Very frustrating not to be able to visit more often but must ask some advice. My 2 large oscars are together for quite a while now (240 litre tank and no tank mates) - I had guests on Saturday (like before) and the one oscar started attacking the other one. Before, when they had a bit of a row, the golden oscar fought back, but this time it only subsided and looked for cover. The fighting went on day and night - I did another water change, cooled the temperature, switched their light of - but no stopping the fighting. They barely ate - the one fish was full of scars by yesterday morning and I was in a terrible state. I don't have another big tank to move one of them and don't know if it will be good to put one of them with the Malawi's (their water is very hard, etc). By last night the situation had calmed down - but what could have ignited this very ferocious fighting? Any advice anyone?

I had two Oscars that were in the same tank together for years. They seemed to be getting along very well until about three years in. Then they got nasty. It was because they were MATING. Have they been digging or cleaning off a flat piece of rock? Do you see a lot of twitching movements or gill flairing? These could all be signs of mating.
Also, I've got to add the inevitable comment about the size of your aquarium. I like to pack my fish in pretty tight, but 240L (63 gal) seems pretty close for a couple of large territorial cichlids. If this is a dominance struggle then it's going to get pretty ugly. My Oscars (and all my other fish for that matter) fight from time to time in my 125 gal. (470L) But there is also plenty of room for them to get away from each other an cool off.

Thank you very much for your input - they have been digging and cleaning for about 3 months now, but ya, I don't like that ugly business - long and short - I'll need to get a larger tank. I also have 2 other oscars, but they are still small (about 10 and 13cm respectively). They are in a 120 litre tank, so I'll have to make a plan very quickly. Thank you once again