Mo River killifish
Fundulopanchax moensis
The Mo River killifish displays striking metallic blue scales and a distinctive elongated body, typically measuring around 3 inches in length.
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About the Mo River killifish
Fundulopanchax moensis is one of those West African stream killies where the males just light up once they settle in, especially in a dim, plant-packed tank. It is a non-annual killi (so not a "live fast, die young" puddle fish) and it really rewards you if you keep it covered and calm - they can be jumpy little rockets.
Also known as
Quick Facts
Size
6.5 cm TL
Temperament
Semi-aggressive
Difficulty
Advanced
Min Tank Size
15 gallons
Lifespan
2-4 years
Origin
West Africa (Cameroon)
Diet
Micro-predator/insectivore - small live/frozen foods (daphnia, mosquito larvae, brine shrimp) plus quality small pellets
Water Parameters
20-24°C
5.5-7.2
1-12 dGH
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Calculate heater sizeCare Notes
- Keep them in a tight-lidded tank - these guys jump like rockets, especially when spooked or during sparring.
- Go soft and a bit acidic: aim around pH 5.5-6.8, low KH, and keep it clean with gentle filtration (sponge filter is your friend).
- Set the tank up like a shady creek edge: dark substrate, floating plants, leaf litter, and lots of cover so the male can chill between displays.
- Feed small, meaty stuff 1-2 times a day: live or frozen mosquito larvae, daphnia, baby brine, cyclops; they color up and spawn way faster on live foods.
- Skip busy or nippy tankmates - no barbs, danios, or fin-nippers; a pair/trio works best, or keep with calm small fish like pencilfish if you have tons of cover.
- Keep more females than males (1 male to 2-3 females) or the male will ride one female nonstop and stress her out.
- Breeding is mop-friendly: toss in a spawning mop or dense moss, pull the eggs every few days, and hatch them in a small container with clean, soft water and a tiny bit of antifungal (they can fungus fast).
- Watch for velvet/ich after shipping and for beat-up fins from male scuffles; warm, stable temps around 72-76F and low stress fixes half the problems.
Compatibility
Good Tankmates
- Fast, midwater schooling fish that mind their own business - stuff like rummynose tetras, ember tetras, or glowlight tetras. The Mo River killies do best when the other fish are quick enough to not get singled out.
- Corydoras catfish (most of the common ones). They stay on the bottom, are pretty bulletproof, and the killies usually ignore them unless food is hitting the sand.
- Otocinclus in a proper little group (and only in a mature tank with algae). They are low drama, stick to glass and leaves, and they do not compete much with killies at feeding time.
- Small, calm rasboras like harlequins or chili rasboras (bigger groups help). They are quick and predictable, so the killies are less likely to get pushy.
- Bristlenose pleco (one, not a big bulldozer pleco). Good clean-up crew, keeps to itself, and does not get stressed by a little surface swagger from the killies.
- Non-nippy dwarf rainbowfish like threadfins (only if your killies are not extra spicy). The movement keeps attention spread out, but keep an eye out because some killies will still chase anything flashy.
Avoid
- Long-finned slowpokes - bettas, fancy guppies, veil tail anything. Moensis males can be little fin inspectors and they will absolutely test those flowing fins.
- Nippy or bossy fish - tiger barbs, serpae tetras, many danios in tight setups. They either harass the killies or turn the tank into a constant chase scene.
- Other male killifish (and honestly most other Fundulopanchax) in the same tank. Territorial posturing turns into shredded fins fast unless the tank is big and packed with sight breaks.
- Fish small enough to be 'snack sized' - tiny nano fish and especially shrimp fry. These guys are micropredators by nature and will pick off anything that fits in their mouth.
Where they come from
Fundulopanchax moensis (the Mo River killifish) comes from West Africa around the Mo River system. Think small streams and forest-edge waters that can change with the seasons - sometimes flowing, sometimes more like quiet pools. That background explains a lot: they like clean water, they appreciate cover, and they can be jumpy if they feel exposed.
Most of the ones in the hobby are line-bred from wild stock. Treat them like a fish that can be a bit less forgiving than your average community fish, especially if water quality slips.
Setting up their tank
These are advanced mostly because they punish sloppy setups. If you like tinkering and you keep up with maintenance, they are incredibly rewarding. If you miss water changes for a few weeks, they will let you know.
I would not keep them in a brand-new tank. Give the tank time to mature so your biofilter is steady and micro-life is established. They just settle in better.
- Tank size: 10-20 gallons works for a trio or a small group, but more footprint is always nicer than more height
- Lid: tight-fitting. They jump. They will find the smallest gap around airline tubing
- Filtration: gentle flow. Sponge filters are perfect, or a small HOB baffled down
- Hardscape: lots of sight breaks - wood, leaf litter, clumps of plants, floating cover
- Plants: Java moss, guppy grass, water sprite, floating salvinia or frogbit
- Substrate: anything, but darker substrate helps them color up and feel secure
If you can see the fish from every angle across the tank, they can see each other too. Break up lines of sight and you will get less chasing, less stress, and nicer behavior.
Water-wise, aim for stable and clean more than chasing a perfect number. Slightly acidic to neutral water tends to go smoothly for most strains, with moderate softness. Temperature in the low-to-mid 70s F is a comfortable zone. Keep nitrate low and do regular, smaller water changes rather than big, shocking swings.
They do not love sudden changes. Big water changes with very different temperature or mineral content can trigger stress and sometimes velvet or other issues shortly after.
What to feed them
They are classic killifish eaters: they look their best and breed best on meaty foods. Mine would take some prepared foods, but they never did as well on pellets alone.
- Staples: frozen bloodworms, frozen brine shrimp, daphnia, mysis (if they will take it)
- Best live foods: baby brine shrimp, grindal worms, white worms (sparingly), mosquito larvae where safe/legal
- Prepared foods: small pellets or granules can work as a backup, but train them slowly
Feed small amounts once or twice a day. If you are trying to condition a pair for breeding, bump up live foods for a week or two, but keep the tank clean. With this species, overfeeding plus warm water is a fast track to problems.
If they turn their nose up at pellets, try mixing pellets into a little thawed frozen food juice. Do that for a week and many will start recognizing pellets as food.
How they behave and who they get along with
Males are flashy and they know it. You will see displaying, flaring, and short chases, especially in smaller tanks or bare setups. Most of it is posturing, but constant pressure on a weaker fish is a real thing.
- Best setup: 1 male with 2-3 females, or a small group in a well-planted tank
- Avoid: multiple males in tight quarters unless you have lots of cover and extra space
- Tankmates: calm, non-nippy fish that like similar water and do not outcompete them at feeding time
- Bad matches: fin-nippers, hyperactive schoolers, aggressive cichlids, or anything that will snack on eggs/fry
They are not true community fish in the way tetras are. You can keep them with others, but you will get the best colors and the least drama in a species tank or with very carefully chosen companions. Also, they are top-to-midwater hunters. Tiny shrimp and micro fish fry are going to look like snacks.
If you see clamped fins, hiding, or a fish that stays in a corner near the surface, do not assume it is just shy. With killies, that is often your first hint that something is off (bullying, water, or disease starting).
Breeding tips
Breeding is absolutely part of the fun with Fundulopanchax, and it is one of the reasons people put up with their pickiness. They are substrate spawners and will use fine plants or a spawning mop like they were made for it.
- Use a spawning mop (acrylic yarn) or dense moss. Give them at least one dark, sheltered spot to spawn
- Condition with live/frozen foods and keep up with water changes
- Collect eggs every day or two if you want a real yield (adults will eat eggs and fry)
- Incubate eggs in clean water with gentle aeration, or on damp peat/coir depending on your preferred method and line
I like two mops: one floating and one sunk. Some pairs clearly have a favorite, and giving options makes them less picky.
Fry are tiny and do best if you have food ready. The easiest path is freshly hatched baby brine shrimp once they can take it, plus microworms or vinegar eels for the first stretch if needed. Keep the grow-out water clean, and do frequent small water changes. They are sensitive little needles at first.
Common problems to watch for
Most issues I have seen with this species trace back to stress: unstable water, temperature swings, or a fish getting harassed. Once they are stressed, parasites and infections show up fast.
- Jumping: the number one 'mystery death' is a dried fish behind the stand. Seal the lid gaps
- Velvet and ich: often show up after a swing in temperature or a big water change with mismatched water
- Internal parasites/wasting: wild-origin lines sometimes struggle; quarantine new fish and watch appetite and weight
- Fin damage: usually from male-on-male pressure or nippy tankmates
- Egg fungus: common if eggs sit in dirty water; use clean incubation water and remove bad eggs
Do not skip quarantine with these. A new fish that looks fine can bring in velvet or worms, and Fundulopanchax can go downhill quickly once something takes hold.
If you keep the tank covered, feed them like predators, and stay consistent with water changes, they are a blast. They are one of those fish that rewards the extra effort with behavior and color you just do not get from easier species.
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