Least Killifish/Dwarf Mosquitofish
Genus: Heterandria
Species: H. formosa
Maximum Size: .8” (males), 1.2" (females)
Aggression: Low, Social
Temperature: 70-78 F
pH: 7-8
Hardness: 10-20 dH
Brackish Tolerance: 1.000-1.005, some sources indicate will acclimate to marine conditions
Minimum Tank Size: 5 gallons
Feeding: Flakes and pellets, frozen brine shrimp, blackworms, glass worms
Notes: Despite the common name “Least Killifish”, Heterandria formosa is a livebearer of the family Poecilidae and is related to Mollies, Guppies, and Mosquitofish. Least Killifish are exceedingly small fish; as of 1991, it is the 7th smallest fish in the world.
Least Killifish do best with similarly sized, mild temperament fish. Bumblebee Gobies and Neocaridina/Caridina shrimps work well with Least Killifish. Endler’s Livebearers may work well, but males may be aggressive to male Least Killifish due to their somewhat similar appearance. Any tank with these fish should have densely planted areas in which to hide from boisterous tankmates. Like many livebearers, they will also graze on algae, given then chance.
Like other Poeciliids, these fish produce live young at regular intervals if males and females are both included in the tank. As opposed to Mollies and Guppies (which produce broods every few weeks), Least Killifish give birth via a process called “superfoetation” in which multiple young at different development stages are present in the uterus. They give birth to single fry in regular, short time spans and generally do not harm or consume the newborns.
Sources
Heterandria formosa - Least Killifish, Seriously Fish
Heterandria formosa, Agassiz, 1853, Viviparos
