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Groups of rainbow trout (Salmo gairdneri) of approximate mean initial weight 8 g were grown in outdoor tanks over a 14-week period at water temperatures between 12 degrees (start) and 6 degrees (end). Four diets were used. Two contained non-oxidized fish oil (120 g/kg) with or without supplementary DL-alpha tocopheryl acetate and two contained moderately oxidized fish oil again with or without DL-alpha-tocopheryl acetate. The measured selenium content of the diets was 0.10 mg/kg. No significant differences occurred as a consequence of the use of moderately oxidized oil compared with the corresponding treatments using non-oxidized oil. Significant differences did occur between dietary treatments that contained supplementary DL-alpha-tocopheryl acetate and those that did not. These differences applied to weight gain, haematocrit, erythrocyte fragility, mortalities, liver and muscle tocopherol concentrations and lipid peroxidation of liver mitochondria in vitro. Liver glutathione peroxidase (EC 1.11.1.9) activity was unaffected by the dietary treatments used and the proportions of fatty acids in polar lipids of liver and muscle were little changed by the diets used. Severe muscle damage occurred in trout given diets lacking supplementary DL-alpha-tocopheryl acetate. Previous experiments carried out on rainbow trout at a constant water temperature of 15 degrees ( Hung et al. 1981; Cowey et al. 1981, 1983), using diets lacking supplementary vitamin E, did not lead to differences in weight gain, pathological changes or mortalities. Vitamin E requirement may increase as water temperature decreases; minimum dietary requirements for vitamin E measured at a constant water temperature of 15 degrees may not be valid under practical conditions where water temperatures vary over the year.

Histological analyses of the retina of Salmo trutta post-embryos exhibit rhythmic disc shedding at 6 weeks, followed by cyclic retinomotor movements at 7 weeks. Diurnal variations in cAMP concentration, as established by a radioreceptor assay, develop simultaneously with retinomotor movements and are fully expressed at 9.5 weeks. In continuous darkness, neither retinomotor movements nor intra-ocular peaks of cAMP occur, indicating that the endogenous oscillator for retinomotor movements and cAMP levels is not yet developed.

Serum levels of L-thyroxine (T4) and L-triiodothyronine (T3) of the masu salmon, Oncorhynchus masou, were measured by radioimmunoassay during the months from March to September. Serum levels of T4 and T3 varied from 0.06 to 1.44 microgram and from 0.06 to 0.35 microgram per 100 ml serum respectively, although T4 content could not be detected in some specimens. T4 levels showed a seasonal fluctuation in which a higher value was observed in April when parr-smolt transformation was proceeding. T4 level in spring, particularly in April and June, was significantly higher in smolt than in parr. T3 content showed a small variation during the observed months and did not increase at smoltification, although the content tended to decrease to a minimum level in September when T4 level showed also the lowest level.