Impact of pre-stocking calcium hypochlorite disinfection on water and sediment quality in shrimp aquaculture systems

Pre-stocking disinfection using bleaching powder (calcium hypochlorite) is a routine biosecurity practice in shrimp aquaculture aimed at eliminating pathogenic microorganisms prior to larval introduction. While effective in microbial control, the environmental implications of such chemical conditioning remain insufficiently evaluated. This study assessed the short-term impact of bleaching powder application on pond water and sediment quality before shrimp stocking. Samples were collected immediately before treatment and 24 hours post-application. Physicochemical parameters (pH, total dissolved solids (TDS), salinity, acidity, alkalinity), organic load indicators (dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD)), nutrients (nitrates and phosphates), and selected heavy metals (arsenic (As), iron (Fe), cadmium (Cd), and manganese (Mn)) were analyzed following APHA and IS:3025 standard methods. Post-treatment results revealed substantial increases in water TDS (+9.8%), COD (+160%), BOD (+160%), salinity, acidity, and nutrient concentrations. Cadmium concentrations reached permissible limits, while arsenic remained above recommended safety thresholds. In sediment, organic load decreased; however, increased acidity and reduced alkalinity indicated altered buffering capacity. Although shrimp were not present during treatment, the findings demonstrate that pre-stocking chemical disinfection substantially modifies pond water–sediment chemistry and may influence subsequent production cycles. Optimized chlorine dosing and environmentally integrated biosecurity strategies are essential to support sustainable aquaculture development.