Potassium permanganate (KMnO4) is used in fish culture for disease treatment, water clarification, rotenone detoxification, and historically for oxygen depletion. Many different treatment regimes have been developed for these uses. Most commonly, KMnO4 is used in freshwater systems at 2 mg/L to control ectoparasites, bacteria, and fungi. Effective concentrations are determined by the KMnO4 demand of the water being treated. Although use of KMnO4 in freshwater systems is well documented, its safety for use in saltwater systems is unclear.
The sailfin molly, Poecilia latipinna, a euryhaline species was used as a model to test the tolerance of fish to varying concentrations of KMnO4 at different levels of salinity. KMnO4 concentrations tested were 0.5 mg/L, 1.0 mg/L, 3.0 mg/L plus the KMnO4 demand. Each concentration was tested at salinity levels of 2 g/L, 15 g/L, and 30 g/L and each salinity level contained a control group. Mortality and behavior were monitored throughout the experiment and histology samples were taken before the treatment, at the end of the treatment (12 hours), and seven days after treatment.
Preliminary results indicate that the tolerance of the sailfin molly to KMnO4 varies with salinity and concentration of KMnO4. At a salinity level of 30 g/L, a concentration of 3.0 mg/L KMnO4 resulted in 100% mortality. As the salinity level increases, the risk of mortality when treating with KMnO4 also seems to increase.
In a pilot study, microscopic changes in gill epithelium of fish exposed to concentrations of 2 and 6 mg/L KMnO4 at salinities of 15 and 30 g/L were remarkable. Interlamellar hyperplasia resulted in partial fusion of lamellae. Mucus production seemed to increase and edematous fluid accumulation was observed under the epithelial lining of the secondary lamellae. These changes to gill structure would result in compromised gas exchange, which may provide an explanation for the mortality observed. More comprehensive results from this project may confirm this observation.
We would like to thank Segrest Farms in Gibsonton, FL for their generous donation of sailfin mollies for this project, The University of Florida's Tropical Aquaculture Laboratory for use of their research facility, and Don Samuelson and Patricia Lewis at The University of Florida College of Veterinary Medicine for use of their histology laboratory.