Effects of Black Soldier Fly Larval (Hermetia illucens) Replacement Diet on Hybrid Grouper (Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀) Through a Multipronged Nutrigenomic Analysis

Abstract

This study investigated the effects of replacing fishmeal (FM) protein with black soldier fly larvae (BSFL) in hybrid grouper (Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀) by integrating growth performance, body composition, serum biochemistry, digestive enzyme activity, histopathology, and transcriptomic analysis. A total of 720 fish (average body weight [ABW]: 56.51 g ± 0.07) were randomly allotted to six isonitrogenous and isocaloric diets (0%, 10%, 20%, 30%, 40%, and 50% FM protein replaced by BSFL), with three replicate tanks per treatment and 40 fish per 500 L tank. After the 56-day feeding trial, survival remained above 95% in all groups (p > 0.05). The highest final weight and growth indices were observed in the BSFL20 group, whereas quadratic regression based on body weight gain (BWG) and specific growth rate (SGR) indicated lower mathematical optima of ~8% BSFL replacement. Feed utilization was improved at 20%–30% BSFL inclusion (p < 0.05), but higher inclusion levels reduced growth and feed efficiency. Muscle lipid content and fillet quality were not markedly impaired by moderate BSFL inclusion. Serum biochemical responses and tissue histology suggested that replacement levels above 20% increased physiological stress, with clear pathological changes in liver and stomach tissues at 40%–50% BSFL. Transcriptomic analysis revealed substantial changes in genes related to cell growth, apoptosis, amino acid metabolism, and lipid metabolism, with the strongest liver response observed in the BSFL30 group. Overall, the data support moderate BSFL inclusion as a feasible strategy for partially replacing FM in hybrid grouper, while indicating that excessive replacement compromises physiological stability.