I've got 2 Oscar's (tiger, and lutino) a 125 gallon tank. They've been together since October last year. For some reason they will get into a fighting match and one of them ends up with his sides missing a ton of scales and marks around both their mouths where they've been lip locking. I'm not sure what to do about it because they'll be fine for a couple weeks, then all of the sudden, I'll come into the room and one's all beat up.
What I'm wondering is if this is just fighting or is it the beginnings of breeding behavior? Every night for the past 2 months the lutino has been digging a pit under his/hers favorite rock cave, and they're always swimming together. The tiger has an eye spot, and is wider (up and down) than the lutino, which is longer and skinny, so I think I may have a male and female.

you can not tell the difference between male and females by their body shape. the only way to do it is with venting and even this way is only successfull about 75-80% of the time. as for if they are entering into a breeding ritual its hard to say. i have a breeding pair and they do lip lock but there is never any damage to the fish just aggressive behavior.
on the other hand i have kept two males in a tank until they reached maturity and the fighting was definetly damaging to the smaller one. even in a 220 they could not get far enough apart so i had to move them.

i would keep an eye on the situation and if its gets constant or some serious damage is being done then you should put together a plan on how you intend to cope with the aggressor.....


hope some of this helps

hmmm, i have the same situation...almost. my lutino beats up my tiger, but not with wounds...just with aggression... so i DO believe mine are mating...tehey dig holes too, and I have heard of males beating females up so badly that they almost die (heard this when my firemouth dies from a brutal beating from my syns) u can also look at genitalia to get an idea. I think I have a male and female too. but when there is damage I agree with necro, usually its from 2 males, cause my male RD caused the most damage to the Lutino, whom I think is male, and not so bad on the Tiger, whom i think is female.

Most males fight to the death, females usually fight to cause harm, not kill...but these are fish so you never know!!
u can try netting the aggressive fish or separation by way of divider to see whats up. the less males the better...lol

thats true with humans too!

So I re-arranged the tank and added another cave. Now their both getting along again. Who knows how long it will last.

i have rearranged my tank numerous times and it definatly effects there moods. I usually keep something in the middle of the tank to seperate sides, it works for me