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 Ichthyophthirius multifiliis, but its effectiveness has not been reported from controlled efficacy studies. The purpose of this study was to determine the acute toxicity of KMnO4 to the I. multifiliis theront and the concentration needed to prevent an initial infestation of I. multifiliis in juvenile channel catfish Ictalurus punctatus and blue tilapia Tilapia aurea. Ichthyophthirius multifiliis theronts were exposed to concentrations of KMnO4 in 100 μL 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. Juvenile channel catfish were exposed to 10,000 theronts/L of well water and immediately treated with a single dose of KMnO4. Infestation occurred in controls 6 d after exposure. The lowest effective dose of KMnO4 was 1.0 mg/L. Juvenile blue tilapia were exposed and treated in the same manner as the channel catfish. Infestation occurred in controls by day 8 after exposure. The lowest effective dose of KMnO4 was 0.5 mg/L. An additional experiment (without KMnO4) indicated that channel catfish were 33‐fold more susceptible to I. multifiliis infestation than blue tilapia. These results indicate that KMnO4 is toxic to I. multifiliis theronts at low concentrations in clean water. However, effective treatment of pond water will be strongly influenced by detoxication of KMnO4 (based on the concentration of easily oxidizable substances in the water) and water temperatures controlling the lifecycle of the parasite.