Scientists Find Toxic Oil Compounds Damage Fish Hearts

Alice Mitchell
27 April 2015, at 1:00am

US - Oil can cause abnormalities in the still-developing hearts of fish embryos and larvae, according to scientists who have been studying the effects of the Deepwater Horizon oil spill on fish reproduction.

The study has shown the causes of the injury caused by oil on a molecular scale, and this new understanding should allow scientists to develop new diagnostic tools to measure the impacts of oil spills in future.

NOAA is using this science to conduct its Natural Resource Damage Assessment in the Gulf of Mexico, including estimating losses of bluefin tuna, yellowfin tuna, and other species that spawned in the northern Gulf during the Deepwater Horizon spill.

Fish are most vulnerable to crude oil during their earliest life stages, when they are tiny, translucent eggs and larvae floating in the water column during the first few days of life. At that stage, they can neither metabolize toxic compounds nor swim away from oil very effectively.

After previous oil spills, research had shown that tiny concentrations of oil can still cause slarval defects, and although these larvae can develop into normal-looking fish, they will still be less likely to survive in the oceans.

Compounds found in oil called polycyclic aromatic hydrocarbons (PAHs) target the hearts of fish, and this causes the other developmental defects.

In the latest study, scientists isolated individual heart cells from tunas and demonstrated that crude oil disrupts the normal rhythmic cycle of excitation and contraction in those cells.

This explains why oil-exposed fish have an abnormal heartbeat, altered circulation, and structural defects in the heart and other organs.

Because fish are most vulnerable during early development, researchers focused their post-Deepwater Horizon efforts on species that were spawning in oiled waters in the Gulf of Mexico. But the effects are likely to be similar across many species of fish.

"Now that we have a more precise understanding of how PAHs affect heart cells, we hope to identify new biomarkers for cardiac-related injury in fish exposed to PAHs," said Nat Scholz, the scientist who led the program.

If an oil spill occurs at a later date, they could test the biomarkers again to assess the impact on fish populations.

PAHs are also present in stormwater runoff from urban coastal areas, and these new techniques are opening new avenues of research into more everyday sources of PAH pollution.

These techniques would be particularly useful in the Arctic, where retreating ice cover is opening new areas to energy development and maritime shipping.

The Arctic ecosystem is still relatively pristine, so the best time to collect baseline data on vulnerable species and habitats is now.

In addition, basic biological information on the early development of polar fish species is limited, including whether their extreme cold-water physiology makes them more or less vulnerable to oil spills.

Collecting that data and answering those questions now would help scientists to assess the damages from a spill after the fact. Perhaps more importantly, it would help scientists and oil spill responders to plan effective response and restoration strategies.

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