The sub-family Rivulinae or New World Rivulines consists of several genera, three of which are included in this section: Cynolebias, Pterolebias, and Rivulus.  These Killifish inhabit North, South, and Central America, and some of the islands of the Caribbean.
Argentine Pearl [
Cynolebias bellottii
SYN : Cynolebias gibberosus, C. maculatus, C. robustus
PD : This laterally compressed species has rounded fins.  Males have an olive-brown back with blue-gray flanks. The body is covered with whitish-blue spots.  At spawning times, the male becomes almost black. A dark stripe runs from the forehead through the eye.  The dorsal fin is colored like the back,while the other fins are colored like the flanks. Males are paler in color, and often have irregular dark bands on the body.
SIZE : Males to 2.8" (7 cm), female to 2.3" (6 cm)
SS : Cynolebias nigripinnis
HAB : South America; Rio de la Plata basin.
S: bottom, middle
TANK : A tank measuring 24" (51 cm) with a capacity of 10-15 gallons (38-57 L) is sufficient.  Use a soft substrate, preferably peat in a tank that is arranged in dark colors.  Provide wood and planted areas to serve as hiding areas. Shallow tanks are preferred.
WATER : pH 6-7 (6.5), 2-12 dH (5), 64-75°F (18-24°C)
SB : Males are territorial, intolerant, and aggressive towards one another.  Males may harass females around spawning times, so keep one male with several females. 
SC : This fish is best kept in a species tank, although small catfish and schooling fish of the upper swimming levels may be tolerable. 
FOOD : Live; insect larvae, insects, worms, crustaceans; flakes.
SEX: Males are larger and darker in body coloring, especially around spawning times.
B : Place an adult pair in a tank (3 gallons is adequate), containing a substrate of peat moss. The water should be soft (2-5°dH) and have a water temperature from 68-77°F (20-25°C).  The female may press the eggs into the peat using her anal fins, or the pair may burrow into the substrate, disappearing entirely for short periods of time. Remove the pair from the tank, and then remove the peat.  After drying the peat, store it for three to four months. After the time has passed, place the peat in a shallow tank having soft water. To induce hatching, sprinkle small amounts of fine dry food on the surface of the water (See introduction to Killifish). Start feeding with Artemia nauplii.  The young grow quickly.
BP : 7. Breeding is not especially difficult.
R : The Argentine Pearl is an annual species that rarely lives longer than a year even under the best conditions.  
DC : 5. This species is short-lived and requires frequent partial water changes, combined with well-maintained water conditions.
Dwarf Argentine Pearl, Black-finned Pearl [
Cynolebias nigripinnis
SYN : None
PD : C.nigripinnis is a smaller species than C. bellotti , although these two species have similar characteristics. Mature males have a blue-black body color that extends on to the fins.  The body is marked with numerous iridescent,blue-white spots. Just below the edges of the anal and dorsal fins, these spots run together to form a broken stripe. The caudal fin has several irregular rows of spots.  Females are dull yellow-gray with irregular dark spots. The fins are brown-gray.
SIZE : To 2" (5 cm)
SS : Cynolebias bellotti
HAB : Inhabits rivers and streams with muddy beds that dry up at parts of the year.  South America; Rio Paranà in Argentina
S: bottom
TANK : A tank measuring 16" (40 cm) with a capacity of 5 gallons (20 L) is sufficient for a male with one or more females. If more fish are desired, a larger tank is recommended.  Follow suggestions for C. bellotti .
WATER : pH 5.5-6.7 (6.2), 1-8 dH (4), 60-72°F (16-22°C)
SB : The Dwarf Argentine Pearl is an aggressive species that is best kept in its own tank.  Males may harass unreceptive females excessively. Do not keep two males in the same tank.
SC : Possibly small catfish and small schooling fish of the upper swimming levels.
FOOD : Live; insect larvae, insects, worms, crustaceans; flakes.
SEX: Males are increasingly more colorful as the spawning season approaches.  Generally males are darker with iridescent spots.
B : A mature pair can be placed in a spawning tank containing a peat or mud substrate and driftwood hiding places for the female. The water should have a pH around 6.0, a water hardness from 1-4 dH, and a temperature from 68-72°F (20-22°C). Follow suggestions for C. bellotti , although the peat containing the eggs should be kept in a dark area. The most peat can be added to a tank containing soft water after a period of 3 months to two or more years. In order to obtain a healthy brood, the peat or mud should be submersed in water only 1 / 2 " to 1" (1.3-2.5 cm) deep.  Start feeding with Artemia nauplii and powdered foods.
BP : 8. Breeding is fairly difficult.
R : Formerly two sub-species were known: C. nigripinnis nigripinnis (profiled above) and C. nigripinnis alexandri ; although the latter sub-species is now recognized as a distinct species.
DC : 7. This sensitive species requires well-maintained water with frequent partial water changes.
Featherfin Panchax, Longfin Killifish [
Pterolebias longipinnis
SYN : Rivulus macrurus
PD : An elongated species with elaborate fins.  Males have a brownish back and brownish-pearl colored flanks with a violet to silver iridescence in reflected light.  The flanks are marked with rows of small iridescent green or yellow spots. Just beyond the gill cover, males have a black and red marking.  The fins are also brownish-pearl colored with irregular brown markings, and the tips of the pelvic fins are white.  The fins of males are far more complex than those of females, which are shorter and rounded. Females are duller in body coloration. 
SIZE : To 4" (10 cm)
SS : The Peruvian Longfin ( Pterolebias peruensis ) of Peruvian Amazon reaches 4.7" (12 cm). The Lace-finned Killifish ( P. zonatus ) is another similar species.
HAB : Marshy, floodplain zones that frequently dry up.  South America; in the Lower Amazon of Brazil and Argentina.
S: bottom, middle
TANK : 24" (60 cm) or 10-15 gallons (38-57 L) is sufficient.  Provide dense planting with a cover of floating plants to diffuse the overhead lighting. The tank should be arranged in dark colors with a peat substrate. 
WATER : pH 6-7.2 (6.5); 3-12 dH (5); 64-73°F (18-23°C)
SB : Males are aggressive toward one another and should be only kept one to a tank with two or three females. A large number of males (more than six) can usually be safely kept in a tank as their aggression is dispersed.
SC : This species is best kept in a species, although it can be combined with small schooling characins and small catfish. 
FOOD : Live; insect larvae, Artemia , insects, Tubifex ; flakes.
SEX: Males are larger, more colorful, and have more elaborate fins.
B : Use water temperatures between 68-75°F (20-24°C), a pH from 6.2-6.5, and water hardness of 2-5 dH. The small tank should include a peat moss substrate and retreats for the female. Place one mature female with two or three mature females. The eggs are laid in the peat.  Remove the peat and place it in a plastic bag for two or three months. Place the peat in a tank containing soft water with a depth of 2-6" (5-15 cm).  Raise the fry on powdered foods and Artemia nauplii.
BP : 7. Breeding is moderately difficult.
R : An annual species that rarely live longer than 16 months in captivity.
DC : 6. This species is sensitive to changes in water chemistry, so small frequent water changes are recommended.
Agila Rivulus [
Rivulus agilae
SYN : Rivulusmanaensis
PD : An elongated fish with an up-turned mouth.  Males have a light olive back with orange to yellow flanks. The flanks often are blue-green in areas.  The fins are also orange in color.  Femalesare duller orange-brown with transparent fins.
SIZE : To 2" (5 cm)
SS : Rivulus geayi, R. uroflammeus
HAB : South America; inhabits shallow areas of small rivers and streams in the coastal plains of Guyana, French Guyana, and Surinam.
S: middle, top
TANK : A tank measuring 16" (40 cm) with a capacity of 5 gallons (19 L).  Provide a cover of floating plants and arrange the tank in dark colors.  Plant the tank heavily along the rear and sides.  Cover the tank well. This species prefers shallow tanks.
WATER : pH 5.5-7.2 (6.9), 2-12 dH (8), 72-81°F (22-27°C)
SB : A peaceful species that should be kept in a ration of one male to two or three females.  More than one male can be kept in a 28" (71 cm) tank. Males are territorial towards others. 
SC : Small catfish, small schooling fish (tetras), Apistogramma
FOOD : Live; insects, insect larvae, crustaceans; flakes
SEX: Males are more colorful.
B : Use a small breeding tank furnished with Java Moss, floating plants, and spawning grass.  The water should have a temperature from 73-82°F (23-28°C), a pH from 5.5-6.5, and a water hardness from 2-7dH.  The substrate should be peat moss. The eggs, which are fairly large, are laid daily for a period of two to four weeks.  The peat can be removed and stored in a plastic bag for a period of three to five weeks.  Place the peat in a dark, shallow tank containing soft water. Start feeding with Artemia nauplii.  The young are slow-growing.
BP : 8. Breeding is difficult.
R : Several color variants exist.  Many Rivulus species inhabit environments that dry up at times during the year. The Rivulus are able to move to pools by hopping along the ground, using their pectoral fins.  Rivulus marmoratus is a hermaphroditic Rivulus , which is capable of self-fertilization.
DC : 6. A sensitive species that requires well-maintained water.
Black-Tailed Rivulus, Blue-Stripe Rivulus [
Rivulus xiphidius
SYN : None
PD : An elongated species with a rounded caudal fin.  The back of males is reddish-brown as are the upper flanks. An iridescent blue band extends from the pectoral fin to the caudal peduncle.  The band become black from the pectoral fin to the snout, and from the caudal peduncle to the end of the caudal fin.  The belly is sliver-white. A fine turquoise stripe runs above the blue and black band.  The fins are reddish-brown, except for the blue base of the anal fin, and the continuation of the black and turquoise stripes on the caudal fin.
SIZE : To 1.5" (4 cm)
SS : None
HAB : South America; inhabits small streams in coastal Surinam and French Guyana.
S: all
TANK : A tank measuring 16" (40 cm) with a capacity of 5 gallons (19 L) is adequate.  Follow recommendations for R. agilae
WATER : 5.5-6.7 (6.2), 2-6 dH (4), 73-77°F (23-25°C)
SB : A peaceful species that is more seclusive than R. agilae .  Males should be given plenty of space in order to set up territories. This species is perhaps best kept in a tank of its own. 
SC : Small schooling characins, Corydoras catfish.
FOOD : Live; insects, insect larvae, crustaceans, Tubifex ; flakes
SEX: Males are larger and more colorful.
B : Use a small tank furnished with Java Moss and a substrate of peat.  Keep one male with two or three females.  Use water with a pH from 5.5-6.0, a dH from 2-4 dH, and a temperature from 75-79°F (24-26°C).  The fish spawn continuously for ten to 14 days. Remove the substrates from the tank and place store them for three weeks.  Soft water can be added, and the fry should be raised on Artemia nauplii.
BP : 8. Breeding is difficult.
R : The two Rivulus species in this book are exceptions from other Rivulus species in their sensitivity.  Several Rivulus species are considered hardy Killifish. 
DC : 7. A sensitive, but beautiful species.