Prevention of an initial infestation of Ichthyophthirius multifiliis in channel catfish and blue tilapia by potassium permanganate treatment

Potassium permanganate (KMnO4) has been used to control infestations of Ich thyophthirius multifiliis, but its effectiveness has not been reported from controlled efficacy studies. The purpose of this study was to determine th e acute toxicity of KMnO4 to the I. multifiliis theront and the concentrati on needed to prevent an initial infestation of I. multifiliis in juvenile c hannel catfish Ictalurus punctatus and blue tilapia Tilapia aurea. Ichthyop hthirius multifiliis theronts were exposed to concentrations of KMnO4 in 10 0 muL of well water in 96-well plates and observed for 4 h to determine the acute toxicity. A concentration of 0.9 mg KMnO4/L caused greater than 95% mortality of the theronts in 4 h in well water; the 4-h LC50 (concentration lethal to 50% of test animals) value was estimated to be 0.77 mg/L. Juveni le channel catfish were exposed to 10,000 theronts/L of well water and imme diately treated with a single dose of KMnO4. Infestation occurred in contro ls 6 d after exposure. The lowest effective dose of KMnO4 was 1.0 mg/L. Juv enile blue tilapia were exposed and treated in the same manner as the chann el catfish. Infestation occurred in controls by day 8 after exposure. The l owest effective dose of KMnO4 was 0.5 mg/L. An additional experiment (witho ut KMnO4) indicated that channel catfish were 33-fold more susceptible to I . multifiliis infestation than blue tilapia. These results indicate that KM nO4 is toxic to I. multifiliis theronts at low concentrations in clean wate r. However, effective treatment of pond water will be strongly influenced b y detoxication of KMnO4 (based on the concentration of easily oxidizable su bstances in the water) and water temperatures controlling the lifecycle of the parasite.