Creek livebearer
Jenynsia eigenmanni
The Creek livebearer features a slender body with a striking olive-green coloration and distinctive vertical bars along its sides.
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About the Creek livebearer
Jenynsia eigenmanni is a little South American livebearer from southern Brazil, and it has that classic Jenynsia "one-sided" mating setup, which is pretty wild to watch once you keep a group. It's not a showy neon fish, but it is super active and always cruising and grazing, more like a tiny, tougher molly-type fish that stays busy all day.
Also known as
Quick Facts
Size
12 cm
Temperament
Peaceful
Difficulty
Intermediate
Min Tank Size
20 gallons
Lifespan
3-5 years
Origin
South America
Diet
Omnivore - algae and biofilm, small inverts, quality flakes/pellets, frozen foods
Water Parameters
20-26°C
7-8
8-20 dGH
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Calculate heater sizeCare Notes
- Give them a long tank with current - they love cruising and will use every inch, so 20+ gallons for a group is way easier than a cramped cube.
- They do best in hard, alkaline water (aim around pH 7.2-8.2 and medium-hard to hard GH); they get sulky and prone to issues if you keep them soft and acidic.
- Keep the temp in the low to mid 70s F (about 72-78F) - they handle cooler better than hot, and high heat tends to ramp up stress and bickering.
- Feed like tough little omnivores: quality flake or small pellets daily, plus frozen foods (daphnia, brine, bloodworms) a few times a week and some veggie stuff like spirulina or blanched zucchini.
- They can be nippy and pushy, especially males, so keep them in a bigger group with more females than males and avoid slow-finned fish like guppies, bettas, and fancy mollies.
- Good tankmates are quick, sturdy fish that do not take nonsense (many tetras, danios, barbs, some corys), and they also do fine with snails if the fish are well-fed.
- Breeding is easy if they are happy - females drop live fry regularly, and the adults will snack on babies, so toss in dense cover (guppy grass, hornwort, floating plants) if you want any to grow up.
- Watch for ragged fins from chasing and for skinny fish in a group - the bold ones can hog food, so spread food out and feed in two spots.
Compatibility
Good Tankmates
- Hardy livebearers like platies or mollies - similar vibe, can handle the constant cruising and occasional little squabbles without drama (just keep the ratios friendly and give them room).
- Active schooling fish like zebra danios or white clouds - they stay up and moving, so they do not get bothered much, and they match the creek livebearer energy.
- Peaceful small tetras like ember tetras or pristellas - good in a planted community where everyone has space and line-of-sight breaks.
- Chill bottom crews like corydoras - they mostly mind their own business on the floor while the Jenynsia do their midwater thing.
- Brlenose pleco or other mellow algae grazers - tough, unbothered tankmates that are not competing in the same zone.
- Small, peaceful loaches like kuhli loaches - they are nocturnal and low-key, so they are not getting in anyone's face.
Avoid
- Slow fish with fancy fins like guppies or bettas - creek livebearers can get a bit too interested in trailing fins, and you end up with shredded tails.
- Super peaceful, delicate fish like long-finned dwarf gouramis - they can get stressed by the constant movement and occasional chasing.
- Anything nippy or aggressive like tiger barbs or bigger cichlids - they will turn a normally chill tank into nonstop sparring.
Where they come from
Creek livebearers (Jenynsia eigenmanni) come from southern South America, where they hang around creeks, ditches, and slow rivers - the kind of places with mixed flow, weedy edges, and a lot of tiny life to snack on. They are not the delicate, glass-cannon type of fish. They are scrappy, curious, and always looking for food.
They are livebearers, but they do not act like guppies. Think more "busy little predator" than "pretty community fish."
Setting up their tank
Give them space and structure. A long tank is better than a tall one because these guys patrol back and forth all day. I have had the best luck with a planted setup that still has open swimming lanes.
- Tank size: 20 long works for a small group; 29+ is nicer if you want a real colony
- Filtration: moderate filtration, plus a sponge prefilter if you keep fry around
- Flow: gentle to moderate; they handle current fine but do not need a river tank
- Plants: hardy stuff like java fern, anubias, vallisneria, guppy grass, hornwort
- Hardscape: wood or rocks to break up sight lines (it cuts down on chasing)
Water-wise, they are pretty adaptable, but stability beats chasing numbers. I kept mine in neutral to slightly alkaline water with a bit of hardness and they were way less touchy than in super soft water. Keep up with water changes because they eat like pigs and they poop like it.
Use floating plants or a dense plant corner. It gives females and smaller fish somewhere to get a break from the constant attention.
What to feed them
They will take flakes and pellets, no problem. But if you want good color, steady growth, and fewer squabbles, feed like they are little opportunistic hunters.
- Staples: quality flake, small pellets, and micro pellets
- Frozen: brine shrimp, daphnia, cyclops, bloodworms (not every day)
- Live (if you can): baby brine shrimp, daphnia, grindal worms
- Greens: spirulina flake or an algae-based food a couple times a week
I feed small amounts 1-2 times a day. If you dump in a big meal, the bold ones get huge and the shy ones get skinny. Spreading it out helps the whole group.
They will absolutely snack on shrimp fry and may pick at slow or fancy-finned fish. Plan your stocking around that.
How they behave and who they get along with
Creek livebearers are active, nosy, and a little pushy. In a group they are fun to watch, but they are not a "set it and forget it" community fish. Males can be relentless with females, and the whole group will test any fish that looks slow or frilly.
- Best kept: in a species tank or with tough, fast fish
- Good tankmates: larger tetras that are quick, danios, sturdy barbs (depending on your water), armored catfish that do not mind the chaos
- Avoid: guppies, bettas, fancy long-fin fish, slow bottom dwellers with delicate feelers, small shrimp colonies
Keep them in groups, not pairs. A lone male can turn into a little terror, and a lone female gets harassed nonstop. I like a bigger group with more females than males so the attention gets spread out.
If you are seeing constant chasing, add more cover and break up the line of sight. Rearranging decor can also reset pecking order drama.
Breeding tips
They are livebearers, and once they settle in, breeding is not hard. The hard part is saving fry, because adults will eat them and tankmates will too.
- Run a group with extra females so no one fish gets pestered to death
- Feed varied foods (frozen/live helps a lot) to condition adults
- For fry survival: thick plants like guppy grass or a dedicated fry tank
- A sponge filter is your friend in fry setups
I do not bother with breeder boxes for these unless it is an emergency. Dense plants work better and stress the females less. If you really want numbers, move a pregnant female to a separate tank and move her back right after she drops.
Newborns are big enough to take crushed flake and baby brine shrimp pretty quickly. Baby brine shrimp makes a noticeable difference in growth.
Common problems to watch for
Most issues I have seen were not mysterious diseases. They were social stress, nipping, or water quality sliding because the tank was being fed heavy.
- Fin nipping and shredded tails: usually stocking choice or not enough cover
- Females getting worn down: too many males, not enough hiding spots
- Skinny fish in a "well fed" tank: food hogs dominating meals - feed smaller portions more often
- Ich after adding new fish: quarantine helps a lot, and keep temperature stable
- Bloat/constipation: ease up on heavy foods, add daphnia or a bit more plant-based food
Watch new purchases closely. Stressed livebearers can look fine in the store and then crash at home if the tank is immature or water quality swings.
If you keep their social setup sane (space, cover, extra females) and do regular water changes, they are hardy little fish. They just have a bigger personality than most people expect.
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