Lipid metabolism and fillet quality of rainbow trout fed diets including Hermetia illucens full-fat larvae

The use of insects as protein source in feed is a hot topic in the present aquaculture scenario. Aquaculture production escalation must be supported by an increase in feed production and the conventional dietary protein sources must be substituted by cheaper and more eco-friendly ingredients, such as insects. Although a substitution of up to 50% of the conventional protein sources with insect meals is possible without jeopardising in vivo performances of salmonids, the effect on fillet quality is still of concern. The present study enquired the effects of three diets (Hi0, Hi25, Hi50) with increasing substitution levels (0, 25, 50%) of dietary fishmeal with Hermetia illucens full-fat larva meal on liver (L), pyloric caeca (C) and mid intestine (M) lipid metabolism and on fillet quality of rainbow trout (Oncorhynchus mykiss), after a feeding period of 98 days. The physical analyses on fillets included colour measurement by a Chroma Metre CR-200 (Chroma Metre CR-200, Tokyo, Japan), water holding capacity determination and pH instrumental measurement. The assessment of fillet fatty acid (FA) profile was also performed. The expression of genes related to lipid metabolism (abcg5, cd36, elovl1, elovl2, fads2, fads6, hmgcr, pparα, pparβ, pparγ, pparδ, srebp1, srepb2) was investigated by two-step RT-qPCR. Dietary treatments did not noteworthily affect physical characteristics. Since the insects were not defatted, saturated FAs (SFAs) were abundant in the diets including insect meal; as a consequence, fillet FA profile showed an increased SFA content comparing Hi50 and Hi0 (p<.05). Significant differences and clear trends were revealed between the treatments as concerns the genes related to the lipid metabolism. To sum up, the inclusion of full-fat H. illucens meal in diets for rainbow trout did not alter the physical traits of fillet but affected fillet cardioprotective lipid profile as well as liver and intestine lipid metabolism. An understanding of lipid metabolism, crosschecked with the lipid status of the fillets, can give hints to modulate diet formulation, aiming to improve the nutritional and functional characteristics of the final product.