Water quality management with Bacillus spp. in the high-density culture ofred-parrot fish Cichlasomia citrinellum x C-synspilum

Red-parrot fish (male midas cichlid Cichlasoma citrinellum x 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, gil l filament ulceration, gill opercula malformation, and high mortality. In a n effort to solve these problems in a high-density culture environment, two bacteria, Bacillus subtilis and B. megaterium, were added to the recircula ting-water systems of the grow-out fa cilities. The addition of Bacillus he ld total ammonia nitrogen concentrations to 5.4 mg/L or less and chemical o xygen 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 f ish 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.