Small Blue Cichlid

Rheoheros coeruleus is a moderately deep‑bodied heroine cichlid distinguished by its bluish body sheen, dark lateral bar patterning, and elongate fins in adults. Males develop more intense coloration and extended dorsal and anal fin rays. Like other rheophilic cichlids, the species shows morphological adaptations to fast‑flowing water, including a streamlined profile and strong fin musculature.

The species is native to the Río Grijalva–Usumacinta basin of Chiapas, Mexico, extending into adjacent Guatemala. It inhabits clear, fast‑moving rivers with rocky substrates, often occurring in riffles and runs. Individuals are typically found in areas with high dissolved oxygen and moderate to strong current.

Rheoheros coeruleus is omnivorous, feeding on algae, detritus, small invertebrates, and organic material scraped from submerged surfaces. Like many Middle American cichlids, it is a substrate‑spawning species that forms monogamous breeding pairs and provides biparental care to eggs and fry.