Effects of nitrogen ammonia and MS-222 on Xenopus laevis development, growth, and foraging behavior

Abstract

The anesthetic MS-222 (i.e., tricaine, Finquel) is widely used by biologists on amphibians in the field, even though field use of MS-222 on amphibians is not approved by the U.S. Food and Drug Administration (FDA). Previous studies have identified the impact of MS-222 on vision, olfaction, stress, heart, and liver, and have documented its lethality to certain microbes that commonly populate amphibian skin. We examined the potential impacts of “off-label” use of MS-222 on a model aquatic amphibian, the African clawed frog (Xenopus laevis Daudin 1802). Animals were exposed to an environmentally relevant concentration of nitrogen ammonia, a pollutant commonly found in U.S. waterways, and unbuffered MS-222 in a manner simulating typical field use of the drug. The animals’ foraging success in the hour post-recovery was observed. MS-222 impacted foraging behavior, with animals exposed to MS-222 eating significantly more food pellets than the control animals (P = 0.01). Although an ANOVA revealed no statistically significant difference in the mean weight and length between the animals exposed to nitrogen ammonia and their controls, the group of animals exposed to nitrogen ammonia had an increased variance in weight and length, which may indicate population-level effects.