Toxicity of Common Aquaculture Disinfectants to New Zealand Mud Snails and Mud Snail Toxicants to Rainbow Trout Eggs

Abstract

The New Zealand mud snail (NZMS) Potamopyrgus antipodarum is an invasive species that threatens North American fish populations. Establishment of NZMS in fish hatcheries is a concern because fish stocking practices could expedite the spread of the species. We evaluated the potential use of chemicals to remove snails that are inadvertently collected during egg take operations involving wild broodstock from the field. We exposed green eggs of rainbow trout Oncorhynchus mykiss for 5 min to several chemicals that have been proven lethal to NZMS: 1,940-ppm Hyamine 1622; Clorox Commercial Solutions 409 Cleaner, Degreaser, and Disinfectant (full strength; hereafter, Clorox Commercial 409); Pine-Sol (50% dilution); household ammonia (full strength); and a 504-ppm copper solution (as copper sulfate). All of the eggs exposed to Hyamine 1622, Clorox Commercial 409, and ammonia died within 24 h. Among eggs treated with Pine-Sol and copper sulfate, hatch and cripple rates did not differ from the control (water); however, eye-up rates among eggs treated with copper sulfate were lower than those for the control. Thus, while more research is needed, it is possible that a 50% dilution of Pine-Sol could be used to kill NZMS that are inadvertently collected during egg take operations. In a second experiment, a probit analysis provided 15-min LD50 and LD90 values for several common fish therapeutic chemicals (formalin, iodine, hydrogen peroxide, and potassium permanganate). For all chemicals, we estimated that concentrations of at least 7,500 ppm are required in 15-min treatments to kill 100% of NZMS. While these chemicals could be used to remove NZMS from hatchery facilities, concentrations required for complete mortality in 15-min exposures exceed concentrations that are considered safe for most fish species. Even though the best method for averting accidental introduction is to prevent the transportation of water from the wild into the hatchery, we feel that hydrogen peroxide may be the most effective chemical for killing NZMS that are inadvertently collected.