Abstract
Perch (Perca fluviatilis) has been used in biological effect monitoring in a program for integrated coastal fish monitoring at the reference site Kvadofjarden along the Swedish east coast, which is a site characterized by no or minor local anthropogenic influences. Using a set of physiological and biochemical endpoints (i.e., biomarkers), clear time trends for early warning signs of impaired health were noted in the perch from this site, possibly as a result of increased baseline pollution. The data sets also showed relatively large variations among years. To identify additional temporal variation in biological parameters, global mRNA expression studies using RNA sequencing was performed. Perch collected in 2010 and 2014 were selected, as they showed variations in several biomarkers, such as the activity of the detoxification enzyme CYP1A (EROD), the plasma levels of vitellogenin, markers for oxidative stress, white blood cells count and gonad sizes. The RNA sequencing study identified approximately 4800 genes with a significantly difference in mRNA expression levels. A gene ontology enrichment analysis showed that these differentially expressed genes were involved in biological processes such as complement activation, iron ion homeostasis and cholesterol biosynthetic process. In addition, differences in immune system parameters and responses to the exposure of toxic substances have now been verified in two different biological levels (mRNA and protein) in perch collected in 2010 and 2014. Markedly higher mRNA expression of the membrane transporter (MATE) and the detoxification enzyme COMT, together with higher concentrations of bioactive naturally produced brominated compounds, such as brominated indoles and carbazoles, seem to indicate that the perch collected in 2014 had been exposed to macro- and microalga blooming to a higher degree than did perch from 2010. These results and the differential mRNA expression between the 2 years in genes related to immune and oxidative stress parameters suggest that attention must be given to algae blooming when elucidating the well-being of the perch at Kvadofjarden and other Baltic coastal sites.
Highlights
The aquatic environment is a final sink for most pollutants
Our results show no differences in NRF2 mRNA expression between the 2 years, which suggests mild oxidative stress where the translocation of NRF2 present in the cytosol is enough for antioxidant gene control (Kobayashi and Yamamoto, 2005)
It was suggested that the time trends in certain biomarker responses in perch from the Kvädöfjärden reference site, studied for more than 30 years, can possibly be the result of changes in the baseline pollution
Summary
The aquatic environment is a final sink for most pollutants. Strategies for environmental monitoring and risk assessment are vital for maintaining the aquatic ecosystem. Methods utilizing biomarkers have been used extensively to investigate exposure, effects and health status in fish (e.g., Larsson et al, 2003; van der Oost et al, 2003, Lehtonen et al, 2014; Asker et al, 2016; Hylland et al, 2017). For this purpose, biomarker measurement of the coastal perch (Perca fluviatilis) have been performed for 30 years in the Swedish National Monitoring Program. The coastal reference sites are located in areas without any known local or regional point sources and are away from large freshwater inflows
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