Long-term exposure of Atlantic cod (Gadus morhua) to components of produced water: condition, gonad maturation, and gene expression

Effects related to offshore contamination have been observed in gadoid species in the North Sea, but uncertainties regarding exposure conditions have led to the need for environmentally relevant exposure studies. In the current study, Atlantic cod (Gadus morhua) were sampled at regular intervals during an 11-month continuous or pulsed water-borne exposure to a mixture of produced water components. There was variation in time to female maturation between and within treatment groups; although differences were not significant, there was a tendency towards delayed maturation in intermittently exposed females not seen in continuously exposed females. Physiological parameters such as condition factor, liver somatic index, gonadosomatic index, or hematocrit did not appear to be affected by the treatments. A range of toxicologically relevant genes were differentially expressed in the exposed fish, including AhR-responsive genes (CYP1A, UDP-GT) and genes relevant to immune function (complement C3, MHC 1, CYP27B), apoptosis (PERP), and oxidative stress (hepcidin, serotransferrin, glutathione peroxidase). Although powerful in their depiction of the complexity of cellular responses to environmental stressors, the use of molecular tools should be accompanied by biochemical and physiological endpoints, and results should be holistically interpreted in terms of individual health and function.