Genetic Parameters and Genotype × Diet Interaction for Body Weight Performance and Fat in Gilthead Seabream

SIMPLE SUMMARY: The use of fishmeal and fish oil has long been an issue of major concern since nutrition for most aquaculture farms entails a considerable cost. To reduce the cost of the nutrition, many efforts have been made to replace the fishmeal/fish oil, either partially or totally, in diets by using plant-based proteins. The selected candidates per generation might be affected and the query of the establishment of a fish line selection used for a plant-based diet is under consideration. In the present study, fish were on different diets: a high-plant-protein diet containing 85% plant proteins and a high-animal-protein diet (standard commercial). During the experiment, fish were weighed and fat content was collected. We subsequently estimated the inheritance of the body weight performance and the fat content (0.39–0.85). Moreover, a genotype by diet interaction was re-evaluated causing a significant re-ranking of the selected candidates per diet. Furthermore, a higher genetic gain for body weight performance can be achieved by using the standard commercial diet, rather than the plant-based one. Thus, the establishment of a plant-based diet breeding line could be possible, if the reduction of the cost of aquafeed could balance the lower genetic gain expected to be achieved in each generation. ABSTRACT: There has been thorough research on the genotype by diet interaction and the extent of its impact on the genetic evaluation, using a partly replaced marine animal protein on the gilthead seabream. To do that, 8356 individuals were gathered from two batches and followed different diets: a high-plant-protein diet containing 85% plant proteins and a standard commercial one containing 30% marine animal protein. During the experiment, body weight, growth and fat content were recorded. High heritability estimates were detected for the body weight performance and fat content. A small effect of genotype by diet interaction was detected in all phenotypes (presented as the genetic correlations from 0.95 to 0.97) but a medium-high ranking correlation between the breeding values for each trait was estimated (0.72–0.70). A higher expected response to selection for the body weight performance was detected using the standard commercial rather than the plant-based diet. Based on the findings, the establishment of a plant-based diet breeding strategy can be achieved provided the reduction of the cost of aquafeed is attained, though a lower genetic gain is expected.