he mite have been hideing. did he swim away when u picked up the rock? mine use to do that all the time. i would find him in a little hole, or between two rocks! but if u have live rock and a well-established tank. u should be fine. i lost about 5 fish in my 55. long story. i had ick problem, meds then different meds. they did mix well, kill almost all the fish. only 3 lived. a watchman goby, scooter blennie, sixline wrasse. i lost about $300 in fish that month!! so now i dont use medicines anymore. i do have sick tank i use (if i can catch them!!) but anyway i didnt have any kind of spike. 55gal with 80lbs lr.