Journal of Fish Biology (2014) doi:10.1111/jfb.12526, available online at wileyonlinelibrary.com Genetic differentiation among distinct karyomorphs of the wolf ish Hoplias malabaricus species complex (Characiformes, Erythrinidae) and report of unusual hybridization with natural triploidy R. Utsunomia*†, J. C. Pansonato Alves*, L. R. S. Paiva‡, G. J. Costa Silva*, C. Oliveira*, L. A. C. Bertollo§ and F. Foresti* *Departamento de Morfologia, Instituto de Biociências, Universidade Estadual Paulista, Distrito de Rubião Junior, s/n, 18618-970, Botucatu, SP, Brazil, ‡Universidade de Ensino Superior Ingá, Avenida Colombo 9727, 87070-000, Maringá, PR, Brazil and §Departamento de Genética e Evolução, Universidade Federal de São Carlos, Rodovia Washington Luis km 235, 13565-905, São Carlos, SP, Brazil (Received 13 January 2014, Accepted 5 August 2014) In this study, genetic differentiation between karyomorphs A (2n = 42) and D (2n = 39/40) of the wolf ish Hoplias malabaricus, which is comprised of several cryptic species that present a wide variety of diploid chromosome numbers and sex chromosome systems, resulting in the identiica- tion of seven distinct karyomorphs (A–G), was investigated using a combination of molecular and cytogenetic tools. Deep sequence divergences for both karyomorphs were observed and indicate a long period of reproductive isolation between karyomorphs A and D. Additionally, one individual with 61 chromosomes was identiied, which, as far as is known, is the irst case of natural triploidy resulting from the hybridization between these highly differentiated karyomorphs of H. malabaricus. Molecular and cytogenetic analyses revealed that this allotriploid specimen carries two sets of mater- nal chromosomes from karyomorph D (2n = 40) and one set of chromosomes from karyomorph A (n = 21). Moreover, ribosomal sites and active nucleolus organizer regions from both parental con- tributors were found in the triploid hybrid. Considering the signiicant genetic distances between karyomorphs A and D, one of the primary reasons for the lack of recurrent reports of hybridization in the H. malabaricus species complex may be due to post-zygotic barriers, such as hybrid sterility or unviability. © 2014 The Fisheries Society of the British Isles Key words: cytogenetic mapping; Erythrinidae; genetic divergence; post-zygotic barrier; reproductive isolation. INTRODUCTION Hoplias (Characiformes, Erythrinidae) is the most diverse genus within the Erythrinidae family, which is composed of 10 species arranged in two main groups. The Hoplias lacerdae group comprises ive species, while Hoplias malabaricus (Bloch 1794) group is represented only by a single species. Hoplias malabaricus shows a †Author to whom correspondence should be addressed. Tel.: +55 38800479; email: utricardo@ibb.unesp.br 1 © 2014 The Fisheries Society of the British Isles