Integrated Multi-Trophic Aquaculture (IMTA) offers a sustainable strategy for modern aquaculture by combining species from different trophic levels to optimize nutrient recycling and reduce environmental impacts. This study evaluated the integration of the polychaete Hediste diversicolor in a Recirculating Aquaculture System (RAS) producing corvina (meagre - Argyrosomus regius), using as input a sludge effluent originally intended for discharge. Three polychaete stocking densities (250, 500, and 1000 ind/m²) were tested over 35 days, with stable environmental parameters monitored throughout the trial.
H. diversicolor exhibited high survival (>93%) in all treatments, with no significant differences in growth performance, suggesting that higher densities increase biomass yield without compromising individuals. Proximate composition showed stable protein and lipid content, while carbohydrate levels increased with density, indicating the feasibility of dense cultivation for valuable biomass production. Fatty acid analysis highlighted the species’ biosynthetic capacity: despite being fed nutritionally poor sludge (EPA: 0.04%, DHA: 0.23%, n-3/n-6: 0.5), enriched levels of essential fatty acids were recorded (EPA: 13.4–14.5%, DHA: 2.2–2.5%, n-3/n-6 ~1.8). This demonstrates the ability of H. diversicolor to convert organic waste into nutritionally valuable biomass.
Beyond its use as fishing bait, H. diversicolor shows potential for aquafeeds and broodstock nutrition (particularly for Solea senegalensis, where its nutritional profile and natural odorants may stimulate feeding and enhance reproductive performance). This innovative system provides a promising model for integrating high-value species into corvina RAS production, reinforcing IMTA as a tool for effluent remediation and circular resource valorization in sustainable aquaculture.