Strain specific patterns in temperature adaptation of CYP isoenzyme levels in Atlantic salmon (Salmo salar)

Several factors, such as developmental stages, sex, diet and seasonal changes in steroid levels and temperature are known to affect the basal levels of cytochrome P450 (CYP) isozymes. Within their natural ecosystem many fish species are able to survive and remain active over a wide range of temperature. This is largely attributable to adaptive changes which allow the organism to exhibit similar rates of physiological activity despite widely differing body temperatures. Compensatory mechanisms at the molecular level may involve changes in enzyme levels and alteration of the microenvironment where the enzyme function. Such changes at the molecular level could have a major influence in determining the capacity of xenobiotic metabolizing enzymes in fish subjected to temperature fluctuations. In this study, we have evaluated the patterns in temperature adaptation of two genetic strains (the Namsen River strain and the Norwegian salmon procreation strain (NLA)) of Atlantic salmon, adapted to 4, 9, and 14°C. The activity of 7-ethoxyresorufin O-deethylase (EROD) was studied, in addition to immunochemical analysis of CYP1A, 2K- and 3A-like proteins in liver microsomes, demonstrating different temperature patterns in the two strains. EROD activity, CYP1A, CYP3A- and CYP2K-like protein levels showed higher levels at 9 and 14°C, compared to 4°C adapted fish in the Namsen-strain. Also, 9°C adapted fish from the Namsen-strain showed higher EROD, CYP3A- and CYP2K-like protein levels compared with the NLA-strain adapted to the same temperature. The present study has considered a factor, namely genetic background, that has not been very much evaluated previously in the use of CYP1A as a biomarker for environmental monitoring. Thus, the genetic history of fish strains should be investigated and considered carefully before using them in biomonitoring purposes. Supported by the Norwegian Research Council (NFR).