Hi, I have two oscars. I recently got them ( about a month ago). One is 11 inch long and the other is 7 inch. Till few days back they used to live peacefully swimming together. Then the bigger one started head butting and nipping the small one. First I thought they were just playing. Now the small one running away and hiding from the big one. Sometimes the small one try to hit the big one with its tail part. But it doesn't deter the big one. Today I noticed scales on the small one are damaged. I read somewhere that this is part of their mating ritual. Is it true or should I worry about it. I recently changed water and the water quality is good. Please advice. They are eating normally and come to the surface of the water when I start feeding them.

how big is your tank? sometimes when they reach maturity they will get aggressive especially is there's 2 males in the tank.

It's a 55g tank with a 6 inch pleco and a 3 inch dwarf gaurami.. Is it over crowded?...The big one also keeps moving gravel to expose glass floor of the tank.. I don't know if it has any significance. It made 3 spots like that in different corners of the tank.

clearing gravel is def a sign of maturity as far as I know. I'm suprised the dwarf gaurami is still alive & yes your tank is def over crowed ( maybe not right now but eventually). 55g is recommended for 1 oscar.

Thanx angmat. I will try to find new tank for them. Gaurami was with them since they were all babies.

11 inches oscar is already considered fully grown. with another 7 inches fish
plus other tankmates is already overstock. bullying is part of territorial issue
or courting. you are the one who can evaluate if bullying is to much: with swollen
mouth, body scrape and shattered fins. if the smaller one is already swimming away
and the bully never stop chasing, perhaps, you need to try the BGH time out bag/net.

don't you have any water issue yet?

It sounds like bullying to me. If this behaviour continues then you will have to rehome one or it will end up getting injured or even killed. Can you post a picture.