RESEARCH PAPER Variable B chromosomes frequencies between males and females of two species of pufferfishes (Tetraodontiformes) Rafael Bueno Noleto • Marcelo Ricardo Vicari • Marta Margarete Cestari • Roberto Ferreira Artoni Received: 20 April 2011 / Accepted: 28 July 2011 / Published online: 5 August 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Cytogenetic analysis in two sympatric species of pufferfish from Parana ´ Coast, Brazil, Sphoeroides spengleri (Tetraodontidae) and Chil- omycterus spinosus (Diodontidae) revealed the pres- ence of 2n = 46 and 2n = 50 chromosomes, respectively. In S. spengleri, the double FISH tech- nique with 5S and 18S rDNA probes showed no syntenical organization, with both multigene families occupying a terminal position on the chromosomes. In S. spengleri the poor pattern of heterochromatin distribution is discussed about its relation with the compactness of their genome. On the other hand C. spinosus presented conspicuous blocks occupying the short arms of several chromosomes, possibly consequence of an accumulative process. Heterochro- matic supernumerary chromosomes were detected in both species, however in S. spengleri they were presented as microchromosomes varying of 0–3 and being more frequent in females than in males, possibly as result of a preferential segregation. Conversely in C. spinosus an extra chromosome was restricted to the males, which to behave as univalent during meiosis. In view of these peculiarities we hypothesized a possible relationship between B chromosome and sex determi- nation, although others aspects on accumulation, maintenance, and frequency of these extra elements were also considered, focusing on the parasitic model. In spite of the karyotypic diversity and others genetic peculiarities in Tetraodontiformes, this corresponds the third report of the occurrence of chromosomes B in the group. Keywords Diodontidae  Tetraodontidae  B chromosomes  Pufferfish Introduction The Order Tetraodontiformes comprises approxi- mately 400 species of highly derived acanthomorph fishes which are grouped into 8–10 families, although many phylogenetic questions, especially their basal relationships, remain unclear (for review see Yama- noue et al. 2008). They are notable for their excep- tional degree of diversity in morphological structure, shape, size, and biological traits. The diversification of the tetraodontiforms has been accompanied by reduction in genome size, once a massive DNA loss R. B. Noleto (&) Departamento de Biologia, Universidade Estadual do Parana ´, Campus de Unia ˜o da Vito ´ria, Unia ˜o da Vito ´ria, Prac ¸a Cel. Amazonas, Caixa Postal 291, Unia ˜o da Vito ´ria, Parana ´ 84600-000, Brazil e-mail: rafanoleto@yahoo.com.br M. R. Vicari  R. F. Artoni Departamento de Biologia Estrutural, Molecular e Gene ´tica, Universidade Estadual de Ponta Grossa, Ponta Grossa, Parana ´, Brazil M. M. Cestari Departamento de Gene ´tica, Universidade Federal do Parana ´, Curitiba, Parana ´, Brazil 123 Rev Fish Biol Fisheries (2012) 22:343–349 DOI 10.1007/s11160-011-9231-9