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

Abstract

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.