Least Killifish

The Least Killifish is one of the smallest fish species found in North America and belongs to the Poecilliadae familiy. Its natural habitat is mainly heavily weedy, slow-flowing to stagnant waters such as ditches or ponds. It occurs in both freshwater and brackish water estuaries. A transparent body color, a wide, dark brown to black longitudinal stripe along the side of the body and a partly orange dorsal fin characterize this species.

Care in the aquarium

With a size of around 3.5 cm, the Least Killifish is suitable for tanks with a capacity of 54 liters or more. It wants to be kept in a group of at least 10 animals and, in order to feel comfortable and safe, it needs dense vegetation as well as shelter and hiding places such as roots, stone structures or caves. In the community tank, this peaceful fish can be kept very well together with peaceful fish of approximately the same size. In terms of water parameters, the Least Killifish adapts very well to a wide range. The temperature of the water should be in the range 16 – 20°C and the total hardness of the water between 10 and 20 dGH.

Feeding

This omnivorous tiny fish is also not too picky when it comes to food. Fine flake and powdered food are eaten as well as smaller live and frozen food.

Sexual characteristics and breeding

Differentiating between the sexes is not difficult in Least Killifish and possible from about the 4th to 5th week of life onwards. With a body length of around 2cm, males remain significantly smaller than females, which can be up to 3.5cm long, and also have a gonopodium (anal fin converted into a copulation organ). Breeding the Least Killifish in the aquarium is, as with most livebearers, easy. Heterandria formosa becomes sexually mature at around 3 months, but females that are not sexually mature can also be mated and store the sperm for later fertilization of the eggs. The females carry eggs at different stages of development and therefore give birth to small quantities of offspring almost every day. The young fish can be fed with copepods and Artemia nauplii as well as fine fish food.