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

Abstract

Bolbophorus 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.

Copper Toxicity to the Ghost Rams‐Horn Snail Biomphalaria havanensis

“…As with marsh rams‐horn snails (Mischke et al. 2021), ghost rams‐horn snail eggs hatched in 10 d. Seven weeks after hatching, ghost rams‐horn snails were about 4.9 ± 0.1 mm (mean ± SEM) (Figure 1) compared with marsh rams‐horn snails growing to 9 mm by this time (Mischke et al. 2021).…”

“…2021), ghost rams‐horn snail eggs hatched in 10 d. Seven weeks after hatching, ghost rams‐horn snails were about 4.9 ± 0.1 mm (mean ± SEM) (Figure 1) compared with marsh rams‐horn snails growing to 9 mm by this time (Mischke et al. 2021). However, like marsh rams‐horn snails, first spawns of ghost rams‐horn snails were seen 7 weeks posthatch (Mischke et al.…”

“…However, like marsh rams‐horn snails, first spawns of ghost rams‐horn snails were seen 7 weeks posthatch (Mischke et al. 2021).…”

“…With laboratory‐reared marsh rams‐horn snails, it required two doses of 0.4 mg/L Cu to kill all snails and four doses of 0.2 mg/L Cu to achieve ~50% mortality (Mischke et al. 2021). Overall, adult ghost rams‐horn snails and marsh rams‐horn snails appear to have similar sensitivity to repeated low‐dose copper exposure.…”

“…Research was conducted to determine if repeated lower doses of copper could be a safer, yet effective snail treatment (Mischke et al. 2021). Adult marsh rams‐horn snails were treated with four weekly doses ranging from 0.10 to 0.76 mg/L Cu.…”