Effect of blue-green algae ( <i>Microcystis aeruginosa</i> ) on the water quality and growth of striped catfish ( <i>Pangasianodon hypophthalmus</i> ) in indoor-tank culture

Water quality plays an important role in aquaculture ponds. During fish farming, the nutrient content in water can increase due to the accumulation of excess feed and fish waste. This creates opportunities for phytoplankton development, especially blue-green algae, which are not beneficial for the growth of striped catfish. The goal of this study was to evaluate the effect of cyanobacteria on the water quality and striped catfish growth in indoor-tank culture. Water samples were collected periodically once a week, for a total of 20 sampling periods. The experiment was designed to include four treatments, consisting of one control treatment (no algae added) and three treatments wherein toxic blue-green algae (Microcystis aeruginosa) were added to the tanks with densities of 10 million cells/L, 30 million cells/L and 50 million cells/L. Each treatment was repeated 3 times. The stocking fish number was 20 fish/tank. The results showed that temperature, pH, DO, alkalinity, and NO 3 - through the collecting periods were within the favorable range for the striped catfish’s growth. Other parameters such as TSS, TAN, PO 4 3- and chlorophyll-a were low at the beginning of the experiment and tended to increase beyond the appropriate threshold towards the end of the experiment. The DO, alkalinity, TSS, TAN, and PO 4 3- parameters were closely correlated with chlorophyll-a content in the striped catfish tanks. The specific growth rate of fish in treatments with different M. aeruginosa densities from 10-50 million cells/L was significantly lower than that in the control. In addition, treatments added with toxic algae also showed higher FCR (p&lt;0.05) than the control group.