Insect meals in feeds for juvenile gilthead seabream (Sparus aurata): Effects on growth, blood chemistry, hepatic metabolic enzymes, body composition and nutrient utilization

Alternative and sustainable fish diets are required by modern aquaculture. We investigated the possibility of using insect (Tenebrio molitor TM, Hermetia illucens HI or Musca domestica MD) larvae meals (as 19.5% of the feed formulation) to replace 30% of the in the fish meal (FM) in a gilthead seabream (Sparus aurata) feed formulated to contain 65% FM. The feeds were isonitrogenous (ca 57% crude protein of dry matter) isolipidic (ca 17% lipid dry matter) and isoenergetic (ca 22 MJ kg⁻¹ dry matter). To achieve similar energy content among the experimental diets, the fish oil inclusion was adjusted. Fish (average initial weight of 29.5 g) were fed up to apparent satiation three times a day, 7 days per week in a 93-days trial. Each diet was assigned to three 500 L tanks with fish density 2 kg m⁻³. Five fish from the initial population and two fish per tank were taken for whole-body composition analysis. At the end of the experimental period, nine fish per treatment were taken for the analysis of plasma metabolites and liver enzyme activities. Growth performance, feed intake, feed conversion and somatic indices of fish fed the different insect meal diets were similar to the FM fish. However, among the insect meal fish groups, the feeding with the TM diet resulted in higher specific growth rate compared to the HI diet (1.57% and 1.51% per day, respectively). The whole-body proximate composition was similar among experimental groups. Fish fed HI had the lowest fat retention (57.0% compared to 69.3–74.2%). Additionally, the HI group had also lower dry matter and energy retention (30.5% and 36.6%, respectively) compared to the FM group (33.8% and 41.5%, respectively). The whole-body saturated and mono-unsaturated fatty acids content was similar to all the experimental groups. Fish fed diets higher in fish oil (FM and HI) had higher eicosapentaenoic, docosahexaenoic and total ω-3 poly-unsaturated fatty acids content. Whole-body amino acid composition was similar among all experimental groups, while the amino acid retention exhibited significant differences. The plasma metabolites and enzyme activities as well as the hepatic lipogenic enzyme activity were not affected by the different diets. Fish fed the HI diet exhibited higher liver alanine aminotransferase (ALT) activity in comparison to the TM group. Overall, this study shows that FM can be successfully replaced by TM, HI or MD meals in 30% by weight in the diets of gilthead sea bream. Comparing insect meals, HI meal was inferior in terms of growth performance and dry matter-fat retention compared to TM and MD, respectively.