Cachama

CARYOLOGIA

Vol. 56, no. 4: 405-411, 2003

Cytogenetic characterization of hybrids offspring between Colossoma macropomum (CUVIER, 1818) and Piaractus brachypomus (CUVIER, 1817) from Caicara del Orinoco, Venezuela
M. NIRCHIO1, A.S. FENOCCHIO2, A.C. SWARÇA3, J.E. PÉREZ4, A. GRANADO5, A. ESTRADA6 and E. RON1
1 2

Escuela de Ciencias Aplicadas del Mar. Universidad de Oriente, Isla deMargarita, Venezuela. Apartado Postal 630-Porlamar. Universidade Federal do Paraná, Departamento de Genética, Centro Politécnico, Curitiba, Brazil e-mail: afenocch@fceqyn.unam.edu.ar. 3 Universidade Estadual de Londrina, Departamento de Biologia Geral, Caixa Postal 6001, CEP 86051-990, Londrina, PR, Brasil. e-mail: szwarcy@sercomtel.com.br. 4 Instituto Oceanográfico de Venezuela, Universidad de Oriente,Apartado 243, Cumaná, Venezuela. e-mail: jperez@ telcel.net.ve. 5 Instituto Limnológico, Universidad de Oriente, Caicara del Orinoco, Estado Bolívar, Venezuela. e-mail: limnologico@cantv.net.

Abstract - Conventional karyotype and nucleolar organizer regions (NORs) of C. macropomum x P. brachypomus hybrids and parental species are reported. A modal diploid number of 54 chromosomes and afundamental number (NF) of 108 were found for C. macropomum, P. brachypomus and their hybrids. P. brachypomus shows a pair of silver stained chromosomes, while cells with three and four Ag-NOR bearing chromosomes were observed in C. macropomum. The hybrids consistently presented cells with a single metacentric Ag-NOR bearing chromosome and cells with three Ag-NOR bearing chromosomes. The FISH techniquewas employed to localize 18S rDNA in the chromosomes of the parentals and the hybrids. In P. brachypomus the FITC signals appeared in the SM pair as when stained with silver salts. In C. macropomum the signals were evidenced in six chromosomes. In the hybrids, as expected, the FITC dots were observed in four chromosomes. All the techniques employed in the present work represent good tools toidentify the parentals and distinguish them of the hybrids. Key words: Fisheries; Interspecific hybrids; Colossoma macropomum; Piaractus brachypomus; Cytogenetic Monitoring; NORs; in situ hybridization.

INTRODUCTION The production of interspecific offsprings to obtain individuals in which the best characteristics of the parental species could converge has been one of the goals of aquaculturists(DUNHAM 1987; CHEVASSUS and DORSON 1990). In Latin America hybridization between different species of the Family Characidae has been

* Corresponding author: e-mail: nirchio@ci.udo.edu.ve

achieved with success in several Research Institutes. Particularly Colossoma macropomum and Piaractus brachypomus have been object of attention because of their high production yields, easiness for cultivation andmassive production of alevins under controlled reproduction conditions (ALMEIDA-TOLEDO et al. 1988; KOSSOSWKI et al. 1983; MARTINO 1994). The analysis of genome structure of hybrid fishes is necessary to achieve an adequate genetic evaluation in order to get a basic understanding that allows to distinguish the types of genet-

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FENOCCHIO, SWARÇA, PÉREZ, GRANADO, ESTRADA

and RON

icproducts resulting from a successful hybridization process (A LMEIDA-T OLEDO FILHO et al. 1994) and to assess the potential biological hazards of the hybrid to the genetic integrity of the parental species, wild or cultivated (PÉREZ and RYLANDER 1998). Cytogenetics provides some techniques that could help to understand better the behavior and structure of the chromosomes that was integrate in thehybrids. So, the analysis of the karyotype and principally of the nucleolus organizer regions (NORs) can be appropriate and sensitive methods to verify the ploidy levels as well as the origin of the chromosomes in fishes (ALMEIDA-TOLEDO FILHO et al. 1994; ZHANG and TIERSCH 1997). Locations of the NORs are easily detected by silver impregnation but this technique has the limitation imposed by...