LEVELS AND TISSUE LIPID RESERVES OF RAINBOW-TROUT ONCORHYNCHUS-MYKISS

Immature rainbow trout, Oncorhynchus mykiss were fed to satiety 4 times a day, either 5 days (5D), 3 days (3D), or 1 day a week (1D), for 42 days (treatment period) and then fed to satiety 4 times a day, 5 days a week, for 56 days (post-treatment period). During the treatment period, the 1D and 3D groups exhibited reduced growth (wet body weight), increased compensatory food consumption on the days of feeding, altered feed: gain ratios (FGRs), reduced visceral adipose tissue and liver wet weight, increased carcass water content, decreased carcass and liver lipid content, lowered plasma T4, T3 and GH (1D group only) concentrations, and reduced hepatic 5'-monodeiodinase activity (hepatic T4 conversion). There were no differences in the relative wet weight of the heart or digestive tract among groups at any time in the study. During the post-treatment period, the 1D and/or 3D groups exhibited compensatory increases in food intake (but no concomitant differences in FGRs among the three groups), and relative accumulation of visceral adipose tissue, carcass and hepatic liver content, carcass water content and liver wet weight. In addition, there was a small, but significant, increase in growth rate of the 1D group, relative to the 3D and 5D groups during the posttreatment period. Plasma thyroid hormone concentrations and hepatic 5'-monodeiodinase activity increased steadily throughout the post-treatment period in the ration-restricted groups, but there was no compensatory increase. Plasma GH levels of the 1D group were lower than those of the other groups throughout the study.