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The clear blood of an Antarctic fish may reveal fundamental insights into our cardiovascular biology

The Antarctic Southern Ocean, a large and chilling body of water that surrounds the snowy continent, is home to many drifting icebergs, penguins, and seals. Because of water temperatures frequently below freezing, there are not many fish species that can survive. However, armed with an antifreeze protein to tolerate life among the ice, the notothenioid suborder of fishes, have adapted to thrive in the frigid ocean that they call home. As the notothenioid fishes diversified around Antarctica, several species adapted in intriguing ways to the opportunities provided by this unique marine environment.    

Northeastern University Marine Science Center postdoctoral researcher Jake Daane, under the mentorship of Professor Bill Detrich, has just received a fellowship from the American Heart Association to study the genetic underpinnings of the rare blood and cardiovascular systems of these fishes. This has the potential to provide insight into fundamental and biomedically-relevant cardiovascular processes.  

The ocean around Antarctica is highly-oxygenated, as cold water more easily holds dissolved oxygen and strong currents mix this oxygen throughout the water column. Within these uniquely oxygen-rich conditions, a family of notothenioid fishes called the crocodile icefishes have evolved the ability to survive without red blood cells and hemoglobin, both of which are normally required to transport oxygen in all vertebrate species, including humans.  Instead of the red blood we are accustomed to, the blood of the icefishes consists of a clear fluid. 

These fish can be considered chronically anemic, a condition caused by a deficiency in red blood cells and/or hemoglobin that has many negative side effects in humans. To compensate for the loss of these necessary blood components, the Antarctic icefishes adapt with increases in heart size, blood volume, and extensive branching of blood vessels. These changes enable survival despite the dramatic loss of a critical physiological system.  

“To give you an idea of how rare this is, the 16 species of icefishes are the only known cases out of the roughly 55-65,000 described vertebrate species, including us, known to be able to survive without either red blood cells or hemoglobin,” Daane said.  

Daane’s research investigates genetic variation in notothenioid fishes. Together with Detrich, they have established a massive genetic dataset representing 45 species of notothenioids, including 10 icefish species and three close relatives. Using this dataset, Daane hopes to track the unique portions of the icefish genome that have undergone extensive changes during their evolution. Through comparison of genetic variation among these fishes, Daane hopes to find genetic elements that are involved in their unique blood and cardiovascular biology.  

“Many of the DNA regions included within this study of Antarctic fishes share high genome similarity with humans,” Daane said. “Thus, the identification for some of these genes as being involved in cardiovascular biology and the subsequent production of animal models for these genes could provide insights into human cardiovascular biology and disease.” 

Daane became hooked on studying the Antarctic crocodile icefishes after starting a collaboration with the Detrich lab late in his PhD. They successfully applied some of the genetic tools Daane developed as a graduate student at Harvard University, to the Antarctic fishes that the Detrich lab specializes in. Through this collaboration, Daane was able to join Detrich at Palmer Station in Antarctica for a fishing expedition, and his passion for the fish at the bottom of the world has grown ever since.  

“This opportunity allows me to work with the Detrich lab for the next few years to hopefully see how we can use Antarctic fishes to identify some new genetic regulators of cardiovascular biology,” said Daane. “I am excited to work in an area that bridges the gap between basic questions in biology and evolution, with relevance to biomedicine and human health.” 

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