Common name: ayu
Synonyms and Other Names: (sweetfish, ko-ayu [land-locked form]).
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Identification: This species is characterized by the presence of an adipose fin; 10-12 dorsal rays; 9-17 anal rays; 5 or 6 branchiostegal rays; usually 59-64 vertebrae; no pelvic axillary process; and more than 300 pyloric caeca (Nelson 1984). Masuda et al. (1984) also gave characteristics. The species was formerly placed in its own family, Plecoglossidae (Nelson 1984).
Size: 30 cm.
Native Range: Marine and freshwater, anadromous. Japan, Korea, Taiwan, and China (Nelson 1984).
Hydrologic Unit Codes (HUCs) Explained
Puerto Rico &
Interactive maps: Point Distribution Maps
Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Plecoglossus altivelis are found here.
Table last updated 11/30/2021
† Populations may not be currently present.
Ecology: Adults live and spawn in freshwater. Larvae live in salt water and ascend streams when they reach 5-8 cm TL (Randall 1987).
Means of Introduction: With approval from the California Fish and Game Commission, about 3,845,000 eggs and fry were stocked in California waters from 1961 through 1965 (Shapovalov et al. 1981; Dill and Cordone 1997). Relished as a food fish by Asians, Dill and Cordone (1997) stated that it was introduced to the state because it was felt to be a plant-eating fish expected to thrive in coastal streams considered marginal trout habitat. An estimated 250,000 fish were imported from Japan and intentionally stocked in Hawaii in 1925 and subsequent years, but failed to establish a reproducing population (Maciolek 1984).
Status: None of the fish in California survived (Shapovalov et al. 1981; Dill and Cordone 1997); it also failed to become established in Hawaii.
Impact of Introduction: Unknown. Likely no impact due to failure to establish.
References: (click for full references)
Dill, W.A., and A.J. Cordone. 1997. History and status of introduced fishes in California, 1871-1996. Fish Bulletin 178. California Department of Fish and Game, Sacramento, CA. http://content.cdlib.org/view?docId=kt8p30069f&brand=calisphere
Hubbs, C. L., W. I. Follett, and L. J. Dempster. 1979. List of the fishes of California. California Academy Science Occasional Papers 133. 51 pp.
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.
Nelson, J. S. 1994. Fishes of the world, 3rd edition. John Wiley and Sons, New York, NY.
Randall, J. E. 1987. Introductions of marine fishes to the Hawaiian Islands. Bulletin of Marine Science 41(2):490-502.
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.
Fuller, P., Nico, L.G., and Neilson, M.E.
Revision Date: 4/30/2018
Peer Review Date: 4/20/2006
Fuller, P., Nico, L.G., and Neilson, M.E., 2021, Plecoglossus altivelis (Temminck and Schlegel, 1846): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=797, Revision Date: 4/30/2018, Peer Review Date: 4/20/2006, Access Date: 12/2/2021
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.