MATERIAL AND METHODS
Forty-six specimens of Hoplias malabaricus were sampled in the main stream and in marginal lakes belonging to the Iguaçu river. Twelve specimens were collected from a population in the western region of the Paraná State (Brazil), in the township of Nova Prata do Iguaçu. Thirty-four specimens were captured from a population in the eastern region of the same state, in the township of Palmeira (Fig. 1).
Metaphases were obtained according to Bertollo et al. (1978), using a cell suspension from the anterior kidney, after in vivo treatment with colchicine (1ml/100g body weight). The detection of the nucleolar organizing regions (NORs) and the constitutive heterochromatin followed the methods described by Howell and Black (1980) and Sumner (1972), respectively. Chromomycin A3 staining was performed according to Schmid (1980). Chromosomes were arranged by size and shape, according to Levan et al. (1964) and the cytotypes were classified as stated by Bertollo et al. (2000).