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341. Obtain brood stocks of the three Gila s ecies from nviolate wild populations in itial~.. Taxonomic studios (see 5) will provide direction towards selecting genetically pule brood •tocka. The humpback chub population in the loves Little Colorado River is now being tried as a hatchery stock. 'Several roundtail chub populations are available. The extreme rarity of the bony- tail chub will limit the choices; any captured bonytail chubs will probably be used is the hatchery programs. 342. Develop replacement brood stock from captivel9 reared chubs: Hatchery-reared chubs can occasionally be used as a sauz+ce of brood stock. This will allow maximum production by making large numbets of brood fish available. 343. Reep brood stocks from geographically_isolated areas separate and occasionally infuse wild-chubs to maintain genetic heterozyAosity. After the rearing program is established and successful, wild chubs should be regularly integzated into the propaga- ti~a program. Thus, the natural heterozygosity of the species can be maintained, i.e., the,hatcherg stocks will not become domesticated. Since htmapback chubs from geographically isolated areas may be genetically distinct, care must be taken to avoid gene pool mixing a®ong Popular tioas. Zn this way overall genetic diversity will be maintained. 4. Determine the taxvnamy of all sysrpatric species and hybrids of the mainstream Colorado River Gila complex at several life stages. The humpback chub species was first described about 30 years ago. Roundtail and bonytaii chubs were originally considered subspecies of Gila robusta, but in the last 10 years were elevated to full species status. Confusion atilt exists regarding-reliable characters to identify these three sympatric species. Patursl and induced hybridiza- tion among these species further compoands the problem. Taxonomic studies of hatchery-produced and wild specimens should be undertaken to clarify the limits of acceptable inter- and iatraspecific variabiLtty. Specimens of known ancestry can be produced in hatchery facilities (sEe 3). 22