I have had two tiger oscars for about 6 years, they are both about 9 inches long and are now in a 360 litre tank.

My water levels are normal I test them regularly especially for ammonia and nitrates.

One of my oscars has always been the stronger , larger, healthier one. The other did have hole in the head but i managed to get rid of it .

They have only been in their new tank about 4 months and they have a varied diet of cichlid tablet food, bloodworm (frozen) , shrimp (frozen) , daphnia (frozen) peas (no shells) and a vegetable flake food.

The problem is that recently the weaker of my two oscars has become swollen, it's not swim bladder and it's not dropsy, he is swimming fine and acting like a healthy fish with no pine cone like scales or anything like that. The lump is on the side (rather than the belly/underside) of the fish , and only sticks out on one side. I have no idea what it is as he is showing no other symptoms! I am so worried about him and i have been told it could be a tumour! The lump has gotten bigger over the last few days ANY advice would be great as so far no one seems to be able to suggest anything

Thankyou x

Welcome to the community

Really, your guess is as good as ours. Without a biopsy, or closer inspection of the lump, it's going to be very difficult to reliably diagnose what could be wrong. To be quite honest, we would just be guessing so the only advice I can personally give you is to contact a fish specialist, maybe somebody who treats ornamental fish, or even a vet who specialises in fish. They will be able to remove the fish from the tank, anaesthetise it and then investigate rather what could be wrong, this happens all the time in the ornamental carp world and it wouldn't be a problem for a professional to do this.

However, in the meantime, please post some photos if you can. There are a number of reasons why finished about the symptoms like this, sometimes they may have problems with internal organs, it may be a case of a blocked intestine. As you say, there is a very strong possibility this is a tumour. If we can see some photos, it will give us an indication of what might be wrong. As you say, if your fish is behaving normally then it obviously is not in distress. A couple of years ago a fish store that I go to sometimes had an Oscar that looked like it had swallowed a golf ball. I don't know what ever became of it, but it was acting perfectly okay when ever I saw it.

Thankyou for your speedy response ! I will try and get some clear pictures up ASAP

I can't really add any more than OFL has said. my first guess would have been spawn but you say more the side than belly? i will wait for the pics. i am surprised its growing daily?