Reducing nitrogen and phosphorus discharges from sea cucumber-based recirculating aquaculture system through dietary binder addition

Sammendrag

The high dispersibility of dietary and fecal particles aggravates excessive nitrogen (N) and phosphorus (P) discharge in Apostichopus japonicus recirculating aquaculture system (RAS). This study evaluated the feasibility of optimizing N&P budgets and water quality through binder-enhanced dietary management. The experimental groups included a control without binder addition and treatments with 5 % of one of four binders: sweet potato starch, xanthan gum, guar gum and carrageenan. This study determined the effects of dietary binders on aquaculture water quality, sea cucumber growth, and the properties (viscosity and particle size) of feed and feces, analyzed the N&P flow in the system based on the principle of mass balance, and applied Spearman correlation analysis to explore the relationships among viscosity, particle size, and N&P budgets. The results showed that the guar gum supplementation significantly reduced total nitrogen and total phosphorus concentrations in aquaculture water by 24.8 % and 38.5 %, respectively, with a significant reduction in ammonia nitrogen concentration (0.08–0.18 mg/L) (P < 0.05). Binders modified sediment-water distribution of N/P components, increasing the retention of N and P by solids while inhibiting the release of dissolved N and P. Mechanistically, sweet potato starch and guar gum optimized dietary/fecal viscosity, enlarged particle size (Dx(50)) and enhanced structural stability, thus promoting nutrient immobilization in bioavailable solid forms. The findings of this study validate binder-assisted dietary management as a dual-functional solution, enhancing aquaculture productivity while alleviating environmental pressure in RAS through targeted nutrient retention.