Ammonia as a tool for eradication of northern crayfish, Orconectes virilis

Authors: David L. Ward

Year: 2010 (xlii)

Abstract

Crayfish are not native to Arizona but have been widely introduced with negative impacts to aquatic ecosystems. Crayfish prey upon and compete with many native fish species threatening their long-term persistence. No effective methods currently exist for control or eradication of crayfish. We performed laboratory tests to evaluate the use of ammonia as a tool for removal of crayfish from aquatic systems. Ten northern crayfish, Orconectes virilis, were placed in each of 12, 38-liter aquaria and treated with varying concentrations and durations of 10 % ammonia solution. Although crayfish appear dead in less than 15 minutes, they will revive if placed back into fresh water. A concentration of 1 ppt for 4 hours was needed to kill 100% of crayfish at a pH of 7.5. Ammonia is a natural byproduct of fish metabolism and is therefore naturally present in the environment at low levels. Natural bacteria in the environment rapidly convert ammonia to non-toxic nitrate which is utilized by plants. Commercially formulated products that remove ammonia from water are also available and could be used if more rapid detoxification is needed. The low cost of ammonia, its effectiveness at killing crayfish without causing them to crawl out of the water, and the ability of natural bacteria in the environment to quickly detoxify ammonia appear to make it ideal as a tool for removal of invasive crayfish.