Chapalichthys is a genus of livebearing fish in the splitfin family Goodeidae, endemic to central Mexico's Lerma-Chapala basin in Jalisco. The atlas covers 3 species - the barred splitfin (C. encaustus), polka-dot splitfin (C. pardalis) and alien splitfin (C. peraticus) - all around 3.5 in. Like other goodeids, Chapalichthys females give birth to fully formed young; embryos are nourished for much of gestation not by a placenta but by trophotaeniae, ribbon-like outgrowths from the embryo's anal region that absorb nutrients from the mother, a reproductive strategy unique to this family. They live in springs, streams and shallow lake margins of the Chapala basin, historically one of Mexico's richest freshwater fish faunas.
The Lerma-Chapala basin has suffered decades of water extraction, pollution and habitat conversion, and Chapalichthys reflects that pressure directly: one species is Vulnerable and two are Critically Endangered, and two of the three are flagged in the atlas's CARES list of conservation-priority species maintained by hobbyist breeding programs. In the aquarium, Chapalichthys is kept mostly by goodeid specialists rather than the general livebearer trade - they are peaceful, do well in cooler, well-oxygenated water reflecting their spring and stream origins, and captive populations held by conservation-minded hobbyists are, for some localities, a meaningful hedge against extinction in the wild.