Chiselmouth

Chiselmouth
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cypriniformes
Family:	Cyprinidae
Subfamily:	Leuciscinae
Genus:	Acrocheilus Agassiz, 1855
Species:	A. alutaceus
Binomial name
Acrocheilus alutaceus Agassiz & Pickering in Agassiz, 1855

The chiselmouth is an unusual cyprinid fish of western North America. It is named for the sharp hard plate on its lower jaw, which is used to scrape rocks for algae. It belongs into the monotypic genus Acrocheilus and is a close relative of the Gila western chubs (Simons & Mayden 1997).

The chiselmouth's body plan generally follows the standard cyprinid form, generally elongated and slightly compressed. The snout is very blunt, with the lower jaw's plate (which consists of cornified epithelium) jutting out slightly. Coloration is rather drab, dark brown above and lighter lower down. Many individuals also have a pattern of black dots, and younger fish may have a dark area at the base of the tail. The single dorsal fin has 10 soft rays, while the anal fin and well-developed pelvic fins each have 9-10 rays. Chiselmouths can reach a length of 30 cm (12 in).

Young fish feed on surface insects. When the chisel develops (at around 0.6 inches length), they shift to scraping, making short darting movements at the substrate to dislodge whatever is on it, and sucking it in. Although they consume filamentous algae, it seems not be digested much despite a long coiled intestine, and their primary food actually consists of diatoms.

They are typically found in warmer parts of streams and rivers in the drainages of the Columbia River, Fraser River, and the Harney-Malheur system of the Great Basin. Some are found in lakes, migrating into streams to spawn. Although abundant in many parts of their range, behavior remains little-known.

References

• Froese, Rainer, and Daniel Pauly, eds. (2006). "Acrocheilus alutaceus" in FishBase. March 2006 version.
• "Acrocheilus alutaceus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=163531. Retrieved 18 April 2006. 
• Sigler, William F. & Sigler, John W. (1987): Fishes of the Great Basin: 149-151. University of Nevada Press, Reno.
• Simons, Andrew M. & Mayden, Richard L. (1997): Phylogenetic Relationships of the Creek Chubs and the Spine-Fins: an Enigmatic Group of North American Cyprinid Fishes (Actinopterygii: Cyprinidae). Cladistics 13(3): 187-205. doi:10.1111/j.1096-0031.1997.tb00315.x (HTML abstract)