Least Killifish
Heterandria formosa
Least Killifish (Heterandria formosa) is one of the world’s smallest freshwater fishes, with males much smaller than females. It is a livebearing fish that inhabits quiet, shallow vegetated waters; in many places it is more often studied than targeted by anglers.
Identification points
- Adult size usually under 4 cm, with females noticeably larger than males
- Slim, silvery to olive body with a dark lateral stripe running from snout toward the tail
- Small upturned mouth and a short, rounded caudal fin; no obvious spines or bold fin markings
Habitat
Shallow, warm freshwater habitats with dense submerged or emergent vegetation, including ditches, marshes, ponds, slow creeks, and spring runs; often near the surface among plant tangles and leaf litter.
Bait notes
Not a typical game fish and is rarely targeted. If collected for observation, very small live or frozen foods such as daphnia, baby brine shrimp, and micro-worms are appropriate; tiny insect fragments can also work.
Behavior
A tiny surface- and midwater feeder that picks at zooplankton, insect larvae, and small invertebrates. It is secretive, tends to stay in cover, and gives birth to live young rather than laying eggs.
Caution
No notable angling hazards, but it is so small that it is easily injured by rough handling. Check local rules before collecting; in some areas native killifishes and wetland species may be protected or restricted.
Fishing notes
Because of its size, it is generally caught only with fine-mesh nets or in aquarium-style collecting. Use very small hooks, light line, and tiny baits only where collecting is legal; handle gently and keep time out of water minimal.