Mummichog
Fundulus heteroclitus
Mummichogs exhibit a slender body with a greenish or brownish back and silvery sides, often featuring dark vertical bars.
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About the Mummichog
Tough little estuary killifish that handles swings in salinity and temperature like a champ, so it is great for a low-fuss brackish setup. In a group they are busy and curious, and breeding is fun to watch when males flash gold-green spangles. They eat pretty much anything that hits the water.
Also known as
Quick Facts
Size
15 cm
Temperament
Semi-aggressive
Difficulty
Beginner
Min Tank Size
10 gallons
Lifespan
1-4 years
Origin
North America
Diet
Omnivore - flakes, pellets, frozen and live invertebrates
Water Parameters
8-24°C
5.7-8.4
8-12 dGH
Need a heater for this species?
This species needs 8-24°C in a 10 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Start with a 20-gallon long for 4-6 mummichogs, with a tight-fitting lid since they launch out of gaps. Use sand or fine gravel, piles of rock or oyster shell, and hardy brackish greens like Java fern or Vallisneria for cover.
- Mix marine salt (not table salt) to 1.005-1.015 SG and keep pH 7.5-8.5; they are happy at 60-75 F and usually do fine unheated. Check SG with a refractometer or hydrometer and change salinity slowly.
- Give them solid filtration with a bit of current and extra air so the water stays lively. Do 25-30% weekly changes and try to keep nitrate under 40 ppm.
- Feed a varied, protein-heavy menu: quality pellets or flakes plus frozen brine, mysis, bloodworms, and chopped earthworms. Small portions twice a day works well, and live foods really bring out their behavior.
- Pair with similar-sized brackish fish like mollies, sheepshead minnows, and sturdy gobies; avoid shrimp and tiny fish because they will vanish. Keep more females than males (1 male to 2-3 females) and add sight breaks to tamp down chasing.
- They spawn readily on floating mops or near the surface; collect sticky eggs every few days and incubate them damp or in a separate tank at 68-72 F for 7-14 days. Adults will eat eggs and fry, so raise the babies separate if you care about numbers.
- Wild-caught mummichogs often bring hitchhikers, so quarantine new fish 3-4 weeks and treat as needed. When shifting between fresh and brackish, move no faster than about 0.002-0.003 SG per day to avoid shock; ich usually fades in brackish but still needs attention.
Compatibility
Good Tankmates
- Tough brackish livebearers like short-fin mollies (wild-type or sailfin adults) that can handle 1.005-1.015 and a bit of chasing
- Sheepshead minnows and other robust pupfish that match the mummichog vibe and temp, quick enough not to be harassed
- Knight gobies that hang mid-bottom, stand their ground, and do fine in brackish with lots of caves
- Brackish flatfish like hogchoker that stick to the sand and mostly get ignored if you target-feed them
- A group of their own kind - 1 male with 2-4 females, plus hardscape and plants to break sightlines
- Bigger, fast schooling estuary fish like silversides in a long tank with current so nobody gets cornered
Avoid
- Tiny or slow community fish that fit in a mummichog mouth, like bumblebee gobies, guppies, or small glassfish
- Anything with long, flowy fins (fancy mollies, bettas, veiltail types) that will just get nipped to ribbons
- Puffers in brackish, especially green spotted or figure-8, since it turns into a nonstop fin-nipping arms race
- Big, hot-running brackish bruisers like monos and scats that prefer warmer water and will outcompete or swallow smaller fish
Where they come from
Mummichogs are little marsh killers from the Atlantic coast of North America, hanging out in salt marshes, tidal creeks, and ditches from Canada down to Florida. They deal with crazy swings in temperature, salinity, and water depth, which is why they handle aquarium life so well.
Setting up their tank
They stay small, but they are busy swimmers. A 30-gallon tank for a group of 6 is a nice starting point. Go bigger if you can. Keep a tight lid; they launch like popcorn.
- Salinity: SG 1.005-1.015 (use a refractometer or hydrometer)
- Temperature: 64-75 F (18-24 C). They tolerate cooler and warmer, but this range keeps them lively.
- pH: 7.5-8.4
- Hardness: medium to high
- Water changes: 25-40% weekly; they are hearty eaters and a bit messy
They look great over sand or fine gravel with piles of rock, driftwood, and fake or real marshy roots. Moderate flow and strong filtration keep the water fresh. Brackish-tolerant plants like Vallisneria, Java fern, Anubias, and mangroves (if you want a project) all work. Leave open swimming space up front.
Use a marine salt mix, not table salt or "tonic" salt. Mix salt in the change water, let it fully dissolve, then add it. Top off evaporated water with plain freshwater so salinity does not creep up.
Cover every gap. They aim for filter cutouts and airline holes. A simple mesh or craft plastic over gaps saves fish.
What to feed them
They eat pretty much anything that wiggles. In the wild they go after insect larvae, small crustaceans, worms, and a bit of algae. In a tank, variety keeps them in top shape.
- Staple: quality small pellet for omnivores/carnivores
- Frozen: mysis, brine shrimp, bloodworms, chopped krill
- Live treats: blackworms, daphnia, mosquito larvae (seasonal, collected safely)
- Extras: crushed snails, chopped earthworms, high-quality flake
New wild-caught fish sometimes ignore dry foods. Start with live blackworms or daphnia, then mix in frozen, then pellets. Feed 1-2 small meals a day and leave a fast day each week to avoid bloat.
How they behave and who they get along with
Mummichogs are bold, curious, and always on patrol. They loosely school, then break off to spar and explore. Males posture at each other more during the breeding season, so run groups of 6+ with more females than males if you can.
- Good tankmates: sailfin mollies, sheepshead minnows (Cyprinodon variegatus), knight gobies, bumblebee gobies (with size match), rainwater-adapted guppies acclimated to brackish
- Use caution: long-finned or very slow fish get nipped
- Skip: shrimp, tiny fry, and delicate nano species
They will eat small shrimp and any fry they catch. If you want to raise babies from other fish, do it in a separate tank.
Breeding tips
They have a cool marsh routine: they lay sticky eggs high in vegetation during spring high tides. The eggs sit damp, then hatch when the next high water covers them. You can copy that in a tank pretty easily.
- Condition a group with live and frozen foods at 68-72 F, SG around 1.008-1.012.
- Add floating spawning mops or a floating tray with damp yarn/peat right at the waterline.
- They deposit eggs that stick to the mops. Collect them every day or two.
- Keep eggs just damp (not submerged) in a ventilated container on moist paper towel for 7-14 days.
- To hatch, flood the eggs with tank water. Most pop within hours.
- Raise fry in shallow, clean water at low brackish (SG 1.002-1.005). Feed newly hatched brine shrimp and microworms.
- Pull adults after spawning; they will snack on eggs and fry.
Sexing: males are darker with brighter fins (often yellow on the belly and anal fin) and more contrast; females are larger and more rounded, often with lighter speckling.
Common problems to watch for
- Jumping: lids save lives. They spook at lights-on and feeding rushes.
- Salinity swings: sudden changes stress them. Match salinity and temperature during water changes.
- Heat waves: warm water holds less oxygen. Add surface agitation or a fan in summer.
- Wild-caught hitchhikers: external parasites are common. Quarantine new fish 2-4 weeks.
- Scuffles: keep groups, add sight breaks, and keep extra females to spread male attention.
- Messy eating: rinse mechanical media often and do regular water changes to keep nitrate under control.
- Ich and meds: brackish helps, but outbreaks can happen. Many copper meds nuke inverts and some plants; dose carefully and research first.
Never release aquarium fish or water into local waterways. If you collect your own mummichogs, check local regulations and only take what you can house long-term.
Keep a simple log: salinity, temperature, pH, and notes on behavior. If something goes off, your notes make the fix quick and painless.
Similar Species
Other brackish semi-aggressive species you might be interested in.
Banded Archerfish
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More to Explore
Discover more brackish species.
African moony
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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.
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-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
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Urocampus nanus (barbed pipefish) occurs in protected inshore and estuarine habitats among seagrass (Zostera) in the Northwest Pacific (southern Japan and adjacent coasts). Like other syngnathids, males brood eggs in a pouch under the tail and produce fully formed young.
Beach silverside
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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.
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