Cytogenetic damage in fish (Oncorhynchus mykiss) exposed in situ to water from a polluted river|Danno citogenetico in pesci (Oncorhynchus mykiss) esposti in situ ad acqua di fiume inquinata.

Specimens of rainbow trout (Oncorhynchus mykiss) were exposed in situ for 7, 15, and 30 days to the water of the Po River either upstream or downstream the immission of the Lambro River, a small affluent which is highly polluted with industrial wastes. A third group of animals was maintained as control in aquarium with a flow of unchlorinated fresh water. Blood smears were obtained from each of the 90 trout specimens and examined under the microscope. The number of micronucleated erythrocytes (MNE) was registered by scoring at least 2,000 cells per animal. No increases in the number of MNE was detected in the animals exposed upstream the confluence, as compared to controls. Conversely, a significant increase in the frequency of MNE after 7 days of exposure to the water of the downstream site was observed. This frequency remained elevated, yet not significantly, after 15 and 30 days of exposure. This study demonstrates the validity of in situ exposure and the usefulness of cytogenetic end-points for environmental biomonitoring.