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
The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through northwestern and western Mexico, and along the Gulf of California. The Sierra Madre is part of the American C ...
of northwestern
Mexico
Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
as far south as
Victoria de Durango
Durango City (, stp, Korian), officially Victoria de Durango is the capital and largest city of the Mexican state of Durango. The city, which is located in Northern Mexico has a population of 654,876 as of the 2015 census, and sits at an altitude ...
in the state of
Durango
Durango (), officially named Estado Libre y Soberano de Durango ( en, Free and Sovereign State of Durango; Tepehuán: ''Korian''; Nahuatl: ''Tepēhuahcān''), is one of the 31 states which make up the 32 Federal Entities of Mexico, situated in ...
. Many forms of the Mexican rainbow trout (''Oncorhynchus mykiss nelsoni'' and ''O. m.'' ssp.), subspecies of the
rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
, have been described. The
Mexican golden trout
The Mexican golden trout (''Oncorhynchus chrysogaster'') is a species of fish in the family Salmonidae. The species is endemic to high-elevation headwaters of the Fuerte River, Sinaloa River, and Culiacán River drainages in the Sierra Madre Occ ...
(''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 northwestern Mexico were published by
paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
E. D. Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy intereste ...
in 1886 where he describes two specimens from Chihuahua as having the appearance of ''Salmo purpuratus'' a name sometimes incorrectly used for
cutthroat trout
The cutthroat trout is a fish species of the family Salmonidae native to cold-water tributaries of the Pacific Ocean, Rocky Mountains, and Great Basin in North America. As a member of the genus '' Oncorhynchus'', it is one of the Pacific tro ...
(''Oncorhynchus clarki''). In 1898 and 1905, naturalistE. 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
Sierra de San Pedro Mártir ( Kiliwa: ʔxaal haq, en, mountains of Saint Peter the Martyr) is a mountain range located within southern Ensenada Municipality and southern Baja California state, of northwestern Mexico.
It is a major mountain ran ...
mountains of
Baja California
Baja California (; 'Lower California'), officially the Free and Sovereign State of Baja California ( es, Estado Libre y Soberano de Baja California), is a state in Mexico. It is the northernmost and westernmost of the 32 federal entities of Mex ...
were described by
ichthyologist
Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of Octobe ...
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
The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja Ca ...
. 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
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
were genetically closer to Pacific salmon (''Oncorhynchus'' species) than to the ''
Salmo
''Salmo'' is a genus of ray-finned fish from the family Salmonidae. The single ''Salmo'' species naturally found in the Atlantic North America is the Atlantic salmon, whereas the salmon and trout of the Pacific basin belong to another genus, '' ...
''s–
brown trout
The brown trout (''Salmo trutta'') is a European species of salmonid fish that has been widely introduced into suitable environments globally. It includes purely freshwater populations, referred to as the riverine ecotype, ''Salmo trutta'' morph ...
(''S. trutta'') or
Atlantic salmon
The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are ...
(''S. salar'') of the
Atlantic Basin
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
. 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. 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.
In 2015, a report delving into the genetics of Mexican golden trout and Mexican rainbow trout from various rivers was published. The authors, in discussing their findings, state:
The
phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
of Mexican native trout is an unsettled science. Some studies suggest that the trout are descendants of the
coastal rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coastal ...
(''O. m. irideus'') based on the idea that in wetter times, rainbow trout (steelhead) could have easily gained access to Baja California and the Sierra Madre Occidental tributaries from the Pacific ocean. Others have suggested a connection to the inland
Columbia River redband trout
The Columbia River redband trout, the inland redband trout or the interior redband troutRío Acaponeta in Durango. The first scientific collections of trout from Mexico were by Prof. Nathaniel Thomas Lupton in the early 1880s. During Edward W. Nelson's 1898 expedition, he observed trout in the Rio del Presidio basin near the town of El Salto, but did not collect any specimens. In 1946, Ralph G. Miller an American researching Mexican ichthyofauna near El Salto collected the earliest surviving specimens of the Rio del Presidio trout, which now reside in the
Smithsonian Institution
The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...
. As of 2002, according to ichthyologist Robert J. Behnke, the Rio del Presidio trout were the southernmost natural distribution of any member of the family
Salmonidae
Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefis ...
. This range was extended by collections from the Ríos Baluarte and Acaponeta in 2004.
The many forms of Mexican native trout are typically described by the river systems they occur in.
Conservation
The Mexican golden trout (''O. chrysogaster'') is listed as vulnerable by the
IUCN Red List of Threatened Species
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biologi ...
. None of the rainbow trout subspecies, including Nelson's trout (''O. m. nelsoni'') are formally listed by any conservation organization. The
World Wildlife Fund
The World Wide Fund for Nature Inc. (WWF) is an international non-governmental organization founded in 1961 that works in the field of wilderness preservation and the reduction of human impact on the environment. It was formerly named the Wo ...
considers the Rio Conchos trout critically endangered. Truchas Mexicanas reported in 2006 that all the populations of Mexican trout face threats from habitat loss due to logging, mining and aquaculture impacts. The greatest threat to the continued existence of genetically pure Mexican native trout appears to be the widespread rainbow trout aquaculture in the river basins where they reside. Escaped hatchery trout or trout stocked in rivers to support
angling
Angling is a fishing technique that uses a fish hook or "angle" (from Old English ''angol'') attached to a fishing line to tether individual fish in the mouth. The fishing line is usually manipulated via a fishing rod, although rodless techniqu ...
can hybridize with native stocks, which can eventually lead to genomic extinction.