Effects of stocking density on the productivity and nutrient removal of Agarophyton vermiculophyllum in Paralichthys olivaceus biofloc effluent

Optimal stocking density of the marine red algaAgarophyton vermiculophyllumwas determined to maximize the produc-tivity and nitrogen removal in biofloc effluent.Agarophyton vermiculophyllumwas cultured at 0.2, 2, 4 and 8 g L−1(FW)stocking densities, 160 ± 10μmol photons m−2s−1and 12:12 L:D photoperiod for 20 days.Agarophytonvermiculophyllumwas cultured in effluent from a juvenileParalichthysbiofloc tank culture system and von Stosch–enriched (VSE) medium at 20 °C. The total nitrogen and phosphorus concentration of VSE medium was adjusted to thebiofloc level, 1000μmol L−1and 33μmol L−1, respectively. Specific growth rate was significantly higher at 0.2, 2, 4 and 8g L−1in both media. However, the productivity was significantly higher at 8 than 0.2 g L−1in both media. Tissue carboncontents were not significantly influenced by the medium at 8 g L−1(34.9% in VSE and 34.0% in biofloc). However, tissuenitrogen content was significantly higher at VSE medium than at biofloc medium at 8 g L−1(3.7% in VSE and 3.4% inbiofloc). The carbon removal rate was highestat the highest stocking density, 1.98 mgC g−1DW day−1(VSE) and1.89 mgC g−1DW day−1(biofloc), respectively. Also, the nitrogen removal rate was highest at the highest stockingdensity, 0.21 mgN g−1DW day−1(VSE) and 0.19 mgN g−1DW day−1(biofloc), respectively. The nutrient removal wasnot significantly influenced by medium at 4 and 8 g L−1. These results show thatA. vermiculophyllumcan grow and havethe potential to remove nutrients in the biofloc medium at high nitrogen concentrations.