Synaptonemal complex analysis in the fish species Piaractus mesopotamicus

The surface-spreading technique for visualization of whole cell synaptonemal complex (SC) complements was employed to study the chromosome synapsis in spermatocytes of P. mesopotamicus, C. macropomum and in their interspecific hybrid (tambacu) with the main objective to analyze possible errors in chromosome pairing that could result in hybrid sterility. SC analysis showed that the parental species P. mesopotamicus and C. macropomum have 27 bivalents homogeneously synapsed. The SC in spermatocytes from the hybrid tambacu showed gross meiotic configurations in all cells analyzed. The spermatocytes exhibited a few chromosomes or well synapsed chromosome segments, while many chromosome segments did not have any synapsis. This result, allied to other genetical and cytogenetical evidence, reinforces the hypothesis that the hybrid tambacu is sterile. Further studies involving other aspects, such as behavior and physiology, should be conduced before the introduction of these hybrids in rivers and lakes.Depto. de Morfologia Instituto de Biociência UNESP, 18618-000, Botucatu, SPDepto. de Biologia Instituto de Biociência USP, São Paulo, SPCtro. Pesquisa Treinamento A. IBAMA, Pirassununga, SPDepto. de Morfologia Instituto de Biociência UNESP, 18618-000, Botucatu, S