They flick around the tank fast and move fast.
They do a lot of swimming.
Yes, for they are both Fancy Goldfish (It's bad to keep Comets with Fancy varities because most likely the comet will become stressed and die).
Well pH has an affect on goldfish health: too low or too high a pH causes the fish to be stressed and if it is stressed it is more susceptable to disease and will not grow.
No they do not, goldfish are egg laying fish only.
Dogs actually do not get stressed out but they can become jealous or hyper.
My Fantail Goldfish did that alot the first time I got him. I think it might be that they need to relax or they might be scared.
It's VERY stressed. Try to put some Goldfish stress relief medicine in the water when you change it, or remove some
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If it's just chasing it: This is a way that goldfish "play". They play rather agressively, but they don't really get hurt or stressed. If it's chasing AND pecking it: Then it's bullying. The victim(s) will seem stressed and hurt. If youhave bully fish put them in a different tank or return them to the pet store.
goldfish need to lay eggs. Because if they don't no goldfish would be alive and would not be any more so they would become gone forever.
Probably, but usually the comet goldfish will get all the food and/or the other goldfish will become miserable. This has happened to me before and I do not recommend putting them in the same tanks. Try putting the fancy and comet godlfish seperate!
you become stressed
This mean to become stressed quite quickly