Dr. Carla Schubiger surfaces from a dive at the Oregon Coast Aquarium.
August 23, 2021
Story and photos by Jens Odegaard
Dry suit. Check. Scuba tanks. Check. Mask. Check. Regulator. Check. Fins. Check.
Dr. Carla Schubiger slips into the water past a giant sturgeon and swims down, bubbles trailing behind. Down toward a shipwreck circled by schools of lingcod and halibut and sablefish.
She’s swimming with a vacuum. Back at the surface, a dive attendant stands on a walkway crisscrossing the Passages of the Deep exhibit at the Oregon Coast Aquarium and holds the end of the tether line connected to Schubiger.
Schubiger is maintaining this middle section of the exhibit, known as Halibut Flats, as a volunteer diver. Down near the “shipwreck,” aquarium visitors peer at Schubiger through the glass tunnel that runs through through the exhibit, opening up a fully immersive experience for anyone walking through.
Schubiger volunteer dives at the aquarium a couple of times per month — drawn to the work by her deep fascination with all things ocean, but particularly the animals and especially the fish.
She is a veterinarian and an assistant professor in the Oregon State University Carlson College of Veterinary Medicine. In addition to her veterinary degree, Schubiger holds a doctorate in immunology and infectious diseases. She runs the Schubiger Lab at the CCVM. Her research is focused on aquatic research, particularly on commercial marine species, one of which is sablefish.
The sablefish swimming with her in the aquarium are extras from one of her recent research projects.
Dr. Carla Schubiger doing tank maintenance at the Oregon Coast Aquarium and diving among sablefish and other species.
Sablefish are also known as black cod or butterfish. “It’s very tasty,” Schubiger said.
Its flaky, buttery deliciousness is becoming more well-known, leading to an increase in commercial demand. To help meet this demand while sustainably managing wild fisheries in the Pacific Northwest and Alaska, scientific and industry experts in aquaculture have started to explore farming sablefish.
To farm fish, you need to establish guidelines for assessing their health.
That’s where Schubiger and her colleagues at Oregon State and the National Oceanic and Atmospheric Administration come in. NOAA has a captive brood stock and rearing program in the Northwest to help support sablefish aquaculture. She and her colleagues recently published a study (funded by the Oregon Sea Grant) establishing blood reference levels for sablefish.
“You know, fish are tricky. You often will only notice that they're sick when like 80% have died,” Schubiger said. By using blood cell counts and establishing normal ranges for blood chemistry — things like how much cholesterol, calcium and potassium are in the blood — those raising sablefish could catch issues early on. “Having a blood reference range, if you do weekly monitoring for example, you could figure out that there's a disease storm coming on a lot sooner,” Schubiger said.
This is especially important for the nascent sablefish aquaculture industry as farmers raise their first brood stocks. “The blood reference range will be really critical to assess whether a stock is healthy and feeding regimes are appropriate and balanced. Because that might be the beginning of the next hundred years of sablefish aquaculture,” Schubiger said. “We need to be very solid in the beginning to have a really good product. Otherwise, it just veers off.”
To establish the reference ranges, Schubiger and her NOAA colleagues took blood samples from sablefish at NOAA’s Newport, Oregon facility (just down the street from the Oregon Coast Aquarium) and drove them the 50 minutes to the CCVM’s Oregon Veterinary Diagnostic Laboratory in Corvallis for processing.
Dr. Elena Gorman works in the OVDL and is also a veterinarian and an associate professor of clinical pathology in the CCVM. She and fellow veterinary clinical pathologist Dr. Jennifer Johns established the blood reference values on the sablefish samples. “So it's a pretty routine thing for us … we do reference range validations for everything,” Gorman said. “Running them through our general chemistry analyzer is not a problem. You just have to recognize that there are going to be some parameters that are going to be different. We had to do some manipulations to get accurate readings.”
With a few tweaks to the protocol, Gorman and Johns established the blood chemistry ranges. It soon became apparent why sablefish taste so buttery. “Their fat content in the blood is ginormous,” Gorman said. “The lipid content in their blood is so much higher than I've seen in other fish species.”
The research team actually ended up needing to fast the sablefish for 24-36 hours before taking samples to cut down on the lipid content to get a clear picture of the other reference ranges. “It interferes with everything. All of that lipid will just block enzyme reactions, and it'll affect values such as electrolyte measurements,” Gorman said.
An image from the study of the sablefish platelets (also known as thrombocytes).
In addition to establishing these blood chemistry ranges, Gorman and Johns did manual blood cell counts (which cannot be run through automated analyzers) with microscopes to establish numerical ranges for the different cells found in blood: red blood cells, several different types of white blood cells and platelets (image above), which are the clotting agents. “They have weird platelets — they are different shapes,” Gorman said in comparing them to platelets from other species. “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. Fortunately, Dr. Johns has extensive experience with many different species. That, combined with our comparisons to other published fish studies, left us feeling confident with our final identifications.”
Gorman and Schubiger both see this study as a jumping-off point for healthy commercial sablefish aquaculture and for future research.
For fish farmers, this will give them the first tools for assessing school health objectively and consistently. These normal ranges “are pieces of a puzzle that can give us a much better indication of overall population health,” Gorman said.
For scientists, knowing the normal blood chemistry and blood cell ranges will give them a baseline for further inquiry. Schubiger already has some other research projects in the works related to sablefish diets. She’s also intrigued by the ability of sablefish to thrive with so much fat content in their blood. “I've never seen anything like that,” she said. “It’s just fascinating the fish live just fine with that; they're really adapted to it. That might be a really interesting model for cardiovascular disease – study that fish!”
Who knows what the future of sablefish research or aquaculture holds, but the baseline is there. “Now that we've got these ranges established for this particular species, this helps people around the world,” Gorman said.