Effects of chronic dietary petroleum exposure on reproductive development in polar cod (Boreogadus saida)

Abstract

Increasing human activities in the Arctic raise the risk of petroleum pollution, thus posing an elevated risk for Arctic organisms to be chronically exposed to petroleum compounds. The endocrine disrupting properties of some of these compounds (i.e. polycyclic aromatic hydrocarbons [PAHs]) present in crude oil may have negative effects on the long and energy intensive reproductive development of polar cod (Boreogadus saida), an Arctic keystone species. In the present study, selected reproductive parameters were examined in feral polar cod exposed to crude oil via a natural diet (0.11, 0.57 and 1.14μg crude oil/g fish/day [corresponding to low, medium and high treatments, respectively]) for 31 weeks prior to spawning. Fish maturing in the current reproductive period made up 92% of the experimental population while 5% were immature and 3% were identified as resting fish. Phase I metabolism of PAHs, indicated by ethoxyresorufin-O-deethylase (EROD) activity, showed a dose-dependent increase in high and medium crude oil treatments at week 6 and 22, respectively. Decreasing EROD activity and increasing PAH bile metabolite concentrations over the experimental period may be explained by reproductive maturity stage. Significant alterations in sperm motility were observed in crude oil exposed males compared to the controls. The investigated somatic indices (gonad and hepatic), germ cell development and plasma steroid levels (estradiol-17β [females], testosterone [males and females] and 11-ketotestosterone [males]) were not significantly altered by chronic dietary exposure to crude oil. The environmentally realistic doses polar cod were chronically exposed to in this study were likely not high enough to induce adverse effects in this ecologically important fish species. This study elucidated many baseline aspects of polar cod reproductive physiology and emphasized the influence of maturation state on biomarkers of PAH biotransformation (EROD and PAH bile metabolites).

Keywords: Gonadal histology; Polar cod (Boreogadus saida); Polycyclic aromatic hydrocarbons (PAH); Reproductive development; Sex steroid hormones; Sperm motility.