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Description
The early life history stages (embryos and larvae) of fish can be especially sensitive to environmental contaminants due to the rapid proliferation, differentiation, and growth of embryonic tissues. Polycyclic aromatic hydrocarbons (PAHs) derived predominantly from the consumption of fossil fuels are pervasive contaminants in rivers, lakes, and nearshore marine habitats. Since the early life history stages of many fish species are associated with sediments or affixed to plants or other substrates, they cannot evade exposure to PAHs, as demonstrated by the 1989 Exxon Valdez oil spill in Alaska. Regionally, the Puget Sound Ambient Monitoring Program conducted tests that detected PAHs in Pacific herring eggs from spawning sites in central Puget Sound, and PAHs are common contaminants in urban streams where efforts are underway to restore salmon spawning habitat. Population projections for the Pacific Northwest indicate that consumption-related sources of PAHs (e.g. automobiles) will continue to rise, and oil spills will continue to be a potential risk in the Puget Sound basin. Understanding the effects of PAHs on fish development is thus especially important in our region for the protection of marine resources and recovery of threatened and endangered salmon species. Most of the fish species that have ecological, commercial and cultural importance in the Pacific Northwest are difficult to study in the laboratory, particularly during the early life history stages. Therefore, we are addressing this problem by analyzing the effects of PAHs on the development of zebrafish (Danio rerio), a small freshwater tropical fish that has become one of the best models for the study of fundamental cellular, molecular, and genetic mechanisms of vertebrate development. We found that 3-ring PAHs most abundant in weathered crude oil (e.g. phenanthrene) induced a suite of malformations in zebrafish embryos essentially identical to those described for herring and salmon embryos exposed to weathered crude oil under post-spill conditions (Picture 1). Using genetic techniques unique to zebrafish, we found that the suite of PAH-induced malformations was secondary to embryonic cardiac dysfunction (Picture 2), while the primary mechanism underlying toxicity of 3-ring PAHs appeared to be inhibition of cardiac conduction. The subsequent loss of circulation and accumulation of edema produced secondary effects on craniofacial structures and the body axis. Because cardiac morphogenesis is intimately linked to cardiac function, and in fish continues well into the juvenile period, the cardiac arrhythmias (Movies 1A and 1B) produced by 3-ring PAHs resulted in altered heart structure (Movies 2A and 2B). Irreversible effects on cardiac structure associated with transient cardiac dysfunction during development could contribute to sublethal effects occurring at later life stages.
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PAHs cause morphological abnormalities in the developing heart. Laser scanning confocal images of the heart in 6 dpf zebrafish show a normal heart on the left and an abnormal heart on the right from a fish exposed to 1 ppm phenanthrene.
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Investigators
John Incardona and Nat Scholz
Support
Oiled Wildlife Care Network
at University of California-Davis
Relevant Publications
Incardona, J.P., Collier, T.K. and Scholz, N.L. (2004) Defects in cardiac function precede morphological abnormalities in fish embryos exposed to polycyclic aromatic hydrocarbons. Toxicology and Applied Pharmacology 196(2):191-205.
Incardona, J.P., Carls, M.G., Teraoka, H., Collier, T.K., Scholz, N.L. (2004) Aryl hydrocarbon receptor-dependent and -independent pathways of polycyclic aromatic hydrocarbon toxicity in fish embryos. Proceedings of the Society of Environmental Toxicology and Chemistry's 4th World Congress, Portland, OR. Oral presentation.
Incardona, J.P., Collier, T.K. and Scholz, N.L. (2003) A novel mechanism of PAH toxicity in fish embryos: direct effects on cardiac function. Proceedings of the Society of Environmental Toxicology and Chemistry's 24th Annual Meeting, Austin, TX. Oral presentation.
Incardona, J.P., Collier, T.K. and Scholz, N.L. (2003) Mechanisms of polycyclic aromatic hydrocarbon (PAH) toxicity in early life history stages of fish. Pollutant Responses in Marine Organisms, 12th International Symposium, Safety Harbor, FL. Winner, Best Postdoctoral Poster Presentation.
Incardona, J.P., Collier, T.K. and Scholz, N.L. (2003) Mechanisms of polycyclic aromatic hydrocarbon toxicity in early life history stages of fish. Proceedings of the Georgia Basin/Puget Sound Research Conference 2003, Vancouver, BC, Canada. Oral presentation.
Related Links:
Exxon Valdez spill/NOAA Auke Bay Laboratory
Puget Sound Ambient Monitoring Program
ZFIN (zebrafish biology)
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