Fancy goldfish need at minimum 20 gallons for one fish, plus 10 gallons for each additional goldfish you are adding (thus 30 gallons for 2 goldfish); so the answer to your question is dependant on the size of your tank.
Goldfish
goldfish
It is obviously internal and in front of the fishes anus. +_+
The collective noun is a troubling of goldfish.
It is quite possible that the black spot is part of the fishes colouration. Goldfish often have many different colours in many different shapes and shades anywhere on their bodies or fins.
People consider Goldfish as good friends too. But they are fishes and cannot socialize back.
Japanese Kai-Ru Fish
Trout, bass, catfish, perch, goldfish,
Goldfish and angel fish
No, this is quite common in goldfish and isn't anything to worry about as it poses no threat to the fishes health.
All fish have a coating of clear slime to protect them. If your goldfish have brownish slime then the fishes water needs changing urgently.
One goldfish chasing (or in this case biting) another fishes rear is how goldfish flirt, however this could also be a display of aggression towards the other fish.