Efficacy and Physiological Response to Chemical Anesthesia in Wild Hickory Shad during Spawning Season

Abstract Anesthetizing fish facilitates handling procedures such as hormone injections to induce spawning, reduces risk of injuries, and may reduce stress response. We conducted two experiments with wild Hickory Shad Alosa mediocris caught by angling during spawning season. Induction and recovery times of fish anesthetized with tricaine methanesulfonate (MS-222 at 50–100 mg/L of water), 2-phenoxyethanol (PhE at 25–400 mg/L), and eugenol (Aqui-S, 25–100 mg/L) were compared in the first experiment, while physiological responses in fish following anesthesia were compared in the second experiment. Total time to induce and recover from anesthesia in fish was lowest with MS-222 at 100 mg/L and eugenol at 100 mg/L. External signs of stress (muscle spasms, coughing, decreased respiration) were evident in fish during anesthesia with highest concentration of PhE (400 mg/L), while physiological indicators of toxicity were evident in fish anesthetized with a lower concentration of PhE (100 mg/L) compared with controls (i.e., decreased total proteins and increased hemolysis, plasma lactate, and glucose). Reduced stress response (lower glucose and plasma lactate) was evident in fish treated with MS-222 (100 mg/L) at 1 h postinjection and with eugenol (100 mg/L) at 6 h. Both MS-222 and eugenol were effective in rapidly anesthetizing wild Hickory Shad with fewer signs of stress than PhE; however, more information is needed regarding effects of these anesthetics on spawning, gamete quality, and fertilization success in hickory shad and other species.