Bacillus subtilis improves growth performance of European eel ( Anguilla anguilla ) and optimizes minerals content in its fresh carcass

Aquatic animals require minerals for normal physiological processes, yet the effects of Bacillus subtilis on host mineral deposition and its relationship with growth performance remain unclear. In this study, the probiotic strain BSP12 (GenBank: OQ612706) was isolated from the intestine of a healthy European eel and identified as B. subtilis by morphological, biochemical, and 16S rRNA analysis. Results showed that the strain exhibited 91.67% antimicrobial activity (11/12), and its growth was observed at 15–45°C (optimal 37°C), pH 5.0-9.0 (optimal 7.0), and tolerated 5‰-80‰ bile concentration (optimal growth at 5‰). The strain produced protease, amylase, cellulase, and lipase. In a 28-day feeding trial, dietary supplementation with 1.0×10⁸ CFU/g BSP12 significantly improved final body weight, weight gain rate (WGR), and specific growth rate (SGR). Muscle Mg, Zn, and K contents in the BH group increased by 2.52%, 13.33%, and 14.77%, respectively (p < 0.05). Furthermore, the increased K, Mg, and Zn contents in BH were significantly and positively correlated with final body weight, WGR, and SGR (R > 0.60). Those results will help elucidate the mechanism linking Bacillus-mediated alterations in mineral deposition to improved growth performance in the food eel.