Have a fish that has gone missing? You think it died sometime during the day while you were at work or school? Sometimes fish will go into hiding if things in the aquarium change. Unfortunately though, dead or dying fish also have a tendency of being hidden somewhere in the rock structure. A good tell-tale sign that a fish is dead and hidden under the rocks is an accumulation of hermits around a particular area. Just follow the trail of crabs to find the remains of a fish, and promptly remove them from the aquarium before they decay further.