Spermiogenesis and spermatozoa in six genera of the African family Alestidae plus the Neotropical genus Chalceus are described. Spermiogenesis is quite similar in all Alestidae and is identified as Type I and its variants. In Type I spermiogenesis, the flagellum of earliest spermatids lies lateral to the nucleus, and rotation of the nucleus towards the centriolar complex is observed. Nuclear rotation is complete reaching 90 degrees in Bryconalestes longipinnis, Brachypetersius altus, Brycinus imberi, B. lateralis, and Alestopetersius compressus; and is incomplete reaching 20 degrees in Micralestes acutidens and Rhabdalestes rhodesiensis. Spermatozoa morphology varies from a medial nucleus with fibrillar chromatin in the most basal genus Brycinus to a strongly eccentric nucleus with highly condensed chromatin in the more derived Rhabdalestes and Micralestes. Chalceus has a very similar spermatozoon to that found in Brycinus sharing the fibrillar aspect of the chromatin in the nucleus. This feature is so far only observed in these two genera among African and Neotropical characiform fishes. © 2014 Sociedade Brasileira de Ictiologia.122419427Arroyave, J., Stiassny, M.L.J., Phylogenetic relationships and the temporal context for the diversification of African characins of the family Alestidae (Ostariophysi: Characiformes): Evidence from DNA sequence data (2011) Molecular Phylogenetics and Evolution, 60, pp. 385-397Burns, J.R., Quagio-Grassiotto, I., Jamieson, B.G.M., Ultrastructure of spermatozoa: Ostariophysi (2009) Reproductive Biology and Phylogeny of Fish (Agnatha and Osteichthyes), pp. 287-388. , Jamieson, B. G. M. (Ed.), Enfield, Science PublishersCalcagnotto, D., Schaefer, S.A., Desalle, R., Relationships among characiform fishes inferred from analysis of nuclear and mitochondrial gene sequences (2005) Molecular Phylogenetics and Evolution, 36, pp. 135-153Eschmeyer, W.N., Fong, J.D., Genera, Species, References, , http://research.calacademy.org/research/ichthyology/catalog/fishcatmain.asp/, Available from, (18 Mar 2014)Géry, J., (1977) Characoids of the World, , Neptune City, Tropical Fish Hobbyist PublicationsMattei, X., Spermiogenése des poisson (1970) Comparative Spermatology, pp. 57-72. , In: Baccetti, B. (Ed.), New York, Academic PressMurray, A.M., Stewart, K.M., Phylogenetic relationships of the African genera Alestes and Brycinus (Teleostei, Characiformes, Alestidae) (2002) Canadian Journal of Zoology, 80, pp. 1887-1899Ortí, G., Meyer, A., The radiation of characiform fishes and the limits of resolution of mitochondrial ribosomal DNA sequences (1997) Systematic Biology, 46, pp. 75-100Santana, J.C.O., Baicere-Silva, C.M., Gusmão-Pompiani, P., Benine, R.C., Quagio-Grassiotto, I., An assessment approach for application of spermatic data in phylogenetic analyses: Within the genus Moenkhausia Eigenmann 1903 (Characiformes: Characidae) (2013) Acta Zoologica (Stockholm), 94, pp. 335-354Sharin, A.A.B., Spermatogenesis and spermatozoon ultrastructure in the Nile pebblyfish Alestes dentex (Teleostei: Characiformes: Alestidae) in Egypt (2006) World Journal of Zoology, 1, pp. 1-16Veríssimo-Silveira, R., (2007) Ultraestrutura Da Espermiogênese E Dos Espermatozoides De Peixes Da Subordem Characoidei (Teleostei: Characiformes): Uma Abordagem Filogenética, p. 131. , 2007. Unpublished Ph.D. Dissertation, Universidade Estadual Paulista "Júlio de Mesquita Filho", São Paulo, SPZanata, A.M., Vari, R.P., The family Alestidae (Ostariophysi, Characiformes): A phylogenetic analysis of a trans-Atlantic clade (2005) Zoological Journal of the Linnean Society, 145, pp. 1-144