Effect of feeding plant-based diet to broodstock on the utilization of plant-based diet in the offspring of rainbow trout Oncorhynchus mykiss

This study investigated the effects of nutritional history during the maturation of rainbow trout Oncorhynchus mykiss on the utilization of a plant-based grower diet in the offspring at the juvenile stage. Fishmeal-based (BF) and plant-based (BP) broodstock diets were fed to an F2 line selectively-bred with plant-based diets (Selected) and to the counterpart line (Control) from two months before the start of gonadal development until the end of ovulation (2 x 2 design). Compared to broodstock fed BF, ovulation tended to be delayed in broodstock fed BP, while nutrient composition of the ovulated eggs and egg quality such as hatchability were similar among treatments. From first feeding, offspring were reared on fishmeal-based diets until they reached approximately 6 g body weight (BW). Then, juveniles of each group (Control-BF, Control-BP, Selected-BF, Selected-BP) were fed a plant-based grower diet (GP) to apparent satiation for 8 weeks at 16 degrees C (3 tanks/treatment). Specific growth rates (% BW/day) of the Selected groups were significantly higher than the Control groups without a significant effect of broodstock diet. Relative feed intake (% BW/day) of the Selected groups and BP groups were significantly higher than the Control groups and BF groups, respectively. Feed efficiency ratios of the Selected groups and BF groups were significantly higher than the Control groups and BP groups, respectively. Whole body manganese and zinc concentrations of the Selected groups were significantly lower than the Control groups. Activities of lipase, trypsin and chymotrypsin in the intestinal digesta, obtained under restricted feeding (2% BW/day), of juveniles from the Selected groups were significantly higher than those from the Control groups, and the ac-tivities of lipase and chymotrypsin of juveniles from the BP groups were also significantly higher than those from the BF groups. These results suggest that the nutritional history of rainbow trout broodstock affects the appetite and digestive physiology of the offspring, but minimally affects their growth. Further fortification of nutrients such as microminerals to plant-based grower diets may be necessary to take full advantage of the effect of se-lective breeding of rainbow trout with plant-based diets, including the effect of feeding them to the broodstock.