Efficacy of copper sulfate for the treatment of ichthyophthiriasis in channel catfish

Ichthyophthirius multifiliis is a protozoan that may infest and significant ly damage cultured fish species. The purpose of this study was to measure t he efficacy of copper sulfate in treating ichthyophthiriasis. Fingerling ch annel catfish Ictalurus punctatus exposed to at least 2,000 theronts of I. multifiliis per liter Of water developed consistent infestations of I. mult ifiliis (20 or more trophonts on the dorsal surface of the head of the fish ). Infestation was observed in untreated controls at day 5 after exposure a nd mortality occurred after day 10. Coexposure studies with theronts and di fferent concentrations of copper sulfate revealed that all theronts were ki lled at concentrations greater than 0.05 mg/L. To determine the effect of c opper sulfate in the treatment of ichthyophthiriasis, fish were exposed to the parasite until trophonts were observed (day 5), and they were subsequen tly treated with copper sulfate. The lowest effective concentration of copp er sulfate for treatment of ichthyophthiriasis (i.e., after infestation was observed in the fish) was 0.4 mg/L. To assess the effects of various water quality conditions on copper treatment, total suspended solids (TSS) and p H were varied during treatment of ichthyophthiriasis. Concentration of TSS was inversely correlated to the efficacy of copper sulfate for I. multifili is infestations, whereas no relationship was observed between pH and effica cy of a single copper sulfate dose. The results indicated that copper sulfa te can be used to treat ichthyophthiriasis at concentrations of 0.4 mg/L fo r at least 5 d under the specific water conditions used in this study (pH, 7.45 +/- 0.27; temperature, 20.5 +/- 0.7 degrees C; alkalinity, 176.6 +/- 2 8.1 mg/L as CaCO3) and that efficacy of copper sulfate was affected more by TSS concentration than by pH.