Oscars can be rough with each other sometimes. However, I don't like to split fish up unless it is absolutely necessary. Even though fish may be receiving injuries, I like to leave it as long as possible before deciding whether to split up or not. In many cases, the fighting stops, or doesn't get any worse than the fish are okay. Fins are very very delicate so can obviously get damaged easily, Oscars often nudge each other in their side, this is how the Finns get damaged. If there is no damage being done to the bodies, I should leave it a bit longer and just monitor the situation. When Oscars fight, they often liplock, also described as jaw locking. The problem is, Oscars also performed this type of behaviour when they are going through their breeding ritual. It can be difficult to distinguish between aggression and non-aggression