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<br />. <br /> <br />(Hamman 1981a). In 1982 at Dexter NFH, 29.4% of Colorado squawfish eggs <br />hatched (Ulmer 1983). In 1983, the percent hatch of Colorado squawfish <br />eggs rose to between 60 and 70%. Percent survival of swim-up fry <br />averaged 80% at Willow Beach NFH in 1980, but was only 8.4% at Dexter <br />NFH in 1982. The causes of low survival of Colorado squawfish eggs at <br />Willow Beach and the low fry survival at Dexter NFH have not been <br />determined as yet. <br /> <br />Survival of eggs and fry among bony tail and humpback chubs has been <br />higher than it has been for Colorado squawfish. Percent hatch of <br />bony tail and humpback chub eggs was 88-91% and 72%, respectively (Hamman <br />1982a, 1982b). Fry survival was 71% for bony tail chub and 75-85% for <br />humpback chub. <br /> <br />Growth for all fishes is dependent on temperature and the availability <br />and quality of food. The optimum growing temperature for Colorado squaw- <br />fish is about 770F (Black 1982). Natural food organisms are believed to <br />produce better growth in most fish than do artificial diets. However, <br />trout food appears to be a sound diet for Colorado squawfish. For <br />example, the 1974 lot of Colorado squawfish at Willow Beach NFH were fed <br />only on trout feed for 5 years and grew to 15 inches, showing no signs <br />of nutritional deficiencies. Some of these fish have been reserved for <br />broodstock at Dexter NFH, where they have matured and produced healthy <br />eggs and fry. No nutritional problems have been reported among chub <br />fingerlings kept in hatcheries or laboratories in recent years. <br /> <br />The fecundity of these Colorado River endangered fishes (the number of <br />eggs per female) greatly effects hatchery production potential and <br />numbers of broodstock needed. Colorado squawfish females produced an <br />average of about 62,500 eggs per female at Dexter NFH in 1982 (Ulmer <br />1983). In 1981, bony tail chub at Willow Beach NFH produced about 25,000 <br />per female (Hamman 1982a), whereas humpback chub only produced an <br />average of 2500 eggs per female (Hamman 1982b). <br /> <br />The numbers of "wild" adult Colorado squawfish, hUMpback chub and <br />bony tail chub held as broodstock in hatcheries have diminished since <br />1981. Due to the theft of Colorado squawfish adults at Willow Beach NFH <br />in 1981, only two "wild" females and about 100 domestic broodstock from <br />a single female are available for breeding at Dexter NFH. Most of the <br />"wild" humpback and bony tail chub adults transferred from Willow Beach <br />NFH to Dexter NFH in 1981 have since died or have been preserved for <br />scientific collections. Chub broodstock now consist of domestic off- <br />spring of "wild" fish produced in 1981 and five "wild" bony tail adults <br />left out of eleven captured in Lake Mohave between 1979-1981. <br /> <br />In order to maintain genetic variability and avoid "inbreeding" geneti- <br />cists advise keeping at least 50 adults for breeding, with equal numbers <br />of males and females (Allendorf and Utter 1979). More Colorado River <br />endangered fishes broodstock wtll be needed in the future. Although <br />Colorado squawfish and humpback chub still can be obtained from the wild <br />with some effort, "pure" bony tail chub are extremely rare and occur only <br />ln the LCRB. <br /> <br />3 <br />