Copper sulfate pre-treatment for snail control reduces channel catfish survival

Authors: MISCHKE, CHARLES - Mississippi State University; WISE, DAVID - Mississippi State University; Tucker, Craig; GRIFFIN, MATT - Mississippi State University; BAKER, BETH - Mississippi State University; GREENWAY, TERRY - Mississippi State University; BYARS, TODD - Mississippi State University; TIWARI, AMBIKA - Mississippi State University

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2019
Publication Date: 4/15/2019
Citation: Mischke, C.C., Wise, D.J., Tucker, C.S., Griffin, M.J., Baker, B.H., Greenway, T.E., Byars, T.S., Tiwari, A. 2019. Copper sulfate pre-treatment for snail control reduces channel catfish survival. North American Journal of Aquaculture. 81:160-168.

Interpretive Summary: The trematode parasite Bolbophorus damnificus has a complex life cycle involving pelicans, snails, and channel catfish (or the channel x blue hybrid catfish). Parasite infections cause significant economic losses on commercial catfish farms by reducing fish growth or, in extreme cases, killing fish. The disease has greatest impacts at the fingerling stage of production. Trematode infections of adult catfish can be managed by disrupting the trematode life cycle by reducing snail populations in ponds with copper sulfate. However, copper sulfate treatment is generally not recommended for ponds with fry or small fingerlings because of potential problems with direct toxicity or indirect negative effects of copper treatment on pond water quality. To avoid the unintended negative effects of using copper-based products in ponds after stocking with fry or small fingerlings, some catfish farmers have used copper sulfate prophylactically for snail control by treating nursery ponds after they are filled but 2-3 weeks before stocking fry. Nevertheless, farmers have reported low fingerling survival in ponds treated prophylactically, and this study investigated this problem. We evaluated water quality and fish production in commercial and experimental catfish nursery ponds treated with copper sulfate before fry stocking. Fry survival and revenue from ponds treated with copper sulfate were reduced in copper-treated ponds, even when ponds were treated 3 weeks before fry were stocked. Free copper concentrations in water took 20 d to return to pretreatment concentrations but did not appear high enough to kill fish. Turbulence caused by aerators may have made copper in sediments bioavailable and toxic to fish or copper treatment may have had indirect effects on environmental quality. Regardless of the cause of low fry survival, copper sulfate should not be used to prophylactically treat catfish fry ponds.

Technical Abstract: Channel catfish Ictalurus punctatus fry farmers are interested in prophylactically treating ponds to prevent trematode infections. Control strategies rely on chemical treatments to reduce snail populations and break the trematode life cycle. On a commercial catfish fingerling operation, we evaluated water quality, zooplankton, phytoplankton, and fish production in catfish nursery ponds treated with copper sulfate 21 d before fry stocking. These variables were also evaluated in controlled experimental ponds treated with copper sulfate 1 d, 7 d, 14 d, and 21 d before stocking. In the on-farm trial, copper sulfate treatment initially reduced phytoplankton and zooplankton populations, but communities recovered to adequate numbers at stocking. However, fry survival and revenue from ponds treated with copper sulfate (17.7% vs 63.0% survival and $10,250/ha vs $27,467/ha) were reduced. Similar results were observed in the experimental study with lower survival in all treatment groups compared to controls, with the lowest survival observed in fry stocked one day after copper sulfate treatment. Free copper concentrations took 20 d to return to pre-treatment concentrations. Copper may be having indirect effects on environmental quality. Until further work is done evaluating environmental effects of copper, copper sulfate should not be used to prophylactically treat fry ponds.