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US: Scientists Discover Key to Tuna’s Speed |
| February 5, 2004 |
Vancouver Aquarium Marine Science Centre
 | Tunas fascinate scientists because of their speed and athleticism, as well as their population decline. Photo: Danilo Cedrone/NOAA
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The Heart of the Matter
A study has given researchers new insights into the incredible swimming ability and temperature tolerance of bluefin tuna. Their findings suggest that a higher level of a special protein in the heart may be one of the adaptations that allow these incredible fish to travel so quickly in cold water.
Tuna are a favourite seafood, and they are also one of the world's fastest and most extraordinary groups of animals. Bluefin tuna can reach speeds of over 60 km/hr and swim 150 miles in one day. In this study, scientists were particularly interested in studying the heart of bluefins because of the species’ ability to travel in colder water than other tuna species.
“Tunas have remarkable hearts. They have higher heart rates and higher cardiac output than other fish,” said Hopkins Marine Station Ph.D. student Jason Blank, co-author of the study.
Warm-blooded, Cold-hearted
According to Blank, they are also interesting because, unlike other fishes, tuna bodies are mainly endothermic, or warm-blooded. Their hearts, however, are susceptible to the cold.
 | Photo: Antonio Pais/NOAA
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“Tuna blood runs through a counter-current heat exchanger. Interestingly, the heart is on the wrong side of this system and operates at seawater temperature. When the heart is exposed to cold water it slows down and has to work harder to supply blood to the rest of the body.”
As a result, yellowfin tuna are not able to deal with cold temperatures. “Yellowfins have a fairly limited tropical range in the wild – they can’t tolerate temperatures colder than about 17 degrees Celsius,” he said. “We see a drop in their heart rate and cardiac output in cold water.”
Bluefins, on the other hand, are able to maintain their strength and power in cold water. During this study, the team discovered that bluefins have higher levels of protein called SERCA2 in their hearts. This protein lets the bluefin heart pump much faster. “The protein is involved in beat-to-beat relaxation. In bluefin tuna, the heart recovers more quickly between beats.”
Tuna Conservation
When asked why he studies tuna, Blank told AquaNews that he was interested in their muscle and cardiac physiology, but was also inspired because they are such athletic fish.
Blank works with the Tuna Research and Conservation Center, a joint project between Stanford University's Hopkins Marine Station and the Monterey Bay Aquarium. The Center studies the biology and husbandry of tunas, and promotes their conservation.
According to Seafood Watch, most of the “canned light” tuna we eat is either yellowfin or skipjack tuna, however, bluefin tuna provides the world's most valuable sushi. Seafood Watch recommends that consumers avoid buying bluefin tuna at this time because the Atlantic and Pacific Southern populations are severely overfished and data is lacking on the Pacific Northern group.
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