Liver transcriptome analysis in polar cod (Boreogadus saida) exposed to the water-accommodated fraction of crude oil
Polar cod (Boreogadus saida), a key arctic fish species spawning during the polar night, may be at risk for crude oil exposure during this potential sensitive life stage. This study investigates the effects of crude oil exposure on Polar cod during spawning season. Wild-caught polar cod were exposed to crude oil water accommodated fraction (WAF) (start concentrations of sum of 44 polycyclic aromatic hydrocarbon (sum 44 PAHs) at 12.5 µg/L) from pre-spawning to post-spawning.  The exposure system consisted of an oiled-rock-column system where running though sweater delivers WAF in the fish tank at decreasing concentrations over time. Samples were taken at three time-points (pre-spawning, spawning window, and post-spawning) and used to evaluate changes in reproductive endpoints such as gonad histology, plasma steroid hormones and sperm motility. For RNA-extraction and sequencing, liver samples from both oil-exposed and control groups of female fish (n = 5 per group) were taken at 47 days after experiment start and submitted for sequencing. RNA-seq analysis showed that hundreds of genes were differentially expressed in the liver.