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Home , Arctic char, Coastal cutthroat trout, Golden trout, Huchen, Lenok, Mexican golden trout

TLre ancestry tf

T that all species in that came from one classificatio",,",."**i,)'T:ffi:J 1T;1 common ancestral species. But we lack ur: tionary evidence in an attempt to arrange ambiguous criteria and all-encompassir: species on a family tree to denote branching definitions of the categories of classification points and degrees of evolutionary relation- Thus, a "lumper" may recognize two or threr ships. Tfaditionally, we have relied on skeletal species in a genus. A "splitter," using the sane features, anatomical characteristics, and the evidence but with different emphasis, mryi: type and arrangement of teeth for evidence. classify these same as two or three sub- Now, we also use more modern methods: species of one species. counting chromosomes, studying protein Controversies and disagreements regardin r patterns, and analyzing DNA. what classification scheme best reflects er-oiu- We assume that a change in a character, tionary relationships, or phylogenies, ari."e such as presence or absence of teeth on a from the fact that if the evidence used u. certain bone or on a particular part of a bone, inconclusive, it is open to individual interpre- denotes a branching sequence on the family tation. For example, the significance anc tree. Branching sequences then can be ar- magnitude of evolutionary divergence ,le- ranged in a system of classification by de- noted by a change in the size or shape of ; scending orders of relatedness. For example, bone, a change in chromosome number- the outer terminal twigs on the tree represent or a change in protein patterns might reflect living species, which are traced to a common a major branching classified as a genus or a stem branch that groups closely related branching of a lesser magnitude denotrnE species into a genus. Further down the tree, a species or even a . representing more ancient periods on the A primitive condition and an advanced o: geological time scale, branches of genera join derived condition must be established fbr to form subfamilies. Finally, the base of the each character. Otherwise the use of an)-' trunk represents the family. change in that character to denote the se- quence of branches is open to interpretation- Luuppns AND sPLrrrERS There is general agreement among modern Trrp raurr,Y TREB taxonomists that classification should reflect Uncertainry is prevalent when we try ro evolutionary relationships. That is, all species reconstmct the lineage ofthe family Salmoru- in the same genus should be more closely dae, because the fossil record is sparse and related to each other than to any species in contains large gaps. We rely on interpreta- other genera. And when we recognize a tions of the evidence from the characters u'c genus as a valid genus) we assume or denote use for classification.

Tnor-r 3 SUBFAMILY GENUS SUBGENUS SPECIES z (,r r hen N gotbwcba nzrha tshawytvha hisutch m4301t

Anrmhrwhus mlbiss Rainbow, clarhi (Rh db drfarh or Pams a lnn ) tila chrysogaster

salar trutta. .ischchon bmica matmmntus

platycEhalus Salmoninae (Plnrysalrno) ohrilnnus -{lthough the oldest known salmonid fos- Acantholitgun :1. Eosalrno d.riftwoofunsis of British Colum- obtusirostris :ia. represents a species living about 45 to 50 Salmothlmus zetensis :rillion years ago, the origin of the family bwh :robably is much older, perhaps on the mag- Bmchymysaa saviwvi :rrude of 100 million years. We base this nature of the Huchen or rrimen (IIwho) Lisumption on the primitive hwho iieietal and anatomical characters of - petYy, rd in relation to other groups of mod- (Pamhurho) we have :rn bony (teleostean) fishes. What (Cristivomer) ,-arned from Eosohno fossils indicates that the rwrnaycush --:ree subfamilies of - Coregoni- (Bainw) fonrha.lis Chars &.lvehnus aae (the whitefishes), Thymallinae (gray- albus (<elinus) confhenws --ngs), and Salmoninae (trout, , and ::rar)-were already separated from each bucomacnis malma . rher 50 million years ago. A g"p in the fossil nlpinus ::cord of about 25 million to 30 million years and others

ccurs between the Eocene and Miocene Although all subfamily mem- :ns. Miocene fossils found in the western bers share certain physical also difer - nited States reveal that several major evolu- characteristics, they Jrom one another These --rnxrf branches of the subfamily Salmoni- kingdom Animalia () diferences sepdrate them into :r.e were established by this time. These ex- phylum Chordata (animals with notochords and distinct gener a, sub gene r a, hollow nerve cords) :nct, fossil species represent the same genera species, and subspecies. Pacifc (animals backbones) subphylum Vertebrata with s almon ( genus O nc orhy nchus), species of trout, salmon, -: l'hich the living class Osteichthes (bony fishes) (Salmo) and :rd char are classified. Evidently, the first order Salmonifirrrnes (fishes with soft-rayed fins, chars () are all clas' rajor branching, or divergence, leading to all adipose fins, and abdominal pelvic fins) sifed as Salmoninae subfamily (trout, salmon, char, whitefish, members in the species of trout, salmon, and char, is family Salmonidae family -',ing gnylings) Salmonidae, based on certain ;:naracterized by a loss ofteeth on the shaft of subfamily Salmoninae (trout, salmon, and char) phy sical similar itie s a mon g --:le vomer bone in the roof ofthe mouth and genera Owmhychus (hooked snout) them. They are further taxo- :.r a peculiar modification of lateral-line Solnn (silmon) n omic ally s ep dr ate d into Salvelinws (dwelling in springs) distinct gener 4, sub ge n er a, One branch leads to the chars of the -ales. species ryhiss, trula, fintinalis, etc. species and subspecies, on the !:nus Snlvelinus and also includes the lenok subspecies bwisi, boraieri, henshawi, etc. basis of the diferences among .: (genus Brailyrnystax) and Eurasian them. .:uchen (the largest living species of Salmoni- of the genus Hwcho). The other branch "e. trl-Har e Tnour Is 3 a E

Although originally limited to of this divergence leads to the living species of subfamilies. We do not know whether this th e n or thern hemisph er e, trout and salmon. By the middle of the Mio- most ancient ancestor was freshwatcr Salmonid,s haye been success- a fully introduced into m(my cene period, the trout and salmon branch species or a marine species. AII species of parts of the southern hemi- forked again, resulting in two major groups. Salmonidae must in fresh water. sphere. They inhabit cool and In the North Pacific basin of which would indicate a freshwater origin. cold waters; the char, a and Asia, one branch subdivided into two species member oJ the family, occurs But most also have the physiological further north than any other main evolutionary lines, one leading to capability to live in the ocean, which suggests freshwater ftsh. species of Pacific Salmon, the other to rain- that the ability to excrete salts and retain bow and cutthroat trout-all now classified water) necessary to survival in marine waters) in the genus Oncorhynchas. In the North At- has been inherited from an ancient ancestor. lantic basin of Europe, branchings of the There are some little-known, troutlike Sahno line gave rise to Atlantic salmon and species whose correct positions on the family and related species. tree are largely unknown, except that their The evolutionary line that developed per- branches belongin the subfamily Salmoninae haps I00 million years ago resulting in all of part of the tree. A peculiar species (probabll' the present species of trout, salmon, char, two species) classified in the genus Salrnothy- whitefishes, and graylings probably began lnus occ'Jrs in a few on the Adriatic when the chromosome number doubled in a of Yugoslavia. The generic name im- common ancestral species. The chromo- plies that this fish originally was thought to somes of all species of the family Salmonidae be intermediate between trout (genus Snlrno contain about rwice the amount of DNA ofsubfamily Salmoninae) and gray'ing (genus found in related families such as the smelt Thyrnallws of subfamily Thymallinae). There family, Osmeridae. This indicates that the is no doubt that Snbnothywtws is a trout (sub- character change in the chromosomes of a family Salmoninae), but where its branching primitive ancestor occurred before the evolu- point joins the tree in relation to the Onco- tionary separation of the family into three rhynchws and Salyno branches is not clear.

4 Tnour 3a-sed on my interpretation of the evidence, In the genus SDbnl,I include six species of itituothyrnws should be connected to the varyrng degrees of relatedness. If the Tirrkish i"rinn branch. But others may disagee and ftotrt Plntysa.lwn platycephnlus is included as :-ace it further down the tree connecting to a one of the six species, there are three "good" . r*tnon ancestral stem before the separation species hghly divergent from one another- ,: rhis stem into Salm.o and Oncorhywhws. the Atlantic salmon, S. salor; the brown \nother species of dubious relationship trout, S. tn'r.ttn; and the Turkish trout, S. (P.) .,..urs onlyin Ohrid, Yugoslavia, and is platycephalws. The other three recognized :-assified in the genus Acantholingon. This species are closely related to brown trout. In .:ecies formerly was classified in the genus some rivers tributary to the Adriatic Sea, the t'ritrntltyrnus, but there is little doubt that marbled trout) S. ma.rrnotatus, occurs. The -:;anthol'ingunshould be recognized as a sepa- marbled trout is a large predaceous fish reach- ::.re genus. Acantholhgcn ohridanws has a rng 23 kilograms (50 pounds) or more. Its .:leltlike appearance and has the most primi- coloration and markings differ greatly from :-!'e type of skeletal characters and dentition those of other species of Sahno. It has only -:: comparison to all other living species of light-colored marbled markings (similar to :out, salmon, and char. Acnntholingua is an the markings of the char of the genrs Sal^ve- ,;icient branch in the subfamily, probably linws). Genetically, however, tnttn and ma.r- : unecting to the ancestral trunk well before rnzratas are very closely related and they are :re separatio n of Snlm.o and Oncorhynchws . AII known to hybridize where they occur to- ::mnants of the Amnthokngun branch have gether. The other two species commonly rec- ''ed out except for the species ohr'idanus tn ognized, S. ischchnn and S. letnirn, are even lie Ohrid. more closely related to S. trutta.. These ^\ species known by only three specimens species probably represent the isolation of :om a in Turkey is also of uncertain S. tywttaancestors in single . S. ischchonis ::r.rLls. Many years ago I named this species restricted to Lake Sevan in the Soviet Union :i.^ce[)hnlus and created a subgenus PI"ty- and S. lttnirn to Lake Ohrid, Yugoslavia. -rtitn rn the genus Salrno for its classification . The genus Oncorhynchws consists of six 3ou'ever, I was not confident about the species of Pacific salmon and four species of :,acement of plntycephalus on the family tree western North American trout. Five species ::Earding its precise relationship to Snlnn. of salmon are native to the Pacific drainages Now that the branches of the family tree of North America: pink, O. gorbwscha; cht- .-ar-e been classified into genera, we can trace nook, O. tsnwytschn; coho, O. hisutch; sock- -:rese generic branches to their terminal twigs eye, O. nerha; and chum, O. hen.In addition, :,r assess how many living species of trout, the masu or cherry salmon, O. rna.soa, occurs ..r-Lmon, and char exist in the world. This is in the Far East. A seventh species, O. rho- :ot a simple task, and there is disagreement d.wras, is often recognized. The rhod.w"r,ts ;r how many species should be recognized. salmon is very closely related to rnasow, andl 3r,rt we can arrive at a best estimate. prefer to classify it as a southern subspecies of

oJ o r U E z s

;.: .\tlantic salmon, Saimo ,:lar rs the closest native "':':tte of the brown trout, ;,:ch was introduced to this :ntinent from Europe.

\\'nereTnourIs 'w-ry rnnsru. Besides ) O. myhiss, and River basin of as H. bbe cutthroat trout, O. clnrki, I recognize the Virtually nothing is known of the l-.anqu* , O. chrysogaster; the huchen. Furtheritudy probably will indi""-- Gila and , in my opinion, are no more than subspecies classification for c:r fwo subspecies of one species: O. gila.e gilaz fish, but we do not know to which specrcs. and O. apache. gihz The golden H. hor.cho or H. perryi, the Yangtze huchen :-o trout generally is classified as a separate most closely related. species, O. aguabonita. Howevet my classi- The char genus, Snhrelinws, is the rnrs: fication, based on the assessment of degees troublesome genus to classify into specres of relatedness typically used in classi- The enormous amount of diversiry four; fication, would place it as a subspecies of throughout the vast distribution of chan ::: rainbow trout, making it O. wlyhiss North America, Asia, and Europe creares n aguabonin. classic example for contrasting differences ft- The Siberian lenok genus Brnchyruysnx is fween lumpers and splitters in the emphasr. generally regarded as a monorypic genus- used to define a species. It helps to divide ri; that is, only one species, B. lemk, is recog- genus into major evolutionary brancher nized in the genus. It has long been known, known as subgenera. Two of these branch* however, that two distinct forms of lenok are represented by single species, the la_n; occur over a broad geographical area-a trout S. nama.ycush (subgenus Cristiyortttt" . "sharp snout)) and a "blunt snout" lenok. and the , S. fontinalis (subgenu, Because the sharp snout and blunt snout Bnione), of North America. Bur as for tt; lenok coexist in the River basin, they third major branch (subgenus Sabel'intu . should be classified as two separate species. only best guesses are possible at presenr rr The genrs Hwc h o, in my classification, con- enumerate the "species." This branch appea_rs tains two highly divergent species, which I to include at least two evolutionary cluster,. classify in different subgenera. The of species. One cluster contains the DolJr River basin huchen, hwcho, and the Varden char, S. rnalrna,,and , S. a- Siberian taimen (the world's largest salmonid pinus, but I estimate that about five or srr: fish) are very closely related. I classi{' the additional species eventually will be recoE- huchen and the taimen as two subspecies, nized for char presently considered as Dollo, H. hucho hucho and II. hucho tairnen, of one Varden or Arctic char. The other cluster ot species. A very different species of Hurho oc- char species includes the Far Eastern char. curs in rivers of Hokkaido and Sakhalin S. bwcornaenis; the North American bul islands in the Far East; it is classifi ed as H. per- trout, S. conflorcntws; the Kamchatkan stone ryi. A huchen was described from the upper char, S. ahws; and perhaps one or two addi- tional species. This chinooh salmon, Oncor- In recent times, two extremely divergent hynchus tsawytscha, (right) species of char were found in a lake on rhe has fnished. spawning and wiLI die soon. Below, a socheye Chukokst Peninsula of the USSR (across rhe salmon, O. nerka, shows bril- Bering Strait from ). This discove n Iiant red spawning colors. The hints at what might be in store for furure socheye is noted for its land- loched varieties. discoveries of char when the fishes of remote lakes across Siberia are studied. Until then. we may estimate about fifteen species of char in the genus Sahrel'inws, but don't place much confidence in such an estimate-there's much to be learned.

Thour BY ANY orHER NAME Those familiar with the literature of the nineteenth and early twentieth centuries on trout are aware of a confusing proliferation of scientific names used in earlier times. Works

6 Tnour la*

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:=rring to the European brown trout) other members of the same species than to In earlter times biologists recognized more than twentJ discuss twenty more any member of another species. fiattt., might or difffent species of what is ::cies recognized at the time for what we Another premise is that geographic races today classified simply as 'u-ciassi{j' as a single species. In the North (subspecies) of a species would hybridize Salmo trutta. the brown trout ---:rerican literature, more than thirry species with others of the same species if they oc- j trout were, at one time or another, recog- curred together. If they would not hybridize, ..zed for what we now classi{, as two they are separate species. The application of :ccies-rainbow trout and cutthroat trout. the critenon of reproductive isolation re- -.re "lumping" of many species into one sulted in the lumping of many formerly rec- ::cies is the result of our changing concept ognized species into a relatively few species at - a species and attempts to make classifica- present. In the nineteenth and early twenti- ,n more accurately reflect degrees of evolu- eth centuries, it was common practice to de- - 'nf,V relationships. scribe each slight variation found as new Cne of the basic premises of classification is species. We now consider many of these ..at all populations of a species can be traced older species as geographic variations within orle common ancestor. That is, all mem- one species, although many of the old species ::rs of a species are more closely related to names are retained as subspecies.

-'\-sar e Tnour Is When what we now recognize as one species has earlier been named as ten or twenty species, which one of the many species names do we keepl The international rules of zoological nomenclature provide the answer. The rule of priority states that when one species has been named two or more times, the valid name for that species must be the first name described and published in the calls literature; subsequent names for the species Judgment then are known as synonyms but can be used for subspecies names. In 1988 the American Society de- T cided to change the genus name for western I here is no single definition or mle that q-e North American from Sahw to Onco- can apply unambiguously in all instances to rhynchws and to change the species name for decide if a certain fish should be classified as a rainbow trout fromgaird.neri to rnyhiss. The species or as a subspecies. A standard defini- rainbow trout had been named many tion of a subspecies is that it is a geographical different species. The oldest name given to race of a species, geographically isolated frorn any North American rainbow rrout was other members of its species and recogmz- Saku gnird.nni in 1836, and gnirfuwi was ably different from other members in one or used to designate rainbow trout for many more characters. This definition assumes thar years. But the same species of rainbow trout only isolation maintains the subspecies dis- also lives on the Kamchatkan Peninsula ofthe tinctions. Ifpopulations of a subspecies were Soviet Far East, and the Kamchatkan rain- to occur together with other subspecies of bow trout was named rnyhiss in 1792. Thus, the same species, they would hybridize and the name rnyhiss clearly has priority over lose their identity. If rwo distinct popula- gairdwri as the valid species name for rain- tions occur together without hybridizing, or bow trout. with very limited hybridization, this is eu- The reason rainbow trout, cutthroat trout, dence that they should be classified as a sepa- and related species were transferred from rate species rather than subspecies of one Snhno to Oncorhynchws concerns the goal of species. Thus, in animal classification, the classification, which is to reflect evolutionary degree of reproductive isolation-rhe abilin' relationships. There is no longer any reason- to avoid hybridization with nearesr rela- able doubt that rainbow trout, cutthroat tives-is a major criterion for deciding be- trout, and the western North American tween species or subspecies classification. trouts are more closely related to the Pacific With salmonid fishes, however, manv of the genus Ornorbynchus than they problems arise that require judgment calls are to the Atlantic salmon and brown trout regarding correct classification. For example of the genus Salnn. the California golden trout, the of The genus Oncorhyrchws thus denotes a New , and the Apache trout of Ari- common ancestor that gave rise to all species zona generally are classified as separate of Pacific salmon and also ro the western species. That is, the American Fisheries North American trout. Society "oficially" recognizes them as three Most people are disturbed over sudden species. The maintenance of their identin-. changes in familiar names. It should be re- however, depends on geographic isolation. membered, however, that name changes do When living with either introduced rainbou- not aflect the fish themselves in any way. A trout or cutthroat trout, all ofthese "species" rainbow trout, by any other name, is still the freely hybridize and lose their identity. same rainbow trout, just as we have always Reproductive isolation between species known it. A rose by any other name still often is not an all-or-nothing phenomenon. smells as sweet. however. The coastal cutthroat trout sub- *RobenJ. Bebnhe species coexists with rainbow trout from

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