The Fish Files - Native Fish of North America - Least Killifish

Least Killifish - Micro Fish of North America

Heterandria formosa (Class: Actinopterygii - Order: Cyprinodontiformes - Family: Poeciliidae)

Image Top: Male, Image Bottom: Female

Native to North America, the Least Killifish can be found in heavily vegetated areas of lakes, ponds, sloughs, ditches, swamps, backwaters and streams. They prefer shallow water with a slow current, river edges and standing water. They can be found in bodies of fresh or brackish water in Florida, Georgia, Louisiana, Alabama, North Carolina, and Texas.

Size & Temperament

The Least Killifish is the 7th smallest fish in the world, and the smallest live-bearer in North American. Males can reach a length of 2 centimeters (0.8 inches) with the females averaging slightly larger at 3.5 cm (1.4 in) in length. They are very docile and do well with fish such as guppies and platties.

Diet

Least Killifish are daytime top feeders that feast on algae, micro-crustaceans and small invertebrates. Water fleas (Daphnia), brine shrimp, mysis shrimp, mosquito larvae, bloodworms, and small particles of fish flakes or pellets can be used to sustain your Least Killifish in captivity.

Breeding

Least Killifish have an unending breeding season and quick birthing rate. Unlike other livebearers, they do not have a single brood (or batch of fry) at one time but give birth to a few fry each day. While the gestation period is around four weeks, the species produce fry in a process called superfoetation* which allows for fry at different stages of development to be present in the female fish at any given time. This means that by the time the female has birthed all of the fry of the first batch over a week or two, the next batch will be ready to birth almost immediately afterwards. Least Killifish do not tend to eat their fry, unlike guppies, when they are well fed.

Tank Requirements

You can have a small colony of up to five Least Killifish in a 2 gallon tank. For breeding, having a five gallon tank for a colony of five fish is ideal. Your tank should be well planted with carpeting plants and bunches of taller vegetation to offer plenty of places to hide. Gentle aeration is recommended as well as a heater to keep the temperature of the water between 70-80 degrees Fahrenheit.

Lifespan

Least Killifish often only live 36 weeks in the wild, but can live 2-3 years in captivity.

Fun Fact

Did you know the Least Killifish is not a true killifish? They most likely came to be called by that name since they are found in small streams, or “killi” in Dutch (which is how killifish got their name).

*superfoetation: The formation or development of a second foetus (unborn offspring that develops and grows inside the uterus) when one is already present in the uterus.

Looking for a setup for Least Killifish? Check out our 2 Gallon Kit below.

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