INTESTINAL HELMINTHS AS POPULATION MARKERS OF THE AMAZONIAN FISH MYLESINUS-PARASCHOMBURGKII, WITH DESCRIPTIONS OF 5 NEW GENERA AND 7 NEW SPECIES OF TREMATODES

Helminths from the intestinal tracts of fish called ''pacus'' were stu died. The fish were found only in rapids areas of Northeastern tributa ries of the Amazon River. Since this species, Mylesinus paraschomburgk ii JEGU, SANTOS & FERREIRA, 1989, does not migrate, each river has a s eparate population in its upper reaches. These populations are believe d 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 wer e: the Uatuma, Pitinga and Capucapu Rivers, Amazonas State (considered one population), the Trombetas and Jari Rivers, Para Start and the Ar aguari River er. Amapa State. Seven species of trematodes were found, namely: Alphamphistoma canoeforma, gen. et sp. nov. which has a body t hat is extremely concave ventrally and short ceca: Betamphistoma jarie nse gen. ct sp. nov. which has parallel testes and a cirrus sac with h eavy muscular walls; Gammamphistoma collaris gen. et sp. nov. a small species with large suckers and an anterior collar; Deltamphistoma piti ngaense 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 cylindricus (DIESING, 1836) with a large , cylindrical body, parallel testes and vitelline follicles that exten d anteriorly to beyond them and the Haploporidae, Saccocoelioides rotu ndus sp, nov. which has a compact body, rounded posteriorly and vitell aria that nearly surround the testis. P. cylindricus was found at all sires except the Jari River. The latter has also been reported from ot her 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 Stare population and B. jar iense appeared only in fish from the Jari River. The haploporid, S. ro tundus was found in the Trombetas River population exclusively. The mo st typical trematode from Araguari River hosts was Z. compacta but thi s species was also found in fish from the Trombetas River. Two nematod e species representing the family Atractidae, namely; Proatractis sp. and Rondonia rondoni TRAVASSOS, 1919, were found in all the fish exami ned. The Former inhabits the pyloric ceca and the first three or four centimeters of upper intestinal tract whereas R. rondoni completely pa cks the rest of the gut. Another nematode, Cucullanus sp. (Cucullanida e), was found in numbers from 1-24 in the upper intestinal tracts of h osts from the Trombetas River only.