Long-term experiment testing the effects of crude oil on polar cod

Jasmine Nahrgang
UiT – The Arctic University of Norway

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The environmental effects of petroleum activities and, in particular, the consequences of larger oil spills for fish stocks and fisheries, have been central issues in Norway since the 1970s. One of the fundamental and enduring challenges for ecosystem management is to understand how exposure to petroleum related compounds affects different life stages of fish and the consequences for individual survival and fitness.

Decades of research have identified early life stages as the most sensitive phase of life in fish. However, the energetical impact and endocrine disruptive effects of crude oil on adult fish undergoing gonadal maturation and the following impact on gamete quality and embryo development constitutes a major knowledge gap.

During the polar night, Arctic fish undergo gonadal maturation to time the hatching of their early life stages to the spring bloom. This period may also coincide with increased risks of accidental oil spills, enhanced by challenging environmental conditions for oil spill clean-up. In order to characterize the sensitivity of reproducing polar cod to a crude oil water accommodated fraction (WAF), Nansen Legacy postdoctoral fellow, Ireen Vieweg (UiT), brought many hundreds of live polar cod to Tromsø from a cruise in 2018.

Polar cod is a key component of Arctic marine food webs and biological effects of crude oil on its early life stages or reproducing adults may have significant impacts on its populations. The study aimed at characterizing the molecular and physiological effects in adults undergoing gonadal maturation with a special focus on reproductive and energetical endpoints. The combined effects of crude oil WAF exposure and food ration were investigated to determine whether specimens under restricted feed supply would show enhanced sensitivity.

In her master thesis from the same experiment, Leah Strople (UiB) reports on an advancement in gonadal development in WAF exposed specimens. Of the WAF exposed females, 90 % had already spawned compared to 56 % of the controls by the end of the experiment. Moreover, there was a significant reduction in the relative expression of specific genes related to gonadal maturation (e.g. estrogen receptor 1 and vitellogenin) in exposed groups. Transcriptome mapping revealed the differential regulation of 947 hepatic genes in female polar cod. Exposure of males to the WAF did not lead to the disruption in any of the endpoints including the gonadosomatic index and sex steroid hormones (testosterone and 11-ketotestosterone).

Similarly, food ration did not have a consistent effect on any of the endpoints. Contrary to the results presented, earlier studies on crude oil and petroleum compound exposure have predominately reported a delay and not an advancement in gonadal development. This difference may be explained by variations in the timing of exposure during the reproductive cycle.