Steel-blue Killifish

The steel-blue killifish (Fundulopanchax gardneri), also called Gardner's killie, is a small, brightly colored egg-laying fish from West Africa. It belongs to the family Nothobranchiidae within the order Cyprinodontiformes and ranges across swampy lowlands and forest streams of Nigeria and Cameroon. Unlike the "annual" Nothobranchius killifish, it inhabits more permanent water bodies and has a comparatively longer lifespan of one to two years. Several regional color forms are recognized across its range, and males display some of the most vivid blue-and-red patterning of any small freshwater fish. It is one of the most widely kept killifish species in the aquarium hobby, valued for its hardiness and coloration.

Steel-blue killifish are compact, reaching about 5-6 cm.

• Body: elongated, slightly cylindrical, with a flattened, upturned mouth for surface feeding
• Male coloration: metallic steel-blue flanks dotted with red-orange spots; caudal fin extended into a lyre shape with red and yellow edging
• Female coloration: uniform olive-tan, rounded fins, no elongated tail extension
• Fins: dorsal and anal fins set well back on the body, males' fins larger and more pointed

It is distinguished from similarly colored Aphyosemion species by the combination of lyre-tail shape and dense red spotting on a blue base color; exact identification of color morphs relies on locality data.

This species occurs across a broad swath of West Africa, from southern Nigeria into Cameroon, favoring slow-moving forest streams, swamps, floodplain pools, and roadside ditches. It tolerates warm, soft, slightly acidic water with dense vegetation or leaf litter, often in shaded, shallow habitats less than a meter deep. Because its wetlands are more stable than the ephemeral pools used by annual Nothobranchius killifish, the steel-blue killifish does not need to survive periods of complete drying, allowing populations to persist year-round. It is typically found near the water's surface among plant roots and submerged debris.

Steel-blue killifish are surface-oriented, opportunistic feeders that pick insects, small crustaceans, and other invertebrates from the water's surface and among vegetation. Males are territorial toward one another, displaying vivid coloration and flared fins during confrontations and courtship. Spawning occurs among fine-leaved plants, where eggs are scattered and adhere to vegetation rather than being buried, hatching within about two weeks under normal conditions. The species is not strictly annual, so adults and eggs can coexist year-round in stable habitats. It plays a role as a mid-level predator of aquatic insect larvae in its native wetlands.