Effects of dietary vitamin A on broodstock performance, egg quality, early growth and retinoid nuclear receptor expression in rainbow trout ( Oncorhynchus mykiss)

Abstract

The objective of the present study was to investigate the effects of dietary vitamin A supplementation on reproduction and fry quality of rainbow trout ( Oncorhynchus mykiss). Two feeding trials were conducted with rainbow trout broodstock at a water temperature of 7 °C over a 6-month period prior to spawning. Three practical diets based on fish meal and fish oil (trial 1) and on plant ingredients (trial 2) were used. Diets 1A0, 1A20 and 1A700 were supplemented with 0, 20 and 700 IU/g vitamin A supplied as retinyl acetate resulting in dietary vitamin A contents of 45, 59 and 627 IU/g in trial 1; whereas, diets 2A0, 2A20 and 2A200 supplemented with 0, 20 and 200 IU/g vitamin A displayed total vitamin A contents of 21, 39 and 194 IU/g diet in trial 2. In both trials, gonadosomatic indices were not significantly different among dietary groups. Egg size remained unaffected by the levels of vitamin A in the broodstock diets. In both feeding trials, the levels of retinyl palmitate and retinol, the two main storage forms of vitamin A, were significantly higher in oocytes from 1A700 and 2A200 groups compared to other dietary groups; whereas, the level of retinoic acid remained unaffected. In trial 2, broodstock females fed diet 2A200 showed better fecundity than females fed diets 2A0 and 2A20. A significant decline in survival from the eyed stage onwards was noticeable in group 1A700 in trial 1 but no differences were found in trial 2. At the swim-up stage, trout fry from broodstock fed diet 1A20 displayed significantly improved growth rates compared to other dietary groups in trial 1; whereas, in trial 2, trout fry from 2A200 group exhibited the best growth performance. The expression of genes coding for retinoid receptors and other associated nuclear receptors was not significantly different among dietary groups at any developmental stage considered and no skeletal malformation was recorded in offspring. The results indicate that feeding rainbow trout broodstock a high level of vitamin A induced mortality at embryonic stages but was not teratogenic as no skeletal malformation was recorded at late developmental stages. However, quite high levels of vitamin A (60–200 IU/g) were necessary to sustain fecundity of broodstock and early growth of offspring.