I hope you realize this thread 3-years old.
Clarias gariepinnis is a good guess. Just wanted to mention ID-ing small Clarias is no slam-dunk by any means.
I do wonder if those who use these cats as feeders snip off their pectoral and dorsal spines. I imagine, if it is fed routinely, it may lead eventually to an unfortunate accident. 100 times it will be fine and the 101st it could get stuck in the mouth/throat/gills or puncture the stomach or, worse of all, an important internal organ.