Sensitivity of adult polar cod (Boreogadus saida) to the water-soluble fraction of crude oil under different food regimes

The Arctic marine environment is characterized by substantial variation in food availability over an annual cycle and Arctic organisms can overcome food restrictions through the accumulation of energy reserves during favorable feeding conditions. Food availability and energy accumulation are essential to ensure reproductive development and growth. The present study aims at investigating the role of food availability for a key species of the Arctic food web, polar cod (Boreogadus saida), especially in combination with an anthropogenic stressor. Increased industrial activity in the future Arctic introduces a higher risk for pollution in Arctic waters by for instance petroleum compounds. The objective of the present study is to examine how different food regimes influence the sensitivity of polar cod to crude oil exposure. In an experiment, 360 polar cod will be exposed to either the water-soluble fraction (WSF) of crude oil at an environmentally relevant level or to control conditions (no exposure to WSF). These treatments are further divided into two food regimes (high and low food ration) with 3 replicate tanks per treatment. An additional tank will hold 40 control fish to follow the natural gonadal development of the fish, resulting in total 400 polar cod for the experiment. The exposure design simulate an oil spill scenario during early winter, exposing fish to exponentially decreasing levels of crude oil WSF from a late gonadal maturation stage (December) until post-spawning (March). The crude oil WSF will be generated by an oiled rock column system (Carls et al. 1999), also used in previous polar cod experiments (e.g. Nahrgang et al. 2010a; 2016, Frantzen et al. 2012). The aqueous oil concentrations are expected to be initially about 80 µg/L for the sum of 26 PAHs, which is known to cause sub-lethal effects in fish but no mortality (Nahrgang et al. 2010a). Under restricted food access, oil exposure is expected to affect the fitness of the fish and alter the energy allocation towards detoxification process at the expense of reproductive development. Hence, exposed fish might show a reduced fecundity and growth compared to control fish, however these effects are sub-lethal and not expected to cause pain or distress for the fish. The sensitivity towards crude oil exposure will be examined based on changes in growth, gonadal development, fecundity and bioenergetics during the experiment (in total 5 sampling points). Feral fish are required for this experiment to ensure the natural reproductive development. Number of fish and replicate tanks are kept at a minimum in order to reduce the amount of experimental animals. Anesthesia will be used to avoid any discomfort or pain during tagging and growth measurements. All biological samples will be taken post mortem.
Results obtained from the present study will improve our understanding of how annual variation in food availability affects the sensitivity of maturing and post-spawning polar cod towards crude oil exposure. This data is of great interest for stakeholders from the industry and environmental management in order to foresee consequences of a potential oil spill in the Arctic during polar night.