|
Mexican native trout (in Spanish "Truchas Mexicanas")—Mexican rainbow trout, sometimes Baja rainbow trout (''Oncorhynchus mykiss nelsoni'') and Mexican golden trout (''Oncorhynchus chrysogaster'') occur in the Pacific ocean tributaries of the Baja California peninsula and in the Sierra Madre Occidental of northwest Mexico as far south as Victoria de Durango in the state of Durango. Many forms of the Mexican rainbow trout (''Oncorhynchus mykiss nelsoni'' and ''O. m. ssp.''), subspecies of the rainbow trout, have been described.〔(【引用サイトリンク】title=Trout Diversity in Mexico sensu Morphological and Molecular Studies by Truchas Mexicanas )〕 The Mexican golden trout (''Oncorhynchus chrysogaster'') is a recognized species. ==Taxonomy== Most of the Mexican native trout are considered subspecies of the rainbow trout (''O. mykiss'') and generally lumped as ''O. m. nelsoni'' Evermann (1908) or ''O. m. ssp''. The exception is the Mexican golden trout (''O. chrysogaster'' Needham and Gard (1964)) which achieved species status in 1964. The first records of trout in northwest Mexico were published by paleontologist E. D. Cope in 1886 where he describes two specimens from Chihuahua as having the appearance of ''Salmo purpuratus'' a name sometimes incorrectly used for cutthroat trout (''Oncorhynchus clarki'').〔 In 1898 and 1905, naturalist E. W. Nelson with the U.S. Biological Survey led explorations into the Mexican mainland (1898) and Baja California peninsula (1905) to document flora and fauna. In 1908, preserved specimens of trout that Nelson brought back from the Rio Santo Domingo (Santo Domingo creek) in the Sierra de San Pedro Mártir mountains of Baja California were described by ichthyologist B.W. Evermann as a new species ''Salmo nelsoni'', the Baja rainbow trout.〔 In 1936, Paul Needham, a fisheries biologist with the U.S. Bureau of Fisheries began a series of explorations (1936, 1937 and 1938) into the Rio Santo Domingo drainage in Baja California seeking to bring back live specimens of the Baja rainbow trout as hatchery stock and further study. Although live specimens reached U.S. hatcheries, none ever survived to spawn. In 1952, 1955 and 1956 Needham again explored the Sierra Madre Occidental tributaries of the Gulf of California. Needham's explorations led to the publication of ''Rainbow Trout of Mexico and California'' (1959) with coauthor Richard Gard. It contains the first full color drawing of the Mexican golden trout. In 1964, Needham and Gard's proposed binomial name ''Salmo chrysogaster'' was accepted as the scientific name for a new species of trout, the Mexican golden trout. The specific name ''chrysogaster'' is derived from the Greek for "golden belly".〔 In 1989, morphological and genetic studies indicated trout of the Pacific basin were genetically closer to Pacific salmon (''Oncorhynchus'' species) than to the ''Salmos''–brown trout (''S. trutta'') or Atlantic salmon (''S. salar'') of the Atlantic basin. Thus, in 1989, taxonomic authorities moved the rainbow, cutthroat and other Pacific basin trout, including the Mexican native trout into the genus ''Oncorhynchus''. In 1997, a group of approximately 40 ichthyologists, biologists and naturalists from several U.S. and Mexican institutions formed a collaborative group, Truchas Mexicanas, to study the diversity of Mexican native trout.〔(【引用サイトリンク】title=Truchas Mexicanas )〕 Between 1997 and 2005, members of the group explored the rivers and streams of the Sierra Madre Occidental collecting specimens for study and documenting the diverse populations of Mexican native trout. In 2002, fisheries biologist Robert J. Behnke published ''Trout and Salmon of North America'' documenting a lifetime study of North American trout and salmon. In ''Trout and Salmon of North America'', Behnke described two species of trout—the Mexican golden trout (''O. chrysogaster'') and the Mexican rainbow trout (''O. m. nelsoni'' and ''O. m. ssp''). He described a number of local forms of the Mexican rainbow trout primarily based on the river systems they occurred in.〔 The phylogeny of Mexican native trout is unsettled science. Some studies suggest that the trout are descendants of the coastal rainbow trout (''O. m. irideus'') based on the idea that in wetter times, rainbow trout (steelhead) could have easily gained access to Baja California and Sierra Madre Occidental tributaries from the Pacific ocean. Others have suggested a connection to the inland redband trout (''O. m. gairdneri'').〔 Others have pointed to evidence in some populations that Mexican native trouts may have descended from cutthroat trout (''O. clarki'').〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mexican native trout」の詳細全文を読む スポンサード リンク
|