Varying black soldier fly (Hermetia illucens) levels as a fish meal replacement in Nile tilapia (Oreochromis niloticus).

The quest for sustainable alternative protein sources in aquaculture has been driven by rising costs and limited supply of traditional fish meal; insect meals have emerged as viable options. Among these, the high nutritional value and environmental sustainability of black soldier fly larval (BSFL) diet have garnered attention. The purpose of this study was to assess how a dietary BSFL meal affected the Nile tilapia's (Oreochromis niloticus) growth performance, antioxidant capacity, immunological response, digestive enzyme activity, and histological features. For 60 days, fish were fed diets with varying amounts of BSFL meal (0, 30, 60, and 100% replacement). The results indicated that fish fed the 60% BSFL diet recorded the numerically highest values of FBW (final body weight), BWG (body weight gain), PER (protein efficiency ratio), and SGR (specific growth rate), along with the numerically lowest FCR (feed conversion ratio), whereas performance declined at the 100% BSFL inclusion level. Dietary BSFL inclusion regulated oxidative stress in a tissue- and dose-dependent manner. Total replacement (100%) markedly raised MDA levels in muscle and liver tissues, whereas moderate inclusion levels (30-60%) had little negative effect. Different tissues responded differently to antioxidants; muscle showed decreased SOD activity, whereas GPx activity peaked at 30% BSFL. At higher inclusion levels, intestinal GSH levels dropped dramatically, but CAT activity remained mostly constant. Fish fed the 60% BSFL diet showed a significant reduction in respiratory burst activity, indicating decreased superoxide production and potential modulation of innate immune responses. At 100% BSFL incorporation, lipase activity remained unchanged, but intestinal amylase activity decreased. Dietary BSFL of 100% inclusion significantly increased pro-inflammatory cytokines, while moderate inclusion specifically increased the expression of TNF-α and IL-21. The highest inclusion level showed severe deterioration, and histological examination showed dose-dependent changes in intestinal, splenic, and hepatic tissues. For Nile tilapia, replacing a proportion of conventional protein sources with BSFL meal (30-60%) showed potential benefits for growth performance and physiological responses, whereas complete replacement (100%) negatively affected oxidative status, immune responses, and tissue integrity. Further studies are needed to optimize BSFL inclusion levels for long-term aquaculture applications.