Monitoring of inner Oslofjord using Atlantic cod (Gadus Morhua) as a bioindicator

Abstract

Inner Oslofjord is vulnerable to contamination due to its enclosed features and threshold separated pools. The area is one of the most densely populated in Norway, which entails to high release of environmental contaminants. The purpose of this study was to investigate the effects of these contaminants on the cod populations in the area. This was conducted by using the outer fjord as a reference site. Both physiological indices and biomarkers were used to assess the effects from planar organic compounds, genotoxic compounds and heavy metals. In the middle of December 2017, 80 cod specimens were collected in total, 40 from each of the sites. The physiological indices showed little difference. Both condition index (CI) and liver somatic index (LSI) showed no difference, but there was found higher values for gonadosomatic index (GSI) in the males from inner fjord. In cod bile, higher concentrations of 2,3-ring and 4-ring polyaromatic hydrocarbon (PAH) metabolites were found in inner fjord compared to outer fjord. This indicates a higher exposure of PAHs for cod in the inner fjord compared to the outer fjord. No difference was found in Metallothionein content in fish liver when comparing the monitored areas, which indicates a heavy metal exposure of similar degree. In blood, the δ-aminolevulinic acid dehydratase (ALA-D) activity did not show any significant difference regarding lead exposure in the cod sampled in inner fjord compared to the ones sampled in outer fjord. The EROD activity measured in the liver did also not show any significant difference between the cods from inner and outer fjord, indicating an exposure of planar organic contaminants like polychlorinated biphenyls (PCBs) of similar degree.