Impact of the Dietary Hermetia illucens Larvae Inclusion as a Sustainable Fish Meal Replacer on Growth Performance, Physiological Status, and Immunological Response of the Nile Tilapia

The consideration of sustainable substitutes for fish meal (FM) in aquafeeds has accelerated with the global rise in demand for protein-rich food from the aquaculture sector. This study examined the impact of FM replacement at incremented levels with black soldier fly (Hermetia illucens) larvae meal (BSFLM) on the Nile tilapia's growth performance, physiological status, and immune response. Six isonitrogenous diets were composed of FM, which was substituted with BSFLM at 0, 20, 40, 60, 80, and 100% replacement rates and fed to juvenile tilapia (4 replicate aquaria of 20 fish per treatment group) over eight weeks. No discernible differences were seen across treatments in feed conversion ratio and other growth metrics, including specific growth rate and final body weight. However, physiological indices, including serum aspartate aminotransaminase (AST), alkaline phosphatase (ALT), creatinine, and oxidative stress markers (malondialdehyde MDA, myeloperoxidase MPO) were significantly elevated at 80–100% inclusion, indicating potential hepatic and renal stress. Conversely, immune responses such as phagocytic, lysozyme, and leukocyte proliferation were enhanced at moderate replacement levels (40–60%) but declined sharply at 100% inclusion. The findings imply that BSFLM may improve immune responses at modest inclusion levels and replace FM in the Nile tilapia diets by up to 60%, without affecting growth or health. Immune and physiological processes may be adversely affected by high inclusion rates. These results support the sustainable use of insect meals at optimal inclusion levels in aquafeeds.