RÉSUMÉ
The integrated System of Treatment of Liquid Effluent, SITEL, has eight tertiary lagoons connected in series, where occurred a natural fish sttlement of several species of the area. Gills of forty five specimens of Astyanax jacuhiensis collected in the tertiary lagoons 1 and 8 and twenty four in the arroio Bom Jardim were analyzed with paraffin routine histological technique and stained with H&E and PAS (periodic Acid of Sciff). Anomalous tissues were observed in all three sites, being more intense in samples from lagoon 1 than from lagoon 8. The anomalies observed in arroio Bom Jardim samples are less tissue, increase in the number of secretory mucous cells, fusion of the secondary branchial lamellae, disarrangement of the epithelial tisue and aneurysms. The fact anomalies at the lagoon 1 are more intense than observed in lagoon 8 suggests there is a reduction in the effect of the eflluent along the tertiary system...