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<br />Sprlnljl, 1950
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<br />FIGURE 1 "'Drainage map of Arizona, showing stations where laroal ,fishes were :ollected Ii'
<br />1950. In addilion, there were lhree slolions in Mexico ond five In New MeXICO...
<br />
<br />I ('....1 ~lc(la fulgida Girard Ptlfchocheilus lueius Girard
<br />ant ,1I aI (, Jt . , 1" b " G . d Plago
<br />Uhi'l!ichthys osculllS 2 (Girard), and 1 taroga. co ~tIST Ira~, .'
<br />tentS argentiss'imus (Cope), formerly presen~ Jl1 the Gila RIver, IS nt dJ
<br />provably extinct in that drainage (no. specImens have bcen ~ePr d"
<br />" " 1898) The following six spCCles of suckcrs "\\:e~e ~tu 1~
<br />sllIce '.,. . d G'.. d C t .t tt S lat1plnnzs' Balr
<br />CatostonlUS 111s1gms BaIrd an . II aI', a o~. on t .' d
<br />and Girard Pantostcus clarki (Baird and GIrard), Pantoste~~ tt
<br />phil/US (Copc), Pantosteus species, and Xyrauchen texanlls (A o.
<br />
<br />I I Hules of Zoological Nomenclature' (J3,u
<br />"' A proposed revision In the Int~~~)t o~~ired the replaeement of oscnlus by nub4 II
<br />Zool. Nomen" vol. 4, 1950, p, re I as revoked however at the Copenha
<br />f'Jr reasons of line priority. ThRDt rull!ng w Zoologlcill Nomenclature, Ed, Fran
<br />Congress in 1953 (Copenhagen ec S10ns on '66 ) _, .;
<br />Hemming. Int. Trust ~or Zool. NOOlen., 1953. .. .,~
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<br />
<br />NATIVE POSTLARVAL FISHES
<br />
<br />275
<br />
<br />Five other families of native fishes are represented in the basin of
<br />thl' lower Colorado HiveI': Elopidae (Elops affini.~), Sa]monidae (Salmo
<br />gilae), Cyprinodontidae (CypritlOdon maclIlarius), Poeciliidae (Poe-
<br />ciliopsis oceidentalis), :\ll1g-ilidae (JfllUi1 ct'pJlltlll.~), and Eleotl'idae
<br />(Eleotris picta), which has only been recorded once (Hubbs, 1~)5~l).
<br />GiUicld hys dctrusus (Gobiidae) does not penetrate the Co]ol'ado River
<br />much beyond tidal illflllellce.
<br />\Ve are grateful to Fred ~\nderegg, Supervisor of Photographic
<br />Serviees, for takillg the photographs, and to 'William L. Brudon, Artist
<br />of the Mus('um of Zoology, for mounting these and retollching the
<br />backgrounds. \Yilliam L, Cristanelli of the }\[jehigan Institute for
<br />Fisheries Research, drafted the map (Figure ]).
<br />
<br />METHODS AND TERMINOlOGY
<br />
<br />The identification of tIle lanaI fishes was based upon critical lab-
<br />oratory stUllies of preserved material (fixed in 10 percent formalin).
<br />~ince there was no opportunity to rear the larvae, the ages of the
<br />specimens are not kno\\'n. Confidence in the accura(~y of our identifi-
<br />cations was assured by the limited fish fauna and by th~ following
<br />mcthods:
<br />
<br />1. The many individuals of each species secured varied in size from
<br />juveniles to the smaller stages that lacked adult characteristics.
<br />Some intermediate specimens exhibited both adult and larval char-
<br />acters in various combinations. 'rhus, we could trace the sequence
<br />of developmental stllges from the t'arIiest (prolarvae, in some
<br />species) to those showing the distinctive featnres of the adult.
<br />
<br />2, "'\ numbCl' of colIedions contained only two species, a sucker and
<br />a minnow, and these species pairs varied sufficiently in different
<br />samples to include all represeutatives of both families. Thus, when
<br />numerous species of suckers and minnows were taken together, it
<br />was possib]c to verify identifications by comparison with the col-
<br />lections that contained only a single species of either group.
<br />
<br />;j. For one cyprinid, Agosia, rlzrysogastel', the young with yolk sacs
<br />(prolarvae) were collected ill the gl'avel nests of the adults.
<br />
<br />Hubbs (194:3) divided the early stages of fishes into the embryo,
<br />]lJ'u]arva, post larva, alevin, and juvenile. He pointed out that the word
<br />larva is used as a general term for all of the young stages of fishes.
<br />The term alevin js lIsed for fipeeies in whieh the yolk sac larva (pro-
<br />larva) transforms directly into the juvenile. It seems more logical to
<br />I'ef('r to such stages as juveniles, although the term alevin will probably
<br />be used, as in the past, by stuuents of sallltonid fishes.
<br />'j'he postlarval stage, with which we are concerned, was defined by
<br />Hubbs as the period after the absorption of tIle yolk and is only applied
<br />whcn the structure and form continue to be strikingly unlike that of
<br />the juvenile. This leaves doubt as to the end of the postlarval period
<br />alld to the interpretation of "strikingly unlike." It may be questioned
<br />whcther many freshwater fishes, in the period after the prolarva, would
<br />IJ(~ ('oIJsidered strikingly unlikc that of the juvenile. However, it seems
<br />advisable to use the term post larva for the period after the prolarva
<br />
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