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<br />The Southwestern Naturalist
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<br />vol. 30, no. 1
<br />cal order. Abbreviations for the Oklahoma counties are as follows: Bryan (BR), Carter (CAR),
<br />Johnston (JO), Marshall (MA), Love (LO), and Stephens (ST). All specimens are on deposit at
<br />SMU with the exceptian o! two fruiting specimens from the Coats collection which were verified
<br />by Crum (NIGH).
<br />We thank Howard Crum for his comments regarding this article.-CATHERINE E. COATS AND
<br />WM. F. MAHLER, Herbarium, Southern Nfethodist Univ., Dallas, TX 75275.
<br />CULTURE OF ROUNDTAIL CHUB, GlLA ROBUSTA ROBUSTA (CYPRINIDAE),
<br />THROUGH THE LARVAL PERIOD.-The cyprinid genus Gila includes three historically
<br />~~ sympatric species endemic to the Colorado River Drainage, i.e., G. robusta (roundtail chub), G.
<br />cypha (humpback chub) and G. elegans (bonytail). Roundtail chub are locally common and
<br />~ widely distributed throughout the Colorado River System, whereas humpback chub and bonytail
<br />ti are presently rare and have extremely restricted distributions (Behnke and Benson, Coop. Ext.
<br />Serv. Bull. 503A, Colorado State Univ., 1983; Lee et al., Atlas of North American freshwater fishes,
<br />North Carolina State Mus. Nat. Hist., Raleigh, 1980; Tyus et al., pp. 12-70 in Fishes of the Upper
<br />Colorado River System: present and future (W. H. Miller, H. M. Tyus, and C. A. Carlson, eds.),
<br />Am. Fish. Soc., Bethesda, Maryland, 1982; Rinne, Wasmann J. Biol., 34:65-107, 1976). The hump-
<br />back chub and bonytail are listed as endangered by several western states (Behnre and Benson,
<br />1983; T1eaC^^. et al., FiS,icrecs, 4:~J-44, i~i9
<br />) and by rite United States Department of the Interior
<br />(Federal. Register, United States Fish Wildl. Serv, Washington, D.C., Part II, 45:33768-33781,
<br />1980). These three species are closely related, systematically and ecologically, and problems exist
<br />over their identification and classification. To complicate .-.,otters, intergrades or hybrids of these
<br />species might occur naturally (Holden and Stalnaker, Copeia, 1970:409-420, 1970; Smith et al., pp-
<br />'i 613-623 in Proceedings of the first conference on scientific research in national parks [R. M. Linn,
<br />ed.), Dep. Inter., Trans. Proc. Ser. 5, 1979).
<br />Several investigators studied the systematics of adult and immature roundtail chub, humpback
<br />chub and bonytail (Holden and Stalnaker, 1970; Smith et al., 1979; Suttkus and Clemmer, Tulane
<br />Univ., Mus. Nat. Hist., Ocras. Pap. 1, 1977); however, no comparable studies were completed Eor
<br />their larvae and early juveniles. Comparative taxonomic research is being conducted on the early
<br />life-history stages of these species by the Colorado Division of Wildlife and the Larval Fish Labor-
<br />`' story, Colorado Stare University, Fort Collins. Pursuant to the goals of this research, we acquired
<br />known-age developmental series of humpback chub, bonytail and six Gila hybrid crosses (Ham-
<br />' man, Prog. Fish-Cult., 43:140-141, 1981; Hammon, Prog. Fish-Cult., 44:201-203, 1982a; Hammon,
<br />Prog. Fish-Cult., 44:213-216, 1982b) from Willow Beach (Arizona) National Fish Hatchery; unfor-
<br />tunately, a similar roundtail chub series was not available. The objective of the present study was
<br />to obtain viable roundtail chub gametes from "genetically pure" wild brood stock and use conven-
<br />tional culture techniques to produce alaboratory-reared developmental series. Results of the first
<br />successful culture of roundtail chub are presented.
<br />During late June and early July, 1983, efforts were made to collect roundtail chub brood stock
<br />From the Roundbottom area of the upper Yampa River (Moffat Co., Colorado). Since no historical
<br />humpback chub records existed [or this locality and the only bonytail recently reported in the
<br />Upper Colorado River Basin (late 1970's) were from the Green River, Utah (Behnke and Benson,
<br />1983; Tyus et al., 19$2), we assumed that roundtail chub found here would have a high degree of
<br />"genetic purity".
<br />On 13 July, two ripe female and four ripe male roundtail chub were collected by gill net from
<br />the Yampa River at river km 174.0. Water temperature ranged From 17 to 19°C, water depth from
<br />1.0 to 3.0 m, water velocity from 0.2 to 0.4 m/s, and the substrate consisted of silt-covered gravel.
<br />Breeding tubercles were present on both males and females. Males had tubercles uniformly dis-
<br />tributed over their bodies, whereas tubercles were limited to the heads, opercula and caudal
<br />peduncles o[ females. Both sexes had moderate to bright orange-red coloration along their ventro-
<br />lateral surfaces and on all fins except the dorsal fin. Total lengths, weights and ages of females
<br />were 444-455 mm, 880-908 g and 5-7 years, respectively; males were 402-450 mm long, weighed
<br />480-700 g and represented ages V-VIII.
<br />Sex products were readily expressed from all individuals of both sexes. Eggs were fertilized and
<br />water hardened on-site following procedures described b Sall and Bacon (Prog. Fish-Cult.,
<br />16:108-113, 1954). Fecundity ranged from about 39,500 to 47,350 eggs/kg body weight. Pre-
<br />fertilization egg diameter (before any water was absorbed) ranged from 1.6 to 2.4 mm with a mean
<br />o[ 2.2 mm (n=50). Egg diameter after fertilization and wafer hardening ranged from 2.5 to 3.1 mm
<br />'l ~ .
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