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<br />\0 <br />~ <br />....... <br />~ <br />~ <br /> <br />~~ <br />i.~ <br />-~'-~ <br />s:: <br />~ <br /> <br />~ <br /> <br />... <br /> <br />,.... J <br />1'.......'......,..... <br />!, .i <br /> <br />I <br />1 <br />I <br /> <br />~ <br /> <br />UJ~ <br /> <br />~~~ <br /> <br /> <br />..~ <br />l~,:,,) <br />.'J,. f! <br />"r"p..i ~" <br /> <br />" <br /> <br /> <br />,. . <br />~: <br /> <br />, <br /> <br />.11. I.. <br />'li, <br />t <br /> <br /> <br />,. , f~~" ... y,"" <br />Th\S I'W;\ ...... ': ij j;. <br />"'.0**. b ""v.rlt'l..1 low (lllie 11 . <br />..."...j 'I co,.., .. <br />',~.<i;'" . <br /> <br />NATIVE POSTLARV AL FISHES OF THE LOweR <br />COLORADO RIV~R BASIN, WITH A KEY <br />TO THEIR JDENTIFICA TION 1 <br /> <br />HOWARD ELLIOTT WINN and ROBERT RUSH MILLER <br />Mu.eum of ZoalllllY, University of Michigan <br /> <br />Little is known about the ~arly life history stages of the fresh- <br />water fishes of North .America, particularly from the point of .view of <br />systematics. The information available for the identification of larval <br />freshwater fishes is largely scattered throl1!dwut life-history' studies <br />except for three important contributions by Fish (1929a, 1929b, 1932). <br />Papers on freshwater fishes fl10m western North America tbat con- <br />tain figures of larval stages include those by Fry (1936); Kopec <br />(1949), Weisel and Newman (1951), and Douglas (1952. Figure 3 is <br />Rhinichthys OSC1tlUS, not XlIra.itchen texallus). A helpful comparative <br />study (with figures) of the young of the five species of Pacific salmon <br />was published by Foerster and Pritchard (1935). <br />It is frequently important that biologists be able to identify correctly <br />1 he eggs and young stages of fishes. 1'his is often necessary for the solu- <br />tion of such problems as the location of breeding sites, the distribution <br />/lnd biology of the larvae, and the conscl'vatjon of populations. (Balin- <br />sky, 1948). The abundance of If. year class may be determined by the <br />('llvirollmental conditions that act on the critical larval peri(.lds. An <br />understanding of the early sequences in its life history may beaJ." signifi- <br />('antIy upon the origin and re~ationships of a species (Orton, 1953). <br />During an ichthyological suryey of the lower Colorado River system <br />in the spring of 1950, the authors collected numerous early stages of <br />man~' of the native fishes (Fig-llJ'e ]). Gatlwring- life-history data was <br />one of tlleob,iectives of the survey. Specimens were obtained witll fine- <br />meshed dip nets and wire strainers, and some of the best larval collec- <br />tions were secured at night with the aid of a bright light. For the <br />purposes of this paper, the lower Colorado River is defined as that <br />part of the river and its tributaries that lie below Lake Mead (Hoover <br />Dam) . This includes all of the .Gila River system, which is the major <br />drainage basin of the southern half of Arizona and of western New <br />l\1exico. Nearly all of the early stages of 12 species are represented <br />in the collections. <br />The species treated in this paper belong to two families, the Cato- <br />stomidae (suckers) and CJ'prinidae (minnows), which are among the <br />most difficult of all freshwater fishes to identify. The following six <br />species of minnows are keyed out, although postlarvae of Ptychochcilus <br />were not obtained: Agosia chrysogaster Girard, O.la robusta Baird <br /> <br />I Suhmltted for publication February, 1954. The field work which made this paper ))08- <br />sible was financed through a research grant to R. R.. Miller from the ~OI'ace H. <br />Hackham School of Graduate StudIes, University of :Mlchllra~. ; <br /> <br />3:-970U <br /> <br />( 273) <br /> <br />C a I; -fO r" /o...h S 1-- ~ ti-?-rr- I!.. <br />, <br /> <br />v. YO) /1 r'f <br />