The Goodeidae, one of four families of the cyprinodont fishes and all of whose species are viviparous have a modified anal fin in males for intromission of sperm. This gonopodium, with structures specific for each species, develop under the dual controls of genetically determined patterns and endogenous androgenic hormones. In males of all species of the family, rays 2 to 7 of the anal fin are shorter than the other rays and in some species they are single instead of bifurcated. The rays of this complex are strongly recurved and slender in some species. A comparative study of rays 2 to 7 in adult males of different species reveals that the primitive unspecialized structure of the juvenile fin is basic and that, in the modifications in the male fin, evolution has proceeded independently and in varying degrees in the several subfamilies.
Proceedings of the Iowa Academy of Science
©1962 Iowa Academy of Science, Inc.
Turner, Clarence L.; Mendoza, Gullermo; and Reiter, Rebecca
"Development and Comparative Morphology of the Gonopodium of Goodeid Fishes,"
Proceedings of the Iowa Academy of Science, 69(1), 571-586.
Available at: https://scholarworks.uni.edu/pias/vol69/iss1/87