I added a ~1.25 inch hi-fin ray goby to my tank to pair with a pistol shrimp that is under the rockwork somewhere on Saturday. He swam around the tank, and I didn't see him start hiding in any caves. I haven't seen him since that Saturday night, and it is Wednesday morning now. I have a pretty tight fitting lid and have not seen any crispy fish laying around, and I have also poked around the rockwork with a flashlight trying to see any glimpses of the goby, to no avail. I haven't seen the pistol shrimp since I added him almost 2 months ago, but I hear him a couple of times a week. Any suggestions or advice?