Investigation of Metomidate Hydrochloride as a Sedative for Transportation of Ornamental Fish
Stress associated with transportation of ornamental fish may lead to poor appearance, decreased immunity, and mortality. Several studies have demonstrated that the drug metomidate hydrochloride prevents a rise in cortisol, an indicator of stress, by inhibiting the release of the enzyme β-11 hydroxylase required for cortisol production. Metomidate hydrochloride is currently being used in Canada, trade name AquacalmTM, as an anesthetic (5-10 mg/l) and a sedative (0.1-1.0 mg/l). Koi Cyprinus carpio (127-152 mm TL, N=150) were shipped with 1.0, 2.0, 3.0, and 4.0 mg/L metomidate hydrochloride and blue gourami Trichogaster trichopterus (50-76 mm TL, N = 150) were shipped with 0.1, 0.2, 0.3, and 0.4 mg/L metomidate hydrochloride. Fish were transported via truck and airplane for approximately 24-hours. Cortisol and glucose were analyzed in koi and glucose was analyzed in blue gourami at times 0, 2, 4, 8, and 12 hours post-transportation. A second group of fish were again transported and observed for appearance, behavior, and activity level at times 0, 1, 2, 4, 6, and 12 hours post-transportation and again 7 days post-transportation.
Cortisol levels for koi transported with 3.0 and 4.0 mg/L metomidate hydrochloride were significantly lower than other concentrations tested, however, this inhibition was only observed at time 0. There were no significant differences in glucose levels for koi at any sample time amongst treatments. In addition, koi were observed to have dropped beyond the sedative plane into an undesirable anesthetic plane at the higher metomidate concentrations (i.e., 3.0 and 4.0 mg/L). Glucose levels in gourami shipped at 0.2 mg/L were significantly lower at each sample time. However, there was no significant benefit to marketability (e.g., appearance, behavior, activity level) of either fish amongst treatments at any sample time. Therefore the short-term benefit of using metomidate hydrochloride as a transportation additive for koi and blue gourami is not apparent. Additional health challenge studies post transportation with metomidate hydrochloride may elucidate long-term benefits of using the product for transporting koi and blue gourami.
The authors would like to thank the funding sources USDA-CSREES and Syndel Laboratories Ltd., Florida Fish Farms, Inc. and 5-D Tropical Inc. for donating fish, and Segrest Fish Farms for assisting with transporting fish.