Cynodonichthys is a genus of small, egg-laying killifish in the rivuline family Rivulidae, native to Central America and the Panama-Colombia border region, with the atlas's coverage spanning Panama, Colombia, Costa Rica, Belize, Guatemala, Honduras, Mexico, and Nicaragua. Unlike the seasonal, pond-dwelling killifish of Africa and South America that lay drought-resistant eggs, Cynodonichthys are non-annual species living in small, permanent forest streams and seepages, so their eggs do not need to survive a dry season. Most species are compact, under 3 in, with the slim body and upturned mouth typical of surface-dwelling rivulines, and males generally carry brighter fin colour than the plainer females. The genus was separated from the old wastebasket genus Rivulus by molecular and morphological revisions of New World killifish.
The hobby's interest in Cynodonichthys sits at the specialist end of killifish keeping rather than the mainstream trade; species such as the dark-lined killifish (C. fuscolineatus), dogtooth rivulus (C. tenuis), and fire-tailed killifish (C. uroflammeus) circulate through killifish clubs and egg-trading networks more than general fish stores. Because they come from small, stable streams rather than temporary pools, care generally calls for cooler, well-oxygenated, current-swept water rather than the shallow, stagnant setups used for annual killifish. Conservation data are thin for much of the genus — several species are listed data deficient or not evaluated — but one is Endangered and one Critically Endangered, and two are CARES conservation priorities, reflecting how vulnerable narrow-range Central American stream fish are even where formal assessments lag behind.