Faunistic comparisons - In the two streams, 71 fish species of 21 families were collected, as listed by Pavanelli and Caramaschi (1997).
Sieve samples. - A total of 2,834 specimens were collected using sieves. The total CPE was 25,510. Species considered abundant were Serrapinnus notomelas, Phalloceros caudimaculatus, Cichlasoma paranaense, Astyanax altiparanae, Aphyocharax cf. anisitsi, Hypostomus ancistroides and Hoplias aff. malabaricus; these represented 82.7% of the total CPE. The Caracu contributed much higher CPE than the São Pedro, 17,716 vs. 7,794, respectively. The Caracu headwater yielded a lower CPE (4,189), while the intermediary site (6,997) and the mouth (6,529) did not show marked difference in abundance. For the São Pedro, the difference between the headwater and the mouth was large, CPE 153 vs. 7,641, respectively.
The results for species constancy at the different sampling sites of the two streams are shown in Fig. 3. It showed that excepting Caracu headwater, all the sampling sites presented more occasional species than accessories and constants. The data for cumulative frequency indicated that only the mouths of the streams did not reach an asymptote (Fig. 4).
The diversity results are expressed in the form of a spectrum of diversity, as proposed by Margalef (1986), adding the samples spatially (Fig. 5) and temporally (Fig. 6) for each stream. Both of them revealed diagonal patterns, but it is more marked spatially.
The stream's headwaters were not so close, but the mouths were closer to each other, and the intermediary site was in an intermediate position (Fig. 7B). Astyanax scabripinnis (species code 5) was found only in S. Pedro headwater, and this species is placed in Fig. 7A in a similar position of that environment in the Fig. 7B.
Callichthys callichthys (code 8) occurred exclusively in both headwaters, and its position was in an intermediary place (Fig. 7A) between the two headwaters (Fig. 7B).
Other species were distributed at Fig. 7A in places closer to the sampling sites where there occurred, or, if widespread, in an intermediate position between the sites (Fig. 7B). Net samples. - A total of 995 specimens were collected using gill nets.
The total CPE was 14,420. Species considered abundant were Astyanax altiparanae, Prochilodus lineatus, Acestrorhynchus lacustris, Hoplias aff. malabaricus, and Steindachnerina insculpta, which made up 66.0% of the total CPE. There was a large difference in abundance between the intermediary site (4,741) and the mouth (10,579). The constancy values for the species collected with nets in the two São Pedro sites and one Rio Paraná site are shown in Fig. 8. All the sites presented more occasional species than accessories and constants.
The Rio Paraná site presented 24 exclusive species, and most of the other was common to São Pedro mouth. Only Prochilodus lineatus was constant in the three sites.
Cumulative frequency is showed in Fig. 9. As observed for the sieve collections, the fauna at the São Pedro mouth did not reach an asymptote for cumulative frequency (Fig. 9). The diversity spectra are shown spatially (Fig. 10) and temporally (Fig. 11) for the net collections in the São Pedro. The first one presented a diagonal pattern and the second an almost rectangular one.
Table 1 shows the similarity between sampling sites. The most similar sites were the Rio Paraná and the São Pedro mouth, followed by the São Pedro intermediary site.