Effect of Sodium Chloride, Tricaine Methanesulfonate, and Light on New Zealand Mud Snail Behavior, Survival of Snails Defecated from Rainbow Trout, and Effects of Epsom Salt on Snail Elimination Rate

Abstract

The New Zealand mud snail (NZMS) Potamopyrgus antipodarum is an invasive species that threatens fish populations in North America. Establishment of NZMS in fish hatcheries is particularly problematic because NZMS could be inadvertently spread through fish stocking. Herein, we present the results of tests conducted to improve our understanding of (1) the risk of stocking fish from NZMS-infested hatcheries and (2) methods of NZMS control. We determined the proportion of NZMS that can survive passage through the digestive tracts of rainbow trout Oncorhynchus mykiss and whether the purgative Epsom salt (MgSO₄) could increase excretion rates. We tested NZMS phototropism and whether light preference is influenced by food availability. Finally, we determined whether NZMS would contract into their shells when exposed to sodium chloride (NaCl) and whether the anesthetic tricaine methanesulfonate (MS-222) would induce NZMS muscle relaxation. Only 4.5% of snails survived passage through the digestive tracts of rainbow trout, and Epsom salt did not increase NZMS excretion rates. This suggests that hatchery stocking could spread NZMS. New Zealand mud snails demonstrated neutral light preference and strongly preferred to occupy regions with food regardless of light presence. Finally, we determined that 59.3 ± 9.0% (mean ± SE) of NZMS exposed to an 11.0-g/L solution of NaCl retracted into their shells within 1 min of exposure and that 32.8 ± 4.1% of NZMS contracted when exposed to a 5.5-g/L NaCl solution. Retraction rates in the NaCl solution were significantly greater (P < 0.05) than those in the control, indicating that NaCl could be helpful for snail removal from portions of a hatchery that are difficult to access. Tricaine methanesulfonate concentrations of up to 400 mg/L did not induce muscle relaxation, suggesting that MS-222 cannot be used in conjunction with other compounds to increase their effectiveness.