I put a new oscar fish in my fish tank yesterday along with the oscar that was previously in it(jamal). As i was assimilating the new oscar i realized a spot the size of a pin needle on jamals head so i decided to watch him carefully and left him alone. Naturally i just put a new fish in his territory and he is being aggressive BUT as far as we have seen jamal keeps him in a corner and as long as he is there he doesnt bother him. When he gets up jamal speeds over and rams into him and we have never seen the new oscar attack back. Now the reason i told you that is becuase i was wondering if it may be a bite on his head because i woke up this morning and it was like a little box on his forhead MUCH MUCH! bigger than last night. Is this hole in the head or a nasty bite.

yesterday-the size of a pin needle

today-

Its difficult to tell from the picture but if i was to guess i would its the result of an injury either from the other fish or from hitting something in the tank. HITH doesnt usually develop this quick (but i may be wrong). Keep an eye on it and if it is from an injury it will cure quite quickly

Just to be sure can you post some test results (the actual readings) for ammonia, nitrite and nitrate.

To help your new fish settle in try taking both fish out of the tank (place them in a bucket of tank water) and re-arrange the tank decor around and then add the fish back

Oscars are generally ok with other oscars and other fish once they have sorted out their pecking order but all are different and some are just plain nasty