Nearly 2,500 fries of Brycon cephalus with a standard length from 0.8 to 5.0cm were collected in Catalão Lake, on the right bank of Negro River and close to Marchantaria Island in Solimões River, in the State of Amazonas. A sample of 136 fishes was taken for parasitological examination and the remaining were placed in tanks at a fish fanning station for 30 days. Of the 136 fishes 49 (36%) were infected by trematodes metacercariae, 32 (23,5%) by the nematode Spirocamallanus inopinatus, 26 (19%) by the monogenoidea Jainus amazonensis, 3 (2%) by the protozoan Trichodina sp., 1 (0,7%) by the acanthocephala Echinorhynchus sp. and 2 (1,5%) by stages of cestoda larval. After 30 days a sample of 60 fish from the fish kept in the tanks was examined: 42 (70%) were infected by J. amazonensis, 14 (23%) by S. inopinatus, 9 (15%) by trematode metacercariae and 2 (3%) by Echinorhynchus sp. The highest average intensity and abundance values were observed related to J. amazonensis (342 and 65), followed by S. inopinatus (1 and 0,3), Trematoda (5 and 2), Cestoda (70 and 1), Echinorhynchus sp. (1 and 0,007) and Trichodina sp. (13 and 0,3). At the fish farming station the average intensity and abundance values were also higher for J. amazonensis (222 and 115) in relation to the other groups. On the other hand, J. amazonensis presented the highest average intensity and the lowest prevalence values in the wild. There was a variation on the parasitological fauna and infestation indexes after 30 days of permanence at the fish farming station.
parasite-fish; Brycon cephalus; wild fish; parasitary indexes