Eight groups of 150 rainbow trout (Oncorhynchus mykiss) (mean weight 8 g) were
randomly kept in fibre glass tanks (1 m diameter X 0.8 m water depth) supplied at 40
1. min- ’ with spring fresh water at a constant temperature of 7 + 0.5”C. The fish were handfed
3 times/day a fish autolysate based diet (Table 1) supplemented with vitamin A ( 18
mg/kg dry diet; Rovimix, Hoffmann-La Roche) and/or astaxanthin ( 100 mg/kg dry diet;
carophyll pink, Hoffmann-La Roche). Diets were designated A+ Ax+ when supplemented
with vitamin A and astaxanthin; A-Ax+ when supplemented with astaxanthin only;
A +Ax- when supplemented with vitamin A only; and A-Ax- when unsupplemented