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Abstract:
Helminths from the intestinal tracts of fish called "pacus" were studied. The fish were found only in
rapids areas of Northeastern tributaries of the Amazon River. Since this species, Mylesinus paraschomburgkii JÉGU, SANTOS & FERREIRA, 1989, does not migrate, each river has a separate population in
its upper reaches. These populations are believed to have been isolated from each other, by high water,
since the last glaciation some 12,000 years ago. It was thought that differences in the helminth faunas
might reflect such isolation. Collection sites were: the Uatumà, Pitinga and Capucapu Rivers, Amazonas
State (considered one population), the Trombetas and Jari Rivers, Pará State and the Araguari River, Amapá State. Seven species of trematodes were found, namely: Alphamphistoma canoefomta gen. et sp.
nov. which has a body that is extremely concave ventrally and short ceca; Betamphistoma jariense gen. et
sp. nov. which has parallel testes and a cirrus sac with heavy muscular walls, Gammamphistoma collaris
gen. et sp. nov. a small species with large suckers and an anterior collar; Deltamphistoma pitingaense gen.
et sp. nov. a form with short to moderately long ceca and testes that extend laterally beyond them;
Zetamphistoma compacta gen. et sp. nov. with a wide body that is convex on both surfaces and thin
marginally; Pseudocladorchis cyclindricus (DIESING, 1836) with a large cylindrical body. parallel testes
and vitelline follicles that extend anteriorly to beyond them and the Haploporidae, Saccocoelioides
rotundus sp. nov. which has a compact body, rounded posteriorly and vitellaria that nearly surround the
testis. P. cylindricus was found at all sites except the Jari River. The latter has also been repotted from
other hosts. From three to four species of trematodes were found in each host population and some of these
appear to be useful as markers. D. pitingaense was found only in the Amazonas State population and B.
jariense appeared only in fish from the Jari River. The haploporid, S. rotundus was found in the Trombetas
River population exclusively. The most typical trematode from Araguari River hosts was Z. compacta but
this species was also found in fìsh from the Trombetas River. Two nematode species representing the
family Atractidae, namely: Proatractis sp. and Rondonia rondoni TRAVASSOS, 1919, were found in all
the fish examined. The former inhabits the pyloric ceca and the fìrst three or four centimeters of upper
intestinal tract whereas R. rondoni completely packs the rest of the gut. Another nematode, Cucullanus sp.
(Cucullanidae), was found in numbers from 1-24 in the upper intestinal tracts of hosts from the Trombetas
River only.
