They probably do occur naturally but not to the same extent. The LF varieties are obviously selectively bred to have longer fins. It's the same way they breed bettas, guppies, veil tail oscars and even breeds of dogs. To get these long fins they would have to inbred or line bred them. When you start inbreeding, some unnecessary traits would also come out. What was once recessive becomes dominant gene. What kind of other abnormalities they have we won't really know since they are only starting to become more available.
