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difficult to observe differences within and between condensed spreads, especially with fish since their chromosomes tend to be smaller than those of other vertebrates (Denton, 1970). Resolll- tion can be increased by analysing chromosomes less affected by mitotic arrestors and, consequently, larger in size (Harris et 21.., 1973; Worton and Duff, 1979). Such spreads are abun- dantly available through tissue culture. In addition, elongate spreads are preferable since mitotic chromosomes do not contract uniformly due to the differential distribution and contraction of euchromatin and heterochromatin (Rowinski et al . , 1979). Measurements from elongate chromosomes, relative to those from contracted ones, will more closely approximate true relative arm lengths and centromeric placements. The results from the cytogenetic investigation confirmed , '- those obtained'earlier wh~n chromosomes were obtained directly " from bony tail, humpback and roundtail chubs. The modal diploid .. values <i.e., the number of chromosomes in a mitotic chromosome spread) were 50 chromosomes for each morphospecies, to include the Utah chub. Most chromosomes appeared similar between the species when care was taken to compare spreads of the same contractile state (Fig. 1). The Utah chub differed from the Colorado River Gila by possession of a subter-minal chromosome 17 instead of a submedian one (Fig. 2). Although there may have been minor morophometric differences between certain chromosomes among thp Co)orCido F:i\.'p, GiJc~. thE" 1TI0~t c1.t-jljr'Ci or-iC. c<.r'pECi" s C't \ 1 J , .