Effect of Tenebrio molitor larvae meal on growth performance, in vivo nutrients digestibility, somatic and marketable indexes of gilthead sea bream (Sparus aurata)

- The inclusion of T. molitor larvae meal in Sparus aurata diets is feasible up to 25%.
- At 25% inclusion no negative effects on digestibility and marketable indexes were found.
- At 50%, nutrients digestibility, dressed yield, VSI were penalized.

The aim of this study was to evaluate the effects of the inclusion of Tenebrio molitor larvae meal in practical diets for gilthead sea bream on growth performance, nutrients digestibility, somatic and marketable indexes. Two separate trials were carried out: in the first a total of 153 gilthead sea bream (105.2 ± 0.17 g average initial body weight) were randomly allocated in 9 fiberglass 220 l tanks (17 fish per tank) in an indoor water recirculating system. The fish were fed three isoenergetic and isoproteic diets formulated to contain increasing levels of TM meal inclusion and precisely: a control diet (TM0), in which fish meal was the main protein source; TM25 and TM50 diets, in which 25% and 50% of Tenebrio molitor larvae meal was added to the diet, respectively. These inclusion rates corresponded to 30% and 60% of inclusion on protein bases and 35% and 71% of fish meal substitution on protein bases for TM25 and TM50 diets, respectively. Each diet was randomly assigned to 3 tanks and the trial lasted 163 days. In the second trial, the apparent digestibility coefficients of the 3 diets were measured on 72 fish randomly distributed to 3 digestibility tank-units (24 fish per unit, average body weight: 86.97 ± 2.3 g) using an indirect method (acid insoluble ash). The group fed TM25 showed a higher (P < 0.05) final weight, specific growth rate, weight gain%, protein efficiency ratio, and a lower feed conversion ratio compared to the other 2 groups. The estimated apparent digestibility coefficients of crude protein and ether extract of the diets were lower (P < 0.01) in TM50 than in the other 2 groups. No significant differences have been found between TM0 and Tenebrio molitor larvae meal groups in morphometric and commodity-related characteristics, except for dressed yield and viscerosomatic index (VSI), that resulted the lowest and the highest, respectively, in TM50. The general evaluation of the results demonstrates that Tenebrio molitor larvae meal can replace fish meal up to 25% of inclusion in the diet for Sparus aurata without negative effects on weight gain, crude protein and ether extract digestibility, marketable indexes after 163 days of feeding. On the contrary, when Tenebrio molitor larvae meal was included at 50%, nutrients digestibility and dressed yield were penalized.