Probiotics have been shown to significantly improve larval oyster survival

With just one application, the probiotics also increased larval growth, metamorphosis and settlement, meaning that in addition to more oysters surviving the larval stage, they did better at transitioning to juveniles and anchoring to shells and other surfaces.

The findings could be a boon to oyster farms, where pathogens can kill larvae costing hundreds of thousands of dollars a season.

“The results definitely exceeded our expectations,” said Carla Schubiger, project leader and study co-author, in a press release from OSU.

“Just a 40 to 50 percent improvement in larval survival would be huge, but here we’ve had survival increases of over 80 percent at times. This is very, very important to the industry. Antibiotics are not allowed in hatcheries, so this will be the first tool they can use to increase their production.”

According to a 2010 report by the Pacific Coast Shellfish Association, oyster sales are close to $5 million annually in Oregon.

As with humans, oysters depend on the good bacteria living in their host’s gastrointestinal tract for their overall body function. The goal of the study was to determine which strains of these beneficial bacteria are best at fighting pathogenic bacteria that can kill oyster larvae.

Prevention of Vibrio infection

The Vibrio corallilyticus The bacteria is widespread and highly pathogenic, especially in marine aquaculture, so oyster farms need an effective way to protect against it, the researchers say.

OSU researchers cultivated several naturally occurring strains of bacteria and tested them for their ability to fight. V. corallilyticus
under laboratory conditions. Then they selected the strains that showed the best effect against pathogenic bacteria.

The team raised the larvae in water conditions comparable to those used in oyster farms. When the larvae were 24 hours old, they were treated with different strains of cultured probiotics, first individually and then with a combination of the most promising strains. Larvae were exposed at 48 hours of age V. corallilyticus.

The results were surprising. Compared to an untreated control group, four of the individual probiotic strains resulted in an average survival rate of 68 percent or better, including one strain that increased survival by 99.7 percent.

The researchers then treated the larvae with combinations of the most promising individual strains. Various two- and three-species combinations increased larval survival rates up to 86 percent.

After 14–16 days, the probiotics still appeared to have an effect, with treated larvae producing significantly larger shells than untreated larvae, as well as significantly higher rates of natural settlement and metamorphosis into juvenile oyster spat.

The exact mechanism helping the oysters is unknown, Schubiger said, but improved growth and settlement rates were an unexpected advantage over improved survival rates.

“It’s possible that we’re affecting something very early in their development, like the immune response, to make them better later in life,” he said.

The research team envisions administering the probiotic treatment as a freeze-dried material that can be sprinkled on the larvae’s spawning tray. Treating the larvae so early in their life cycle means they need very little material, making probiotic treatment more cost-effective.

Their next steps will be to test the combination with a fourth probiotic and work on growing the probiotic bacteria alongside the microalgae that serve as the oyster larvae’s primary food source, so the treatment can be integrated into their spawning process from the start, Schubiger said. .

The research team previously included lead author David Madison of OSU’s College of Agricultural Sciences, along with co-authors Spencer Lunda of the College of Veterinary Medicine, Ryan Mueller of OSU’s College of Science, and Chris Langdon of the College of Agricultural Sciences.

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