swordtailed

Swordtailed refers to a characteristic found in certain species of fish, most notably in the family Xiphophoridae, commonly known as swordtails. This defining feature is a prominent, elongated ray at the base of the caudal fin, which extends beyond the rest of the tail. In males of many swordtail species, this appendage is notably extended and often has a pointed, sword-like appearance, giving the fish its name.

The presence and development of this "sword" are often a secondary sexual characteristic, meaning it is more pronounced in males and plays a role in mate selection. Females typically lack this prominent extension or possess a much shorter, rounded caudal fin. The color and pattern of the sword can vary greatly depending on the specific species and subspecies of swordtail, as well as selective breeding in aquarium populations.

Beyond the visual characteristic, the term "swordtailed" does not denote a separate taxonomic group but rather describes this specific morphological trait. The most well-known examples are found within the genus Xiphophorus, which includes popular aquarium fish like the Green Swordtail (Xiphophorus hellerii) and the Platy (Xiphophorus maculatus), though the latter typically exhibits a less pronounced sword. The development of the sword can be influenced by factors such as water quality and diet, in addition to genetics.