Audra Johnson wrote:
Last year, an unidentified cichlid appeared in my roommate's feeder
fish (for her turtles.) He never got eaten, and by the time he got
about three inches long, we took him out and put him in a ten gallon
of his own. He's now around four inches, a dark bronze with faint
iridescense, blue iridescent line patterns below his eyes and a black
spot rimmed with yellow/bronze iridescence on his gill covers. His
fins are edged with white. I have no idea what he is, but he's
certainly aggressive and has a big mouth.

Not totally related to your original question, but you might want to
identify this fish properly so you can give it a suitably sized home. One
thing to consider, based on the spot on the gill cover, is that you have a
sunfish instead of a cichlid. This is especially probable if the feeder
fish were from an outside water source in the USA. Sunfish are all over
the place in the USA waterways. They resemble cichlids in shape too. You
can try doing a web search for pictures. Bluegill (a common sunfish) is
another name to search for. They're often caught in sports fishing, so a
page of that sort might have good identifying pictures.

There are also cichlids which have a gill spot, although most have other
markings as well. One which might fit your description that comes to mind
is one of the Neolamprologous brichardi/pulcher complex of African
cichlids. There are some of those that have nice irridescent patterns
under the eyes although they usually have two dark spots/stripes. Some of
the various African species lumped under "tilapia" also resemble that
coloration. You should look through a good book like Loiselle's "The
Cichlid Aquarium" or other picture oriented reference books to see if you
can find your fish.

I suspect you'll find the fish will get larger than 4" and will need a
larger home in the future. If that is the case, you may want to save up
for that instead of spending money further furnishing its current home.