Abstract: This study aimed to screen for an efficient starch-degrading bacterium and optimize enzyme production conditions to enhance the capacity of recirculating aquaculture systems in treating residual feed starch. A starch-producing strain, HY-1 was isolated from recirculating aquaculture water. Based on morphological observation, physiological and biochemical characteristics, and 16S rDNA sequence analysis, it was identified as Bacillus cereus. Genomic analysis revealed that strain HY-1 possesses strong starch metabolism ability and environmental adaptability. Furthermore, antimicrobial susceptibility tests and zebrafish safety assessments indicated excellent environmental safety. Single-factor experiments were conducted to optimize the medium composition for enzyme production, identifying starch as the optimal carbon source, urea as the best nitrogen source, no need for sodium salts, and Mn²⁺ as the most suitable metal ion. Response surface methodology further optimized fermentation conditions: temperature at 37 °C, agitation speed at 200 r/min, and inoculum size at 2%. After optimization, the amylase activity of the crude enzyme solution increased significantly from an initial value of 26.75±2.90 U/mL to 510.28±1.53 U/mL. In water purification performance evaluation, the fermented broth achieved a flocculation rate of 74.81% and removed 49.47% of COD and 61.97% of starch from simulated aquaculture wastewater. In practical applications, the strain achieved a COD removal efficiency of 75.15% within seven days, with a maximum enzyme activity reaching 268.95 U/mL. The results demonstrate that Bacillus cereus HY-1holds great potential for water quality improvement and provides valuable microbial resources and process references for degrading starch-based organic matter in recirculating aquaculture systems.