This species is distinguished by having a medium to large swordtail with a long straight caudal appendage; midlateral stripe may be dusky or brownish (northern populations) or red; 2 additional reddish stripes may be present above midlateral line and one beneath; terminal segment of gonopodial ray 3 produced into a crescent-shaped hook and blade pointed distally; ray 4a curves strongly backward over the blade at an angle greater than 90°; distal serrae of ray 4p reduced in size and number and proximal serrae rather slender; terminal segment of ray 5a produced into a claw, several times larger than the distal serrae of ray 4p (Ref. 52914).

Description: Body elongated; head pointed. There are many color forms due to the very extensive natural habitats. For green swordtail, the ground color is olive gray; scale rows along the middle of the body are green to blue; belly is white and there is a light red, dark red or brown longitudinal line on the flanks in all populations (regional forms). In a few variants, there can be one or two additional lines above and one or two below this line. In almost all populations, the dorsal fin has spots or flecks of red. This coloration can also appear in the caudal fin. The sword of males is bright yellow and edged more broadly in black below than above. Old fish (3 to 4 years old) can have a totally black sword from the caudal fin all the way to the tip of the sword.