The family is divided into two subfamilies, the Goodeinae and the Empetrichthyinae. The Goodeinae are endemic to shallow freshwater habitats in Mexico, particularly along the Mesa Central area, west of Mexico City, with some species found in brackish fringes at both the Atlantic and Pacific coasts. There are 36 species of Goodeinae in 16 genera. The Empetrichthyinae are typically found in the southwestern Great Basin of the United States, and contains 4 species in two genera.
The name "Splitfins" comes from the fact that, in the male fish, the anterior rays of the anal fin are partly separated from rest of the fin. Splitfins can be up to 20 cm in length, though most species are much smaller, around 5cm. Goodeid fish have internal fertilisation, with males positioning themselves with a flexible part of the front anal fin, separated by a notch, which makes up the andropodium. Embryos hatch out of the egg within the womb, and possess trophotaenia, a ribbon-like structure unique to Goodeids, positioned in front of the anal fin on the dorsal surface of the juvenile. These allow the absorption of nutrients within the womb (matrotrophy), and are shed by juveniles shortly after birth. Female Goodeids do not store sperm, and so a copulation event must precede each pregnancy.
In recent years there has been a significant reduction in the range and size of Goodeid populations in this region, mainly due to anthropogenic disturbances, such as pollution, eutrophication, habitat modification and desiccation; recent estimates put habitat loss at 80% compared to historic ranges . The low economic importance of Goodeid fish to Mexican fisheries and industry has led to this family being largely ignored by conservation efforts, but their small size and the dedication of a small number of aquaria hobbyists has led to a recent increase in the amount of research dedicated to the family. These investigations have highlighted the implications for conservation efforts concerning other global freshwater ichthyofauna.
Several species are threatened or extinct according to the IUCN: