First let me state, that I dont believe they actually eat the poo, But i've never kept them so what do I know 
I was watching dirty jobs the other day, and Mike was at a zoo cleaning hippo pens.
at one point Mike asks what kind of fish they have living in the water and the biologist replies "cichlids, they help eat the hippo poo, and keep the water a little cleaner" ..... or something along those lines.
but anyway, is that true by any stretch? I would think a marine biologist at the zoo knows what hes talking about, but it seems odd that a fish would eat poo.
probably just eating leftover undigested things right?

I was watching dirty jobs the other day, and Mike was at a zoo cleaning hippo pens.
at one point Mike asks what kind of fish they have living in the water and the biologist replies "cichlids, they help eat the hippo poo, and keep the water a little cleaner" ..... or something along those lines.
but anyway, is that true by any stretch? I would think a marine biologist at the zoo knows what hes talking about, but it seems odd that a fish would eat poo.
probably just eating leftover undigested things right?