The bonytail, Bonytail Fish or bonytail chub is the most endangered of the Colorado River’s native fish species, and it is thought to have evolved around 5 million years ago. It features a sleek body with big fins and a pencil-thin tail. The bonytail (Gila elegans) is an extension of freshwater species native to the Colorado River basin in Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming in the southwestern United States; it is extinct in Mexico.

The fish’s name describes it as a graceful swimmer who belongs to the “chub” collective of minnows.  It was previously plentiful and widespread in the basin, but its numbers and distribution have plummeted to the point where it has been categorized as endangered since 1980 (ESA) and 1986 (Natural Resources Conservation Service) (IUCN). It is presently the Colorado River’s most endangered endemic big-river fish. Gila is a genus of 20 species, seven of which are native to Arizona. Any of the long-lived fish native to the Colorado River system’s main stems experienced the most dramatic loss of this fish species.

Bonytail fish navigating through water
credit:earth.com

Bonytail chubs or Bonytail Fish were one of the first fish species to respond to changes in the Colorado River basin following the completion of Hoover Dam; between 1926 and 1950, the fish was extinct from the lower basin. They could still be found in Utah’s Green River, as well as the bigger Colorado River water basins. Gila elegans was initially listed as Endangered by the IUCN in 1986, after being placed on the US list of endangered species on April 23, 1980. It was classified as Critically Endangered by the IUCN in 2013.

Habitat

Although they have been seen in fast-moving water, Bonytail Fish or bonytail chub prefer backwaters with stony or muddy bottoms and flowing pools. They are now primarily restricted to stony canyons, but they were once common in the river’s wide downstream parts. The number of bonytail chubs is limited, and it is continuing to shrink. The population is being depleted mostly as a result of habitat changes induced by dams, as well as competition and predation by non-native species.

Bonytail fish swimming in the water
credit:coloradopolitics.com

Body characteristics

  • Bonytail chub has a streamlined body and a mouth that is at the end.  They have bodies that occasionally arch into a smooth, rounded shape.
  • The bonytail has a concave contour and a large, flattened skull. An adult can reach a length of 17 inches and a weight of over 1 pound. The majority, though, are between 8 and 13 inches long and weigh less than a pound.
  • It has a huge mouth with a corner that extends to the front half of the eye.
  • Barbels are missing from the lips.
  • The eyes are elliptical and tiny. It has a less noticeable back hump than a Humpback whale.
  • The body is slim but bloated, giving the impression that the head is smaller. This fish either doesn’t have any scales on its body or has small scales buried in it.

The back of the bonytail is gray or olive in color, with silver sides and a white belly. Bonytails can reach lengths of up to 22 inches. Bonytail chubs are normally dark dorsally and paler ventrally in coloring, but in exceptionally clear water, they seem virtually black all over. Males and females have different coloring during the breeding season. Males have brilliant red-orange lateral bands between their paired fins as they mature, while females have a more muted hue.

Spawning

Bonytails reproduce in the spring when the water temperature rises over 64 degrees Fahrenheit. Females lay between 1,000 to 17,000 eggs, which are strewn across gravel bars at random. The eggs stick to the rocks or fall into depressions. Once the eggs are laid, they get no parental care. Approximately 9 hours after fertilization, eggs begin to hatch, and swim-up occurs 48-120 hours later. Juveniles have a survival rate of 17-38 percent. Bonytails reach maturity between the ages of two and three.

Bonytail fish in its habitat
credit:lcrmscp.gov

Diet

Adult bonytail chubs eat small fish, algae, plant debris, and terrestrial insects, whereas young bonytail chubs eat aquatic vegetation. Bonytail chubs have a long life span and can live up to 50 years.

 

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