Effects of temperature on the Marsh Ram's Horn (Planorbella trivolvis) and Ghost Ram's Horn snail (Biomphalaria havanensis)

Objective The marsh rams-horn Planorbella trivolvis and the ghost rams-horn Biomphalaria havanensis are intermediate hosts of the trematode Bolbophorus damnificus, which causes economic losses in the commercial catfish industry. Snail activity, survival, and egg laying and hatching are temperature dependent; thus, the timing of copper sulfate treatments can also influence efficacy of snail control. This study was conducted to determine the effects temperature on the survival, growth, and reproduction of these snails to improve the timing of copper sulfate treatments. Methods Four laboratory-reared adult snails were placed into each of 20 200-mL glass containers. Ten containers had adult marsh rams-horn and 10 containers had adult ghost rams-horn. Five containers of each species were maintained at 21°C throughout the study. The other five containers of each species began at 21°C, decreased to 5°C, then increased to 51°C (at 5°C/week). Growth, mortality, and reproduction were monitored weekly. Results The risk of snail mortality was significantly higher when the treatment group was in the 31–51°C range. Decreasing temperatures slowed growth, and increasing temperatures increased the growth of ghost rams-horn. Growth was stagnant for marsh rams-horn at all temperatures. Temperature had a significant effect on the spawning rate of both snail species. Decreasing temperatures slowed spawning, and increasing temperatures increased spawning to a peak at 31°C (6.9 spawns/week) for ghost rams-horn and 21°C (4.2 spawns/week) for marsh rams-horn. Spawning then decreased at temperatures that were above the respective peak temperatures. Conclusions Reactively responding to ponds that are infected with B. damnificus by treating snails in the summer with a uniform application of copper sulfate is risky because of the algicidal properties of copper and increased toxicity with increased temperatures. Based on the snail reproduction data from this study, peak reproduction occurs in the temperature range of 21–31°C. Although treating all ponds proactively with copper may be financially prohibitive, it may be beneficial to proactively treat ponds with a history of trematode infections with multiple low doses of copper in the spring, thus targeting snails and eggs before populations have a chance to increase drastically.

North American Journal of Aquaculture, 88(3)