Cooperative Fish and Wildlife Research Units Program: New Mexico
Education, Research and Technical Assistance for Managing Our Natural Resources

Sykes, C.L., C.A. Caldwell, and W.R. Gould. Physiological effects of potassium chloride, formalin and handling stress on bonytail Gila elegans. North American Journal of Fisheries Management. 31:291-298.


A standard treatment of a 1 h bath in 750 mg/L potassium chloride (KCl) followed by a 2 h bath in formalin has been established for removal of mussel veligers when moving fish from waters positive for zebra mussels Dreissena polymorpha and quagga mussels D. bugensis. Quagga mussels have recently been found in waters inhabited by endangered bonytail Gila elegans, making bonytail a candidate species for the KCl and formalin treatment. The chemical treatment, however, also subjects the fish to a series of handling stressors which may increase the susceptibility of bonytail to pathogens and predators upon stocking. We characterized physiological changes of plasma cortisol, glucose, and osmolality over 24 h and at 14 d post-handling after exposing bonytail to KCl with one net stressor, KCl+formalin with two net stressors, and one net stressor and two net stressors without chemicals. Elevated plasma cortisol (322-440 ng/mL) and glucose (254-399 mg/dL) concentrations were observed in all treatments compared to plasma cortisol (56 ng/mL) and glucose (43 mg/dL) concentrations in control fish. While there were no detectable differences in plasma osmolality among the treatments and control fish, a detectable difference was observed between fish that were handled once versus twice. Chemical effects of stress were not observed in any of the physiological responses when the KCl treatment was compared to the one-net stressor or when KCl+formalin treatment was compared to the two-net stressor treatment. Cumulative responses, however, were observed between one net stressor and two net stressors for plasma glucose and osmolality but not for plasma cortisol. Within 24 h post-handling, plasma cortisol and glucose levels remained elevated and anecdotal observations of reduced response to stimuli was noted up to 14 d post-handling, indicating bonytail may not have completely recovered and could be more susceptible to pathogens and predators upon release.