H. compressus is the type species of the genus Hyphessobrycon but is not well-known in the ornamental trade.

Hyphessobrycon was raised by Durbin in Eigenmann (1908) as a subgenus of Hemigrammus, differing from the latter by the absence of scales on the caudal-fin.

This species has been a popular aquarium fish for a considerable period and virtually all fish traded are now raised commercially for the purpose.

It is easily identified by the characteristic bright red or orange underside of the head, which is more pronounced in adults.

Following Miller and Taylor (1984), the genus Thorichthys is identified…

Wild swordtails are a fairly basic green colur. However the vast majority of swordtails available in the hobby today are hybrids of X.helleri with X.maculatus or X.variatus. There are a huge number of selectively-bred varieties available, including wagtail, lyretail, tuxedo, albino, neon, red, green and hi-fin.

Swordtails may undergo what appears to be a change in sex. In young fish this may simply be late development. However some adult females develop male characteristics which is thought …