swordtail

sword +‎ tail

swordtail (plural swordtails)

1. One of many species of freshwater fish, in genus Xiphophorus, others of which are called platyfish.
   • 1998 August 21, Gretchen Vogel, “EVOLUTIONARY BIOLOGY:Doubled Genes May Explain Fish Diversity”, in Science‎, volume 281, number 5380, DOI:10.1126/science.281.5380.1119, pages 1119-1121:

     But ongoing efforts to sequence genes from other fishes, including salmon and swordtail, will also help to test the theory, Postlethwait says.

• green swordtail