EFFECT OF RESTRICTED ACCESS TO DEMAND-FEEDERS ON DIURNAL PATTERN OF LIVER COMPOSITION, PLASMA METABOLITES AND HORMONE LEVELS IN ONCORHYNCHUS-MYKISS

In order to study the relative importance of the feeding time and the light/dark alternation, as synchronizers of metabolic and endocrine pa rameters, the hepatosomatic index, liver glycogen contents, plasma glu cose, nonesterified fatty acids, cortisol, growth hormone and thyroid hormone concentrations between dawn - 2h and dawn + 12h are described in immature rainbow trout (Oncorhynchus mykiss). Trout were held in gr oups of 30 individuals and given access to a demand-feeder for only 3h per day, between dawn and dawn + 3h for 6 aquaria, and between dawn 4h and dawn + 7h for another series of 6 aquaria. There was a clear e ffect of the time of food access on most of the studied parameters, wi th a decreased amplitude of variation, or a decreased mean level, in t he fish eating in the middle of the photophase, compared with the fish eating at dawn. Superimposed on this apparent depressive effect of ph ase shifting of food access, some parameters also show direct response s to the shift of eating time, with a post-prandial increase or decrea se.