Vitamin A metabolism and early biological responses in juvenile sunshine bass (Morone chrysops×M. saxatilis) fed graded levels of vitamin A

Abstract The present study evaluated the effects of increasing levels of dietary retinol on diet utilisation, growth, mortality, retention of vitamin A 1 plus its conversion to vitamin A 2 in liver and whole body of juvenile sunshine bass. In addition, early indications of disturbed intestinal cell kinetics, as well as liver heat-shock protein 70 (HSP70) responses were included. Feeding juvenile sunshine bass a purified, casein-based diet with no added retinol resulted in significantly lower growth. Feeding diets containing from 509 to 40 516 μg retinol kg −1 resulted in equal growth, survival, feed efficiency, condition factors as well as liver and carcass indices. However, dietary retinol levels were reflected in both liver and whole body in a linear manner, but with no retention in the groups fed a deficient or 509 μg retinol kg −1 diet. The conversion of vitamins A 1 to A 2 in all groups depended on the dietary level of vitamin A 1 . Fish fed the 40 516 μg retinol kg −1 diet had reduced conversion of vitamins A 1 to A 2 and altered distribution of proliferating cell nuclear antigen (PCNA)-positive cells along their intestinal folds and crypts. The resistance to temperature stress and expression of liver HSP70 appeared to be efficient in all dietary treatments, but fish fed the 1614 μg retinol kg −1 diet showed the greatest increase in HSP70 following heat shock, compared to the other groups. Based on growth, mortality, retention and conversion of vitamins A 1 and A 2 , distribution of PCNA-positive cells and increase in HSP70, we conclude that the requirement for optimal growth and health of sunshine bass is greater than 509 μg retinol kg −1 diet and less than 40,516 μg retinol kg −1 diet.