Weed cardinalfish
Foa brachygramma
The Weed cardinalfish features a dark brown body with distinctive vertical black stripes and bright red-orange eyes, reaching up to 10 cm in length.
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About the Weed cardinalfish
This is a tiny Hawaiian cardinalfish that hangs around sheltered shallows - think seagrass, algae, and rubble - and it even wanders into brackish and sometimes fresh water. Its vibe is classic cardinalfish: mellow, a little shy, and way more interesting once the lights go down. Also cool trivia: the males mouthbrood the eggs.
Also known as
Quick Facts
Size
6.4 cm SL
Temperament
Peaceful
Difficulty
Advanced
Min Tank Size
30 gallons
Lifespan
3-6 years
Origin
Central Pacific (Hawaii)
Diet
Carnivore - small meaty foods like mysis, finely chopped seafood, and small frozen/live crustaceans
Water Parameters
24.2-28.8°C
8-8.4
8-12 dGH
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This species needs 24.2-28.8°C in a 30 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give them a bigger, calmer tank than you think - lots of rock piles, mangrove-style roots, or stacked caves so they can hover in shade and duck out of sight fast. Bright, bare tanks make them sulk and stop eating.
- Run brackish that stays steady, not swinging around - aim around SG 1.005-1.010, 76-80F, and keep nitrate low because they go downhill in dirty water. Do slow, regular water changes instead of big resets.
- Low flow is your friend; they are hoverers, not sprinters. Put the strong flow on the far side and give them a quiet corner to hang in.
- They are picky at first, so start with frozen mysis, finely chopped shrimp, and enriched brine, then wean to small sinking pellets once they are bold. Feed after lights dim a bit, because they often eat better when the tank is calmer.
- Avoid fast, nippy fish and anything that outcompetes at feeding time (chromis-types, big mollies, aggressive gobies). Best tankmates are chill brackish fish that do not harass them and do not mind the same salinity.
- Keep them singly or as a known pair; random groups can turn into one bully and a bunch of hiding fish. If you want a group, add them all at once and give way more caves than fish.
- Watch for skinny bellies and 'spitting food' - that usually means internal parasites or they are not getting enough at meals. Quarantine if you can and be ready to treat for worms if they keep losing weight despite eating.
Compatibility
Good Tankmates
- Small, calm gobies that like the same low-end brackish vibe - bumblebee gobies (Brachygobius) are a solid pick as long as everyone is eating and you have lots of little hiding spots
- Figure 8 puffers only if its a big, well-structured tank and you already know your puffer is unusually chill - otherwise they get too curious and turn into fin/nip inspectors
- Peaceful monos (Mono argentus or Mono sebae) when they are still small and the tank is roomy - they are active but usually not jerks, and they handle brackish just fine
- Brackish mollies (and other livebearers that do well in brackish) - they are easygoing dither fish and keep the vibe calm, plus they help the cardinals feel out in the open more
- Knight gobies (Stigmatogobius sadanundio) in a decent sized tank with territories broken up - they mostly mind their own business on the bottom and the weed cardinals hang midwater
- Small, peaceful archerfish in a bigger brackish setup - they are bold feeders but not usually aggressive, so the main trick is making sure the weed cardinals actually get their share of food
Avoid
- Anything nippy or fast-and-pushy that will outcompete them at feeding time - tiger barbs, most active barbs, and similar 'always in your face' fish will stress them and keep them hiding
- Big or aggressive brackish predators - scats, big archerfish, bigger puffers, or anything that sees a small cardinalfish as a snack
- Fin nippers and 'peckers' - even if they are not trying to eat them, constant picking makes these cardinals sulk and stop coming out
- Crabby tankmates or anything that likes to grab slow fish at night - brackish crabs are a classic 'seems fine until its not' situation
Where they come from
Weed cardinalfish (Foa brachygramma) show up around shallow coastal areas in the Indo-Pacific, where you get a mix of tide, grass beds, rubble, and murky water. They are the kind of fish that likes cover and broken sight lines, not big open water. That background helps a lot when you set up their tank and pick tankmates.
You will see these sold into fully marine setups sometimes. They can live there, but if you are keeping them as a brackish fish, commit to stable brackish conditions and choose tankmates that match that plan.
Setting up their tank
This is one of those fish where the tank layout matters more than raw gallons. Give them lots of places to hover and hide, and they settle down. Keep the lighting on the calmer side if you can, or at least add plenty of shade with decor.
- Tank size: I would not do them in under 20 gallons, and 30+ makes life easier if you want a small group
- Salinity: keep it consistently brackish (pick a target specific gravity and stick to it - stability beats chasing numbers)
- Filtration: strong biofiltration and steady flow, but avoid blasting their favorite hiding spots
- Decor: rock piles, driftwood, mangrove-style roots, and macroalgae or tough plants that tolerate brackish (even fake plants work fine for cover)
- Substrate: sand or fine gravel is easiest to keep clean in brackish
- Lid: they can jump if spooked, especially in a new tank
I have the best luck giving them a few tight little caves and overhangs, plus one bigger shaded zone. They will pick a home base, and once they do, feeding and general confidence improves a lot.
Keep nitrates under control. Brackish tanks can fool you because the fish might look fine right up until they do not. Regular water changes and not overfeeding are your best friends here.
What to feed them
These are small-mouthed, hover-and-pick predators. Think tiny meaty foods drifting by. They can be finicky at first, especially right after shipping, so plan on a gentle ramp-up with foods they cannot resist.
- Great starters: live or frozen baby brine shrimp, mysis (small), calanus, finely chopped krill, copepods
- Staples once settled: frozen mixes for small carnivores, finely chopped seafood, quality micro pellets (if they will take them)
- Feeding pattern: smaller portions 1-2 times a day tends to work better than one big dump
Watch during feeding if you keep them with faster fish. Weed cardinals can starve in a tank where everything else rushes the food. Target feeding with a turkey baster or pipette is a game changer.
If yours refuses prepared food, do not panic. Offer frozen food with the pumps turned down for a few minutes, keep the room quiet, and try again later. I have had individuals that took a week or two to really flip the switch.
How they behave and who they get along with
They are generally peaceful and a little shy. Most of the day they hover in cover, then pop out to feed. They are not flashy swimmers, so you want tankmates that are not constantly in their face.
- Good tankmates: calm brackish species that will not outcompete them at feeding time
- Avoid: aggressive feeders, nippy fish, and anything big enough to view them as a snack
- Group vs single: you can keep a small group if the tank has enough cover and you feed well, but be ready to separate bullies if one starts claiming all the best spots
If you want multiples, add them together and rearrange decor right before introduction. It cuts down on the 'this is my cave' attitude.
They are crepuscular-ish in vibe. You might see more natural behavior if you run a gentle ramp on your lights or keep some shaded areas where they feel safe during the day.
Breeding tips
Like a lot of cardinalfish, they are mouthbrooders. If you get a comfortable pair, the male may hold eggs in his mouth for a while and go off food. It is really cool to witness, but it can be tricky in a community tank.
- Conditioning: lots of small meaty meals and very steady water conditions
- Spawning behavior: the male may look like he is chewing or has a slightly fuller jaw and will often hide more
- During brooding: keep stress low, skip big rescapes, and do not harass him trying to 'check' the mouth
- Raising fry: if you want to try, you will need tiny live foods (rotifers and/or very small planktonic foods) ready ahead of time
Moving a brooding male often ends with him swallowing or spitting the clutch. If you are serious about raising fry, plan the breeding tank first instead of trying to improvise after you notice eggs.
Common problems to watch for
Most issues I see with weed cardinals come down to stress and feeding. They do not handle chaos well. If they are constantly hiding, losing weight, or getting pushed off food, fix the environment first.
- Not eating after purchase: common - start with small frozen/live foods and provide heavy cover
- Slow starvation: they look 'fine' but get thinner over weeks if tankmates outcompete them
- Salinity swings: brackish tanks can fluctuate if top-off habits are sloppy
- External parasites and shipping damage: watch for flashing, heavy breathing, clamped fins, or frayed fins
- Secondary infections: small mouth injuries can turn into bacterial issues if water quality is rough
Do not treat brackish fish blindly with random meds in the display tank. Some medications behave differently with salt in the water, and invertebrates/plants can get wrecked. Quarantine and identify the problem first.
If you keep them calm, keep the salinity steady, and make sure they actually get their share of food, they are rewarding fish. The 'advanced' part is mostly about being patient and consistent, not doing anything fancy.
Similar Species
Other brackish peaceful species you might be interested in.
African moony
Monodactylus sebae
This is that shiny, diamond-shaped "mono" that cruises around in a tight pack and looks like a little silver dinner plate with black bars when it's young. The big thing with African moonies is they're euryhaline-so they'll tolerate freshwater as juveniles, but they really shine long-term in brackish (and can be transitioned toward marine as they mature). Give them a big, open tank and a group, and they turn into nonstop, super fun midwater swimmers.
American shadow goby
Quietula y-cauda
This is a little mudflat goby from California down into the Gulf of California that loves hanging tight to the bottom and vanishing into burrows. The neat tell is that sideways Y-shaped blotch right at the base of the tail, plus the row of dark spots along the side. Its whole vibe is brackish estuary life - calm water, soft substrate, lots of hiding holes.
Banded-tail glassy perchlet
Ambassis urotaenia
This is one of those see-through glassy perchlets where you can literally watch the organs shimmer when it turns-super cool in the right lighting. In the wild it hangs around river mouths and mangroves and cruises in groups, so it does best when you keep a little gang of them and give them some open swimming room.
Barbed pipefish
Urocampus nanus
Urocampus nanus is a skinny little pipefish from sheltered seagrass and estuary areas around southern Japan and nearby coasts, where it hangs out down low among eelgrass. The really wild part is the males brood the eggs in a pouch under the tail and give birth to fully formed mini pipefish. Its care is basically "pipefish rules" - calm tank, lots of live/frozen tiny meaty foods, and tankmates that will not outcompete it at feeding time.
Beach silverside
Atherinella blackburni
This is a little coastal silverside that cruises the shallows in loose groups and flashes like a tiny chrome dart when the light hits it right. In the wild it hangs around beaches, estuaries, and lagoons, picking at small drifting foods in the surf zone. It is cool, but its real "gotcha" is that it is an open-water, salt-tolerant schooling fish that does best in bigger, well-oxygenated setups rather than a typical planted community tank.
Buffon's river-garfish
Zenarchopterus buffonis
This sleek, surface-dwelling halfbeak has a distinct dark stripe along the snout and is typically found at the surface in coastal waters, estuaries, and rivers where it feeds on terrestrial insects. In aquaria it does best with floating/surface foods and a secure cover, and it requires brackish (or marine) conditions long-term. Reproduction is internally fertilized; FishBase lists the species as ovoviviparous.
More to Explore
Discover more brackish species.
Atlantic Mudskipper
Periophthalmus barbarus
This is that wild little amphibious goby that straight-up climbs around on land like it forgot it was a fish. They've got big googly eyes, tons of personality, and they'll perch, hop, and patrol their territory-honestly more like a tiny crabby lizard than a "regular" aquarium fish.
Banded Archerfish
Toxotes jaculatrix
This is the fish that literally spits jets of water to knock insects off branches-watching one "take aim" is unreal. They're super aware of what's going on outside the tank and will even learn to beg and snipe food from the surface once they settle in. Give them height and some open swimming room and they act like little aquatic sharpshooters.
Barred mudskipper
Periophthalmus argentilineatus
This is one of those classic "walks around like it owns the place" mudskippers-big goofy eyes, climbs, hops, and spends a ton of time out on the mud when it's humid. In the wild it lives on intertidal mangrove/nipa mudflats and even shuttles between little pools and open air, hunting worms, insects, and small crustaceans. It's super fun to watch, but it really wants a brackish paludarium setup (not a normal aquarium).
Blotched eelpout
Zoarces gillii
Zoarces gillii is a cold-temperate eelpout from the Northwest Pacific that hugs the bottom over sandy-mud inshore areas and even pushes into estuaries. It's got that long, eel-like body and a sneaky, sit-on-the-bottom predator vibe - very much a cool-water, brackish-to-marine oddball rather than a typical tropical aquarium fish.
Bumblebee goby
Brachygobius doriae
Brachygobius doriae is one of the classic "bumblebee gobies" - tiny, bottom-hugging little characters that perch on rocks and sand and stare at you like they own the place. They're at their best in a calm setup with lots of caves and leaf litter, and they really shine once you get them eating frozen/live foods reliably (they're slow, picky eaters). Also: they're one of the species that gets mislabeled a lot in shops, so it's super common to see them sold under the wrong bumblebee-goby name.
Bumblebee goby (Bumblebee fish)
Brachygobius xanthozonus
This is that tiny little goby with the bold black-and-yellow bands that likes to perch on the bottom and stare back at you like it owns the place. It's happiest in lightly brackish water with lots of little caves and sight-breaks, and it's one of those fish that often refuses flakes-frozen/live meaty foods usually flip the "yes, I will eat" switch.
Looking for other species?