Yersinia ruckeri is a bacterial pathogen that causes a nasty disease in salmon and trout called enteric redmouth disease. Affected fish can experience hemorrhaging in their mouths, eyes, and fins. Certainly not a pleasant pathogen- but believe it or not, researchers think that a toxin created from Yersinia ruckeri could be effective against human cancer cells!
This toxin, called Afp18, deactivates a protein called RhoA. RhoA plays a role in tumor spread, and the theory is that Afp18 can be used to block cell division. Researchers figured this out by working with zebrafish in the laboratory. Zebrafish are becoming very popular research models, and hopefully, they will give scientists some insight as to a possible treatment route for this fish toxin. Read more about this research here.