[Galaxy The Betta Fish]

He's either a Double Tail or Halfmoon. I'm not completely sure though:

 

[Plinkploop]

It's not super clear in the picture but true double tails have a split with 2 "moons" often overlapping each other, a half moon will not have a split with the 2 overlapping. There's any number of in betweens within the 2 categories so it's often hard to tell.