Blood is drawn from a sablefish

By Jens Odegaard, director of marketing and communications at OSU’s Carlson College of Veterinary Medicine

CORVALLIS, Ore. – Researchers have established blood reference levels for captive sablefish, which may advance efforts to farm the lucrative groundfish.

With funding from Oregon Sea Grant, the team established ranges for parameters that included albumin, cholesterol, potassium and plasma protein.

These baselines could help farmers catch diseases early through regular monitoring, said Carla Schubiger, a veterinarian at Oregon State University’s Carlson College of Veterinary Medicine and one of the researchers on the study, which was published in the journal PLOS ONE. She added that the work could also help the nascent sablefish aquaculture industry raise brood stocks.

“The blood reference range will be really critical to assess whether a stock is healthy and feeding regimes are appropriate and balanced,” she said. “Because that might be the beginning of the next hundred years of sablefish aquaculture, we need to be very deliberate in the beginning to have a really good product.”

To establish the ranges, researchers took blood samples from sablefish, also known as black cod, that were reared by the National Oceanic and Atmospheric Administration. In the lab, researchers found what they suspect is the reason sablefish are so tender.

“Their fat content in the blood is ginormous,” said OSU veterinarian and clinical pathologist Elena Gorman, a coauthor on the paper.

“I've never seen anything like that,” Schubiger said. “It’s just fascinating the fish live just fine with that. They're really adapted to it.”

The scientists had to fast the sablefish for 24-36 hours before drawing the blood to reduce the lipid content so it would not interfere with the other measurements. “It interferes with everything. All of that lipid will just block enzyme reactions, and it'll affect values such as electrolyte measurements,” Gorman said.

Using a microscope, researchers also counted different types of blood cells to establish numerical ranges. Blood cell counts can warn about infections and environmental or management issues such as water quality or nutrition. Researchers found that lymphocytes made up 98% of the leukocytes, while eosinophils were rare, and basophils were not detected. Gorman noted that blood-clotting platelets, also known as thrombocytes, were different shapes.

“They have weird platelets,” Gorman said. “We would see them, and at first, it took me a while to know that some of them weren't parasites, because they’re so diverse. And then I would see them clumping and go, ‘Oh, OK, that's just the way their platelets are.’ When I wrote [the study] up, I had to describe and provide photos so others don’t mistake these as something else.”