Technical Report

Effects of Propagation, Augmentation, and Salvage Activities on Recovery and Survival of Rio Grande Silvery Minnow (Hybognathus amarus)

URL: https://webapps.usgs.gov/mrgescp/documents/Caldwell%20et%20al_2009_Effects%20of%20Propagation%2C%20Augmentation%2C%20and%20Salvage%20Activities%20on%20Recovery%20and%20Survival%20of%20RGSM%20%28Hybognathus%20amarus%29.pdf

Date: 2009/10/01

Author(s): Caldwell C.A., Cho S., Remshardt W.J.

Publication: Report prepared for U.S. Bureau of Reclamation and Middle Rio Grande Endangered Species Act Collaborative Program, 94 p.

Abstract:

In an attempt to re-establish populations of Rio Grande silvery minnow Hybognathus amarus within its former range, several initiatives were set forth designed 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 which increases vulnerability of the minnow to opportunistic pathogens and predation, possibly decreasing post-stocking survival. We assessed the physiological stress response to standard management practices by characterizing changes in plasma cortisol, glucose, and osmolality in the minnow. When subjected to the individual stressors of 30 s handling, 3 h confinement (density, 100 kg/m³ ), or 3 h transport (density, 40 kg/m³ ), and observed throughout recovery, moderate changes in plasma glucose were observed while changes in plasma osmolality were not detectably different. Plasma cortisol peaked at132 ng/mL after 3 h confinement and at158 ng/mL after 3 h transport. Within 6 h post-stress, plasma cortisol returned to unstressed levels. When subjected to consecutive stressors (30 s handling only, 30 s handling plus 3 h confinement, 30 s handling plus 3 h confinement plus 3 h transport), plasma glucose exhibited a cumulative increase that was not observed for plasma cortisol. This increase in plasma glucose was observed within 3 h post stress when 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 265 mOsm/kg compared to unstressed levels (279 mOsm/kg) when the minnow was subjected to three consecutive stressors indicating severe osmoregulatory dysfunction. Plasma cortisol, glucose, and osmolality returned to unstressed levels within 48 h indicating the species can regain its physiological homeostasis within a relatively short time as long as the stressors are reasonable in duration and intensity.