Fish hepatic micronuclei as an indication of exposure to genotoxic environmental contaminants

An In vivo assay protocol for detecting hepatic micronuclei in fish was performed to evaluate whether this genotoxic response could serve as a bioindicator of environmental exposure to genotoxic substances. The incidence of hepatic micronuclei was compared in brown bullheads (Ameiurus nebulosus) with external lesions collected from a contaminated site and fish showing no externally visible pathologies collected from reference sites. Laboratory experiments were performed by exposing hatchery-raised rainbow trout (Onchorhynchus mykiss) to a pulp mill effluent extract (XAD-4-NaOH) with known genotoxic activity. Both bullhead and trout were injected with allyl formate to induce hepatic necrosis and regenerative proliferation of hepatocytes prior to examining the liver tissue for micronuclei. An elevated incidence of hepatic micronuclei was observed in Hamilton Harbour bullheads showing visible lesions relative to the micronucleus incidence in bullheads from reference sites with no external pathologies. Similarly, rainbow trout exposed to pulp mill effluent extracts exhibited an elevated incidence of hepatic micronuclei compared to controls. These results suggest that the hepatic micronucleus assay could serve as a valuable biomonitoring tool for assessing the impacts of genotoxic environmental contaminants on fish. (C) 1997 by John Wiley & Sons, Inc.