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The Least Killifish (Heterandria formosa) holds the title of one of the smallest fish species, making it an exquisite choice for nano aquariums and highly planted tanks. Reaching an adult size of merely 0.8 inches (2 cm) for females and an even more diminutive 0.6 inches (1.5 cm) for males, their tiny stature belies a captivating personality. These livebearers are incredibly peaceful and make excellent community fish for similarly small and docile tankmates like celestial pearl Danios or pygmy corydoras. Their natural habitat includes slow-moving waters in the southeastern United States, so they thrive in aquariums with dense vegetation, including floating plants, which provide security and breeding sites. While not overly picky eaters, a varied diet of high-quality micro pellets, crushed flakes, brine shrimp, and daphnia will ensure optimal health and coloration. What truly sets them apart is their unique reproductive strategy; unlike most livebearers that give birth to a clutch of fry at once, female Least Killifish give birth to a single fry daily over an extended period. This 'superfetation' means you'll often see fry of varying sizes emerging from the same female. They are generally hardy and adaptable, making them a wonderful species for both beginner and experienced aquarists looking for a truly miniature marvel.

One of the world's smallest fish. Technically a livebearer.