In vitro and in vivo study of chlorine dioxide to treat Ichthyophthirius multifiliis in silver catfish Rhamdia quelen

Abstract

This study evaluated the efficacy of chlorine dioxide in the treatment of Rhamdia quelen infected with Ichthyophthirius multifiliis. The experiment was divided into two stages: in vitro and in vivo. The in vitro assay was conducted to determine the lowest concentration of chlorine dioxide (ClO₂) capable of immobilizing the theronts of I. multifiliis. Parasitized fish (degree III severity) with I. multifiliis were exposed to short-term (0 mg L^-1, 25 mg L^-1, 125 mg L^-1 and 250 mg L^-1 for 1 h) and longterm baths (0 mg L^-1, 25 mg L^-1, 35 mg L^-1 and 45 mg L^-1 for 48 h) of chlorine dioxide. Chlorine dioxide was effective in immobilizing theronts at the lowest concentration (25 mg L^-1) in vitro. The same concentration in long-term exposure for 48 h reduced more than 50% of theronts in the gills of fish. Fish exposed to a short-term bath with 125 mg L^-1 and 250 mg L^-1 chlorine dioxide (ClO₂) showed reduced parasitism in the gills (62%). It could be suggested the use of chlorine dioxide at 25 mg L^-1 for up to 48 h to reduce more than 50% of the I. multifiliis infestation.