Simply because of the thin black line edging the dorsal fin, which is comparable to that of a mourning card, this delightful small fish has been given the well-liked name of merry widow.
Females, like the guppies, are twice as big as the males, but lack the subtle beauty of the dorsal fin. This fin, which is generally carried proudly erect, is marked with two arcs parallel to the outside edge. Both arcs are dark but the inner one is slightly lighter.
Other markings are narrow, dark vertical lines along the body, which is a shade of olive green, along with a short black line that passes via the eye. Their gill covers reflect an iridescent blue-green, and this colour may also be detected on the body when caught by the light.
An additional outstanding feature of the merry widow is the long gonopodium. The latin generic name of Phallichthys means fish with phallus or gonopodium.
Usually a lively fish, the merry widow could be relied upon for constant animation of the aquarium.
Breeding is fairly effortlessly accomplished at a temperature of 78° F.