Positive impact of moderate food restriction on reproductive success of the rainbow trout Oncorhynchus mykiss

Rainbow trout (Oncorhynchus mykiss) egg production is a key sector for aquaculture. This industry relies on well-controlled reproductive cycles and the extensive use of photoperiod control to obtain year-round egg production. However, feed management practices are very diverse among producers and not always designed to optimize egg production. Among these different practices, feed restriction is of major interest due to its direct impact on the reduction of egg production costs. It is however not always used under optimal conditions. The aim of the present study was to evaluate the impact of moderate feed restriction on reproductive performances and egg quality in rainbow trout. For that purpose, two feeding strategies were implemented during the last five months before the second reproduction. Females were either fed (1) ad libitum, or (2) 80% of ad libitum (i.e. restricted) with a commercial diet. An artificial photoperiod was applied to trigger reproduction during the summer. As expected, feed restriction resulted in smaller females in comparison to those fed ad libitum whereas gonado-somatic index was significantly higher in restricted females. In addition, hatching rate was significantly higher for eggs from originating from restricted females. Feed restriction led to the production of bigger eggs with less size variability and lower number of non-viable eggs. These restricted females also exhibited lower viscero-somatic index suggesting an impact of feed restriction on the allocation of reserves. However, lipid content in eggs and muscle were not different between groups, while fatty acid profile of eggs presented some differences. PUFA analysis revealed that proportions of ALA, AA and EPA were higher in eggs from restricted females, a feature possibly linked to higher egg quality. Together, these results demonstrate that feed intake of female rainbow trout broodstock can be reduced by at least 20% without any negative impact on egg production and egg quality.