Abstract

Fifty-one immobilizations were performed using southern stingrays (Dasyatis americana) over a period of 12 months. Three immersion agents were used for 17 immobilizations per drug, including: eugenol (20 ppm), Aqui-S™ (Isoeugenol) (15.7 ppm), and tricaine methanesulfonate (MS-222) [65 ppm (n=6); 55 ppm (n=11)]. Immersion agent exposure lasted 10–15 minutes. Stingrays were placed in dorsal recumbency at 5 minutes for phlebotomy. A second blood sample was collected at the end of the trial (either at 10 or 15 minutes) to evaluate changes in lactic acid and pH. Cardiac and gilling rates were measured at 5-minute intervals.

Induction-associated excitation was observed in all three treatment groups (42 out of 51 trials) with a lower percentage observed with eugenol. Of the three agents, Aqui-S™ resulted in more “no response to stimulus” trials (n=12) than eugenol (n=10) and MS-222 (n=9). Gilling was maintained during all trials with exception of 2 Aqui-S™ trials during which gilling ceased for 20–30 seconds, as well as one Aqui-S™ and one eugenol trial during which respiratory arrest also occurred. These latter two cases were transferred to recovery water and provided ram ventilation support; spontaneous gilling resumed within 1 minute. Cardiac rates were stable and similar for all regimens. Stingrays were released from the recovery water when directed wing movement was noted. Median time from placement in recovery water to release was 9 minutes for MS-222 and 12 minutes for Aqui-S™ and eugenol. Lactic acid increased during 65% of the trials with roughly equal distribution between the agents. For MS-222 and eugenol, a decline in blood pH was noted for most trials.

Although variation was noted between the three immersion agents, they are all considered appropriate agents for short-term immobilization in southern stingrays.