That is a psuedocromis. I have one myself. Mildly agressive, and
medium-warm in the teritorial dept. Best to introduce last in the tank.
They like meaty food, such as brine shrimp, nuapili, pods, etc. Adults
reach 3 to even 4 inches nose to tail. These fish are smart, and like
to watch the world outside the tank. They love anything alive to eat,
but will eat frozen food. I've seen mine harrash peppermint shrimp
before. The fish is a good pet and would be best kept in no less than
55g.