Abstract

A population of sub-adult yellowtail jacks, acquired from the wild in early 1998, was housed in a three-story, 539,600 L (142,000 gallon) natural seawater exhibit at the Aquarium of the Pacific, along with other temperate teleost and cartilaginous fishes. Diet consisted of pieces of capelin, herring, squid hand-fed twice daily by volunteer divers. By June 2000, several jacks had developed superficial abrasions of the rostrum and flanks and/or mild kyphosis or scoliosis. Lesions were attributed to limited tank width (approximately 25 m), and plans were made to translocate 15 adult fish into a holding tank for ultimate transfer to another aquarium’s significantly larger habitat.

To minimize stress and skin abrasions during transport, sedation or anesthesia of fish is recommended.^1,4-6 Attempts to remove the jacks (approximately 6–9 kg each) from the exhibit using ketamine IM (Ketaset, Fort Dodge Animal Health, Fort Dodge, IA 50501 USA), delivered via modified Hawaiian sling, had limited success. The jacks proved difficult for staff divers to isolate and dart safely underwater, and a recommended dosage range of 66–88 mg/kg ketamine IM² was likely never reached due to volume limitations per dart.

Oral sedation was considered preferable in terms of safety and ability to deliver doses to the jacks individually. Published reports of successful oral sedation of large teleost fish are scarce.⁴ Our initial trials using a variety of sedatives and anesthetics injected into food pieces and hand-fed to the jacks were ineffective; the fish apparently detected an abnormal taste or texture and immediately regurgitated medicated food.

Tiletamine-zolazepam (Telazol, Fort Dodge Animal Health, Fort Dodge, IA 50501 USA) has proven efficacy in multiple species and a rapid onset of action, particularly at low doses.³ To our knowledge, there are no published reports of sedation of teleost fish using tiletamine-zolazepam. We used Telazol in its dry form for oral sedation of 14 yellowtail jacks. First, total powdered drug in each 500 mg vial of tiletamine-zolazepam was weighed and mg of active drug per mg of powder calculated (usually 0.5 mg active drug/mg powdered drug). Powder equivalent to 35 mg of active drug was measured and placed in a gelatin capsule. A dosage range of 8–9 mg/kg PO, or an average of 70 mg per yellowtail jack, yielded the best results overall.

Capsules were placed behind the gills of a thawed capelin and immediately fed to individual jacks by staff divers within the exhibit. Attempts were made to identify individual fish swallowing medicated food and to note time of ingestion. Restricting intake of food to only the yellowtail jacks was challenging for divers; therefore, it took six procedures to remove 14 fish. One yellowtail jack never took medicated feed and thus remained on exhibit.

Within 6–8 hours of ingestion, fish receiving an intended 70-mg dose began to show signs of sedation consisting of dark coloration, altered swim patterns, and loss of righting ability. Divers approached affected fish, trapped them in a hand-held net, and moved them to the surface. Although obviously sedated, fish remained reactive to touch, especially around the peduncular region. During acclimation to the holding tank, jacks were restrained within a canvas stretcher. Blood samples for complete blood counts, serum chemistries, and serum banking were collected from the vertebral vein using a lateral approach. Due to net-induced skin abrasions, all jacks received broad-spectrum antibiotics IM before transfer to a 30,400 L (8,000 gal) round holding tank.

Maximum sedative effect of oral tiletamine-zolazepam was 8–12 hours. Recovery from sedation, defined as return of normal swimming patterns and equilibrium, ranged from 12–48 hours. All fish refused to eat while in holding for 15 days. Skin lesions due to netting and contact with the tank sides were treated with nitrofurazone immersion (2 mg/L, renewed every 72 hours, for a duration of 7 days).

Four (28.6%) of the yellowtail jacks died during oral sedation procedures. Husbandry staff observed or suspected these four fish of taking additional doses of medicated food for estimated total doses of 140 or 160 mg (an average 15–20 mg/kg PO per fish). One of the four fish (25%) had a seizure-like episode and was found dead on the bottom of the tank shortly after a medicated feed session, and the other three fish (75%) failed to regain normal equilibrium post-procedure, sustained traumatic skin abrasions, and died from septicemia secondary to severe integumentary compromise. Liver, spleen, kidney, and serum samples from all four fish were banked for future analysis.

Sedation and translocation was successful in 10 out of 14 (71.4%) yellowtail jacks at our facility using oral tiletamine-zolazepam at a dosage of 8–9 mg/kg.

Acknowledgments

We thank the aquarists and divers at the Aquarium of the Pacific (Matt Ankley, Kim Stone, Akira Kanezaki, and Paul Clarkson) for their assistance in completing procedures. Special gratitude is extended to Dr. P.K. Robbins for her idea of trying powdered Telazol orally in the yellowtail.

Literature Cited

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2.  Carpenter, J.W., T.Y. Mashima, and R.J. Rupiper (eds.). 2001. Exotic Animal Formulary, 2nd edition. W.B. Saunders Company, Philadelphia, Pennsylvania. Pp. 15–17.

3.  Plumb, D.C. 2000. Veterinary Drug Handbook, 3rd edition. Iowa State University Press, Ames, Iowa. Pp. 456–457.

4.  Ross, L.G., and B. Ross (eds.). 1999. Anaesthetic & Sedative Techniques for Aquatic Animals, 2nd edition. Blackwell Science Ltd., Malden, Massachusetts. Pp. 1–41.

5.  Stoskopf, M.K. (ed.). 1993. Fish Medicine. W.B. Saunders Company, Philadelphia, Pennsylvania. Pp. 79–90.

6.  Stuart, N.C. 1981. Anaesthetics in fishes. J. Sm. An. Prac. 22, 6:377–383.