Hermetia illucens meal as potential protein source in diets for farmed rainbow trout (Oncorhynchus mykiss): preliminary results on quality meat characteristics

This work aims to evaluate the effect of partial replacement of fish meal (FM) with Hermetia illucens prepupae meal (HI), as alternative protein source, in the diet of rainbow trout (Oncorhynchus mykiss) on the final quality meat. Three experimental diets were formulated: HI0, HI25, HI50, with 0, 25 and 50% of HI replacing fish meal, respectively. Diets were tested in quadruplicate (30 fish/tank) for 78 days. At the end, 12 fish (4 individuals per each diet group) were devoted for physical (colour, pH, Water Holding Capacity, texture) and chemical (proximate composition, fatty acid profile) analyses on fillets. Colour, pH and Water Holding Capacity were not affected by different diets. Instead, shear force was significantly lower in HI0 group (16.00 vs 21.12 and 21.15 N in HI0, HI25 and HI50, respectively). No differences were observed in proximate composition of fish fillets, whilst fatty acids composition was strongly affected by insect meal content. Saturated fatty acids, as lauric acid (C12:0), significantly increased in fish fed H. Illucens inclusion diet (p<0.001), while monounsaturated and polyunsaturated (particularly EPA and DHA) fatty acids significantly decreased with the inclusion of insect meal (p<0.001). Preliminary results obtained showed that Hermetia illucens prepupae meal seems to be a good alternative protein source in feeding of rainbow trout, but they highlighted the importance of the feed ingredients on nutritional/health quality of the fleshes. To avoid detrimental effects on fillets health properties, more attention should be paid in the choice of the substrate utilised for the insect larvae rearing.