Goldfish is a type.
There are over 21 different types of goldfish.....I can only name a few of the top of my head.
. Veiltale
. Pearlscale
. Ryukin
. Lionhead
. Lionchu
. Common/comet (same thing!)
. Bubble eye
. Oranda
. Black moor
. Shubnukin
. Telascope eye
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.