Hermetia illucens larvae meal as an alternative protein source in practical diets for gilthead sea bream (Sparus aurata): A study on growth, plasma biochemistry and gut microbiota

The effects of dietary Hermetia illucens (HI) larvae meal on growth, plasma biochemistry and gut microbiota was tested in gilthead sea bream. Four isonitrogenous and isolipidic extruded diets (50% protein; 14% lipid) with different levels of HI larva meal (0% CTRL, 5% HI5, 10% HI10, and 15% HI15) in partial substitution to fish meal (FM) were administered to triplicate fish groups over 113 days. Diets were designed to partially replace FM, using FM level for practical application. No significant differences (p > 0.05) were observed in terms of final body weight, specific growth rate (SGR), feed intake (FI), feed conversion rate (FCR) as well as feed efficiency parameters such as protein efficiency ratio (PER), gross protein efficiency (GPE), gross lipid efficiency (GLE). At the end of the trial there were not significant differences on growth, feed intake, feed conversion rate and protein efficiency. Among over 20 plasma parameters analyzed, HI inclusion level reduced iron (Fe), potassium (K), creatinine (CREA), aspartate aminotransferase (AST), alanine amino transferase (ALT), creatine kinase (CK), alkaline phosphatase (ALP), lactate dehydrogenase (LDH). The reduction of AST, ALT and ALP might suggest a potential beneficial role of HI for liver integrity and functionality. Concerning gut microbiome (GM) layout, HI was able to induce a shift in the GM structure at any inclusion level considered compared to the control diet increasing the abundance of Bacillaceae (mainly Bacillus and Oceanobacillus) and Paenibacillaceae (Paenibacillus). Taxa that can be involved in chitin degradation and has been recently recognized as novel probiotics for aquaculture. In conclusion, the results of feed intake, growth, feed utilization and plasma biochemistry indicate that HI larvae meal can be successfully incorporated up to 15% in practical aquafeed diets to partially replace FM without any negative effects on growth and feed efficiency. Beyond being a valid alternative protein source for fish meal replacement in this species, it displays gut health functional properties already at low inclusion level.