Trematode parasitism increases mortality in marsh ramshorn snail Planorbella trivolvis exposed to repeated low dose copper sulfate treatments in laboratory trials

Authors: Richardson, Bradley; MISCHKE, CHARLES - Mississippi State University; ROSSER, T. GRAHAM - Mississippi State University; BALAMI, SUJITA - Mississippi State University; SLIFKA, CELENE - Mississippi State University; ROSE, DIVYA - Mississippi State University; TIWARI, AMBIKA - Mississippi State University; Wood, Monica; Waldbieser, Geoffrey; WISE, DAVID - Mississippi State University; GRIFFIN, MATT - Mississippi State University

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2025
Publication Date: 10/15/2025
Citation: Richardson, B.M., Mischke, C.C., Rosser, T., Balami, S., Slifka, C.M., Rose, D., Tiwari, A., Wood, M.L., Waldbieser, G.C., Wise, D.J., Griffin, M.J. 2025. Trematode parasitism increases mortality in marsh ramshorn snail Planorbella trivolvis exposed to repeated low dose copper sulfate treatments in laboratory trials. North American Journal of Aquaculture. 87(4)293-302. https://doi.org/10.1093/naaqua/vraf023.
DOI: https://doi.org/10.1093/naaqua/vraf023

Interpretive Summary: Bolbophorus damnificus is an important parasite that detrimentally impacts the US commercial catfish industry, and uses pulmonate snails as an intermediate host. Parasite infections are thought to reduce snail survival and increase the susceptibility to various stressors. In this study, scientists from Mississippi State University and the Warmwater Aquaculture Research Unit at the National Warmwater Aquaculture Center in Stoneville, MS conducted a study to evaluate survival of industry-relevant snails to multiple low-dose treatments of copper sulfate. Bolbophorus is typically found in low prevalence, so a more common trematode, Alloglossidium kenti, was used in its place. Results showed that uninfected lab-reared snails were most resistant to copper sulfate treatments, while infected wild-caught snails were most susceptible, and uninfected wild-caught snails were intermediate. This study suggests that while low-dose pond treatments may not eradicate all snails, those that pose the most risk to the catfish stock are the most susceptible to the treatment and are likely being removed from the system.

Technical Abstract: Controlling the trematode Bolbophorus damnificus in catfish aquaculture relies on disrupting the parasite life cycle by targeting the snail intermediate hosts. Copper sulfate pentahydrate (CSP) is a common and effective molluscicide but can have adverse effects on fish health. In laboratory studies designed to improve safety and optimize CSP treatments, nontreated wild-caught snails have demonstrated poor survival. This may be an indication of poor snail vigor from handling and transport, environmental stressors, or trematode parasitism. Herein, CSP toxicity of laboratory-reared Marsh Ramshorn snails Planorbella trivolvis was compared to wild-caught individuals actively shedding trematode cercariae. Given the relatively low prevalence of B. damnificus in snail populations, snails parasitized with a more common trematode, Alloglossidium kenti, served as proxy for the effects of trematode parasitism on P. trivolvis exposed to CSP. Two trials were conducted, consisting of 4 weekly treatments of varying CSP concentrations. In both trials, survival curves and hazard analysis revealed laboratory-reared snails were most resistant to CSP, followed by non-shedding pond snails. Pond snails actively shedding A. kenti cercariae at the time of collection were most sensitive to CSP treatment. Increased susceptibility of parasitized snails to lower CSP doses demonstrates a targeted approach selective against parasitized snails within catfish pond systems. Therefore, complete eradication of P. trivolvis from catfish ponds may be unnecessary for effective trematode control and lower doses than those previously reported may prove effective at mitigating trematode associated losses in US catfish aquaculture.