The catfish would be in the breeder box? There should be no way for any fish to enter the breeder box. Here's a pic. (Not mine, off the internet.)I have South American Bumblebee catfish which would swallow the fry whole. I'm going to add females Thursday. Might move some males to the 37g and keep the silvers and Dalmatians in the 55. not sure yet.
Gk