Agree with the others, looks like young Heterotilapia buttikoferi (or cessiana) riverine African cichlids.
They will follow hippos eating their feces, as they are ejected in rivers they inhabit, so great recyclers.
They can reach about 20" and have a tendency to help an aquarist euthanize all the other fish in a tank, once they hit somewhere close to maturity.
I find them to be great fish, if kept alone, or asa mated pair pair in a tank of not much under 300 gallons