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I have 2 Oscars about 7-8 inches long, a tiger and a red, in a 55 gallon tank.

They were showing the signs of breeding. Tail slaps, mouth locks, being agressive towards each other. The man at the store we bought them from said we should turn the heater up a bit to get them more in the mood. The tank is at about 82F right now. We bought a piece of slate rock for them, but they haven't touched it.

Lately the fish we thought is the female has been going crazy. She constantly attacks the other fish, tearing big chunks of scales off and chasing him around. It seems he is terrified now. We have plants covering our heater, and now he constantly hides up behind the filter because the other fish can't get him there.

He hardly comes out now. He hardly eats now. When we got the fish the Tiger was a couple of inches smaller than the Red but now it's as big, if not bigger.

I have no clue why he is doing this. I suppose because the other fish is picking on him??

I would turn the temp down to 76 OR 78F and let it come down on its own.. warmer water may trigger a spawn, but it also triggers aggression.. IF you do have a female, she may not be ready to spawn.. GET a divider and another GOOD filter and keep them seperated for a while until she?? heals..  No sence keeping them together if HE is going to attack her??..

I agree with Barb you should turn down the temp and separate the two! Also you should consider getting a bigger tank...having two 7 to 8 inch Oscars in a 55gl tank will surely trigger aggression whether they are a pair or not! I have two breeding pairs and each pair is in a 150gl tank, Now you don't have to purchase a big tank like that... A 110gl tank will do the job! 

I agree with lowering the temp (78 would be good) and the divider. One thing, though, is that it is not mating that is going on, just simple aggression. With mating play, in my experience, they do become "aggressive" but not so that one fish dominates the other.

Oscars respond to stress differently than other species. They are very sensitive to their surroundings, in and out of the aquarium, and will respond to negative stimuli. Most other species do not hide, feel sorry for themselves, etc. -- but Oscars generally do. Occasionally, when there's a negative influence causing stress, it causes agression. Therefore, after seperating your Oscars, you need to find the "stressor" that caused the agression. First, check water conditions and tank maintenance and make sure they are in line. Test Nitrite, Nitrate, and ammonia; especially nitrate. Maintain a diligent water change/gravel vacuum schedule. Maintain correct temperature. Make sure there's enough filtration. And, importantly, do not overfeed the aquarium! Feed as much as the oscars want, but no more. Floating, decomposing food is an aquarists worst enemy!!!

Secondly, and this is very important, take a look at the things outside of the tank that may be causing stress. First, make sure the lighting in the tank is dimmer than the lighting in the room. This removes the reflections in the glass and gives the fish the impression that the area he is in is much larger, lowering stress. Next, move any furniture from the front of the aquarium, creating a wide open space. (In concert with correct water maintenance, this is how you keep Oscar pairs successfully in 55s --). Next, lower noise levels near the tank -- is there a TV or loud stereo near the aquarium? A slamming door? Any other noise source that can be moderated?

The point is, Oscars never just "become" aggressive, especially with a tankmate that they've been peaceful with for a while. There is a stressor; you need to seperate the Oscars, then find and rectify the problem.   --Mark