I recall seeing one of those floating dead in one of the smaller lakes a few years ago. The koi they believe have been sterilized to avoid having a problem. No idea about the catfish. Years ago there was a ranger who used to walk around the place talking to everyone. He was a friendly old guy and told me they had turtles released in the lake. I have never seen any and he was murdered not long after so I could never find out. It probably would have been 20 years ago now.