For the past few days, my gourami has been very aggressive. He has started to chase around the other fish in the tank quite often. (Before, he was only slightly aggressive around feeding time) Any ideas on why? The other fish in the tank are very stressed because of his behavior and I am concerned about them. He’s nearly killed one already. When he’s not seen chasing the other fish, he’s usually darting back and forth. He used to be very calm. I don’t understand what has changed. I’ve had these fish for two months and they got along fine before this week. I suspect it’s due to the fact that the tank he is being kept in is too small. He was very young when we first got him, so he could be kept in a 20gal. He’s grown a lot since then and I need to move him into a 29gal. My parents, however, don’t agree to buy one with their money (understandable) so I’m still saving up for that, and it’s not going to be another month or so until I can set up another tank.