Effects of formalin, chemotherapeutic treatments on biofilter efficiency in a marine recirculating fish farming system

摘要

Formalin (a 33-38% aqueous formaldehyde solution) is currently used for bath treatments to control ectoparasitic infections of fish. Its effects on nitrification were evaluated in a semi-closed pilot scale saltwater recirculating turbot culture system. Tested treatments included I It static exposure to 20, 30, 40, 50, 60, 70, 90 mg l(-1) formaldehyde without flushing, and long-term (i.e., 2, 4 and 6 h) exposures with constant 60 mg 171 formaldehyde in a recirculating system. Formaldehyde has no apparent effect on the ammonia oxidative bacterial community. However, a significant effect on nitrite oxidation was observed in 1. h static exposures of concentrations higher than 40 mg l(-1), and in recirculating system exposures of 60 mg l(-1) formaldehyde for more than 4 h. Repeated treatments may be hazardous for nitrifying bacteria, which could induce an increase in nitrite concentration. Nitrite concentrations should be monitored when treatments are repeated or when they last a long time in recirculating aquaculture systems.