Image source: Ryan O'Donnell | inaturalist.org
The longfin dace (Agosia chrysogaster) is a species of leuciscid fish found in western North America in the United States and Mexico. It is the only member of the monotypic genus Agosia. The Gila longfin dace is considered the nominate subspecies. The Yaqui longfin dace is considered as a form. Lower Colorado River drainage (primarily Gila and Bill William River systems) in New Mexico and Arizona, USA and south through southern Arizona and Pacific drainages of Mexico. Max length: 10 cm TL Anal soft rays: 7. Agosia chrysogaster can be distinguished by its elongated lower lobe on anal fin in large female, 70-95 small lateral scales, small barbell at corner of mouth, long coiled intestine, black peritoneum, rounded snout, slightly subterminal mouth, dorsal fin origin above or slightly in front of pelvic fin origin, 7 anal rays, pharyngeal teeth 0,4-4.0. Color consists of dark gray above, dusky black band along silver side enlarged into black spot at caudal fin base, often gold flecks on side. Large male is light yellow below, with yellow paired fin bases, large dorsal fin.
