| Summary: | The work in this thesis is a part of a strategic work at the Institute of Marine Research, which aims to develop a variety of methods to be used in investigating potential endocrine disruption in Atlantic cod (Gadus morhua). Produced water, a by-product of offshore oil production, contains significant amounts of alkylphenols (APs). Many studies have shown that long-chain para-substituated APs cause endocrine disruption in freshwater fish, but relatively little is currently known about their long-term effects on the biology of marine fish. Here we describe the results from two experiments studing in detail the effects of some APs present in produced water on the reproductive potential of first-time spawning Atlantic cod. Groups of cod were fed pastes containing four APs (4-tert-butylphenol, 4-npentylphenol, 4-n-hexylphenol and 4-n-heptylphenol), at different concentrations for either 4 months (experiment 1) or 5 weeks (experiment 2). AP-exposed fish were compared to unexposed fish and to fish fed paste containing natural estrogen (17 β- estradiol). The results of the present study suggest that multiple mechanisms underlie the responses in the AP treated cod. The exposure to APs influences the plasma concentration of several male and female sex hormones and the egg yolk precursor protein, vitellogenin, in Atlantic cod. This study also shows that AP-exposure down to 20 μg/kg body burden interferes with the maturation of the sex organs, and that this effect is likely caused by disruption of the sex hormone system. There were also found effects of the AP treatment on the hepatic P450 systems (CYP1A and CYP3A) as well as glutathione, glutathione-related enzymes and changes in the lipid composition in liver and brain membranes. Even though the concentrations used in our experiments are higher than may be reasonably expected as the result of oil production alone, measurements of actual AP levels in the sea indicate that APs may still be a significant risk factor in the marine environment.
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