Why does a black moor attack other fancy goldfish he is much bigger and they have plenty of room?

There are a few reasons why a black moor might attack other fancy goldfish, even if they have plenty of room.

1. Territorial aggression: Black moors are known to be territorial fish, and they may attack other fish that they perceive as a threat to their territory. This is especially true during breeding season.

2. Competition for food: If there is not enough food for all the fish in the tank, the black moor may attack other fish in order to get more food for itself.

3. Boredom: If the black moor is bored, it may attack other fish simply for entertainment. This is more likely to happen if the tank is too small or if there are not enough hiding places for the other fish.

To reduce the risk of aggression, make sure that the tank is large enough for all of the fish, that there are plenty of hiding places, and that the fish are fed regularly. You can also try to distract the black moor by providing it with toys or other objects to play with.