Are northern crayfish, Orconectes virilis, resistant to CFT Legumine Fish Toxicant?

Authors: Jeff A. Sorensen

Year: 2010 (xlii)

Abstract

The short answer: apparently, yes. In advance of a planned chemical renovation of a small impoundment in southern Arizona, a series of bioassays were conducted on resident northern crayfish, Orconectes virilis, exposed to various concentrations of two commercial brands of fish toxicants (5% rotenone) to determine lethal dose thresholds. CFT Legumine Fish Toxicant was used in the first bioassay, where at the end of the test, crayfish had survived over 88 hours in rotenone solutions up to 50 ppm in concentration. In the second bioassay, Chem Fish Regular toxicant was used, and achieved 100% mortality of crayfish exposed in separate trials of 3, 5, and 10 ppm concentrations over 7 hours. While these tests were very preliminary in scope and design, it appears that crayfish were unaffected by CFT Legumine Fish Toxicant even when exposed to concentrations of rotenone that were more than ten times the maximum labeled application dose. More robust testing should be done to examine the difference in effects to crayfish between these two brands of fish toxicants. As a management consideration, planned rotenone treatments for areas with undesirable fish and invasive crayfish may be more effective at removing both nuisance species with Chem Fish Regular toxicant. In areas that have native crayfish and undesirable fish, CFT Legumine Fish Toxicant may be the preferred choice to apply where it removes fish with possibly little to no effect on the native crayfish.