|Bully who caught red handed|
For a long time I thought Goldfish are the most innocent aquarium Fish in the world. But few years back I found enough proof to think other way. Something similar happened today too. I told about this pretty guy with butterfly fin and I found he is a bully. This guy was biting and pecking at Black Moor and was keeping doing it till I remove the Black Moor to another tank.
It seems this guy was having a serious hatred toward the Black Moor. There are two other smaller and weak Oranda Goldfish but they were completely ignored. He / She was only picking on the poor Black Moor. Poor bugger was doing his/her best to stay out but this Goldfish thug would go after and trying bite fins. At end I just had to remove him and add to the bigger tank where other Goldfish are in.
So if you also thought Goldfish are all innocent fish then better keep an eye on your fish and find they are really innocent or not. Like all other fish these guys seems to have personalities too. There might be few evil guys at least and you might be owning one of them.
There are times Goldfish become aggressive. You could see males because bit aggressive toward females in mating season which is normal. You would notice lots of pushing. Also sometimes Goldfish would gang up and tear apart a sick Goldfish. Its natural thing too just to protect the rest. But none of these can't be the reason in this case. It just might be his/her personality.
It's better remove the victim if you notice something like this in Goldfish community tank. If only fish bullying everyone else just remove the bullying bugger. Goldfish are smart fish like Disucs fish so they get stressed too. Stress can lead to deceases.