Hello everyone!! I recently took over the care for 2 large oscars - They are my bosses fish and he is undergoing chemo and he ask me to take care of them....So here I am!! First of all- A couple of weeks ago (3 to be exact) I come into work and immediately noticed that one of them looked like it had been fighting all night for it's life and was quickly losing the battle!! I panicked and that is how I come across this site - I read that I should quarantine the aggressive fish for a while......I got a tank (55 gallon) separator and gave the aggressive fish about 6 inches of the length of the tank.....I have tried to let them come together again but this meanie INSTANTLY attacks the other one!!! The fish that was barely hanging on 3 weeks has since healed nicely and all of his fins have grown back BUT when I place them together - the attacker is back at it and the other fish looks to be having a seizure! He(or she) blows it's face out like a puffer fish and vibrates. It scares the daylights out of me as I dont want anything bad to happen to either of them. Is this normal - Does anyone know what I should do in this situation?

Ok a couple questions.

1. How big are these O's?
2. How big is the tank?
3. Have you checked the water peramiters? what were the results?

This could be bullying, and from the seizure movement you are describing it sounds like a mating dance. But please answer the best you can. these questions so we can better help you!

Nickisue wrote:


he told u tthe size it 55 g

I would say that if the water parameters check out ok (if you don't know how to do this then take a sample of the water to a local pet store they should do it for free) then I would guess that you have a pair of oscars getting ready to mate. Oscar fish are very agressive when they mate. Many of them will get very injured, but they do heal. Let us know how big the oscars are and what the water parameters are and we can help

I will upload a pic when I get home - but I would say they are 5 1/2 to 6 inches long. The tank is 55 gallons. As far as the water parameters we have someone that comes in and cleans and checks and he didn't answer my call so I do not know that answer. The day I come in and seen the fish beat up there was only the night that had lapsed - the fish were normal the day before and they got along for months before this happened - but the fish look like he has been scratched and bitten all night long the next day???
Thanks for your help!

Ok first let me say that 2 O's in a 55 is too many. Do you know how often the guy comes to clean the tank? Do you know what filter(s) are running? Sorry about all the questions but we need this info to help you.

If the O's are only 6 inches long I would say they are probably too young to breed.
But if you have 2 boys they will fight for dominance and territory in the tank. This could be horrible.

And if your water is toxic this will cause aggression too.

Yeah I agree with Nickisue. they are two small to be breading( unless Nik you think that the oscars growth has been stunted?).But, I would bet that you have to boys pushing eachother around in a tank where there is not a lot of room

That is my bet. Although the stunting is possible. My money is on them being boys!

Ok - Someone here just said they are about 8 inches (and I have the one separated with a about 12 inches)...Not sure if that matters. To me they look huge!! I left the tank guy a VM - I am pretty sure he comes every Sat.......As soon as I get answers to your questions - I will post them. So, how big of a tank would be sufficient?

No less that 110 gallons. And you will need filtration for 330 gallons. Size of tank times 3. That will keep your water in check. Oscars produce HUGE amounts of waste. And require very clean water. I hope this all helps you.

And just a side note, if they are both boys that will never work. One will have to either go to a new tank or a new home. Sorry.

And keep them separated for now.

55 gal tank for two x 6 inches oscar is becoming to small.
do you have any idea how long have your boss keeping them?
i am not sure if they are matured enough for mating but yawning,
shivering and mouthing are just indication of maturing oscar...
trying to muscle up who is the boss.

if you do not have water test kit to determine water quality,
better do large water change to be safe... better safe that sorry.
clear water doesn't mean clean.... ammonia, nitrite, and nitrate
are bad elements that could not be seen by naked eye and will
stress the fishes if not check accordingly..

PAUL wrote:


does that mean that murky water isnt necessarily bad water