Ive been keeping a very young kelberi with big kelberis. It would easily fit their mouth.
Ive been keeping a crenicichla bigger than that lil bass, and the crenicichla was eaten, the lil bass not (even starving the big bass for like 15 days..)
The only problem was the constant bully with the small bass. So I needed to change him.
I know Cichla is a very voracious fish, but never seen myself they doing canibalism, but I have a fishermen friend that said that have seen lots of times tons of small cichla inside of bigger ones and papers saying they would do so in feeding conditioning.