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'r to Iq1~ ft:MV\e) ~}f.{onz.&!- Transactions of the American Fisheries Society 118:435-440, 1989 @ Copyrigh' by Ihe American Fisheries Society 1989 1~3~ Biochemical Genetics of Endangered Colorado Squawfish Populations LoREN K. AMMERMAN Department of Zoology, The University of Texas Austin, Texas 78712, USA DONALD C. MORIZOT1 The University of Texas M. D. Anderson Cancer Center Science Park, Research Division, Post Office Box 389 Smithville, Texas 78957, USA Abstract. - We examined the relationships between two hatchery and two wild populations of the endangered Colorado squawfIsh Ptychocheilus lucius by use of starch gel electrophoresis of 44 presumptive locus products. Samples of fish from the Green and Colorado rivers were found to be very similar to two hatchery stocks established in 1973 and 1978 (unbiased genetic identity = 0.99; Nei 1978). At least 9 of the 44 loci were polymorphic. Average heterozygosities were high (2.6-5.3%) for an endangered species but were similar to those for nine other cyprinid genera. The proportion of polymorphic loci ranged from 9.1 to 13.6%, which was also high when compared with reported values of 4% for a congener. Genotypes deviated from Hardy-Weinberg proportions at two loci (EST-I*, GPI-2*) in the Colorado River samples and at one locus (EST-I*) in the Green River samples. Also, as a secondary objective we resolved five of the nine polymorphic loci from samples of fin tissue. The Colorado squawfish Ptychocheilus lucius, the largest North American cyprinid, has been listed as endangered by the U.S. Fish and Wildlife Service since 1967 (U.S. Office of the Federal Reg- ister, 32;43[1967]:40001). This large minnow was once important throughout the Colorado River ecosystem and most of the larger tributaries as a top predator (USFWS 1987a). However, the Col- orado squawfish is now restricted to the Green, Yampa, and upper mainstream Colorado rivers (Holden and Wick 1982; Figure I). A few indi- viduals make long spawning migrations of up to 200 km to preferred white water canyons (Tyus 1986). Historically, squawfish that weighed over 30 kg were not uncommon, but in the past two decades, wild-caught squawfish rarely have ex- ceeded 7 kg in weight (Behnke and Benson 1980). Two captive populations of the Colorado squawfish are maintained at the Dexter (New Mexico) National Fish Hatchery. In 1978 and 1979, 29 fish were collected from the Colorado and Green rivers to make up one hatchery stock. The fish from both locations were mixed together and 3 females and 10 males were bred in 1981. The second hatchery stock was derived from eight fish (unknown sex ratio) that were collected from I To whom correspondence should be addressed. the Yampa River in 1973 and bred in 1974. From their offspring, one female and five males were used to produce the 1987 year class. Despite the time required for the fish to reach sexual maturity (5-6 years), techniques for rearing Colorado squawfish have been very successful (Hamman 1981). More than 176,000 young have been re- introduced into the Salt and Verde rivers of Ari- zona (USFWS 1987b). Plans to introduce more of these fish into the lower Colorado River are in progress. A particular concern regarding the suc- cess of these and other restocking programs is that the hatchery fish be genetically representative of wild populations. No prior genetic analyses of either wild or hatchery stocks of Colorado squaw- fish have been conducted, We compared hatchery and wild populations of Colorado squawfish by use of enzyme electropho- resis. A secondary objective was to determine whether isozymes could be assayed with biopsied tissues, such as fin epithelium, whose use does not endanger the fish (Carmichael et al. 1986). Methods We obtained samples of frozen Colorado squawfish from the U.S. Fish and Wildlife Service, Dexter National Fish Hatchery. We sampled two hatchery stocks from this facility: fish of the 1981 year class deri ved from the Colorado and Green 435