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American flagfish

Jordanella floridae

A North American cyprinodont with a livery resembling the American flag: red and blue horizontal stripes with a yellow shoulder spot in the male. Native to Florida's marshes and streams. Invaluable in fishkeeping: it is one of the very few fish that actively eats black beard algae (BBA) and hair algae — an 'anti-algae army' in a 5 cm fish. However, the diet must include a significant vegetable component, not just meat, or longevity suffers. Males are territorial during breeding: ratio of 1M:2–3F recommended.

Taxonomy

Class:Actinopteri

Order:Cyprinodontiformes

Family:Cyprinodontidae

Genus:Jordanella

Species:Jordanella floridae

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Water Temperature

18 - 28 °C

pH Value

7 - 8

Water type

Freshwater

Tank level

Bottom and middle

Adult size

6 cm

Minimum tank volume

>= 60 L

Minimum group

>= 3

10 - 20 dGH

5 - 10 dKH

TDS

200 - 400 ppm

Conductivity

313 - 625 uS/cm

Species description

Geographical Origin and Habitat: Endemic exclusively to the subtropical, heavily vegetated, sluggish freshwater networks of the Florida Peninsula in the United States, extending slightly into southern Georgia. Jordanella floridae (universally known as the American Flagfish or Florida Flagfish) natively colonizes intensely overgrown, stagnant swamps, shallow drainage ditches, sluggish canals, and the heavily weed-choked margins of clearwater lakes. These specialized habitats are characterized by massive, impenetrable tangles of submerged aquatic plants, intense sunlight, and vast blooms of hair algae.

Taxonomy and Morphology: Scientifically classified within the Cyprinodontidae family (the pupfishes), it is a unique, spectacularly patterned, heavily built micro-predator/herbivore. Morphologically, fully mature adults reach roughly 5.0 to 6.0 centimeters (2.0-2.4 inches) in length. It possesses a deeply robust, highly compressed, distinctively "stubby" or box-like body profile, evolved for navigating through dense tangles of aquatic weeds rather than open-water swimming. Its defining anatomical feature is an incredibly strong, slightly upturned jaw lined with specialized teeth designed specifically for ripping tough, filamentous hair algae off rocks and plant stems.

Social Behavior: They are complex, highly active, and intensely territorial fish. They are NOT schooling fish; rather, they form loose, highly structured hierarchies. While females are generally peaceful and constantly graze on algae, mature males are fiercely territorial. A dominant male will violently claim a specific dense thicket of plants or a breeding mop as his absolute domain, aggressively chasing away rival males and persistently courting females. They spend their entire day relentlessly picking and grazing at every surface in the aquarium, constantly searching for algae.

Coloration and Sexual Dimorphism: Sexual dimorphism is spectacular and instantly undeniable. Mature males are breathtaking: their base body is a glowing, olive-green heavily overlaid with a spectacular, alternating checkerboard pattern of highly iridescent metallic blue, gold, and blood-red scales. An intense, large, dark-red or black rectangular spot sits squarely on the mid-flank (the entire pattern deeply resembling the stars and stripes of the American Flag). Females, in stark contrast, are significantly duller: they exhibit a pale, olive-grey body with faint mottling, and possess a distinct, stark black spot specifically located on the trailing edge of their dorsal fin.

Care, breeding and tankmates

Aquarium Setup: The aquarium architecture MUST flawlessly replicate a sun-drenched, intensely overgrown Florida swamp. A minimum 60-liter (15-gallon) tank (at least 60 cm long) is required for a single male and a harem of females. The absolute most critical requirement is massive, overwhelming, dense vegetation. The tank MUST be heavily planted with tall, hardy background plants (like Vallisneria or Hornwort) and massive tangles of moss. They strongly prefer bright lighting to encourage natural algae growth, which forms a massive part of their diet. The substrate should be soft sand.

Diet and Feeding: They are highly specialized omnivores with a massive, absolutely critical requirement for plant matter—specifically, they are one of the few aquarium fish that will aggressively and ruthlessly eradicate Black Beard Algae (BBA) and stringy hair algae. However, they cannot survive on algae alone. You MUST feed them a heavily varied diet. Daily offerings of high-quality spirulina flakes and sinking algae wafers are mandatory. To maintain their spectacular coloration and trigger breeding, this MUST be heavily supplemented with meaty live or frozen foods: bloodworms, Daphnia, and Artemia.

Water Quality: Originating from the subtropical swamps of Florida, they possess water requirements that differ completely from tropical Amazonian fish. They are extremely robust and thrive in significantly cooler, unheated water (18-24°C / 64-75°F); they do NOT require a heater in most homes and prolonged exposure to tropical heat (above 26°C) will drastically shorten their lifespan. Crucially, they demand moderately hard to very hard, alkaline water (GH 10-20) and a slightly alkaline pH (7.0 - 8.0). They possess a high tolerance for less-than-perfect water, but rigorous weekly water changes remain necessary.

Compatibility and Cohabitation: Compatibility requires careful planning due to the male's intense territorial aggression and their distinct preference for cooler, hard water. They are absolutely NOT suited for standard tropical community tanks. They are best kept in a dedicated subtropical biotope. Excellent companions include fast-swimming, cool-water schooling fish (like Zebra Danios, White Cloud Mountain Minnows, or Bloodfin Tetras). They MUST NEVER be housed with slow-moving, long-finned fish (like Fancy Guppies or Betta fish), as the Flagfish will aggressively nip and shred their fins.

Aquarium Breeding: Breeding is highly rewarding, fascinating, and frequent in well-maintained, planted tanks. They are prolific, plant-spawning pupfish. Breeding is triggered by a drop in temperature and heavy feeding of live foods. The intensely colored, dominant male will violently claim a specific breeding mop or dense patch of moss. He will aggressively drive a female into the mop, where she lays a few adhesive eggs daily over several days. The male is fiercely protective of the eggs, violently driving away all other fish, but the parents MUST be removed once the fry hatch, as they will eat them.

Risks and Diseases: The absolute greatest physical risk is severe fin damage to tankmates; Flagfish are notorious fin-nippers if housed with slow-moving or long-finned species. The second major risk is lethal metabolic exhaustion caused by housing them in a heated tropical tank (above 26°C); they are strictly subtropical, cool-water fish. Finally, keeping multiple males in a small, sparsely decorated tank will result in relentless, violent territorial battles leading to severe injury or death for the weaker males; massive plant cover is strictly mandatory.

Geographic Origin and Distribution

Endemic exclusively to the subtropical, heavily vegetated, sluggish freshwater networks of the Florida Peninsula in the United States, extending slightly into southern Georgia. Jordanella floridae (universally known as the American Flagfish or Florida Flagfish) natively colonizes intensely overgrown, stagnant swamps, shallow drainage ditches, sluggish canals, and the heavily weed-choked margins of clearwater lakes. These specialized habitats are characterized by massive, impenetrable tangles of submerged aquatic plants, intense sunlight, and vast blooms of hair algae.

Origin

North America

Fish profile

Temperament: Semi-aggressive
Diet: Omnivore
Sex ratio: Harem
Feeding frequency: Twice daily
Bioload: Low to Medium
Flow: Strong
Jump risk: Yes
Reproduction: Substrate spawner
Compatibility & tankmates: Community
Tank level: Middle/Bottom

FishBase

Window to the official scientific data of the species

Data synced on: 06/15/2026

Scientific Parameters & Models

Trophic level: 2.9 ± 0.32 se
Resilience: Low (4.5 - 14 years)
Phylogenetic uniqueness (PD50): 1
Bayesian Length-Weight: a = 0.01995, b = 3.13

Image gallery

Licensed images linked to the species or, when marked, to the closest representative taxon.

Related species

Recommendations grouped by close relatives, companion choices, and similar care.

Variants and close relatives

Same atlas type, nearby scientific identity, genus, or family.

Sheepshead Minnow

Cyprinodon variegatus

Species description

Care, breeding and tankmates