| Hypomesus nipponensis | |
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Osmeriformes |
| Family: | Osmeridae |
| Genus: | Hypomesus |
| Species: | H. nipponensis |
| Binomial name | |
| Hypomesus nipponensis McAllister, 1963 | |
Hypomesus nipponensis (Japanese smelt, in Japanese:wakasagi[2]) is a commercial food fish native to the lakes andestuaries of northernHonshu andHokkaido, Japan,Korea, andSakhalin,Khabarovsk Krai, andPrimorsky Krai, Russia.[1] It has been introduced in other locations, including theSan Francisco Delta of the United States. It is raised in fisheries, and is very similar in appearance to thedelta smelt (H. transpacificus).
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| Phylogeny of the genusHypomesus includingH. chishimaensis underH. nipponensis.[3][4] |
Hypomesus chishimaensis was described as being a new species in the lakes ofKunashir andIturup in 1997 based on claimed morphological differences. After later studies failed to find these morphological differences, it regarded as anecotype ofH. nipponensis. A 2007 genetic analysis supported this classification, and recommended thatH. chishimaensis not be given its ownbinomial designation.[3]
Native to the lakes and estuaries of Hokkaido, Japan and introduced to the lakes onHonshu andKyushu, the Japanese wakasagi was introduced toCalifornia waterreservoirs by theCalifornia Department of Fish and Game to provide more prey for stockedrainbow trout after failed attempts to introduce native delta smelt to threefoothill reservoirs.[5][6] At the time, the California-native delta smelt and the Japanese smelt were thought to be separated members of the same species,H. olidus.[7] In 1959 the CDFG imported 3.6 million fertilized eggs attached topalm fiber mats from a population in Suwa Lake, located east of Tokyo; many of these eggs were dead on arrival. The fiber mats were placed in streams feeding into six lakes and reservoirs that appeared to be ecologically suitable for the smelt.[nb 1] It was thought at the time that these reservoirs could be chemically treated toeradicate the fish if they were found to be undesirable.[8] In 1972 and 1973 about 77,000 fish from theShastina Reservoir were moved to theAlmanor Reservoir inPlumas County. All attempts to introduce the fish were successful, except theDodge andBig Bear Reservoir introductions,[5] the latter of which may have been partially attributable to chemical treatments meant to eradicate stuntedcrappie andgoldfish.[8]
Although a retrospective analysis of preserved delta smelt samples caught in 1972 and 1982 from the Delta region has shown that wakasagi had been invading the estuaries in undetected quantities since at least the early 1970s, wakasagi expansion from these original introduction sites southward was not tracked until several years later.[5] In 1994 they were detected at theState Water Project pumping plant for the first time, and by 1998 the fish could be found throughout the estuary including theSuisun andSan Pablo Bays.[5][7][9]
Because the two species are very similar inmorphology andlife history, the wakasagi presents several potential threats to theendangered delta smelt. Besides direct competition for nutritional resources and the possibility that wakasagi may prey on the eggs andlarvae of delta smelt,[5]hybridization could either dilute the species or cause population decline due tosterilizing effects. In fact, a few hybrids have been captured in the wild, although all of them were first generation crosses and no evidence ofback-crossing has been found, which would suggest that the hybrids were not viable. Misidentification of the species is an additional concern, which could lead to inaccurate assessments critical to making policy decisions; however this problem may be mitigated ifgenetic markers are used for identification.[7]
In addition to its negative effects on the delta smelt, the wakasagi significantly reducedKokanee fisheries, but helped increase growth rates of other salmon and trout fisheries.[10]
Authority control databases: National |
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