A Comprehensive Analysis of Dietary Fishmeal Replaced by Black Soldier Fly (Hermetia illucens L.) in Largemouth Bass (Micropterus salmoides).

Black soldier fly larvae meal (BFLM) is characterized by high yield and a well-balanced nutritional profile, making it a promising alternative protein source for aquafeeds in the near further. Previous studies have demonstrated its potential to partially replace fishmeal (FM) in aquatic diets. Therefore, a 56-day feeding trial was conducted in largemouth bass (LMB) to evaluate the effects of graded level of BFLM (0%, 17%, 34%, 51%, and 68%) as a substitute for FM on growth performance, antioxidant, immune responses, and muscle quality. The results showed that dietary BFLM replacement levels above 17% significantly reduced SGR, FER, and whole-body crude lipid content, thereby impairing growth performance. In addition, higher substitution levels disrupted the antioxidant system, promoted the expression of inflammatory cytokines through activation of the nrf2-keap1 pathway, and consequently induced inflammatory responses. Furthermore, BFLM replacement exceeding 17% decreased muscle hardness and chewiness, reduced the content of aroma-, umami-, and sweet-related compounds, and increased the levels of off-flavor substances and SFAs, ultimately leading to deterioration in muscle quality. Based on the present results, the optimal replacement level of BFLM in diets for LMB should not exceed 17%. A comprehensive analysis of the adverse effects associated with high levels of BFLM substitution indicated that the high content of saturated fatty acids (FAs) and the low content of long-chain polyunsaturated FAs in BFLM were the key factors limiting growth performance, inducing oxidative stress, and reducing muscle quality. To improve the efficiency of BFLM as a substitute for FM, it is necessary to optimize FA composition while comprehensively considering growth performance, antioxidant and immune status, and muscle quality.