Diversity of the sperm morphology in gobioid fishes

Abstract The fine structures of mature spermatozoa were studied using TEM and SEM for 38 gobioid species, representing six families. Spermatogenesis was observed for three species. Gobioid spermatozoa were found to be exceptionally diversified comprising most of the known teleostean sperm morphs. They were classified into 6 types based on a combination of morphological characters: Type I (20 species, including Rhyacichthys aspro)--Nucleus ovoidal to spherical, with distinct or indistinct hiatus in chromatin on lateral surface; single mitochondrion, located opposite chromatin in all but one species; single flagellum. Type 2 (8 species, including Sicyopterus japonicus)--Spherical nucleus without hiatus in chromatin; mitochondria numerous, in several longitudinal columns around base of flagellum; single flagellum. Type 3 (3 species of Odontobutidae and 4 species' of Gobionellinae)--Nucleus spherical to cone-shaped; numerous, multilayered mitochondria; single flagellum. Type 4 (Leucopsarion petersi)--Spherical nucleus with special anterior accessory; numerous irregularly-shaped mitochondria, around base of flagellum; two flagella. Type 5 (Ptereleotris hanae)--Nucleus bell-shaped anteriorly attenuated; mitochondria numerous, spherical, around base of flagellum; single flagellum. Type 6 (Schindleria sp.)--Nucleus elongate, cylindrical, penetrated by flagellum to well beyond anterior tip; single mitochondrion enclosing fiagellum at base; single flagellum. Comparison between these types and current gobiod systematics revealed the following points: (1) Rhyacichthyidae and the two subfamilies of Eleotridae shared uniform sperm morphology within Type 1. (2) Types 4, 5 and 6 were distinct in having exceptional features. (3) Of six families of Gobioidei, Gobiidae has the most diversified sperm morphology. In addition, present grouping of sperm morphs was compared with gobioid phylogenies derived from molecular evidence. Results suggested that spermatozoa are potentially useful in evaluating the relationships within the Gobioidei.