Meleiro livebearer
Jenynsia sanctaecatarinae
Meleiro livebearers exhibit a slender body with a vibrant yellow-green hue and distinct dark spots along their flanks.
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About the Meleiro livebearer
This is a little onesided livebearer from southern Brazil that stays pretty small, with males topping out around 3.7 cm and females around 4.2 cm. In a planted stream-style tank they are always cruising and picking at tiny foods, and like other Jenynsia they have that cool livebearer biology (no eggs to babysit). I'd treat them like a slightly feisty nano livebearer and give them space and a group so nobody gets singled out.
Also known as
Quick Facts
Size
4.2 cm (female) / 3.7 cm (male) SL
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
20 gallons
Lifespan
3-5 years
Origin
South America
Diet
Omnivore/micropredator - quality flake/micro pellets plus frozen/live foods (daphnia, brine shrimp, mosquito larvae)
Water Parameters
18-22°C
7-8
10-20 dGH
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Calculate heater sizeCare Notes
- Give them a longer tank with room to cruise (20+ gallons is way nicer than a tall nano), plus a tight lid - they can jump when spooked.
- They do best in hard, alkaline freshwater: aim around pH 7.2-8.2 and medium-high GH; they sulk and get ratty fins in soft, acidic water.
- Keep the water moving and clean with a decent filter and some current, but add plants/rock piles/wood so weaker fish can duck out of the way.
- Feed like a livebearer with attitude: good flake/pellet as a base, then rotate in frozen foods (brine shrimp, daphnia, bloodworms) and some veggie stuff (spirulina, blanched zucchini).
- They can be nippy and pushy, so skip slow, long-finned tankmates (guppies, bettas, fancy angels) and go with quick, sturdy fish like larger tetras, barbs, danios, or other hard-water livebearers.
- Run them in a group with more females than males (like 1 male to 2-3 females) or the girls will get ridden nonstop.
- Breeding is classic livebearer: females drop fully formed fry regularly, and adults will snack on babies, so use dense plants (guppy grass, hornwort) or pull the pregnant female to a breeder box only if you actually want to raise fry.
- Watch for fin damage from chasing and for skinny fish that are getting outcompeted at feeding time; spread food across the tank so everyone gets a shot.
Compatibility
Good Tankmates
- Hardy livebearers that can handle a little attitude - platies and mollies (not long-finned fancy types). In my experience these guys do fine because they are quick, social, and not easily bullied.
- Fast, midwater schoolers like zebra danios or black skirt tetras. They are speedy enough that the Meleiros do not get to boss them around all day.
- Tougher barbs like cherry barbs (in a decent group). They hold their own and are not delicate, and they stay active which helps spread out any chasing.
- Peaceful bottom crews that keep to themselves - Corydoras (chunkier types) and bristlenose plecos. The Jenynsia are mostly about mid/top squabbles, so bottom dwellers usually get ignored.
- Loaches that are busy and not shy - kuhli loaches or small Botia species in a proper group and with hiding spots. They are usually too slippery to be bothered much.
- Other Jenynsia or similarly sized, sturdy livebearers in a bigger tank with lots of sight breaks. They do the best when you keep them in a group so the attitude is spread out, not focused on one victim.
Avoid
- Slow fish with fancy fins - guppies, fancy mollies, bettas. These livebearers can be little fin-checkers and stress out anything floaty or frilly.
- Tiny, delicate nano fish - ember tetras, chili rasboras, small endlers. Meleiro livebearers are mouthy and pushy, and the little guys get harassed or outcompeted at feeding time.
- Very aggressive or territorial fish - most cichlids (even some of the smaller ones). You end up with nonstop chasing and shredded fins because neither side backs down.
Where they come from
The Meleiro livebearer (Jenynsia sanctaecatarinae) comes from southern Brazil around Santa Catarina. Think lowland streams, ditches, and slow edges where the water can be warm, a little murky, and full of weeds and bugs. They are one of those fish that do fine in less-than-picture-perfect water, but they still appreciate stability in the tank.
Setting up their tank
Give them swimming room and a lot of visual breaks. Jenynsia are active, always on the move, and they do this constant pecking and investigating. If the tank is too bare, the chasing gets more intense.
- Tank size: I would not bother under 20 gallons for a group. A 29-40 gallon makes life easier.
- Group size: 6+ is where you start seeing more natural behavior. Bigger groups spread out aggression.
- Filtration: moderate filtration and steady oxygenation. They do not need a river tank, but they like clean water.
- Temp: mid 70s F works well (roughly 23-26 C). They can handle a little cooler, but breeding slows down.
- Hardness/pH: they are pretty flexible, but they tend to look best in neutral to slightly hard water.
Decor-wise, I have the best luck with a planted layout that still leaves open lanes. Floating plants plus a few clumps of stem plants or guppy grass does a lot of work here. Rocks and wood are fine too, just avoid creating one tight corner where a dominant fish can pin others.
If you only do one thing for this species, pack the tank with plant cover (especially at the surface). It cuts down on harassment and it gives fry a chance.
What to feed them
They eat like livebearers with attitude: always hungry, always sampling. Mine took flakes on day one, but they really color up and bulk out with variety. Think small insects, crustaceans, and whatever else drifts by in the wild.
- Staples: quality flake or small pellets
- Protein boosts: frozen baby brine, daphnia, cyclops, bloodworms (not every day)
- Live foods: grindal worms, mosquito larvae (if you have a safe source), live daphnia
- Plant matter: spirulina flake, blanched zucchini or spinach now and then
They will overeat if you let them. Feed small portions and watch bellies. A little lean is better than constantly stuffed.
How they behave and who they get along with
Jenynsia are not delicate, shy community fish. They are lively, sometimes pushy, and they like to nip fins if they get bored or crowded. In a roomy tank with a decent group, they spend more time sparring with each other and less time bothering everyone else.
- Good tankmates: other sturdy, active fish that are not long-finned (many tetras, danios, hardy barbs, some corydoras if the Jenynsia are well-fed and the tank is big)
- Use caution with: slow fish and fancy fins (bettas, fancy guppies, long-finned mollies, angelfish)
- Avoid: tiny timid fish and shrimp colonies you care about (they will pick off shrimplets and may harass small adults)
Male-to-female balance matters. Too many males and the females get chased nonstop. I like at least 2-3 females per male, and more females if the tank is on the smaller side.
Expect a bit of pecking order behavior. A little chasing is normal. Torn fins and one fish hiding all day is your sign to add cover, increase the group, or separate a bully.
Breeding tips
They are livebearers, and if you keep males and females together, you will get fry sooner or later. The tricky part is not getting them to breed - it is getting babies to survive in a tank full of hungry adults.
- Run a female-heavy group to reduce nonstop chasing and stress
- Give birth cover: floating plants, guppy grass, hornwort, or a dense mossy corner
- If you want numbers, move a pregnant female to a separate tank (I skip breeder boxes - they stress the fish)
- Feed fry finely crushed flake, baby brine shrimp, and microworms if you have them
- Do frequent small water changes in the fry tank so growth stays steady
If you want a low-effort approach, keep a jungle of floaters and accept that only a few fry will make it. You will still end up with youngsters over time.
Common problems to watch for
Most issues I have seen with Jenynsia come from crowding and boredom: fin nipping, stressed females, and constant skirmishes. The fix is usually more space, more cover, and a better ratio.
- Fin nipping: usually shows up with long-finned tankmates or too small a tank
- Female harassment: too many males, not enough plants, or the group is too small
- Ich or other parasites after purchase: they are hardy, but new fish can bring problems - quarantine if you can
- Bloat/constipation: from heavy dry-food diets and overfeeding - add roughage and frozen foods
- Jumping: they can launch when startled, especially in sparse tanks
Put a lid on the tank. I have had livebearers hit the floor after a water change or a sudden light switch, and Jenynsia are plenty capable of that.
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