Mealworm as dietary protein source for rainbow trout: Body and fillet quality traits

The present study tested a partial substitution of fish meal (FM) with increasing levels of full-fat Tenebrio molitor larvae meal (TM) in diets for rainbow trout (115.6±14.0 g initial body weight) on body morphological and marketable characteristics, and on fillets physical and chemical traits. Fish were fed three diets: a control diet (TM0) and two other diets (TM25 and TM50) corresponding to 0, 25 and 50% of TM inclusion level, respectively. After 90 days of rearing, no statistical differences were detected for morphometric and slaughter traits and for pH, water holding capacity, cooking loss and shear force in raw and cooked fillets. Moreover, diets did not affect the colour of raw and cooked fillet; however, significant variations were observed in colour of skin (dorsal region), that showed higher redness index (a*) in TM0 and TM25 groups. No differences were observed in proximate composition of fillets (raw and cooked), whilst fatty acid (FA) profile was strongly affected by the diet insect meal content. The FAs C16:0, C18:1n9 and C18:2n6 increased whilst EPA and DHA progressively diminished in fillets when TM inclusion in feeds increased. Regarding the FA quality indexes (both for raw and cooked fillets), TM50 group had a higher thrombogenicity index than the TM0 group; PUFA/SFA and n3/n6 ratio gradually decreased with the increase of FM replacement in the diets. In conclusion, TM could partially replace FM in rainbow trout diet, without having a negative effect on fish characteristics and on most quality traits of the fish flesh, except for fatty acid profile.