The Classification and Scientific Names of Rainbow and Cutthroat Trouts

Abstract

Two unambiguous discoveries involving rainbow trout require scientific name changes. First, the rainbow trout has been demonstrated to be the same species as the Kamchatka trout. Second, studies of osteology and biochemistry of trout and salmon show that rainbow and cutthroat trout, and their close relatives, the golden, Mexican golden, Gila, and Apache trouts, are more closely related to Pacific salmons (Oncorhynchus) than to brown trout and Atlantic salmon (Salmo). The different names required by these two discoveries will cause some confusion in communications in which the formal classification is used, so we present evidence to acquaint biologists and managers with the rationale for the changes. The species name of the rainbow trout becomes mykiss, an older Latinized indigenous name of the Kamchatka trout. The generic designation of rainbow and cutthroat trout poses a more subjective problem, involving four possibilities: Salmo, Oncorhynchus, Rhabdofario, and Parasalmo. The balance of evidence indicates to us that the generic name for Pacific trouts and salmons should be Oncorhynchus. We suggest recognition of two divergent sister lineages, (1) Atlantic trout and salmon, and (2) Pacific trouts and salmons, as the genera Salmo and Oncorhynchus, respectively. Alternative generic classifications considered include the following: (a) Enlarge Salmo to include all Atlantic and Pacific trouts and salmons. This would be well supported by morphological and biochemical characters, but would fail to emphasize the distinctions between the Pacific and Atlantic groups. (b) Use a separate generic name, Rhabdofario, for rainbow and cutthroat trout, and their inland relatives. This would be valid, but would fail to recognize the gradation between Pacific trouts and Pacific salmons. (c) Continue to assign Pacific trout to the genus Salmo, separate from Oncorhynchus. This would be stable, but at the expense of evolutionary information in the classification—rainbow and cutthroat trout are on the same branch of evolution as the Pacific salmon. To reflect these biological relationships in the classification of trouts and salmons will contribute to better understanding of their life histories and better predictions for their management.

Phylogenetic relationship of the genus Oncorhynchus species inferred fromnuclear and mitochondrial markers.

“…(1) Masu salmon is clustered with other Pacific salmons and is not clustered with only B-lineages of the Pacific salmon group (tree II). This result is supported by morphology (Smith and Stearley, 1989) and SINEs (Takasaki et al, 1996) data. (2) Pink salmon and chum salmon are clustered (topology II).…”

“…3) indicated the same relation- Table 6 The pacific trout group * 1: morphology (Hikita, 1962), 2: morphology (Smith and Stearley, 1989), 3: allozyme electrophoresis (Utter et al, 1973), 4: RFLP of rDNA (Phillips et al, 1992), 5: RFLP of mtDNA (Thomas et al, 1986), 6: D-loop sequences of mtDNA (Shedlock et al, 1992), 6': D-loop sequences of mtDNA reanalysed (present study), 7: ATPase 6 and ND 3 sequences of mtDNA (Domanico and Phillips, 1995), 8: SINEs (Takasaki et al, 1996), 9: allozyme electrophoresis (present study) ship with that estimated from the present allozyme data (Fig. 2).…”

“…Allozyme (Utter et al, 1973) and RFLP of rDNA (Phillips et al, 1992) data suggest that A-and Blineages of the Pacific salmon group form a cluster and masu salmon forms a cluster with the Pacific trout group (topology I). Morphology (Smith and Stearley, 1989) and SINEs (Takasaki et al, 1996) data suggest that masu salmon forms a cluster with A-and B-lineages of Pacific salmons and diverged first (topology II). Morphology (Hikita, 1962) data suggest that masu salmon forms a cluster with A-lineage of the Pacific salmon group (topology III).…”

“…The genus Oncorhynchus belongs to the family Salmonidae and have been the subjects of numerous phylogenetic studies using morphology (Hikita, 1962;Smith and Stearley, 1989), allozyme electrophoresis (Utter et al, 1973), restriction fragment length polymorphism [RFLP] of ribosomal RNA genes [rDNA] (Phillips et al, 1992), RFLP of mitochondrial DNA [mtDNA] (Thomas et al, 1986), HindIII fragment (ATPase 6, CO III, tRNA GLY , ND 3, tRNA ARG , and ND 4L) sequences of mtDNA (Thomas and Beckenbach, 1989), D-loop sequences of mtDNA (Shedlock et al, 1992), ATPase 6 and ND 3 sequences of mtDNA (Domanico and Phillips, 1995), and short interspersed repetitive elements [SINEs] (Kido et al, 1991;Murata et al, 1993;Takasaki et al, 1996). These studies are in general agreements that Oncorhynchus had branched into four groups; (1) the Pacific trout group that consists of rainbow trout (O. mykiss; nijimasu) and cutthroat trout (O. clarki), (2) coho salmon (O. kisutch; ginzake) and chinook salmon (O. tschawytscha; masunosuke) of the Pacific salmon group [we call them A-lineage in this paper], (3) pink salmon (O. gorbuscha; karafutomasu), sockeye salmon (O. nerka; benizake), and chum salmon (O. keta; sake) of the Pacific salmon group [we call them B-lineage in this paper], and (4) masu salmon (O. masou; yamame) of the Pacific salmon group (Fig.…”

Development and Application of a Salmonid EST Database and cDNA Microarray: Data Mining and Interspecific Hybridization Characteristics

“…The GRASP EST database, and an improved salmonid presence in GenBank databases, will facilitate identification of additional members in gene families, contributing to a better understanding of the evolution of related genes within and between genomes. (Smith and Stearley 1989;Kido et al 1991). Arrows indicate putative genome duplication events (Wolfe 2001).…”