Laboratory and field validation of multiple molecular biomarkers of contaminant exposure in rainbow trout (Oncorhynchus mykiss)

Abstract

Novel primers for three different genes (CYP1A1, vitellogenin, and metallothionein) for use in reverse transcription-polymerase chain reaction (RT-PCR) were developed and tested in laboratory flow-through experiments using model compounds benzo[a]pyrene, estradiol, and cadmium. Field validations of the molecular biomarkers were performed using 8-d or 48-h in situ, cagedexposure of juvenile rainbow trout (Oncorhynchus mykiss). Expression levels of genetranscription(messengerRNA [mRNA]) were monitored in gill and liver tissue after exposure at sites downstream of a known source of creosote contamination in the Little Scioto River (Marion, OH, USA) and metals and hydrocarbon contamination in Dick's Creek (Middletown, OH, USA). Significant increases of liver cytochrome P4501A1 gene (CYP1A1) and vitellogenin were measured in both streams at sites downstream of contaminant sources. Significant increases of gill CYP1A1 were also observed. Significant increases of gill and livermetallothionein occurred in Dick's Creek. A sample of gill tissue taken from each fish prior to placement in the Little Scioto River provided a pre-exposure control measurement for each individual. Expression of CYP1A1 and vitellogenin in trout at both streams indicated that exposure to bioavailable hydrocarbons and endocrine-disrupting compounds had taken place. Previous to this study, estrogenic compounds had not been detected in the Little Scioto River. Metallothionein expression confirmed the presence of metals in Dick's Creek. These results suggest a mixed contaminant environment that poses physiological hazard to existing teleost populations. Multiple molecular biomarkers provided a sensitive, physiologically based method of determining contaminant presence and bioavailability to aquatic organisms.