Perhaps you mean 'Clamped fin'. Clamped fin is caused either by parasites or poor water quality.
If you mean 'Fantail'. A fantail is a fish with 2 tails instead of one. They are harder to keep than goldfish but are much prettier
By the bottom fin, under the belly. The male's fin looks like a straight line and the female's is fanned out.
I would name my black goldfish Fin
it my not your
yes
Yes, but normally they grow back slowly. However, if fin rot has reached the base of the fin, then the goldfish would be in pain the rest of its life.
yes, but it may kill the goldfish
A goldfish has about 1,500 bones inside of it.
Because there is no hard or tough tissue inside of the fin to keep a erect shape.
Caudal fin
Use a medicine called Mr. Yellow found in medical stores and pet shops. This cures fin rot.
That's probably its poo, that's what my goldfish did. Their waste has to come out somewhere. maybe finrot. may be not nvm
Blotches on the dorsal fin and tail fin(s) can be the diseases fin and tail rot, easily cured with medication.