An Ounce of Prevention: Probiotics Hold Potential for Shellfish Disease

Deep lacerations  scar the shells of lobsters. Entire populations of oysters die in less than 24 hours. These are the results of disease, potentially caused by bad bacteria. And although bacteria may be the cause, in it also lies potential for a solution.

Can something as simple as a probiotic, the good bacteria, like the ones found in yogurt, help prevent, treat, or even cure these diseases?

Lobster Shell Disease impacts the outer shell. While it doesn't harm the meat, it does harm its marketability.

Lobster Shell Disease impacts the outer shell. While it doesn’t harm the meat, it does harm its marketability.

David Rowley, an associate professor of biomedical sciences and pharmaceutical sciences, and Kathleen Castro, a fisheries scientist and lobster ecology specialist at the University of Rhode Island think so.

Rowley and his team experimented with oyster larvae and probiotic treatments to prevent disease outbreaks – outbreaks that could compromise entire oyster populations in the hatchery in fewer than 24 hours. The bacteria, Vibrio tubiashii, works by settling on the oyster’s cilia—the tiny hairs that aid in feeding and movement. They bind the cilia together, stopping the oyster from moving or feeding. “It happens very, very rapidly,” Rowley said.

“Once a hatchery manager recognizes that there’s a problem in the hatchery, it’s too late to do anything about it,” he said. “Neither antibiotics nor vaccines can work quickly enough to treat a disease outbreak once it occurs.”

So for now, the solution lies in prevention.

URI Pharmacy Professor, David Rowley, studies how probiotics might be able to fight disease in shellfish.

URI Pharmacy Professor, David Rowley, studies how probiotics might be able to fight disease in shellfish.

There are a variety of options such as chemically treating the water or using ultraviolet light, or heat treatments, in addition to filtration. “And after all this, you may still have a pathogen outbreak,” Rowley added.

So he and his team looked into probiotics as a prevention option. “After sifting through 100 [different probiotics], we settled on two,” he said. “One of the first things we wanted to see was that these didn’t have an adverse effect on the oyster larvae.”

Typically probiotics have potential to improve the host’s immune system, compete for more of that site (essentially kicking out the disease-causing bacteria), or enhance the nutrition to the host.

The probiotics in oysters aren’t all that different from the probiotics that you’d get through eating yogurt,” Rowley said.

The two probiotics he studied are already present in parts of the inner shell of a healthy adult oyster, or in invertebrates common in the Narrow River. “These are live bacteria that provide a beneficial effect to the host. So these are the good bacteria if you will.”

He treated a group of oyster larvae in his lab with the probiotics, then introduced the bad bacteria. Rowley saw an increased rate of survival in the oyster larvae treated with probiotics. After this initial test, he was ready for the real thing. He took his hypothesis to the hatchery at Roger Williams University in Bristol where he performed his experiments on a larger scale.

Probiotics Show Promise

After the first probiotic treatment, the Vibrio was largely absent from the water, and after the second probiotic, the number of Vibrio that were present decreased. And finally, when both probiotics were combined, there were almost no Vibrio in the water at all.

There was a clear decrease in the number of disease-causing pathogens in the tanks when these probiotics were introduced. But were the oysters more resilient? After three days, the probiotic-treated oysters had a 26 percent higher survival rate than the control group. And after eight days, that rose to 47 percent.

Oyster larvae with healthy cilia. Photo NERRS NOAA

Oyster larvae with healthy cilia. Photo NERRS NOAA

The resulting probiotic treatment is primarily geared towards hatchery use. It dissolves rapidly in salt water (as quickly as 25 seconds), is stable and effective, and is relatively inexpensive. This is good news for hatcheries, not just in the state, but also throughout the country. Disease mitigation is essential to the sustainability of the aquaculture industry. Oysters were a $136 million market in 2012 with yields of 35 million pounds, according to a U.S. Marine Aquaculture study. While captured seafood remains at a consistent level, aquaculture production is on the rise. Disease, however, can spread rapidly, wiping out an entire hatchery.

Disease mitigation is essential to the sustainability of the aquaculture industry. Oysters were a $136 million market in 2012 with yields of 35 million pounds, according to a U.S. Marine Aquaculture study. While captured seafood remains at a consistent level, aquaculture production is on the rise. Disease, however, can spread rapidly, wiping out an entire hatchery.

“If this industry is going to continue to grow, it has to be sustainable,” Rowley said.

Castro agrees and is applying Rowley’s research to ensuring the future of lobster stocks. Since 1996, lobster shell disease has been ravaging lobsters in New England waters. And without a known cause or treatment option, many affected lobsters have been thrown back into the ocean to die.

“We saw an increase to almost 30 percent in a very short time,” Castro said of the number of lobsters affected, particularly reproducing females.

As the disease has increased, young lobsters present in the water have decreased. And worse, the latest stock assessment by the Atlantic States Marine Fisheries Commission declared this area to be undergoing recruitment failure, meaning the population is not sustaining itself.

Fishermen helped Castro and her team by providing diseased lobsters for their research. The researchers exposed them to different treatments. One group of affected lobsters was placed in freshwater, with the expectation that the bacteria that might cause the disease would dislike it. A second group was treated with a probiotic, and a third group, the control, was placed in regular salt water.

Castro found the control lobsters tended to get worse, while the freshwater and probiotic-treated ones, on average, tended to remain the same or fare better. “We do believe both freshwater and probiotics may slow down the spread of shell disease,” she said.

But the study needs more work. “This was considered to be a very preliminary experiment. We just wanted to see what would happen,” she said.

The results are not statistically valid, and more replicated trials are needed. “We weren’t sure oyster probiotics were going to work on lobsters. We weren’t even sure anything would work on lobsters. So this was all very preliminary… but we were very encouraged by the results,” she said.

Both Castro and Rowley plan to continue to research probiotic uses with shellfish. Rowley said there may be even more effective probiotics out there. “I don’t think there’s going to be a magic bullet here – one bacterium to rule them all,” he said. But even so, each effective probiotic gets is a step towards more sustainable aquaculture, which is good for businesses and marine ecosystems in the state.”

Rowley’s research was funded in part by Rhode Island Sea Grant. He and Castro spoke at the Coastal State Discussion Series on March 23 about their research efforts.

 

By Kelsey Quinn | Rhode Island Sea Grant Communications Intern and URI Journalism student

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The Coastal State Discussion Series is a forum dedicated to highlighting current scientific research, finding solutions, and building partnerships centered around coastal issues impacting Rhode Island’s coastal communities and environment.

This series is sponsored by Rhode Island Sea Grant with the support of the University of Rhode Island’s Coastal Institute, College of Environment and Life Sciences, and the Graduate School of Oceanography.