Catching black soldier fly for meagre: Growth, whole-body fatty acid profile and metabolic responses

This study aimed to evaluate the effect of diets including 10%, 20%, and 30% of black soldier fly larvae (Hermetia illucens) meal (HM) (diets HM10, HM20, and HM30, respectively), replacing 17%, 35%, and 52% of fishmeal (FM), on growth performance, whole-body composition and fatty acid (FA) profile, plasma biochemistry, and intermediary metabolism of meagre (Argyrosomus regius) juveniles. For that purpose, triplicate groups of 18.0 ± 0.02 g fish were fed a control diet (CTR) without HM, and the experimental diets for 9 weeks. Growth, feed efficiency, protein efficiency ratio, nitrogen and energy retentions linearly decreased with the increase of dietary HM level. With the exception of ash, whole-body composition was not linearly affected by dietary HM inclusion. Regarding whole-body FA profile, total saturated fatty acids (SFA), SFA: polyunsaturated fatty acids (PUFA) ratio, and total n-6PUFA linearly increased with increasing levels of dietary HM, while total n-3PUFA, n-3 long chain PUFA (LC-PUFA), n-3:n-6 ratio, and unsaturation index linearly decreased with increasing levels of HM in the diets. Docosahexaenoic acid (DHA) whole-body retention linearly decreased while lauric acid (12:0) retention increased with the increase of HM in the diet. Plasma glucose linearly increased, while plasma triglycerides and total lipids decreased with the dietary level of HM. Hepatic amino acid catabolic (alanine aminotransferease and aspartate aminotransferease), and lipogenic (glucose-6-phosphate dehydrogenase and malic enzyme) enzymes activities were unaffected by diet composition, whereas lipid catabolic (3-hydroxyacyl-CoA dehydrogenase) enzyme activity linearly decreased with dietary HM level. Glutamate dehydrogenase, an amino acid catabolic enzyme, was lower in fish fed the HM20 diet than the other HM-including diets. Overall, 10% of HM, corresponding to 17% of FM replacement, might be included in meagre diets without major adverse effects on growth, feed utilization, whole-body composition and FA profile.