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This Toxic Release Can Actually Help Rainbow Trout

Feb 20, 2015 05:07 PM EST
(Photo : Roger Tabor (USFWS)) Juvenile rainbow trout are most susceptible to Coldwater Disease, growing lethargic with bulging eyes and little appetite before dying.

So let's talk about toxins... and fish. They normally don't go together. In fact, most living things would prefer to avoid living near toxins. However, at times they can be very helpful, as shown in a recent strategy to help protect the beautiful rainbow trout against Coldwater Disease.

A great deal of toxins, of course, come from industry and pollution. However, there are a whopping number of natural toxins as well, the majority of which can be found in powerful venoms and even produced by microbial life going to war.

Microcystin, for instance, is a cyanotoxin that is produced by blue-green algae when it's undergoing certain processes or is under stress. This is what makes the harmful algae blooms that you hear about every summer so dangerous.

Now a study published in the journal Applied and Environmental Microbiology is proposing that experts could trigger toxin releases in the microbes found in rainbow trout - not to harm the fish, but to help fight off a bacterial infection that is currently killing up to 30 percent of hatchery stock across the United States, taking a big chunk out of a $13.7 billion industry.

"Coldwater Disease is the number one bacterial illness affecting US trout aquaculture and to a lesser extent Coho salmon," researcher Douglas Call recently explained in a statement. "Once an outbreak starts, the only way we've had to treat it has been with antibiotics."

"The problem with antibiotics is that they can lead to bacterial resistance and also contaminate the water and soil," he added. "Only two antibiotics are approved for use and one, florfenicol, is particularly nasty and persists in the environment for a very long time."

The scientist proposes that instead of introducing new antibiotics, we could simply trigger microbes found naturally in the fishes' guts to fight the disease for us. That's where probiotics can play their part. Broadly speaking, these are bacteria and other microbial life that are good for you, like the balanced community of microbes that reside in the human gut.

Kenneth Cain, who was also involved in the study, recently discovered the trout probiotic C6-6 can produce a toxin it normally would use in turf wars with competing microbes. He and his colleagues found that this toxin could kill Flavobacterium psychrophilum, the parasitic cause of Coldwater Disease. (Scroll to read on...)

(Photo : Shelly Hanks, WSU) Trout food coated with a coldwater disease-fighting probiotic developed by Cain and Call.

This was after repeated field trials, as part of a larger 15-year study, showed that fewer fish were dying from Coldwater when boasting large populations of C6-6.

"We found C6-6 produces a toxic protein called an entericidin which inhibits the Coldwater bacteria," Cain said. "It could also present new opportunities for treatments against closely related pathogens."

The researcher and his colleagues added that the greatest benefit of this approach is that it's also inexpensive.

As things stand, "it costs the Idaho trout farm industry and Washington aquaculture facilities over $10 million each year to combat Coldwater Disease [with antibiotics]," Cain explained. However, "the bacteria that produce the entericidin are fast growing, cheap to produce and easy to put on food for the fish - all the attributes of an ideal preventative treatment."

Thanks to the discovery of the C6-6 produced toxin, Call said he is hopeful for regulatory approval and commercial licensing of the probiotic as well - a boon for experts concerned about things like widespread antibiotic resistance.

"If C6-6 is as effective as our research is showing," he added, "it will reduce disease losses for fish producers, improve animal welfare and reduce the demand for antibiotics in aquaculture."

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