pearlscale butterfly

Good evening, I have a relatively new 40 gallon tank that I began back at the end of Jan of this year. Got it up and running and introduced 2 clowns, a couple of hermits, 1 emerald crab, and most recently a pearlscale butterfly about 8 weeks ago. I'll start by saying he was extremely skittish...

I introduced a Pearlscale Butterflyfish into my fish only tank last night, he was swimming around the tank and swimming throughout the rocks like any other fish would first being introduced into a tank, went to sleep and this morning he is in the back of the tank behind my rocks breathing heavy...