Crowntail Betta

The Crowntail has become a hugely popular tail type variation. It is unlike any other in the sense that the rays are extended to varying degrees on all fins giving the fish a "spiky" appearance. In show standards, for a fish to be classed as a Crowntail there has to a minimum of 33% reduction in webbing. The reduction on the webbing on Crowntail bettas also varies vastly, sometimes it can be quite full, some times dramatically reduced so only the rays are left. There are three recognised types of crowntail: the double ray, the single ray and the crossed ray. Crossed rays are the most desirable and the most expensive to purchase. There have also been lesser known variations such as the triple ray, even the quadruple ray! Crowntails can have their tails in a full 180 degree spread, or less than a 180 degree spread depending on their breeding. Crowntails are prone to fin curling, especially those with little webbing, if their water is not kept immaculate. Breeders are known to "sun bathe" their Bettas for an hour or so in order to keep their rays straight. It has been found also that when breeding, Crowntails have a heightened amount of aggression compared to other tail types, which can make it challenging to get a successful spawn. Petstores often supply inexpensive Crowntails, who's fins are closer together and not as "crownlike".

(Taken from here)