IMPACT OF SUPPLEMENTATION OF MICRO ALGAE Schizochytrium sp. IN PLANT DIET ON REPRODUCTION OF FEMALE RAINBOW TROUT Onchorhynchus mykiss AND CONSEQUENCES ON PROGENY

IMPACT OF SUPPLEMENTATION OF MICRO ALGAE SCHIZOCHYTRIUM SP., IN PLANT DIET ON REPRODUCTION OF FEMALE RAINBOW TROUT (ONCORHYNCHUS MYKISS) AND CONSEQUENCES ON PROGENY

Introduction

 In the last years, the increase in aquaculture production has forced a change in fish feed composition, with increasing substitution of fish meal  (FM)  and fish oil  (FO)  by more available plant sources. D espite the fact that their inclusion rates in compound feeds for aquaculture have shown a clear downward trend in the  twenty past years

 , their total replacement  by plant feedstuff  is still not optimal, leading to reduced growth and reproductive performance

.

 The  broodstock diet, and in particular the lipid and fatty acid composition of the diet , is known to play a key role in reproductive efficiency and survival of the  progeny

.  And a major problem when replacing both FM and FO by plant sources is the lack of n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Materials & methods

 For that purpose, we studied the effect, in rainbow trout female broodstock ,  of the plant  diet supplemented with microalgae (MA)  compared to a conventional commercial diet rich in FM and FO (C ) on a reproductive performance and egg quality. The m icroalgae Schizochytrium sp., chosen to supplement plant-based diet in this study, is known to be a rich source of DHA. An  18 months  trial involving two reproductive cycles was carried out. During two spawning seasons , we followed  the performance of female reproduction measuring fecundity and egg quality. We also investigated the consequences of maternal nutritional history on offspring after the second spawning season.  Experimental design is presented in figure 1.

Results & discussion

 Despite a significantly lower growth rate in female fed MA diet, the reproductive performances were not affected (egg weight, absolute fecundity ). Moreover, in terms of egg quality, during the second cycle of reproduction, the egg diameter was significantly lower with the MA diet , but the eggs presented a significant better egg integrity (less white eggs after 24 hours of hydration) than with a C diet , which is a sign of a better egg quality.  Regarding embryonic development, eggs from females fed MA diet had significantly higher hatching survival rate than eggs from females fed C diet . No effect was observed on fry weight at resorption. W e linked this better egg quality to a better-balanced fatty acid profile.

Moreover, f eeding  female  with the MA diet had no effect on the growth and survival of the  progeny compared to feeding with C diet.  However, consequences of maternal nutritional history were observed in the lipid metabolism of progeny . Progeny from female fed MA diet had increased fatty acid biosynthesis and cholesterol synthesis metabolisms. Genes involved in these metabolisms were up-regulated in progeny from female fed MA diet  compared to  progeny from female fed  C diet , whether challenged with an MA diet or fed a commercial diet (figure 2).

Conclusion

 To conclude, in the present study, we  demonstrated that  DHA-rich microalgae supplementation in a plant-based  diet  allowed  to maintain reproductive performance and egg quality comparable to a conventional commercial feed rich in FM and  FO. Moreover, this study confirms a reprogramming of the lipid metabolism of  progeny  in relation to the  origin of  maternal nutritional .

 Acknowledgements: This study is funded by FEAMP (NutriEgg N° PFEA470016FA1000002)

References

Food and Agriculture Organisation (FAO), 2018. The state of world fisheries and aquaculture 2018 - Meeting the sustainable development goals. Rome. Licence CC BY-NC-SA 3.0 IGO.

Izquierdo, M.S., Fernandez-Palacios, H., Tacon, A.G.J., 2001. Effect of broodtsock nutrition on reproductive performance of fish. Aquaculture 197, 25–42.

Lazzarotto, V., Corraze, G., Leprevost, A., Quillet, E., Dupont-Nivet, M., Médale, F., 2015. Three-year breeding cycle of rainbow trout (Oncorhynchus mykiss) fed a plant-based diet, totally free of marine resources: Consequences for reproduction, fatty acid composition and progeny survival. PLoS One 10, 1–17. https://doi.org/10.1371/journal.pone.0117609