Physiological impact of waterborne crude oil exposure to reproducing polar cod (Boreogadus saida)

Abstract

Climate change-driven sea ice decline is increasing access to Arctic oil reserves and shipping routes, raising the risk of oil spills. Harsh polar conditions of extreme cold, darkness, and unpredictable weather will exacerbate these risks. The polar cod (Boreogadus saida), a key species in the Arctic ecosystem, may be particularly affected. With its spawning window in January and February, an oil spill during the polar night could disrupt reproductive development and spawning activity. To investigate this, adult polar cod were exposed to two concentrations (high and low) of the water-soluble fraction (WSF) of crude oil for 20 days (25.11.22–15.12.22) during late gonad development, one month before spawning. The fish were exposed using crude oil-coated gravel column, simulating the decline of polycyclic aromatic hydrocarbons (PAHs) due to weathering. Fish were sampled throughout the exposure period and spawning window. Female polar cod exposed to high WSF levels (64.2 ± 25.35 µg/L PAHs) showed a significant advancement in reproductive development, spawning 20 days earlier than unexposed females. By the time the first unexposed female entered the regressing stage, 86% of the high-exposure group had already spawned. Low WSF exposure (19.29 ± 0.36 µg/L PAHs) resulted in a 6-day advancement. Estrogen levels did not significantly change, but elevated testosterone levels were found in the active spawning phase of the high-exposure group. In the high-exposure tank, with the greatest advancement in spawning time, a significant reduction in fertilized egg diameter was observed compared to all other experimental tanks. In males, exposure to WSF did not affect reproductive development, GSI, testosterone (T), or 11-ketotestosterone (11-KT). These findings support the results of previous studies that exposure to crude oil in the late stages of vitellogenesis leads to an advancement in gonadal development. The present study suggests that this advancement may lead to premature spawning and reduced egg quality.