Goodeidae is a family of teleost fish endemic to Mexico and some areas of the United States. Many species are known as splitfins. This family contains about 50 species within 18 genera. The family is named after ichthyologist George Brown Goode (1851-1896). Distribution 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 (especially the Lerma River basin, smaller rivers directly south of it and inland to around the Valley of Mexico region), with some species found in brackish fringes at the Pacific coast, and north to central Durango, central Sinaloa and north San Luis Potosí. There are about 45 species of Goodeinae in 16 genera (some list 2 additional genera). The Empetrichthyinae are found in the southwestern Great Basin in Nevada, the United States, and contains 4 species in 2 genera. Physical information The name "splitfin" 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 in length, though most species are much smaller, around . 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 ovarian follicle, and possess trophotaeniae, ribbon-like structures that emerge from the cloaca in front of the anal fin, on the ventral surface of the juvenile. These allow the absorption of nutrients within the ovary (matrotrophy), and are shed by juveniles shortly after birth. Female goodeids do not store sperm, and so a copulation event must precede each pregnancy. Conservation status 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