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Least Killifish

Stocking Fish Tips: For new tanks, be sure the fish that you add to your tank are hardy. After the tank has aged for a few months, less hardy fish can be added. A tank needs to “mature” (complete the aquarium nitrogen cycle) before it can accomodate certain species of fish. Submitted by: Dahly
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The Least Killifish, or Dwarf Livebearer, (Heterandria formosa) is a species of livebearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and swordtails. The Least Killifish is not as commonly kept in aquaria as these species. The Least Killifish is one of the smallest fish in the world (7th smallest as of 1991)[1], and is the smallest fish found in North America.[2]

The Least Killifish is the only member of the genus Heterandria to be found in the United States.[3] Its range covers southeastern United States, from South Carolina south to Georgia and Florida, and through the Florida Gulf Coast to Louisiana.[3][4] It is one of the few aquarium fishes to come from North America.

The Least Killifish lives primarily in slow moving or standing freshwater but also occurs in brackish waters.[4]

The Least Killifish is one of the smallest fish and smallest vertebrates known to science.[3] Males grow to about 2 centimeters (0.8 inches), while females grow a little larger, to about 3 centimeters (1.2 inches).[3][5]

The fish is generally an olive color, with a dark horizontal stripe through the center of the body. There is also a dark spot on the dorsal fin and females also have a dark spot on their anal fin. Like most poeciliids, males’ anal fins are modified into a gonopodium that is used for impregnating females during mating.