Bioremediation of organic sludge from a marine recirculating aquaculture system using the polychaete Abarenicola pusilla (Quatrefages, 1866)

Organic sludge, the principal residual product from recirculating aquaculture systems (RAS), is one of the main environmental and logistical challenges associated with aquaculture production. Polychaetes have been described as potential remediating organisms of aquaculture sludge due to its ability to survive in organic enrichment conditions and its capability to assimilate particulate organic waste from intensive aquaculture. The aim of this study was to evaluate the removal performance of Abarenicola pusilla (Quatrefages, 1866) when fed with organic sludge from a marine RAS. Experiments consisted of the addition of fish sludge (0.5, 2.0, 4.0 and 10.0% respect total inert sediment) at different densities of A. pusilla (60, 75, 150 and 200 organisms m⁻²), with 3 replicates each, and during 45 days. The highest removal rate of total organic matter (85.37%; 35.77 ± 0.05 g m⁻² day⁻¹), total N (33.63 ± 0.003 mg day⁻¹) and total C (236.78 ± 0.003 mg day⁻¹) were obtained with 10% of sludge and 200 organisms m⁻². Assimilation was corroborated by obtaining significant increase (p <.05) in total carbon (24.75%), organic carbon (24.68%) and lipid content (0.65%) in the biomass of organisms. Highest specific growth rate achieved by A. pusilla was 3.06% day⁻¹ and the highest survival was 91.67% over the 45 days trial period. These results indicated that A. pusilla could be used as remediating species of organic compounds contained in marine aquaculture sludge. The results also suggest that A. pusilla is a potential candidate for nutrient recycling from marine aquaculture systems on land. Further studies should determine the possible changes in the fatty acid profile of A. pusilla in order to use it in aquaculture feeds.