Xyrauchen texanus

Systematik

The razorback sucker, Xyrauchen texanus, is an endangered sucker (Catostomidae) of rivers in the Colorado River drainage of western North America.

This large (up to 91 cm length) sucker is most notable for the sharp-edged bulge on the anterior part of its back, between the head and dorsal fin, giving rise to its common name, as well as to the alternative "humpback sucker". The dorsal fin is longer than high, and somewhat quadrilateral in shape, with 15 rays.

Formerly it occurred throughout the medium-sized and large rivers of the Colorado basin, and was apparently a staple food in the diet of Native Americans dwelling along those rivers. It was also recorded from the Salton Sea in the early part of the 20th century. Its range has shrunk to the river above the Grand Canyon, and to Lake Mead, Lake Mohave, and Lake Havasu on the lower part of the river. The likely reason for the decline is habitat loss from damming and the diversion of the river through irrigation canals. The state of California designated it as endangered in 1974, followed by the United States government in 1991. A young population of over 3,000 fish in Lake Mohave has been created by an augmentation program in Lake Mohave using larvae that were produced naturally in the lake. In addition, reintroduction programs have released hatchery raised fish into Lake Havasu, the Colorado River below Parker Dam, and the Verde River.

The razorback sucker's eyes are receptive to the UV range of the spectrum. The portion of the retina that is receptive to UV is an area that receives light from below. The razorback spends most of its life at depths too deep for UV light to penetrate but they move into the shallows for breeding. In the shallows, males stake out a breeding territory and hovers near the riverbed. When another male enters the breeding area, the defending male rolls his eyes downward to reveal the upper third of the eye generating a flash of reflected sunlight. The strongest reflected component of the flash lies in the UV spectrum. The intruding male, swimming overhead, can see the flash below and will shy away from it. The eye flashes are not visible from a distance underwater and can thus warn off intruding males without alerting predators. Females do not react to the eye flashes.

References

• Vorlage:IUCN2006 Listed as Endangered (EN A1bc v2.3)
• Ira La Rivers, Fishes and Fisheries of Nevada (University of Nevada Press, 1994), pp. 357-362
• California Department of Fish and Game page on the species
• Vorlage:FishBase species