Nutrigenomic effects of plant protein-based aquafeeds on fish muscle and spleen

Over the last decade, the use of plant-based proteins in aquafeeds has largely increased, currently amounting up to 70% in salmon feeds. With this transition from fish meal to green diets, fish may be exposed to anti-nutritional factors, mycotoxins and other plant-associated contaminants leading to new challenges for fish health and welfare, as well as product quality. Replacement of fishmeal with plant-based proteins has shown to affect the growth and health of the farmed fish, depending on the percentage of plant proteins, fish species and various other factors. However, the molecular basis of these effects is not well understood. Therefore, this study aimed to investigate the effect of green aquafeeds on fish growth and health at the molecular level by exploring global transcriptome changes using zebrafish as a model. Diets containing 30% of typical plant proteins that are frequently used in salmon feeds, i.e. wheat, soy or pea, were evaluated in comparison with a control diet containing only marine proteins. Feeding trials were conducted for 6 weeks and the zebrafish were fed a daily ratio of 2.5% of their bodyweight. A nutrigenomic approach (RNA seq) was used to identify differentially expressed transcripts at a global scale in key organs related to growth performance (muscle) and immunity (spleen). Libraries were prepared with total RNA from 6 replicate samples from each dietary group and sequenced on a NextSeq500 (Illumina) to yield over 25 million single reads per sample. Trimmed sequences were mapped to the zebrafish genome assembly available from Ensembl using TopHat2 and differential transcript abundance with diet was determined with DEseq. The findings of this study indicated that the partial inclusion of soy or pea protein concentrate or wheat gluten in the diets did not have any significant effect on the specific growth rate of zebrafish. On the other hand, inclusion of those proteins caused moderate alterations in transcript levels associated with health and growth performance in zebrafish. The potential molecular markers identified in zebrafish will be cross-referenced in Atlantic salmon (Salmo salar) fed with diets containing similar levels of the same plant proteins used in the present study. Acknowledgements This work was supported by the Norwegian Research Council through a post-doctoral fellowship to A.K.S.D. and a research grant to C.K.F. (NFR 267944 and 254822, respectively).