Tenebrio molitor meal in diets for European sea bass (Dicentrarchus labrax L.) juveniles: Growth performance, whole body composition and in vivo apparent digestibility

Two trials were carried out on European sea bass (Dicentrarchus labrax L.) juveniles to evaluate the effects of dietary inclusion of a full-fat Tenebrio molitor (TM) larvae meal. A first growth trail was performed on 450 European sea bass using three isonitrogenous and isolipidic experimental diets (3 tanks/diet, 50 fish/tank) formulated to contain increasing levels of TM meal inclusion and precisely: 0 (TM0), 25 (TM25) and 50% (TM50) as fed basis. The performances, proximate body composition and fatty acid (FA) profile of whole fish fed the experimental diets were evaluated. A digestibility trial was then conducted on 180 fish to evaluate the in vivo apparent digestibility coefficient (ADC) of diets having 25% of TM inclusion in absence (TMD) or presence of exogenous enzymes (Carbohydrases, TM-Carb; Proteases, TM-Prot) compared to a fish meal based control diet (CD). The growth trial results showed that the highest inclusion level (TM50) led to a worsening of final body weight, weight gain, specific growth rate, and feeding rate if compared to the control diet (TM0). Regarding the whole body composition, crude protein and ether extract were not significantly influenced by the use of TM, while changes were observed in the FA profile. In particular, C18:2 n6 increased (+91% and +173% in TM25 and TM50, respectively vs TM0) with the inclusion of TM while sharp decreases of C20:5 n3 (−30% and −58% in TM25 and TM50, respectively vs TM0) and C22:6 n3 (−35% and −67% respectively vs TM0) were highlighted. Consequently, the ∑ n3/∑ n6 FA ratio showed a significant decrease (−63% and −84% in TM25 and TM50, respectively vs TM0). As far as digestibility trial is concerned, the crude protein ADC of the fish fed TMD was significantly higher than that of the fish fed CD (92.31 vs 89.97, respectively). The supplementation of digestive enzymes did not improve the protein and ADF digestibility.