The Veterinary Health Management of the Life Cycle Stages of the Japanese Medaka (Oryzias latipes)
American Association of Zoo Veterinarians Conference 2006
Horace E. Walcott, DVM, MSPH, MSc
Brooklyn Technical High School, Brooklyn, New York, NY, USA


For more than 3 yr, a colony of 1200 adults and hatchlings of Japanese medaka, Oryzias latipes, were maintained under optimal conditions. The water pH was 6.8±1.2. The optimal temperature for each tank was maintained at 21±6°C.1 A specific chemical-free environment was maintained by using filtered water. A light to dark cycle of 12 hr:12 hr, each day was maintained.6 The fry were maintained on brine shrimp. The sub-adults and adults were fed Tetramin® flakes ( [VIN editor: The original link was not accessible as of 1-20-21.]) three times per day and brine shrimp once per day every other day. A four-panel water-chemistry profile was conducted once per week to monitor the aquarium concentrations of ammonia, nitrites, nitrates, and pH.4 Fertilized eggs were collected from mature females during the breeding season and incubated in filtered water containing methyl blue, which was used as a fungistatic and bacteriostatic agent. The eggs were allowed to hatch and fries transferred to a nursing aquarium for growth to adults. The developing embryos, larvae and adults were used in the treatment groups, background control groups and concurrent control groups for chronic carcinogenicity and developmental toxicology studies.3 Terminally ill fish were euthanatized with tetracaine (MS222) and examined by necropsy with the aid of a dissecting microscope prior to fixing in phosphate buffered saline.5 Slides for microscopic examination of the tissues were prepared and stained for examination using routine histologic techniques.2 A mathematic model of the egg production during the 3-yr period was polynomial.


This study was supported by a multiple year grant from the United States Department of Defense. The Principal Investigator was Dr. William Hartley. The author is most grateful to Drs. Asaf Abdelghani and William Toscano.

Literature Cited

1.  Boyd KW. 1990. The Complete Aquarium Problem Solver: A Total Trouble Shooting Guide for Fresh Water and Marine Aquariums. Tetra Press, Morris Plains, NJ.

2.  Hinton D. 1990. Histological techniques. In: Schreck CB, PB Moyle, eds. Methods for Fish Biology. American Fisheries Society, Bethesda, Maryland.

3.  Hoover KL. 1981. Use of small fish species in carcinogenicity testing. Proceedings of a symposium held at Lister Hall Center, Bethesda, Maryland. Dec 8–10. National Cancer Institute. NIH Publication Number 86-2653 PHS NIH, Pp. 1–404.

4.  Stoskopf MK. 1993. Fish Medicine. W B Saunders Company, Philadelphia, Pennsylvania.

5.  Summerfelt RC, LS Smith. 1990. Anesthesia, surgery and related techniques. In: Schreck CB, PB Moyle, eds. Methods for Fish Biology. American Fisheries Society, Bethesda, Maryland.

6.  Yamamoto T. 1975. Medaka (Kilifish) Biology and Strains. Tokyo, Keigaku, Pp. 1–365.


Speaker Information
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Horace E. Walcott, DVM, MSPH, MSc
Brooklyn Technical High School
Brooklyn, NY, USA

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