rest assured that any fish more slim than the Clarias can end up as food unless it's spiny and grumpy, like Ancistrus or so, or a doradid.
the thickness of the body is a good indicator. highbuild fishes are generally ignored, the Clarias is quite good at "taking measures" wich fits and wich doesn't
on the other hand, despite all the horrorstories out there, a well fed Clarias is not such a piscivore than, say, Sorubim lima.
the backdraw is that it takes insane amounts of food to keep a Clarias "well fed"
Clarias is the king of gluttony
