I know that I don't know very much about alot of this stuff, and sometimes I am misinformed, but this I am sure of. It isn't actually poisonious in the common, it is just a replent in the slim from the skin that makes fish deject them as a food source, or anything else that you put the slime on. They would get the fish in their mouth, and then spit the manderian back out. I read this in an artice from the Marine Hobbiest Magazine, I believe, it includes articals about fresh and salts.