Effectiveness of coagulants-flocculants for removing cells and toxins of Gymnodinium catenatum

Laboratory experiments compared the removal efficiency of cells and toxins of the dinoflagellate Gymnodinium catenatum, using three concentrations of cells and three concentrations of red clay, montmorillonite, clinoptilolite, calcium oxide, calcium hydroxide, aluminium sulfate, chitosan, activated silica, and polyaluminium chloride, as coagulating or flocculating agents. Chitosan, calcium oxide, and calcium hydroxide were selected using the criterion of minimum concentration for maximum efficiency for removing cells. These were combined in pairs to measure their joint performance. In all cases, removal efficiency of cells was 95–99%. A combination of calcium oxide+chitosan effectively removed the cells, but failed to remove extracellular toxins produced by G. catenatum. •We used combinations of coagulants and flocculants to remove cells and toxins of Gymnodinium catenatum.•Gymnodinium catenatum is a paralyzing toxin-producing dinoflagellate that affects farmed shrimp.•Only some coagulant–flocculant agents were effective for removing cells of G. catenatum.•This approach to algae control can be used in fish and crustacean aquaculture.