Information from noninvasive ultrasounds is able to tell researchers which animals are the most mature and ready to reproduce
By SONORA SLATER — science@theaggie.org
Giant sea snails that graze on plankton and algae, abalone are sometimes called the ‘bison of the ocean.’ Abalone meat and shells have been popular for hundreds of years, and much like bison, their commercial popularity paired with climate change, ocean acidification and the die-off of their main food source has contributed to the species’ current endangered status.
There was once a robust commercial fishery for abalone along the West Coast, but as of 2018, harvesting wild abalone is illegal in the state of California. In order to fulfill the demand that still exists and to raise their numbers up from endangerment, aquaculture and captive breeding efforts are underway — but abalone are notoriously difficult to spawn.
Scientists at UC Davis have discovered a creative new way to improve spawning efforts, according to a recent press release, and it involves repurposing a tool that already exists: an ultrasound transducer.
Their research was published in February in the journal Frontiers in Marine Science, and it was funded through a grant from the U.S. Navy Pacific Command Fleet.
Jackson Gross, an assistant professor in the UC Davis Department of Animal Science and the corresponding author on the paper, had seen a video of a land snail crawling across a transducer and was convinced that the method could be applied to sea snails like abalone as well.
“There were a lot of naysayers initially,” Gross said. “But I was like… I’m pretty sure this is going to work.”
Sara Boles, first author on the paper, explained why spawning abalone with traditional methods can be so difficult.
“Abalone are gastropods,” Boles said. “So in order to observe their gonad visually, you actually need to remove them from the surface that they’re on.”
Isabelle Neylan, a fifth-year Ph.D. student at UC Davis and a coauthor on the paper, elaborated on what this looks like.
“They’re basically giant snails, and they suction to the surface,” Neylan said. “So to get them unstuck is a process. You’re basically using a spatula or a gift card, getting up under them and popping them off. We’ve gotten very good at it, and sometimes it’s necessary, but the less you can interfere, the better.”
Abalone are hemophiliacs, which means that they lack the ability to clot, according to Boles. Because of this, if they sustain an injury during the removal process, they can essentially bleed to death.
“When you have a hundred animals in a population, every one of those animals is precious,” Gross said.
Because of this, the team didn’t use the endangered black abalone for their research. Instead, they used farmed red abalone as a proxy species, as it is biologically very similar but has higher population numbers; although, they have since had the opportunity to perform successful ultrasounds on black abalone as well.
Apart from the problem of removing the animals for inspection, it can also be very difficult to get accurate results with a visual inspection due to similarities in the appearance of male and female abalone. The main tell is a slight difference in color when they are in season, with the male gonad appearing white and the female’s bright green. But even then, there is no guarantee that they’re ready to spawn.
So, how does the ultrasound transducer solve these problems?
“First and foremost, it’s noninvasive,” Boles said. “When you’re working with an endangered species, you want to reduce any handling stress. Even if you don’t injure them when you remove them from the tank, the act of removing them off the tank can induce stress, and you don’t want to stress out endangered animals.”
Boles and the rest of the team found two ways to do an ultrasound on the abalone, with a set-up that is remarkably similar to what you would use on a human woman.
“I’ve assisted on many many abalone ultrasounds, but I’ve never assisted in one on a human, which is bizarre and cool,” Neylan said. “But it’s the same technology.”
The first method involves performing an ultrasound through the sides of a container while the entire tank is submerged in water. The second uses clear transparency film.
“[The abalones’] feet immediately suction to whatever surface they can,” Boles said. “We line the bottom of their buckets with clear transparency film, like you use on an overhead projector, and I can actually ultrasound right through that clear material.”
Apart from improving convenience and animal welfare, the ultrasound is also able to provide more detailed information than a visual analysis could.
“The ultrasound has the ability to see the changes in the thickness of the gonad, which is indicative of the maturation process,” Boles said. “So it’s been very reliable in predicting which animals will spawn when induced.”
According to the press release, they were able to use this information to create a gonad index score ranging from one to five, which “indicates the abalones’ readiness to reproduce,” with abalone measuring in the three to five range being the most optimal candidates for spawning.
The ability to take quantitative measurements in order to choose the most ideal candidates is extremely important, according to Gross, because the spawning process can take a lot of resources — so it’s important to get it right the first time.
“You stress out the abalone to spawn it,” Gross said. “Once you do it, you might have to wait months before you can do it again, to allow the animal to recover. There’s a lot of labor and timing and coordination and people involved in spawning days, and even after the spawning days, there’s a lot of work involved in the care of the larvae […] now for the first time, we can watch and say, okay, these animals are ready.”
Gross went on to explain that, traditionally, there aren’t as many animal welfare regulations applied to aquatic animals, especially invertebrate aquatic animals. This could be a step toward using technology to explore more humane ways to study them.
“More people are starting to think: ‘Hey, these animals could be more complicated than we want to let on,’” Gross said. “That was kind of the point here, was that we needed to come up with a better way to increase this animal’s population that takes animal welfare into account. I think this opens up the door for [exploring other] health metrics of the ocean and how these animals are handling a climate change scenario. We’re just kind of at the cusp of starting to explore that.”
Written by: Sonora Slater — science@theaggie.org
