Effects of Multiple, Low‐Dose Copper Sulfate Treatments on the Marsh Rams‐Horn Snail

Abstract

AbstractBolbophorus damnificus has caused epizootics in catfish aquaculture since the mid‐1990s. To mitigate the losses that are associated with trematode infestations, research has focused on eradicating snails from ponds. Whole‐pond treatments with 0.64–1.27 mg/L Cu have been effective in killing snails; however, Cu can be toxic to fish and may result in oxygen depletions due to its algacidal properties. Given these constraints, the potential for repeated low doses of Cu as a safe, yet effective snail treatment was investigated. Adult marsh rams‐horn snails Planorbella trivolvis received four weekly doses of 0, 0.10, 0.19, 0.38, and 0.76 mg/L Cu. All of the snails died after the first treatment of 0.76 mg/L Cu. The lowest doses of 0.10 and 0.19 mg/L Cu resulted in 68% and 88% cumulative mortality, respectively. This experiment was repeated with laboratory‐reared adult marsh rams‐horn snails in two different laboratories, resulting in 100% mortality in the 0.38 mg/L Cu treatment. A second study evaluated the effects of repeated Cu doses on egg and juvenile snail survival. Two weekly doses of 0.19 mg/L Cu were enough to kill embryos, and all of the doses ≥0.05 mg/L Cu prevented the snails from hatching. In a pond trial, 0.51 mg/L Cu killed 100% of the adult snails after two doses. The lowest dose of 0.13 mg/L Cu killed 60% of the snails after three doses. Repeated weekly doses <0.38 mg/L Cu may reduce adult snail populations, prevent eggs from hatching, and be safer for fish than a single dose of 0.64–1.27 mg/L Cu. These data also suggest that weekly doses <0.05 mg/L Cu may suppress marsh rams‐horn snail populations by limiting hatching and impeding juvenile survival.