BiochemicalSystematicsand Ecology, Vol. 11, No. 4, pp. 383-388, 1983. 0305-1978/8353.00+0.00 Printed in GreatBritain. PergamonPressLtd. Biochemical Systematics of AIIodontichthys: A Genus of Goodeid Fishes THADDEUS A. GRUDZIEN and BRUCE J. TURNER Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A. Key Word Index - AIIodontichthys; Goodeidae, Cyprinodontoid; alloenzymes; morphology; viviparity. Abstract - AIIodontichthys Hubbs and Turner 1939 of the family Goodeidae is comprised of three species: A. tamazulae and A. hubbsifrom the Rio Coahuayana and A. zonistius from the Rio Armeria in Estados Jalisco and Colima, Mexico. These fish are found throughout the shallow riffles of small streams. Their systematics has been based on morphological and karyological traits. An alloenzymic study of the genus produced results which agree well with the previous morphological studies. Moreover, a dendrogram of Nei genetic identities agrees well with the zoogeography of the species. The data indicate a high degree of congruence between alloenzymic and morphological systematic inferences in this group of fishes. Introduction The use of gel electrophoresis as a tool in popula- tion genetics has raised an important question: does electrophoretically observed genetic diversity between species agree with the accepted syste- matics of a group? The answer to this question among teleosts has been 'yes' and 'no'. For example, three distinct morphotypes of brown trout (Salmo trutta) were found to comprise three separate, isolated gene pools [1]. On the other hand, Turner [2[ found very little genetic diver- gence among four morphologically differentiated pupfishes (Cyprinodon). This present study is an examination of genetic diversity among three species of the ra re goodeid genus AIIodontichthys, a stream-dwelling darter-like group of Mexican fishes. The family Goodeidae is comprised of approx. 30 species of live-bearing cyprinodontoid fishes endemic to the Mesa Central of the Mexico plateau and several rivers which flow from the plateau into the Pacific Ocean. The most recent classification of the family has been carried out by Miller and Fitzsimons [3]. Goodeids are unique among live-bearing cyprinodontoids in that the anal fins of males are not modified into a gono- podium and developing embryos are nourished from ovarian fluids once their yolk sac reserves have been depleted ('matrotrophy' see Wourms [4]). Nutritive material is absorbed by means of (Received 19 No vember 1982) highly modified extensions of the gut known as trophotaenia. The goodeids share this peculiar reproductive method only with a marine genus of ophidioid fishes, Parabrotula. Despite their high degree of endemism and unique reproductive adaptations, the goodeids remain a little known group of fishes. The three species of AIIodontichthys, A. zonistius [5], A. tamazulae [6] and A. hubbsi [3], are distinctive among the Goodeidae in their adaptations for a stream (and riffle) existence. The general body form a slender and elongated, unlike many other members of the family. The fish have a reduced swim bladder [3], enlarged pectoral fins, and appear to be the goodeid analogs of the North American darters (e.g. Etheostoma). A diagnostic character of the genus is the presence of a dark comma-shaped spot just posterior of the operculum (Fig. 1). Some useful species distinguishing characteristics are given in Table 1. AIIodontichthys species also have an interesting zoogeography. AIIodontichthys zonistius was first reported from the Rio Colima, Colima, Mexico by Hubbs [5] and it is generally regarded as endemic to the Rio Armeria system [7]. We have collected this species in the Rios Colima, Comala and Pozol in the Armeria drainage, and also in two tributaries of the Rio Salado in the neighboring Coahuayana drainage. The occurrence of A. zonistius in the Coahuayana system is probably due to stream capture from the Rio Colima caused by the 383