im assuming youre talking about goldfish??? if so, water quality is likely to be more of an issue than aggression although a fancy goldie is at a physical disadvantage to the comet type. their fins are longer and harder to swim with as opposed to the comet types sleek body type. i feel the cumbersome goldies shoudl not be kept with the natural ones.
how large is the tank??? how many fish are in it?
Chris- Husband, 04/30/77
Cailyn- Daughter, 07/05/99
Jeffrey- Son, 03/24/06
Alex- Son, 03/25/09
Mister- Black LabX, M, 08/06(?)
The Shadow Stalker- Gray Tux DSH, M, 04/04
The Mighty Hunter- Black Tux DSH, M, 04/04
Baby Girl- Tabby DMH, F, 12/03(?)
Frances- Tortie, DSH, F, 2007(?)