American flagfish
Jordanella floridae
The American flagfish exhibits vibrant coloration with iridescent blue-green scales, bright red-orange patches, and a distinctive vertical stripe pattern.
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About the American flagfish
Jordanella floridae is that little Florida native with the red-and-cream striping that really does look like a tiny flag once a male colors up. They graze algae like champs (especially stringy/hair algae), but they have a bit of attitude - give them plants and space so the bossy behavior stays manageable. Bonus: the male guards the eggs and will actively fan them, which is pretty fun to watch.
Also known as
Quick Facts
Size
6 cm
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
20 gallons
Lifespan
3-5 years
Origin
North America
Diet
Omnivore - algae/plant matter plus worms, crustaceans, insects; in tanks: quality flakes/pellets, spirulina/algae foods, blanched veg, frozen/live foods
Care Notes
- Give them a planted, messy tank with lots of cover (java fern, hornwort, rocks/wood) because males get territorial and will claim a corner.
- They are primarily a freshwater species but can be kept in lightly brackish conditions; stability matters more than chasing a specific SG, and many keep them successfully in hard/alkaline freshwater.
- They generally prefer cooler/temperate conditions than many tropical community fish; many references place them around the mid-to-upper 60s to low 70s F, with higher temps sometimes discouraged.
- Feed like an omnivore that loves greens: spirulina flakes, blanched zucchini/spinach, and algae wafers, plus small frozen/live stuff (brine shrimp, daphnia) a few times a week.
- Tankmates: tough, fast brackish fish that will not be bullied (mollies, bumblebee gobies, knight gobies in bigger tanks); avoid slow long-finned fish and anything that needs pure fresh water.
- Keep one male with 2-3 females if you can, otherwise two males will spend all day lip-locking and shredding fins unless the tank is big and broken up.
- Breeding is often described as straightforward; eggs are laid among plants/substrate and adults may eat eggs/fry, but males may also guard/fan eggs depending on setup (territory-based spawning/egg guarding is commonly reported).
- Watch for fin damage and mouth injuries from fighting, and keep an eye on constipation/bloat if you overdo protein and skip the veggie-heavy foods.
Compatibility
Good Tankmates
- Mollies (especially sailfin or common mollies) - same brackish-friendly vibe, tough enough to handle flagfish attitude, and they stick to their own business most of the time
- Fast, short-finned tank mates that do fine in cooler water; be careful not to assume they'll get along with large brackish fish (archerfish need bigger tanks and special care).
- Bumblebee gobies - work best if you keep them well fed and give lots of hiding spots; flagfish can be pushy at feeding time, so spread food out
- Knight gobies - sturdy brackish bottom fish that can hold their ground; just make sure theres enough floor space and caves so nobody squabbles nonstop
- Figure 8 puffers - sometimes works in bigger, well structured brackish tanks because both are assertive, but you really have to watch personalities and have a backup plan
Avoid
- Slow fish with fancy fins like guppies, endlers, bettas, fancy mollies, or longfin anything - flagfish love to nip and theyll shred tails when they get in that mood
- Tiny, chill fish that cant take heat (neon-type tetras, small rasboras, etc) - even if they survive the salinity question, theyll get bullied and outcompeted for food
- Other nippy or aggressive fish (some cichlids, aggressive barbs) - you end up with a constant fin-war and stressed fish instead of a fun tank
Where they come from
American flagfish (Jordanella floridae) are native to Florida - slow, weedy canals, ditches, ponds, and spring runs. Theyre used to warm water, lots of plants, and a bit of mineral content. Youll see them sold as freshwater fish a lot, but they do really nicely with a touch of salt, especially if youre already running a brackish setup.
Setting up their tank
Think planted, cluttered, and with broken lines of sight. Flagfish are small but theyve got big attitudes, and they calm down a lot when they can duck into plants and hardscape. I get the best behavior out of them in tanks that look a little overgrown.
- Tank size: 20 gallons long is a comfortable starting point for a small group
- Layout: dense plants (or plant-like cover), wood/rock to create territories, open swimming lane in front
- Filtration: moderate flow is fine, but dont blast them around
- Temperature: mid 70s F works well (they handle warmer, but they can get grumpier)
- Brackish: use marine salt mix, not aquarium salt; go light brackish unless youre keeping them with higher-salinity species
If youre converting them from freshwater to brackish, raise salinity slowly over a week or two. They handle the change way better than a sudden jump.
Theyre tough fish, but they do react to sloppy water. Keep up with water changes and dont let the tank stew. In brackish tanks, stable salinity matters more than chasing a magic number.
What to feed them
Flagfish are famous for eating algae, and yes, they will pick at it. But they are not little lawnmowers that live on green fuzz alone. Mine colored up and acted less bitey when they got real food every day.
- Staples: quality flakes or small pellets (theyre not picky once settled)
- Greens: spirulina flakes, algae wafers, blanched zucchini or spinach in a clip
- Protein treats: frozen brine shrimp, daphnia, bloodworms (not every day, but regularly)
- Live foods: they go nuts for them, and it helps conditioning for breeding
If you keep them underfed, they dont just get skinny - they start sampling tankmates fins. A little extra feeding goes a long way with this species.
How they behave and who they get along with
Theyre feisty. Males especially will posture, chase, and claim patches of plants like they own the place. In the right setup thats just normal flagfish drama, but in a bare tank it turns into nonstop bullying.
- Best kept: in a small group with more females than males (spreads out the attention)
- Good tankmates: sturdy, fast fish that like similar water (think tough livebearers and other brackish-friendly species)
- Risky tankmates: slow fish, long fins, fancy guppies, bettas, angelfish, anything that looks like a snack to a fin-nipper
- Bottom buddies: most armored catfish are a mismatch for brackish long-term; pick brackish-capable bottom fish if you want company down there
Youll see a lot fewer issues if you give them visual cover. Even just adding extra plants (real or artificial) can change the whole vibe.
Breeding tips
Theyre egg scatterers and pretty willing breeders once they settle in. A well-fed pair or trio will often spawn in fine-leaved plants or a spawning mop. The male usually guards the area and gets extra spicy during this time.
- Conditioning: feed heavier for 1-2 weeks with frozen/live foods plus some greens
- Spawning site: java moss, guppy grass, or a mop works great
- After spawning: if you want fry, pull the adults or move the eggs/mop - they will snack on eggs and tiny fry
- Fry food: infusoria/microworms at first, then baby brine shrimp as soon as they can take it
If you only have one tank, the easiest method is a spawning mop you can lift out each morning and hatch separately in a small container with an air stone.
Common problems to watch for
Most trouble with flagfish isnt mysterious disease - its attitude, stress, and people expecting them to behave like peaceful community fish. Fix the environment and feeding, and half your problems disappear.
- Fin nipping and fighting: usually too small of a tank, too many males, not enough cover, or not enough food
- Thin fish that wont fill out: internal parasites can happen; quarantine new arrivals and watch for stringy poop and weight loss
- Ich and other spotty stuff: stress from shipping and swings in salinity/temperature are common triggers
- Plant destruction: they may peck soft plants while grazing; tougher plants or lots of plant mass helps
Dont use plain 'aquarium salt' as a stand-in for brackish. If youre running brackish long-term, use marine salt mix so the minerals are there and the chemistry stays steadier.
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