Physiological Stress Responses of Rio Grande Silvery Minnow: Effects of Individual and Multiple Physical Stressors of Handling, Confinement, and Transport

Abstract

AbstractIn an attempt to reestablish populations of Rio Grande silvery minnow Hybognathus amarus within its former range, initiatives were set forth to propagate the species in hatcheries, augment wild populations through repatriation, and rescue the species from isolated and receding pools. Physical stressors associated with these recovery efforts, however, result in stress that increases the vulnerability of the minnow to opportunistic pathogens and predation, possibly decreasing poststocking survival. We assessed the physiological stress response to standard management practices by characterizing the changes in plasma cortisol, glucose, and osmolality. When subjected to the individual stressors of 30 s of handling, 3 h of confinement (density, 100 kg/m3), or 3 h of transport (density, 40 kg/m3), moderate changes in plasma glucose and plasma osmolality were observed during recovery whereas changes in plasma cortisol were not detectable. When fish were subjected to consecutive stressors (30 s of handling only, 30 s of handling plus 3 h of confinement, or 30 s handling plus 3 h of confinement and 3 h of transport), plasma glucose exhibited a cumulative increase that was not observed for plasma cortisol. This increase in plasma glucose was observed within 3 h poststress when fish were subjected to a single stressor (22 mg/dL), two consecutive stressors (28 mg/dL), and three consecutive stressors (63 mg/dL). Plasma osmolality decreased from 282 to 269 mosmol/kg (compared with unstressed levels of 279 mosmol/kg) when minnows were subjected to three consecutive stressors, indicating moderate osmoregulatory dysfunction. Plasma glucose and osmolality returned to unstressed levels within 48 h, indicating that the species can regain its physiological homeostasis within a relatively short time as long as the stressors are reasonable in duration and intensity.