Water Quality Management withBacillusspp. in the High-Density Culture of Red-Parrot FishCichlasoma citrinellum×C. synspilum

Red-parrot fish (male midas cichlid Cichlasoma citrinellum × female redhead cichlid C. synspilum) is one of the most important tropical fish in Taiwan. In high-density culture, poor water quality often induces emaciation, gill filament ulceration, gill opercula malformation, and high mortality. In an effort to solve these problems in a high-density culture environment, two bacteria, Bacillus subtilis and B. megaterium, were added to the recirculating-water systems of the grow-out facilities. The addition of Bacillus held total ammonia nitrogen concentrations to 5.4 mg/L or less and chemical oxygen demands to 40.8 mg/L or less; it also maintained the transparency of the recirculated aquarium water at 30–50 cm. Survival rate and quality of fish were dramatically improved with this microbial water quality management process. This method is easy to perform and can be adapted effectively in the commercial culture of red-parrot fish.