As a matter of fact some of them do Mr Fish expert. I've seen the underwater footage of it when I was a Cichlid mad breeder. I kept open water predators in swimming pools. The largest fish I grew was a Peacock Bass (it's a cichlid) and it was about 85cm long and had a mouth like a bucket with teeth. Do your research and you will find that a number of South American esturine Cichlids go upriver to chow on the dreaded Piranha as well as camo hunting river Cichlids that also eat them. In a tank, Piranha will wallop most fish, especially the black variety (except the convict cichlids they make piranha piss). Your average Piranha is about 11 inches long mature so it stands to reason that larger fish will chomp then down out in the open water. I had a Dovii (wolf cichlid) about 24 inches long and that thing ate ANYTHING, I got it a large armoured catfish and it ate it like it was a happy meal. It was the meanest bastard fish I have ever seen. All of the above Big Cichlids are also known as 'Tankbusters' because of their ability to actually break fishtanks.
On topic, these fish all did really dirty messy turd/farts. I needed major filtration to keep the tanks clean. You could actually smell it in the air after they turd/farted.
I'm not going to post any more on this topic cos I'm wayyyy to interested in this for it to be healthy lol.