Yes.
not better in groups
I think you mean "Fantail" and the answer is goldfish can see no better or worse in the dark than most other fish. They are normal in their light requirements.
Normally goldfish are peaceful and calm.But incase your goldfish is doing so then its better to separate the new goldfish.
I am sure the meaning is quite literal. They are goldfish that eat other goldfish.
Other goldfish, preferably This will ensure that the goldfish will not be injured by other tankmates and also ensures that the other tankmate's gills are not damaged by the large amounts of toxic wastes (ammonia) that the goldfish produces daily.
yes
It's not uncommon for goldfish to hang around each other in a tank; sometimes they don't bother with each other, and other times they are bumping into each other.
ID3541807423 says: They aren't attacking each other, they are just playingPuertoRicoRocks says: Actually, it is rare, but goldfish can fight.But when goldfish are kept together it benefits them. (Unless it's a regular goldfish with a fancy goldfish, because in that case the regular goldfish would eat the food up before the fancy one gets to it.)It benefits them because they're not alone and they will swim more often, have more fun, and live a better life
No. A goldfish can only breed with other Carassiusspecies.
Get a second goldfish.
No
Shubunkins are goldfish, so therefore mixing goldfish with goldfish is usually not a problem. However, if the other goldfish are fancy then mixing them together would not be recommended.