I have had my Oscar for three years. I used to feed him a lot of feeder fish until I found out it caused holes in his body, so I stopped. Recently, I gave a 25% water change. The tank temp is 76 degrees, and I noticed for about three days now that the fish has been laying on the bottom of the tank. He won't eat and is very lethargic. Usually, when I go to the tank he swims over to me. Now he just lays there. He shares a tank with a plecko and an african cichlid. Can you please tell me what is wrong. I am worried. He looks so sad.