RAPD primers amplified a total of 74 bands in all samples taken together (Figure 2). High levels of within-population genetic variation were suggested by a positive correlation between the number of scorable bands and sample size (r = 0.82). The population with the highest number of scorable bands was Porto Rico (51 bands), while the lowest number of bands was observed for Londrina (27 bands).
Although in many cases the alleles were not fixed (not present in all individuals of a given sample), some alleles were unique for some populations: in the Tibagi River, five alleles were unique to the Sertanópolis population, and one was unique to the Londrina population. In the Iguaçu, only one allele was unique to the Segredo population, and in the Paraná River, three alleles characterized the Porto Rico population, while two alleles were typical of the Reconquista population.
Five alleles were shared by at least one member of each population. Excluding alleles shared by members of all populations, the number of shared alleles among populations was also significantly correlated with sample size (r = 0.77).
The samples from Tibagi River and the Paraná River displayed high levels of variation, while the samples from Ponta Grossa and Segredo were very similar (Figure 2). All alleles of Ponta Grossa (Tibagi River) were also present in the population of Segredo (Iguaçu). The reverse did not happen, because the population from Segredo had 48 alleles, one third more than the population of Ponta Grossa (Figure 2).
Molecular similarity was represented by a phenogram (Figure 3). The matching matrix grouped all specimens into three major clusters. The first cluster was composed of four specimens from the Tibagi River at Sertanópolis. The second cluster included all specimens from samples of the Paraná River at Porto Rico, Reconquista, and Corrientes. This major cluster also included all specimens from Tibagi at Londrina, plus one of the specimens from the Tibagi at Sertanópolis, and another from the Iguaçu at Segredo. The third cluster joined all the specimens from the Tibagi at Ponta Grossa, and almost all the specimens from Segredo.