Abstract

Wild-caught sub-adult yellowtail jacks (Seriola lalandi) were acquired by the Aquarium of the Pacific in early 1998 and placed in a three-story, 539,600 L (142,000 gal) natural seawater exhibit, along with other temperate teleost and cartilaginous fishes. Resident fish were hand fed food pieces (capelin, herring, squid) twice daily by volunteer divers. By June 2000, many of the yellowtail jacks had developed superficial abrasions of the rostrum and flanks and subtle vertebral abnormalities (mild kyphosis or scoliosis). These lesions indicated that the yellowtail jacks were outgrowing the width of the exhibit (approximately 25 meters), thus curators decided to translocate the fish into a holding tank for eventual transfer to another aquarium's larger habitat.

Sedation or anesthesia of fish is recommended to minimize stress and skin abrasions during transport,^1,4-6 therefore, sedation of the highly active, agile yellowtail jacks was desired. Attempts made to remove the jacks from the exhibit using ketamine i.m. (Ketaset, Fort Dodge Animal Health, Fort Dodge, IA 50501), delivered via modified Hawaiian sling, had limited success. The jacks were estimated to weigh 6-9 kg; however, a recommended dosage range of 66-88 mg/kg ketamine i.m.² was likely never reached due to technical limitations. Furthermore, this species was difficult for staff divers to isolate and dart safely underwater.

Aquarists felt that an oral sedative would be 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 Initial trials using a variety of sedatives and anesthetics injected into food pieces and hand-fed to the jacks were ineffective, as they apparently detected an abnormal taste or texture and immediately regurgitated medicated food.

The anesthetic combination tiletamine-zolazepam (Telazol, Fort Dodge Animal Health, Fort Dodge, IA, 50501, USA) has a rapid onset of action and proven efficiency in multiple species, particularly at low doses. 3 To our knowledge, there are no published reports of sedation of teleost fish using tiletamine-zolazepam. We chose to use this drug orally in its dry form for sedation of the yellowtail jacks. Total powdered drug in each 500 mg vial of tiletamine-zolazepam was weighed and mg of active drug per mg of powder calculated. Powder was measured and placed in a gelatin capsule such that each capsule contained approximately 35 mg of active drug. A dosage range of 8-9 mg/kg orally (an average of 70 mg per yellowtail jack) yielded the best results overall.

Capsules were concealed in thawed capelins that were immediately fed to individual jacks by staff divers within the exhibit. Throughout the feed, an aquarist stationed at the tank window (dry side) attempted to identify individual fish swallowing medicated food and to note what time the fish received the drug. Restricting intake of food to only the yellowtail jacks posed a challenge for divers, therefore it took six procedures to remove 14 fish.

In general, the fish receiving an intended 70 mg dose began to show signs of sedation (darkened coloration, swimming lower in the water column, loss of righting ability) within 6-8 hr of ingestion. Divers were able to approach the sedated fish, trap them in a hand-held net, and move them to the surface; however, fish remained reactive to touch, especially around the peduncle region. During acclimation, jacks were restrained within a heavy plastic stretcher and blood samples for complete blood counts, serum chemistries, and serum banking were collected from the vertebral vein using a lateral approach. Fish with skin abrasions caused by netting received antibiotics and topical wound treatments before transfer to a 30,400 L (8,000 gal) round holding tank.

Maximum sedative effect of oral tiletamine-zolazepam was approximately 12 hr. Time for recovery from sedation, defined as return of normal swimming patterns and equilibrium, ranged from 12-48 hr. The fish refused to eat while in holding for 15 days. Persistent skin lesions were treated with nitrofurazone immersion (2 mg/L for 72 hr).

Four (28.6%) of the yellowtail jacks were lost during sedation procedures. Husbandry staff observed or suspected these fish of taking additional doses of medicated food for estimated total doses of 140 or 160 mg (averaging 15-20 mg/kg p.o.). Three fish never regained normal equilibrium post-procedure and were lost to complications secondary to severe integumentary compromise. One fish had a seizure-like episode and was found dead on the bottom of the tank shortly after a medicated feed session. Liver, spleen, kidney, and serum samples from these fish were banked for future analysis.

Successful sedation and translocation occurred for 10 out of 14 (71.4%) yellowtail jacks at our facility using oral tiletamine-zolazepam at a dosage of 8-9 mg/kg.

Acknowledgements

We thank the curator of fishes and invertebrates, Sandy Trautwein, aquarists, and divers at the Aquarium of the Pacific, especially Matt Ankley, Kim Stone, Akira Kanezaki, and Paul Clarkson for their assistance in completing procedures. Special gratitude to Dr. P.K. Robbins, staff veterinarian at the Los Angeles Zoo (and beyond) for her brilliant idea of using the powdered form of Telazol in gel capsules.

References

1.  Brown, L.A. 1988. Tropical fish medicine. Anesthesia in fish. Vet. Clin. North Am. Small Anim. Pract. 18(2): 317-330.

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.

4.  Ross, LIG., and B. Ross (eds.). 1999. Anaesthetic & Sedative Techniques for Aquatic Animals, 2nd edition. Blackwell Science Ltd., Malden, Massachusetts.

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. Journal of Small Animal Practice 22 ;:377-383.