Detection of new pathways involved in the acceptance and the utilization of plant-based diet in isogenic lines of rainbow trout fry. Oncorhynchus mykiss

We investigate mechanisms behind the response to a plant based diet at short term, by analyzing the transcriptome of 3 isogenic lines of rainbow trout (R23, AB1, A22). These families represent an interesting genetic material to work on as they have similar responses when fed marine based-diet (M diet) but highly different responses when fed a plant-based diet (V diet). Transcriptomic analyses of whole fry revealed 1740, 1834 and 246 probes differentially expressed among the three isogenic lines. Gene ontology enrichment analysis revealed different enriched pathways. Among them, some were related to immunity and perception. Among ontologies related to metabolism only the methionine metabolism pathway was found to be significantly enriched. First, the use of these isogenic lines of rainbow trout led to find new pathways related to plant-based diets utilization which had not been described previously. Secondly, difference in expression of genes related to immunity suggest that this function play an important role but specific effect on immune status was difficult to assess, and further investigations are needed. Finally, results suggested that mechanisms underlying the use of plant-based diets is more linked to feed intake rather than to metabolism. Research on plants components affecting feed intake should be further explored to continue to improve feed formulation and reduce the reliance of aquaculture on marine resources without affecting fish performance. Overall design: Transcriptomic response was studied in whole-body fry from 3 isogenic lines (R23, AB1, A22). Just before the first feeding, fish were randomly distributed into 18 tanks supplied with natural spring water at a constant temperature of 11.4°C (6 tanks/isogenic line with on average 350 fish). For each isogenic line, three tanks received the control diet (M diet) and the three other, the plant-based diet (V diet). Feed was distributed ad libitum. The control diet contained fish meal, fish oil and whole wheat as major ingredients (M diet). The plant-based diet (V diet) was totally devoid of marine ingredients, and contained a blend of vegetable oils (rapeseed, palm and linseed oil) and vegetable meals (faba bean, corn, soybean, wheat gluten, peas, and white lupin) added with L-Lysine and L-methionine to meet nutrient requirements of rainbow trout. The V diet also contained an attractant mix. Sampling took place after 5 weeks of feeding (n=6/condition).