I have an 80 gallon fresh water aquarium. It has had my tiger Oscar(less than 6 inches) , firemouth and green terror in it for a few months. I just recently added a new red oscar(8 inches) and he is very calm but now my tiger Oscar is shaking and twitching (most likely aggressive behavior). The tiger Oscar does not go after the red oscar, they follow each other and nip very lightly. But when it comes to the tiger Oscar and the firemouth and the green terror he is constantly going after them now. I'm not sure if it's because the tiger Oscar and red oscar are male and female and want to breed. Can you help me figure out why this is happening?