Influence of Hermetia illucens meal dietary inclusion on the histological traits, gut mucin composition and the oxidative stress biomarkers in rainbow trout ( Oncorhynchus mykiss )

Insect protein meals are considered as a promising alternative feedstuff in aquafeeds, but until now the effects induced by its dietary inclusion on histological features, gut mucin composition and oxidative stress in fish are still not assessed. In the present study, we describe these effects after inclusion of a partially defatted Hermetia illucens (HI) larvae meal in Oncorhynchus mykiss diets. Three isoproteic, isolipidic and isoenergetics diets were formulated containing HI larvae meal in partial substitution of fish meal: 0% (HI0, control diet), 25% (HI25) and 50% (HI50), corresponding to dietary inclusion levels of 0, 20% and 40% of HI. Fish were fed for 78 days with the experimental diets and at the end of the growing trial, histological and histochemical evaluations were performed on spleen, liver and gut samples of control and treatment groups. Oxidative stress biomarkers, such as superoxide dismutase, catalase, glutathione peroxidases, ethoxyresorufin O-deethylase, glutathione S-transferase, glutathione reductase, total glutathione and malondialdehyde were investigated in liver and kidney of experimental groups. Histopathological examination of liver, spleen and gut revealed no adverse effects following increasing levels of insect meal inclusions. Hermetia illucens consumption stimulated higher production of neutral than acidic mucins. Altered values of several antioxidant biomarkers indicated an unbalance of oxidative homeostasis in liver and mainly in kidney, linked to the feeding conditions. While lowering of glutathione peroxidase activity may reflect slight adverse effect of HI meals in both tissues, strengthening in levels of ethoxyresorufin O-deethylase, glutathione S-transferase and total glutathione may indicate the shielding of HI meals-mediated oxidative process. Although the administration of both inclusion levels of insect meal did not negatively affect the histological features in fish, the changes of oxidative stress biomarkers advise for an HI dietary inclusion lower than 20%.