This is probably the most spectacularly colored of all the Rivulus species. It is also one of the smallest and more challenging members of the genus and is definitely not a fish for beginners. It has a life span of about two and a half years. Females are smaller than the males, and they lack the blue-and-orange coloration. Instead, they have a dark gray vertical band.
Unlike some other members of the family, Rivulus species do not bury their eggs. If pools dry out in the wild, the eggs of some species may withstand desiccation for a while, but they do not go into the extended resting period (diopause) exhibited by annual species. Rivulus species tend to live for 18 months or more, and Green Rivulus has a life span of up to four years.
The Lace-finned Killifish is a truly magnificent species. It has brownish speckling and body bands on a light metallic-blue base color. Fully mature males have an almost sail-like anal fin and a substantial caudal fin. Of the other four species in the genus, P. longipinnis (the Long-finned Killifish) is the most frequently encountered. Its requirements are similar to those of the Lace-finned Killifish.
As in the other Cynolebias species featured, the body in male C. whitei is spangled with numerous white, cream, or bluish “pearls.” Males also exhibit a brownish base body color and elongated dorsal and anal fins. An aquarium-bred albino form is occasionally available.
Many authors recognize two subspecies of C. nigripinnis: C. n. nigripinnis (Black-finned, or Dwarf, Argentine Pearl) and C. n. alexandri (Entre Rio Argentine Pearl). Others—perhaps a majority—consider each one to be a valid species in its own right. While being overall similar to each other, C. n. alexandri males have brownish, almost vertical bands on the body. C. n. nigripinnis lacks the bands but has the characteristic black fins that are indicated in both the scientific and common names.
The Argentine Pearl was among the first New World killifish to be introduced into the hobby almost 100 years ago, but there is ongoing debate surrounding the classification of Cynolebias. Some authors classify the genus as Austrolebias, Nematolebias, or Simpsonichthys. Mirroring the lifestyle of their Old World relatives in the genus Nothobranchius, the Argentine Pearl and other Cynolebias species are annual fishes—their reproductive behavior is virtually identical.
Palmqvist’s Nothobranch is one of several species in which the caudal fin is blood-red throughout. As in so many other Nothobranchius species, the body coloration shows variation, depending on locality of origin. Generally, it has a bluish body with a network of red lines covering it. Females are smaller and duller in color than the males.
This colorful annual species, known in the hobby since the mid- 1910s, is one of the best-known representatives of its genus. Nothobranchius species are highly variable and often cause confusion with regard to precise identification. Some aquarium strains are also known. Like many other killifish, it is available only occasionally in general aquatic outlets.
This species has similar oblique body bands to A. chaperi (Chaper’s Panchax). As its common name suggests, it has six of these vertical bands. It is extremely variable, both in color and body patterning, and there are five known subspecies, each exhibiting variability according to location.
The Blue Panchax is one of the earliest species imported into Europe (1899). Despite this, it has never become as widespread within the hobby as its obvious beauty deserves. It has a greenish body with blue coloring along both sides that serves to highlight the outline of the scales.