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<br />embryos moved vigorously at 60 h. Hatching began at
<br />86 h and ended at 95 h; length of newly hatched fry
<br />averaged 5.5-6.5 mm. After hatching, the yolk sac was
<br />absorbed by 72 h and all fry were swimming by 96 h;
<br />length of the swimming fry averaged 6.5-7.5 mm.
<br />These hybrids reached a total length of 12-13 mm in
<br />16 days.
<br />
<br />Bony tail chub x humpback chub. All males produced
<br />milt of a low viscosity after two injections, whereas
<br />females became ripe after one injection. Eggs were
<br />1.5-2.0 mm in diameter after water hardening, with a
<br />volume of 103 eggs/ mL. Fecundity was 22,660 in the
<br />one female stripped.
<br />Eggs placed on slanted trays at 120Cfailed to hatch;
<br />although embryos formed by 96 h, all were dead after
<br />110 h.
<br />
<br />Eggs placed on slanted trays at 2JoC developed
<br />more slowly than the eggs of the bony tail x round tail
<br />cross. The first cleavage was at 4.8 h, and the embryo
<br />moved vigorously at 72 h. Hatching began at 10 I h
<br />and ended by 172 h; average length of newly hatched
<br />fry was 5.5-6.5 mm. By 96 h after hatching the yolk
<br />sac was absorbed and after 120 h, all fry were swim-
<br />ming; length of swim-up fry averaged 6.5-7.5 mm.
<br />These hybrids reached 13-14 mm in IS days.
<br />
<br />A total of 12,000 bony tail x round tail hybrids and
<br />8,000 bony tail x humpback hybrids were transferred
<br />for further culture to Dexter National Fish Hatchery
<br />at DeXter, New Mexico. Seven months after hatching,
<br />500 to 1,000 hybrids from each cross survived.
<br />Embryos in eggs from both crosses incubated at
<br />watertemperatures of 12-130 C were dead after I 10 h.
<br />Death of the embryos at the lower temperatures
<br />suggests one cause for the decline of such endangered
<br />species - eggs may not survive the low water tempera-
<br />ture characteristic of the upper Colorado River basin.
<br />The combinations of bony tail x round tail and
<br />bony tail x humpback failed to spawn naturally,
<br />despite their simultaneous sexual maturity and the
<br />presence of seemingly suitable spawning substrate in
<br />the brood stock tank. Nevertheless, natural hybridiza-
<br />tion apparently occurs, since hybrids or integrades
<br />have been observed in the upper Colorado River basin
<br />(Holden and Stalnaker 1970). Alterations in the upper
<br />basin may increase the potential for hybridization and
<br />the decline of genetically pure stock (U.S. Fish and
<br />Wildlife Service 1979).
<br />Parental individuals involved in successful matings
<br />are retained in a separate facility at the Willow Beach
<br />
<br />National Fish Hatchery for validation of species
<br />designations. Progeny from the hybrids, including a
<br />preserved developmental series, should enable reso-
<br />lution of some of the questions concerning taxonomy
<br />of the three species. Spawning techniques used for the
<br />bony tail x roundtail and bony tail x humpback crosses
<br />may also be applied for culturing genetically pure
<br />bony tail, humpback, and roundtail chubs.
<br />
<br />Acknowledgments
<br />
<br />I thank Lyle Miller, Peter Carboni, and the staff at
<br />Willow Beach National Fish Hatchery, Arizona, for
<br />ad vice and assistance throughout this project, and
<br />James E. Johnson for reviewing the manuscript.
<br />
<br />References
<br />
<br />Ball, R.C., and E. H. Bacon. 1954. Use of pituitary ma terials
<br />in the propagation of minnows. Prog. Fish-Cult. 16(3):
<br />108-113.
<br />Clemens, HP., and K.E. Sneed. 1962. Bioassay and use of
<br />pituitary materials to spawn warm-water fishes. U.S. Fish
<br />Wildl. Servo Res. Rep. 61. 30 pp.
<br />Deacon, J.E., G. Kobetich, J.D. Williams, and S. Contreras.
<br />1979. Fish of North America endangered. threatened, or
<br />of special concerns: 1979. Fisheries (Am. Fish. Soc.)
<br />4(2):29-44.
<br />Holden,P.B., and C.B. Stalnaker. 1970. Systematic studies
<br />of the Cyprinid genus Gila, in the upper Colorado River
<br />basin. Copeia 1970(3):409-420.
<br />[hering, R. von. 1937. A method for inducing fish to spawn.
<br />Prog. Fish-Cult. No. 34:]5~16.
<br />Leitritz, E. 1960. Trout and salmon culture. Calif. Dep. Fish
<br />Game. Fish. Bull. 107. 169 pp.
<br />Smith, G.R., R.R. Miller, and W.O. Sable. 1979. Species
<br />relationships among fishes of the genus Gila in the upper
<br />Colorado River drainage. Proc. First Conf. Sci Res. in
<br />Natl. Parks (1)613-623.
<br />US. Department of the Interior. 1980. Federal R egistcr
<br />U.S. Fish Wild!. Serv., Washington, D.C. Part II
<br />45(99):33768-33781.
<br />U.S. Fish and Wildlife Service. 1979. Humpback chub
<br />recovery plan. Denver, Colo. 70 pp.
<br />
<br />-Roger L. Hamman, Us. Fish and Wildlife Service.
<br />Willow Beach National Fish Hatchery. P. 0 Box
<br />757, Boulder City, Nev. 89005.
<br />
<br />Accepted 12 February 1981.
<br />
<br />Prog. Fish-Cult. 43(3), July 1981
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