The fish tank outside my office is home to about 20 fish of 4 different species, all under stringent management systems and quotas, naturally. Last Monday, one of our beautiful long-finned silver fish (one of the more expensive ones) took to repeatedly shooting from the bottom of the tank upwards, out of the water, and cracking its head on the lid (audible from down the corridor). He wouldn't stop even though we told him to. He seems to have caused some damage, because after a few days of this, he curled up in a ball and sank like a stone. He refused to die though, but became paler and paler, only reviving long enough to shoot again upwards and crack his head. We left him for the weekend in the hope he would still be there by Monday. Alas, he appeared to be a contender for the porcelain highway when we couldn't see him alive and kicking on Monday morning. After some hunting though, we still couldn't find his little fishy corpse. We emptied the entire tank of all its contents (the fish stayed put). Nothing. Until we spotted a very fat looking snail, and very dead. And hanging out of his mouth was a perfectly formed pure white fish skull - only bones left. The current theory is the greedy snail tried to eat his dead friend and croaked.
There's a moral in there somewhere.