How to make goldfish's tail longer?

[Trioracles]

Being a first time goldfish owner, I ordered some goldfish online. The bad thing is, you don't know what the fish looks like until u open the package. I really like fishes with long flowing tails and fins. If I get a small finned and tailed goldfish , is their a way to make them grow longer?

 

[tnfinfan]

It's mostly genetic. But, keeping them healthy and with ample space is what allows them to grow to their full size which includes their fins. Goldfish require a whole lot more room and care than most folks realize.