Acute hypoxia reveals diverse adaptation strategies to fully substituted plant-based diet in isogenic lines of the carnivorous rainbow trout

Rainbow trout—a carnivorous fish—are increasingly fed oil and meal from plant origin for environmental purposes but full substitution of fish meal leads to pathological responses and deterioration of growth performances. Fish may also be more sensitive to environmental perturbations. In this study we investigated whether genetic determinism linked to the ability to growth under PB diet was paired to robustness to environmental perturbation. In this aim we performed an hypoxic challenge on three heterozygous isogenic lines of rainbow trout, fed a marine (M) or a fully substituted plant-based (PB) diet. In addition, we considered two feeding status, fed or starved. Isogenic line responsiveness, i.e. time elapsed between water arrival cut-off and loss of equilibrium, was evaluated using a Cox proportional hazard model. We showed that feeding status, diet and host genotype had a significant impact on trout tolerance to hypoxia. One isogenic line, A22h, exhibited higher tolerance to hypoxia under PB diet when fed. In contrast R23h and AB1h lines, behaved indifferently regardless the nutritional history, highlighting their robustness to diet substitution. Under the M diet, the three lines behaved similarly when starved whereas, when fed, only R23h and AB1h responded similarly. At the opposite, the three lines behaved differently under PB diet regardless the feeding status. These results indicate that response and robustness were related to hypoxia resistance. Thus hypoxic challenge per se is a promising test to assess trout adaptive capacity in response to diet replacement. It may help to identify robust individuals, i.e. presenting minimal responsiveness to fully substituted diets, and implement breeding programmes for better adapted fish.