Need help identifying my fish species.

[CanukAimara]

Hello! I recently obtained a fish from Craig's list. The guy was not sure what type of fish it was and I am new to fish keeping.
He is 4" long with a narrow body and extremely mean. I have him in my 150G with my 6" Ted devil whom he recently killed. I want tk at-home this evil little fish but first need to know what species he is.
I want to tell his next owner as much about him.as I can. Any help.ide tidying him wpdbe greatly appreciated! Ty in advance!View attachment 1425297

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[duanes]

When the fish I have now were collected, they were mature adult Andinoacara, and topped out at maybe a little over 5"-6" for males.
The most dominant male, drove 2 similar size males out of a 180 gal tank. (less predatory than your Parachromis, which more than double their size.

As you can see (above) they were collected with a number of similar size crustaceans.
But within about 2 weeks, all the crustaceans were gone, eaten.