Members of the family of single tailed goldfish are very closely related to the common goldfish, or wild goldfish if you prefer the single tailed variety is a direct descendant of the carp family and much hardier than the twin tailed variety.
If you are thinking of getting a goldfish for the first time choosing a fish from this group would make perfect sense.
Twin tailed goldfish are closely related to the common goldfish, or wild goldfish if you prefer. Twin tailed fish need a little to a lot more attention than their common single tailed brothers and sisters
If you are thinking of getting a twin tailed goldfish as your first goldfish be prepared to run into many more things that need to looked after compared with the single tailed varieties.