The fish fauna of the Iguaçu river is well known for its high degree of endemism and for the absence of several fish families common in other Brazilian basins (Júlio Jr. et al., 1997). The Iguaçu falls have acted as an efficient geographical barrier between the ichthyofauna from the first and the second plateaus along most of the river length (Maack, 1968). Garavello et al. (1997) described 36 endemic species, 11 introduced species and 3 exotic species at Iguaçu river. The occurrence of Hoplias malabaricus in this basin, popularly known as traíra, is quite controversial being referred as an introduced species (Garavello et al. op. cit.). Dergam et al. (1998) stated that the introduction of H. malabaricus in the Iguaçu river could have been done from the Tibagi headwaters, based on the similar genetic patterns of the populations, as well as in the proximity of both rivers.
Cytogenetical data clearly indicate that H. malabaricus is a complex species, probably related to its wide distribution over Neotropical region, requiring a careful taxonomic revision (Bertollo et al., 1983; Dergam and Bertollo, 1990; Scavone et al., 1994; Bertollo et al., 2000). Bertollo et al. (2000) differentiated seven distinct cytotypes in this fish group, based on their chromosome numbers and morphology and the absence or occurrence of distinct sex chromosome systems.
The present paper aimed to contribute for a better understanding of the biogeography of H. malabaricus and its probable natural origin on the Iguaçu river basin.