Development of a Non-Lethal Tool to Assess the Physiological Condition of Endangered Fish Species in Grand Canyon, USA

Previous research on the endangered Humpback Chub, Gila cypha, in the Little Colorado and Colorado Rivers has primarily focused on determining population size and fish growth rates in response to physical and biological factors. Physiological condition is also an important attribute of fish population health, but its determination often involves sacrificing individuals or relying on rough condition estimates using length-weight relationships. This laboratory research tests the feasibility of developing a more sensitive technique to assess the condition of native fish. Bioelectrical Impedance Analysis is a tool that has been successfully developed for cyprinids and other fishes in freshwater and marine environments, but this technique has not been refined for native cyprinids in the Colorado River basin. Using hatchery-raised Humpback Chub and Bonytail (Gila elegans, a surrogate species), we assessed the relationship between measures of impedance and proximate body composition in laboratory specimens. Preliminary results indicate there is a positive relationship between percent body fat and measures of impedance, resistance, and reactance in Bonytail. These data will allow us to calibrate the models for potential use in field monitoring efforts, which will provide a non-lethal method to assess the status of endangered fish populations.