Hi ive had my tiger oscar for just over a year now. Today i went to my local aquatic shop and he had just had delivery of a lovly looking tiger oscar which was a little larger than mine. I was assured that as this fish was a female it would be no problem to put him into my tank with my existing oscar. However as soon as i introduced them i could tell it wasnt going to go well. My oscar is being very aggresive towards his new tank mate and has caused some of the new fishes scales to come off. What can i do to help them get on as im very worried about the new fishes wellbeing even though it is bigger than my existing oscar. Please help! Thanks you

welcome to oscarfishlover

First of all, how old and big is your Oscar?

Did they tell you how they know it's a female? You can't tell the sex just by looking at them, however somebody may have had it and seen it to lay eggs which is how they would know it is a female. Of course somebody may have vented it, other than that I don't see how they would know.

Exactly how bad is the fighting? Since you any got them today, they might need time to settle down and start getting on. If it still looks like there is aggression between them in a day or two, you could put a divider between them and leave it like that for a week, just let them get used to each other and then try introducing them together again. If it is quite obvious it is not going to work, you will probably have to rehome one of them, or maybe get another tank, which I suspect is probably not an option.

My oscar is roughly 18 months old and is around 5-6 inches. my new oscar is around 7 inches. They said they knew because it has been with a catfish and as it had not been aggresive towards it they were 95% sure it was a female. The fish keep locking mouths together and when i can homne from the supermarket the new oscar was lying on his side on the bottom of my tank and the existing oscar was still going for it! My main concern is that the new oscar looks very "scabby" after just a few hours in the tank already. I have now put a clear divider between the fish to keep them from harming each other. Would introducing them both into a new tank together solve the problem as i guess my existing oscar is just being terratorial of his home?

I must say that your is not very big for an 18-month-old fish.leave the divider in there and let your other fish recover. Putting them in a much larger tank might help, but I honestly couldn't guarantee it would help. Try introducing them together again in a few days, if it doesn't work, I think you're going to have to think about getting rid of one
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by the way, you cannot tell the sex of an Oscar by the way it behaves towards other fish

how big would you say he should be? What can cause him not to grow properly? Thank you for your help. i think ill reintroduce them in a few days and see how they are, if not im going to have to say good bye to one. But which one!?!?! Thank you very much for your advice.

based on all the Oscars I had over the years, I would say that the average size for an 18 month Oscar should be between nine and 10 inches. Now, there are a few factors that could either slow the growth rate down , or actually accelerate it.giving fish a lot of room will certainly help them grow properly and you shouldn't have any problems with Oscars reaching a good size.

Fish can be stunted by keeping them in poor water conditions. Keeping them in a very small tank will also slow their growth rate. For instance, an Oscar is very unlikely to reach 12 inches plus in a very small tank, whereas if you put it in a very large tank, it will easily get there.

How big is your tank? How often do you carry out water changes? Do you test the water on a regular basis? These are three factors that will play a very very big part in an Oscars health. an Oscar that is growing properly will reach 6 inches within six to seven months of its life.

So if you can test your water and give us some answers to the questions, we may be able to determine if you're fish is actually stunted