title: Ultrastructural features of spermatogenesis in Melanorivulus punctatus (Cyprinodontiformes: Rivulidae).
abstract: Fish belonging to the family Rivulidae possess one of the most complex reproductive systems. Rivulus, a genus of freshwater fish in the Rivulidae family, was recently reclassified into five genera, including Melanorivulus. Its type species, M. punctatus, is widely distributed and probably represents a species complex. The ultrastructure of sperm has been broadly used in systematics, and we hereby describe the ultrastructural features of spermatogenesis in M. punctatus. Ten M. punctatus males were collected from the reservoir of Parque Estadual da Quineira, municipality of Chapada dos Guimarães, Mato Grosso, Brazil, and prepared for analysis by light microscopy and transmission electron microscopy. M. punctatus undergoes cystic spermatogenesis. Its cysts consist of groups of germ cells that are in synchronous development and are surrounded by cytoplasmic projections of Sertoli cells. With the breakdown of the cysts, the spermatozoa are released and their maturation is completed in the duct, where part of the cytoplasmic material is discarded through the vesicles. The mature spermatozoon is characterized by a spherical head with homogeneously condensed chromatin, a symmetric midpiece consisting of a pair of perpendicular centrioles, a ring of mitochondria, several vesicles, and one flagellum medial to the nucleus. Early stages of spermatogenesis show no peculiarities; however, in spermiogenesis, we observed that the spermatids remain interconnected by cytoplasmic bridges and have pockets of residual cytoplasm. The sperm is of the aquasperm type and is similar to that observed in the members of the family Rivulidae. The spermatozoa have a single flagellum that consists of a classic axoneme (9+2), as found in most groups of fish, despite the lateral extensions.
authors.affiliation: Instituto de Biociências, Universidade Federal de Mato Grosso, Av. Fernando Corrêa da Costa, n° 2367, Bairro Boa Esperança, Cuiabá, MT 78060-900, Brazil. Electronic address: monicassel@hotmail.com.
authors.forename: Mônica
authors.initials: M
authors.lastname: Cassel
authors.affiliation: Instituto de Biociências, Universidade Federal de Mato Grosso, Av. Fernando Corrêa da Costa, n° 2367, Bairro Boa Esperança, Cuiabá, MT 78060-900, Brazil. Electronic address: adelina@ufmt.br.
authors.forename: Adelina
authors.initials: A
authors.lastname: Ferreira
authors.affiliation: Laboratório de Biologia e Genética de Peixes, Departamento de Morfologia, Universidade Estadual Paulista "Júlio de Mesquita Filho" - UNESP, Campus de Botucatu, Distrito de Rubião Junior, S/N, Botucatu, SP 18618-970, Brazil. Electronic address: mahmoudmehanna@hotmail.com.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Mehanna
mesh_terms: D000818:Animals; D001938:Brazil; D003532:Cyprinodontiformes / Q000033:anatomy & histology*; D008297:Male; D046529:Microscopy, Electron, Transmission; D012708:Sertoli Cells / Q000648:ultrastructure; D013077:Sperm Head / Q000648:ultrastructure; D013082:Sperm Tail / Q000648:ultrastructure; D013087:Spermatids / Q000648:ultrastructure; D013091:Spermatogenesis; D013094:Spermatozoa / Q000648:ultrastructure*
keywords: Aquasperm; Germ cells; Morphology; Phylogeny; Spermatozoa