Redfish, mahi mahi subject of study looking at oil’s effects on fish hearts

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Courtesy of Daniel Kelly of FishSens Magazine.

We know that oil spills have plenty of negative effects on organisms living nearby, but little is known about the precise impacts that exposure to oil can have on the health of fish hearts. For the Gulf of Mexico, that is an important question to answer because it could hold clues to the long-term chances of fish survival there.

To find out what sort of impacts oil exposure has had on fish in the Gulf, scientists at the University of California, Riverside, University of Miami, University of North Texas and the University of Texas at Austin are focusing on redfish and mahi mahi. The two economically important sport fish need to be studied to protect their ecotourism value, researchers say.

“We’re interested in the effects that oil exposure has on embryonic development,” said Daniel Schlenk, professor of environmental toxicology at UC Riverside and co-principal investigator on the project. “But the two fish species are obviously very important economically.”

Not only that, says Schlenk, but redfish and mahi mahi are key ecologically for the Gulf because they’re apex predators. There are few other animals that prey on them. They cover wide areas too, as the mahi mahi live most of their lives in the open ocean while redfish spend most of theirs in coastal estuaries.

It’s known that petrol, oil and compounds related to oil have unique impacts on cardiac development, says Schlenk. But the exact effects to redfish and mahi mahi remain to be seen.

“If you hurt the heart, you impact or adversely affect the energetics of an animal,” said Schlenk. “It makes it so they can’t survive in an ecological setting and that’s why it’s a target organ for us to examine.”

While each investigator on the project would explain the project in their own way, Schlenk says the whole thing is pretty exciting. By looking at changes in genes that are turned on or off in fish hearts by exposure to oil, scientists will be able to tell how the changes affect fishes’ abilities to swim and survive in the ocean.

“That helps us to explain how that affects the overall population of the two species,” said Schlenk.

High-speed video imaging will be used to analyze cardiac function in embryos after they’ve been exposed to oil. After fish age to an adult size, probes will be implanted in their heart vessels to take measurements of blood flow from heart to gills during different swim velocities. Schlenk’s efforts will focus on redfish and mahi mahi hearts by doing genetic experiments.

Colleagues from the other three schools will take those tests a step further and digitize the movement of fish tails. This will involve tagging tails with fluorescent markers and recording how fast or slow they move following oil exposure.

“The whole purpose is to determine if fish are recovering,” said Schlenk. “If we can find an indicator of heart function while they’re still alive, that has a lot of relevance to the whole animal and its population overall.”