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<br />
<br />appl ied on'fishes. 'Inadequate p
<br />suitable methodology for fishes has
<br />
<br />
<br />. --':;-$~o--t.i/ ."<3,~'.:, ,,~-j?,L1
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<br />,^' ~0"
<br />
<br />chubs (genus Gila) of the Colorado R[ver _
<br />adjacent drainage, the Utah chub (G._atraria),ar~ used t() gernonstrate the po-
<br />tential of chromosome study, or cytogenetics, infish~...ie~ work, ~i~hlllethod-
<br />ological improvements worked out in-this laboratory.. . Two species, the bony-
<br />tai 1 chub(~.elegans) and the humpback chub (~. cypha), 'a.re currently 1 isted
<br />as endangered, while a third one, theroundtail chub (G. robusta robusta),.
<br />occurs in abundance throughout the Colorado River system. External meristics
<br />and morphomeristics have given limited success with regard to species and
<br />population determinations (Holden and Stalnaker, 1970; Smith et al., 1979)..
<br />Although the Utah chub is native to the Bonneville Basin and the upper Snake
<br />River drainages, it has been introduced into the Colorado River system (Sig-
<br />ler and Miller, 1963). The presence of this non-native species complicates
<br />the already difficult problem of differentiating between the native ones.
<br />
<br />MATERIALS AND METHODS
<br />
<br />With the exception of the roundtail chub, all fishes were juveniles.
<br />The Utah chubs were collected by seine from Timpie Springs, Utah while the
<br />roundtail chubs were captured at an unspecified locality on the Gunnison
<br />River, Colorado, by the U. S. Fish and Wildlife Service. Hatchery samples
<br />from the Black Rocks, Colorado, and Little Colorado River populations of
<br />humpback chubs were obtained from the Willow Beach, Nevada, U. s. Fish and
<br />Wi ldl ife Service faci 1 ity. Specimens of Lake Mojave, Arizona, bony tail
<br />chubs were obtained from the same place. Ten animals from each population
<br />we re exam i ned_
<br />
<br />
<br />:h
<br />IS
<br />
<br />Chromosomes are characterizable by size and location of the centromere.
<br />The latter is a small body located in a constricted region of the chromosome,
<br />dividing the latter into two arms, and is involved with moving chromosomes
<br />during cell division. Giemsa-stained chromosomes for the evaluation of size
<br />and centromere location were obtained using a modification of the Kligerman
<br />and Bloom (1977) technique. Fish were intraperitoneally injected with 20 ug
<br />colchicine / g animal. Injected fish were placed in a well-aerated container
<br />at room temperature for six hours. Specimens were sacrificed by MS 222 over-
<br />do"se and the gill arches removed. The extirpated tissue was gently washed with
<br />0.4% hypotonic potassium chloride solution. The tissues. were then placed in
<br />a vial with about 15 times ,their volume of 0.4% potassium chloride for 20 -
<br />30 min at room temperature. After removal of the potassium chloride solution,
<br />the gi 11 arches were fixed in at least three changes .of freshly prepared 3: 1
<br />anhydrous methanol-acetic acid at 40 C for at least 30 min each_ Tissues
<br />were usually made into sl ides on the same day, but they were sometimes stored
<br />in the refr.~gerator for up to three days.
<br />
<br />;;To make slides, agill arch was ~removed.from fixative,tollched toa,
<br />clean paper ,towe lto . remove excess I iquid ,and J,l aced Into ...ithe:w~1J of a.,,,
<br />depress ion slide.:Four.to s ixdropsof 5o<'Ioacet i C ,act d wer:~oadded ,an~"~h~,,,
<br />tiss,ue .wasgently minced,with ,filJescissors~f()r. '.' . -'l1inuteJt()'J()rm,a l~eJL;<i1
<br />, s ~ urry. l:fA'llltcrohematocri t ;;tubeJ(Sc ie.n~ifjc d~l~-: U ,~~s_ !ilJ~~;",o
<br />WIth cell i~m_ '~;Thi .was.~xpell.ed ".sl)cJe,.;~~pt"::a~:#9, 7".lZJ~?" C
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