Uniform application of copper sulfate as a potential treatment for controlling snail populations in channel catfish production ponds

A digenetic trematode identified as Bolbophorus sp. has been implicated as a cause of severe mortality and reduced production in commercially raised channel catfish Ictalurus punctatus in the southeastern United States. Currently, chemical control measures to limit the impact of this disease focus on pond shoreline treatments with hydrated lime or copper sulfate to kill the marsh ram's-horn snail Planorbella trivolvis, an intermediate host that inhabits aquatic vegetation around the pond perimeter. Although effective, these treatments have little impact on snails that are not within close proximity to the pond bank. Tests were conducted to determine the feasibility of using elevated levels of copper sulfate pentahydrate (CSP; CuSO(4)(.)5H(2)O), uniformly applied to the surface of the pond water, to eradicate snails from the pond environment. Results demonstrated that uniform application to deliver between 2.5- and 5.0-ppm CSP (0.64-1.27-ppm Cu) was effective in killing snails around the margins of the pond and throughout the water column but may have negatively affected fish health at the high treatment dose. On average, pond treatments killed more than 96% of the test snails, while mortality of the control snails was less than 8.5%. Results of the commercial field trial were similar to those of tests conducted in experimental ponds, where application of CSP at 5.0 ppm was effective in killing snails at all sampling sites. The treatment was also shown to reduce the natural population of snails along the pond margin by 98.3%. These trials indicate that CSP, when uniformly applied to the water, can be used with caution as an effective treatment against the marsh ram's-horn snail in commercial channel catfish production ponds that have chemical characteristics similar to those of tested waters (alkalinity and hardness > 200 ppm as CaCO3).