• Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)
  • Least Killifish (Heterandria formosa)

Least Killifish (Heterandria formosa)

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* For the safety of our animals, we now ship live fish exclusively via UPS Next Day Air.  If your order contains this item, you will only see UPS Next Day Air as a shipping option during checkout *


The Least Killifish is a lovely US native that is one of the smallest fish species in the world!


The Least Killifish (Heterandria formosa) is a colorful, peaceful fish that is native to the southeastern Unites States. This peaceful species is one of the tiniest fish species in the world. Males are the most colorful, but females are typically colorful in their own right. In addition to being an excellent display fish in the community and planted aquarium, the omnivorous Least Killifish is also an effective algae eater. In an outdoor pond, it is very useful for algae control as well as for eating insect larvae. It even inhabits some brackish areas.


The Least Killifish often occupies the top level of the water column, although it will inhabit all areas of the aquarium. It is not afraid to jump, so it must be kept in an aquarium with either a lid/hood/canopy or at least a significantly lowered water level. It will not eat or bother ornamental plants and it will appreciate the cover, especially with floating plants. The Least Killifish is possibly compatible with other peaceful fish and some invertebrate species that thrive in low to moderate water flow. The fry of dwarf shrimp might be considered prey, but most other shrimp can make good tankmates. This species is still best kept in a group. It is rather undemanding regarding water parameters, and it can be kept in both tropical and subtropical setups.


The Least Killifish is an omnivore that feeds on tiny invertebrates as well as algae. It is not a particularly picky eater, so most dry, frozen, and live foods of appropriate size will be accepted. This species requires plenty of meaty foods as well as foods with high plant (preferably algae-based) content, especially if there is not plenty of algae growing in the aquarium.  


What We Like About This Fish:

  • Beautiful coloration and small size
  • Peaceful disposition with fish and peaceful invertebrates
  • Easy to breed in the aquarium
  • Very versatile regarding most water parameters
  • Excellent algae eater    



  • Temperature: 64° - 78° F (18° - 26° C)
  • pH: 7.0 - 8.0
  • KH: 5 - 20 dKH
  • Minimum Tank Size: 5 gallons for a small group



  • Diet:  Omnivorous. Will accept most meaty foods and also requires plenty of vegetable (particularly algae) content.
  • Social Behavior: Peaceful, schooling/shoaling.  
  • Origin: Tank-bred, but indigenous to southeastern United States
  • Average Adult Size:  Male - .8 inch (2 cm), Female - 1.4 inches (3.5 cm) 
  • Average Purchase Size: .5 - 1 inch (1.3 - 2.5 cm)


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