459 Journal of Zoo and Wildlife Medicine 35(4): 459–470, 2004 Copyright 2004 by American Association of Zoo Veterinarians ENDOSCOPIC SEX DETERMINATION AND GONADAL MANIPULATION IN GULF OF MEXICO STURGEON (ACIPENSER OXYRINCHUS DESOTOI) Stephen J. Hernandez-Divers, B.Sc., B.Vet.Med., Dipl. R.C.V.S. Zoo.Med., M.R.C.V.S., Dipl. A.C.Z.M., Robert S. Bakal, D.V.M., M.S., Brian H. Hickson, B.S., Clarence A. Rawlings, D.V.M., M.S., Ph.D., Dipl. A.C.V.S., Heather G. Wilson, D.V.M., Dipl. A.B.V.P. (avian), MaryAnn Radlinsky, D.V.M., M.S., Dipl. A.C.V.S., Sonia M. Hernandez-Divers, D.V.M., Dipl. A.C.Z.M., and Samuel R. Dover, D.V.M. Abstract: Seventeen Gulf of Mexico sturgeons (Acipenser oxyrinchus desotoi) underwent endoscopic sex determi- nation, gonadal biopsy, and various reproductive surgeries as part of a conservation development plan. The fish were anesthetized with tricaine methanesulfonate (MS-222) buffered with sodium bicarbonate and maintained on a recircu- lating water anesthesia circuit. A 6-mm Ternamian EndoTip Cannula, placed through the ventral midline, midway between pectoral and pelvic fins, permitted the introduction of a 5-mm telescope. Swim bladder aspiration and CO 2 insufflation of the coelomic cavity provided excellent observation. Second and third cannulae were placed under direct visual control, lateral and cranial or caudal to the telescope cannula. Sex determination was successfully performed in all fish; however, five of 17 sturgeons (29%) required endoscopic gonadal biopsy to confirm sex. Bilateral ovariectomy or orchidectomy was successfully performed in three males and four females. Unilateral ovariectomy and bilateral ligation of the mu ¨llerian ducts using an extracorporeal suturing technique was accomplished in an additional three females. No apparent morbidity was associated with the anesthesia or endoscopic surgery in any fish. The ability to safely perform minimally invasive reproductive surgery in fish may have important management and conservation benefits. Key words: Gulf sturgeon, Acipenser oxyrinchus desotoi, endoscopy, orchidectomy, ovariectomy, sterilization. INTRODUCTION Restoration and recovery efforts of threatened and endangered fish populations are more success- ful when population dynamics, physiology, life his- tory, and behavior are understood. For instance, te- lemetry tracking can identify animal habitat use. However, there are problems associated with telem- etry that makes it less desirable for threatened or endangered species, in particular, morbidity and mortality of capture, immobilization, and surgical placement of a radio transmitter device in or on a free-ranging piscine. 13 In situations where the num- bers of animals are extremely low, the loss of even a single individual is significant and may be detri- mental to the overall population. To overcome these problems and eliminate the From Department of Small Animal Medicine & Sur- gery, College of Veterinary Medicine, University of Geor- gia, Athens, Georgia 30602-7390, USA (S. J. Hernandez- Divers, Rawlings, Wilson, Radlinsky, S. M. Hernandez- Divers); the United States Fish and Wildlife Service, Warm Springs Regional Fisheries Center, 5308 Spring Street, Warm Springs, Georgia 31830, USA (Bakal, Hick- son); and the Channel Islands Marine and Wildlife Insti- tute, Santa Barbara, California 93117, USA (Dover). Cor- respondence should be directed to Dr. S. J. Hernandez- Divers. risk to the natural population, hatchery-reared ani- mals could be fitted with telemetry devices and in- troduced into the wild as research animals. This eliminates the risks associated with using the en- dangered population and ensures that implanted an- imals survived the procedure and were released in adequate numbers to achieve the desired goals. A major disadvantage of using hatchery-reared fish is the potential for these animals to enter the breeding pool of the free-ranging population, thereby chang- ing the genotype of the remnant indigenous inhab- itants. One solution is to sterilize hatchery animals fit- ted with transmitters before their release. Potential methods for preventing reproduction in fish include chemical sterilization, surgical sterilization, and in- duction of triploidy. Each of these methods has its shortcomings. The disruptive effects of certain chemicals and exogenous hormones on normal re- production have been extensively studied. 6,7,27 Most of these investigations have concentrated on the ad- verse effects of pesticides, insecticides, and estra- diol compounds on fish reproductive success. For example, sea lampreys (Petromyzon marinus) have been chemosterilized by immersion in an aqueous solution of bisazir. 12 Induction of triploidy has also been used to induce sterility in several species. 25 This may serve as an acceptable means of steril-