SUMMARY
As parts of the environmental studies conducted by INPA, from 1980 to 1986 in conjunction with ELETRONORTE in the area of influence of the Tucuruí Hydroeletric Instalation, twenty species of fish of the family Anostomidae from de lower Tocantins river, between Cametá and Itupiranga, state of Pará, are redescribed and ilustrated: Leporinus affins, L. tigrinus, L. desmotes, L. sp. 4, L. trifasciatus, L. friderici, L. sp. 1, L. sp. 2, L. sp. 3, L. granti, L. pachiycheilus, Laemolyta petiti, L. taeniata, Anostomoides laticeps, A. sp. 1, Anostomus ternetzi, Leporellus vittatus, Schizodon vittatus, Sartor tucuruiense and Abramites hypselenotus. Five of the species found (Laemolyta petiti, Leporinus affinis, L. sp. 2, Anostomoides sp. 1 and Sartor tucuruiense) have only been reporterd from the Tocantins-Araguai basins. On the other hand, several anostomid species, thar are widely distributed in the Amazon basin, were not encountered in the lower Tocantins basin. This fact may suggest that, from the rest of the Amazon basin and shows a high degree of endemimism. Most of the fish species are widely distributed in the lower Tocantins river but some showed a distinct preference for certain biotopes, for example Leporinus pachycheilus, L. desmotes, L. sp. 1 and Sartor tucuruiense for rapids; Leporinus sp. 3, Anostomus ternetzi for "igarapés", Schizodon vittatus and Laemolyta taeniata, for the analysis of meristic and morphometric characters, especially the number, form and distribution of the teeth, position of the mouth and number os scales.