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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Japanese medaka

Taxonomy: available through www.itis.gov

Identification: Distinguishing characteristics are provided by Masuda et al. (1984). Photographs or illustrations appear in Lee et al. (1980 et seq.), Masuda et al. (1984), and Axelrod et al. (1985:600).

Size: 4 cm.

Native Range: Eastern Asia. Japan, Korea, Taiwan, middle and eastern China as far south as Hainan (Lee et al. 1980 et seq.; Mauda et al. 1984).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Means of Introduction: The California introduction reportedly resulted from an aquarium release (Snyder 1935). It was intentionally stocked in unknown numbers in Hawaii (Brock 1960; Maciolek 1984), possibly as a potential biological control for mosquitoes. Sources of and reasons for introductions in New York are not known, but may be associated with research or aquarium releases (Lee et al. 1980 et seq.).

Status: The New York population was extirpated as a result of the cold winter of 1978; the California population disappeared for reasons unknown (Courtenay et al. 1984). Contrary to information provided by some authors, the species was reported but apparently never established in California (Dill and Cordone 1997). In Hawaii, the species never became established (Brock 1960; Maciolek 1984).

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: According to Coates (1950), the California populations were thriving. Shapovalov et al. (1959, 1981) stated that there have been no records of Oryzias being taken from open waters of that state since about 1935. It was not mentioned by Moyle (1976a) or Swift et al. (1993) in their reports on freshwater fishes of California. Dill and Cordone (1997) referenced an early letter by Snyder and indicated that the first (and possibly only) record of this fish in California is based on a single specimen taken from San Francisquito Creek by Stanford University students. According to these authors, that single fish may be the only basis for Snyder (1935) and all subsequent mentions of this fish recorded for that state. This freshwater species shows broad temperature and salinity tolerances. Various color varieties or mutants are known and some of these are in the aquarium trade (Sakaizumi et al. 1983).
There are no known voucher specimens.

References: (click for full references)

Axelrod, H. R., W. E. Burgess, N. Pronek, and J. G. Walls. 1985. Dr. Axelrod's atlas of freshwater aquarium fishes. Tropical Fish Hobbyist Publications, Inc., Neptune City, NJ.

Courtenay, W. R., Jr., and J. R. Stauffer, Jr., editors. 1984. Distribution, biology and management of exotic fishes. Johns Hopkins University Press, Baltimore, MD.

Courtenay, W. R., Jr., and D. A. Hensley. 1979. Survey of introduced non-native fishes. Phase I Report. Introduced exotic fishes in North America: status 1979. Report Submitted to National Fishery Research Laboratory, U.S. Fish and Wildlife Service, Gainesville, FL.

Lee, D. S., C. R. Gilbert, C. H. Hocutt, R. E. Jenkins, D. E. McAllister, and J. R. Stauffer, Jr. 1980 et seq. Atlas of North American freshwater fishes. North Carolina State Museum of Natural History, Raleigh, NC.

Maciolek, J. A. 1984. Exotic fishes in Hawaii and other islands of Oceania. Pages 131-161 in W. R. Courtenay, Jr., and J. R. Stauffer, Jr., editors. Distribution, biology, and management of exotic fishes. The Johns Hopkins University Press, Baltimore, MD.

Masuda, H., K. Amaoka, C. Araga, T. Uyeno, and T. Yoshino, editors. 1984. The fishes of the Japanese Archipelago. Tokai University Press. Text: i-xxii + 437 pp.; atlas: pls. 1-370.

Moyle, P. B. 1976. Inland fishes of California. University of California Press, Berkeley, CA.

Shapovalov, L., W. A. Dill, and A. J. Cordone. 1959. A revised check list of the freshwater and anadromous fishes of California. California Fish and Game 45:159-180.

Shapovalov, L., A. J. Cordone, and W. A. Dill. 1981. A list of freshwater and anadromous fishes of California. California Fish and Game 67(1):4-38.

Swift, C. C., T. R. Haglund, M. Ruiz, and R. N. Fisher. 1993. The status and distribution of the freshwater fishes of southern California. Bulletin of the Southern California Academy of Science 92(3):101-167.

Other Resources:
US Fish and Wildlife Service Ecological Risk Screening Summary for Oryzias latipes

Author: Pam Fuller, and Leo Nico

Peer Review Date: 3/5/2011

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.