Comets need pointed tail lobes, as in an open pair of scissors, and the tail and its carriage are the most important features of the type. They are fast swimmers and do well in ponds.
Comets were probably first produced in USA (or possibly in Europe). They are known as swallowtails in the Far East.
The colour may be metallic (self-coloured or variegated in a pleasing pattern and similar on each side) or calico. Metallic colours should appear as burnished metal, extending into the fins. Calico fish should have a blue background with patches of violet, red, orange, yellow and brown, spotted with black.