The Doubletail has been an object of adoration ever since it first appeared on the betta scene. The Doubletail, or DT, betta, as it's name would imply, has two distinct caudal lobes, or tails. They are not arranged side-by-side like the Wakin or Jikin Goldfish, but one on top of the other. In addition, the dorsal is greatly increased in length, and the bodies are typically shorter and stouter than that of a Singletail (ST), as this makes the fish better able to carry its extra finnage.

The DT phenotype is controlled by one gene which, when double-recessive, produces a betta with two tails and a greatly increased dorsal fin. There are likely other factors involved in the appearance of the DT since not all have the same degree of the split in the caudal fin. The gene also seems to be variable in expression, producing some specimens with perfectly-balanced lobes and others with lobes that are dramatically disproportionate to one another. (source: bettysplendens[dot]com)