Remarks: The Least Killifish (Heterandria formosa) is the smallest live-bearing fish species in the world and is also native to the United States. While their common name calls them a killifish, these fish are not actually killifish and belong to the family Poeciliidae which includes other live-bearers such as guppies. They are a shoaling fish so should be kept in groups of 3 or more. Least killifish inhabit shallow, heavily vegetated areas of still or sluggish waters so lots of plants and little to no current are needed. They have been recorded living in brackish conditions but thrive best in freshwater. Females are much larger than males have rounded bellies. In fact, it is rare for males to exceed 0.5" in length. Due to their small size and peaceful disposition, it is important to not house these fish with large, aggressive species.

Scientific Name: Heterandria formosa

Common Name: Least Killifish

Max Size: 1-1.5"

pH: 7.0-8.0

Hardness: Soft or hard 

Temperature: 64-82F

Aggressiveness: Peaceful

Region of Origin: United States 

Captive Bred or Wild: Captive

Diet: Flake, baby brine, or very small powder food.

Compatibility: Small, peaceful community fish and small catfish

Tank Mate Options:

• Swamp Darter ”Green Swamp” (Etheostoma fusiforme)
• Three Line Pencilfish (Nannostomus trifasciatus)
• Mystery Snail (Pomacea bridgesii)

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