As far as I know they're not poisonous in the conventional sense that they have any venom in their spines like a Lion fish does. How ever most catfish and many fish have barbed and serated spines that are covered in a irritant to aide in the prevention of predation. If a predator tries to eat them the spines pierce the roof of the mouth and the irritant outside the spine add to the already unconfortable wound. If you've been stuck by one of course it's gonna hurt bad and the irritant is gonna help increase the amount of swelling, not to mention all the bacteria that was delivered thru the wound. I'm kind of anal when it comes to stuff like that. If you can take the pain you can do what I do to try and be safe which is putting my hand in as hot water as you can stand. Otherwise if the wound doesn't heal right you may have to go to a doctor to make sure you don't get a serious infection.