Testicular structure and spermatogenesis of the oviparous goodeids Crenichthys baileyi (Gilbert, 1893) and Empetrichthys latos Miller, 1948 (Teleostei, Cyprinodontiformes).

Abstract

The cyprinodontiform family Goodeidae comprises some 51 species, including subspecies, of freshwater fishes all of which are at risk or are extinct in the wild. It is classified in two allopatric subfamilies: the Goodeinae, endemic to the Mexican Plateau, and the Empetrichthyinae, known only from relict taxa in Nevada and southern California. The 41 species of goodeins are all viviparous and share a set of well-documented reproductive characters. In contrast, the recent species or subspecies of empetrichthyins are all oviparous and relatively poorly known, yet of critical interest in understanding the evolution of livebearing in the family. We previously described ovarian structure and oogenesis in empetrichthyins using archival museum specimens of females and here extend that study to males. Testicular characters of two species of empetrichthyins, Crenichthys baileyi, and Empetrichthys latos, are studied and compared directly with those of one species of viviparous goodeid, Ataeniobius toweri. The testis is a restricted spermatogonial type in both the Empetrichthyinae and the Goodeinae: spermatogonia are found solely at the distal termini of lobules, a diagnostic character of atherinomorph fishes. Morphology of the differentiation of germinal cells during spermatogenesis is similar in both subfamilies. In the oviparous C. baileyi and E. latos spermatozoa are free in the deferent ducts. In contrast, the spermatozoa of viviparous goodeids are organized into numerous bundles called spermatozeugmata, a characteristic of most fishes that practice internal fertilization. Differences between the goodeid subfamilies are interpreted relative to the oviparous versus viviparous modes of reproduction. Archival museum specimens are a reliable source of data on reproductive morphology, including histology, and may be the only specimens available of rare or extinct taxa.