American Flagfish Care Guide – Aquarium Setup, Diet & Breeding

The American Flagfish is a colourful North American killifish named for the red, white and blue markings displayed by mature males. Males typically have an olive to blue-green body marked with reddish horizontal lines, a dark side spot and bright red, blue and yellow accents in the fins. Females are usually less intensely coloured, though they can still be attractive fish.

These are active, alert fish that spend much of their time exploring the middle and lower areas of the aquarium. Males can be territorial and may spar with one another, particularly in confined quarters or around preferred spawning sites. Their behaviour is lively rather than timid, and they often become bolder when provided with cover and maintained in a stable group of compatible fish.

In the wild, American Flagfish are found in quiet canals, ditches, marshes, ponds and sluggish streams. Their habitats often contain dense aquatic vegetation, submerged branches and abundant algae. Seasonal changes in temperature and water level influence their breeding cycle, and wild populations can tolerate a relatively broad range of conditions.

American Flagfish are valued both for their appearance and for their tendency to graze on filamentous algae. They are not ideal for every community aquarium, however, because individuals may nip long fins or harass slow-moving tankmates. A spacious, well-planted setup gives them room to establish territories and display their natural behaviour.

American Flagfish are native to the southeastern United States, especially Florida, with populations also occurring in parts of southern Georgia. They inhabit slow-moving and still freshwater environments across the Atlantic coastal plain of North America.

A minimum aquarium of about 75 litres is suitable for a small group or a carefully planned community, with a footprint of at least 60 by 30 cm; a longer aquarium is preferable for multiple males or community housing. Use a secure lid, gentle to moderate filtration and open swimming space alongside dense planting, driftwood, rocks and floating cover that break up lines of sight. A fine gravel or sand substrate works well, and smooth surfaces are preferable because these fish frequently graze around the aquarium. Leave some open areas for activity while allowing algae to grow on selected surfaces.

Males reach about 7.5 cm (3 inches) in maximum length, while females are usually smaller at around 6 cm (2.4 inches).

American Flagfish are omnivores with a strong appetite for algae and plant material. Offer a varied diet of quality flakes or small pellets, algae-based foods, blanched spinach, zucchini or other soft vegetables, supplemented with frozen or live foods such as brine shrimp, daphnia and bloodworms. Regular access to vegetable matter helps support their natural grazing behaviour, although aquarium algae alone is rarely enough to meet all their nutritional needs.

American Flagfish can live with peaceful, active fish that prefer similar cool to moderate temperatures, including larger danios, white cloud mountain minnows, some peaceful barbs, robust livebearers and suitable North American native species. Avoid delicate or long-finned fish such as bettas, fancy guppies and many gouramis, as well as very slow-moving species that may be harassed. Males can be aggressive toward one another, so provide plenty of visual barriers and avoid overcrowding; a male with several females is generally more manageable than multiple males in a small aquarium.

American Flagfish are egg-scattering killifish that can be bred in a dedicated aquarium containing fine-leaved plants, spawning mops or other suitable surfaces. A male courts several females and fertilises eggs deposited among the vegetation. The adults may eat the eggs, so remove them after spawning or transfer the spawning material to a separate container. Eggs generally hatch in around 7–14 days, depending on temperature, and the fry can be raised on infusoria or other very small first foods before moving on to newly hatched brine shrimp.

Males are larger and much more vividly marked, with stronger red, blue and yellow patterning and often more colourful fins. Females are generally shorter-bodied and plainer, with a fuller abdomen when carrying eggs.