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Springs pupfishes to determine the extent of genetic change after 10 years of maintenance in a hatchery environment. He found that genetic diversity did not change, that heterozygosity was retained in these fish during that time period. Buth and Murphy (1984) compared razorback sucker from Lake Mohave, AZ-NV with F1 razorbacks produced at Dexter NFH (parental stock from Lake Mohave, AZ). They looked at these fish to evaluate genetic composition of the samples as well as possible introgressive influence of flannelmouth sucker (Catostomus latipinnis). They determined that in terms of introgressed genes, the hatchery stock was "at least as good as, if not better than, the Lake Mohave natural populations". They further concluded that "as long as the breeding stock" is obtained "from natural populations, the breeding program at the Dexter hatchery can be quite successful". In an attempt to incorporate even greater diversity into the Dexter maintained razorback sucker brood, 2,000 larval razorbacks were collected from Lake Mohave in spring 1985. They are being reared at Dexter and will be utilized as broodfish when they reach sexual maturity in 1987. Of the 1,539 surviving fish, 625 were kept for broodfish, 100 sent to Don Buth at UCLA for electrophoretic analysis (results not available), and 814 stocked in Eagle Creek, a tributary of the Gila River in eastern Arizona. Because the majority of the mature Colorado squawfish broodstock held at Dexter is F1 progeny produced from a single wild female (Toney 1974), attempts have been made to secure a more genetically diverse lot of broodfish. Anew lot of squawfish broodstock is being reared at Dexter to take the place of the existing brood. They were produced from 4 or 5 female and 7 or 8 male wild squawfish at Willow Beach National Fish Hatchery (Willow Beach NFH) in 1981 (Hamman 1981b). Although extremely scarce, attempts are still being made to collect wild adult bonytai] from Lake Mohave in order to incorporate greater diversity into the bonytail broodstock. The current bonytail broodfish were produced from six females and five males in 1981 (Hamman 1982); no other fish were available. In order to maintain the genetic diversity of other captive held fishes at Dexter (i.e., gambusia, pupfishes, etc.), additional wild fish are now brought it periodically to mix .:nth ?nual numbers of hatchery wish. OPERATIONAL PROCEDURES Holding such an array of fishes requires care to ensure isolation to prevent mixing of genomes and/or other adverse interactions -34-