7723

• UCREFRP Catalog Number: 7723
• Author: Snyder, D. E. and R. T. Muth
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1990
• Copyright Material: NO

DESCRIPTIONS AND IDENTIFICATION OF
RAZORBACK, FLANNELMOUTH, WHITE,
UTAH, BLUEHEAD, AND MOUNTAIN
SUCKER LARVAE AND EARLY JUVENILES

ABSTRACT

Larvae of the endangered razorback sucker (Xyrauchen texanus) and six other suckers
(genus Catostomus) in the Upper Colorado River System are broadly similar in appearance.
To facilitate identification, developmental series of all species except longnose sucker (c.
catostomus) were studied for differences in morphology, meristics, pigmentation, size relative
to developmental state, and skeletal features. The razorback sucker is most similar to
bluehead sucker (C. discobolus) as protolarvae and flexion mesolarvae and flannelmouth
sucker (C.latipinnis) as metalarvae and early juveniles. Some razorback sucker larvae can
be distinguished by early yolk absorption, early scattering of dorsal pigmentation, few or no
melanophores along the ventral mid-line between heart and vent, and generally lighter or
less widely distributed body pigmentation. Later larvae and juveniles can be distinguished
by 14 or more dorsal fin rays; a correspondingly long dorsal fm base; a large, fan-shaped,
first interneural bone; and a large, oval-shaped, frontoparietal fontanelle. Bluehead sucker
and mountain sucker (C. platyrhynchus) represent subgenus Pantosteus and are best
characterized by early scattering of dorsal pigmentation; early folding of the gut; dark
peritoneum; a generally smaller dorsal fin; a small, blocky, first interneural bone; a narrow
fontanelle; and, for early juveniles, a distinctive mouth. The midventralline of pigment from
heart to vent is often complete for mountain sucker larvae and highly variable for bluehead
sucker larvae. The remaining species represent subgenus Catostomus. Flannelmouth sucker
are distinguished by their large size at hatching, yolk absorption, and onset of other
developmental events; also by delayed gut folding, generally lighter or less widely distributed
body pigmentation, limited midventral pigmentation, distinctive "tractor-tread" pigment
pattern on the dorsum of some mesolarvae, and very small scales in juveniles. A complete
midventralline of melanophores from the heart or branchial region to vent is typical of
white sucker (C. commersoni) larvae while large scales, frequently well outlined with
pigment, and a series of three large lateral spots characterize larger young-of-the-year
juveniles. Utah sucker (C. ardens) usually have larger eyes relative to head length than the
other species. They are similar to white sucker, but larvae usually have much less midventral
pigmentation, sometimes none, and juveniles have only two, if any, prominent lateral spots.

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