Combining Hermetia illucens and Tenebrio molitor meals in diets for European seabass: Effects on growth, nutrient utilisation, intestinal morphology and muscle quality

This study explored the potential of an insect meal (IM) mixture of black soldier fly larvae (BSFL) and yellow mealworms (YMs) to substitute 3% (diet IM3), 25% (diet IM25) and 50% (diet IM50) of the fishmeal (FM) protein in a control diet (CTRL; 15% FM) for European seabass (Dicentrarchus labrax) juveniles. The four diets were isoproteic and isolipidic and were tested in triplicate in a recirculating aquaculture system with water at 22 °C and 35 ppt salinity, under a 12 h light/12 h dark photoperiod. After a 75-day feeding period, the fish growth performance, nutrient utilisation, intestinal morphology, muscle fatty acid profile and antioxidant capacity were evaluated. The diets containing IM ensured similar growth (DGI = 2.0) and feed efficiency (FCR = 1.0–1.1) to CTRL. Moreover, they promoted comparable nitrogen and energy retention efficiencies (38–40% and 44–47%). However, fish fed with the IM diets presented 20–27% lower faecal phosphorus losses than the control group. Anterior intestine integrity was maintained in all fish, but those fed IM50 displayed longer villi than the control. The muscle fatty acid profile of IM-fed fish also resembled that of the control, with 364–405 mg EPA + DHA per 100 g of fillet. IM25 and IM50 promoted higher lauric acid deposition in the muscle, and the muscle of fish fed with IM50 presented the highest oxygen radical absorbance capacity, suggesting higher antioxidant capacity. Overall, the study shows that the IM mixture can be an adequate protein source for seabass juveniles, also offering functional benefits.