CYP1A Expression in Caged Rainbow Trout Discriminates Among Sites with Various Degrees of Polychlorinated Biphenyl Contamination

It has become increasingly apparent that resident fish can develop resistance to chemicals in their environment, thus compromising their usefulness as sentinels of site-specific pollution. By using a stream system whose resident fish appear to have developed pollutant resistance (Brammell et al., Mar Environ Res 58:251–255, 2005), we tested the hypothesis that the pollutant-inducible biomarker, cytochrome P4501A (CYP1A), as measured in field-caged juvenile rainbow trout (Oncorhynchus mykiss), would reflect relative pollution differences between reference and polychlorinated biphenyl (PCB)-contaminated sites. Trout were caged in the Town Branch/Mud River system (Logan County, KY), a stream system undergoing remediation for PCBs. Fish were held in remediated (Town Branch), unremeditated (Mud River), and reference sites for 2 weeks during spring 2002. At the end of this period, gill and hepatic CYP1A expression were measured. To evaluate the relative PCB exposure of caged trout and provide a reference point against which to calibrate CYP1A response, PCB levels were quantified in sediments from each site. Hepatic CYP1A expression in caged trout clearly detected the presence of PCBs in the Town Branch/Mud River stream system. Sediment PCB levels and hepatic CYP1A expression in caged trout produced identical pollution rankings for the study sites. Gill CYP1A expression, although suggestive of site differences, was not statistically different among sites. Unlike resident fish, which failed to show site differences in hepatic CYP1A expression in this waterway (Brammell et al. 2005), caged fish proved to be a sensitive discriminator of relative PCB contamination in this system. In summary, we determined that CYP1A expression in caged fish reflected relative in situ pollutant exposure. The exposure paradigm confirmed that 2 weeks was a sufficient caging period for evaluating CYP1A response in this species at these temperatures (13–19°C). In addition, these studies demonstrate that tissue-specific CYP1A expression can provide insights into likely routes of exposure. We conclude that CYP1A expression in caged trout is a reliable and inexpensive first-pass determination of relative environmental pollutant exposure and bioavailability in aqueous systems.