Serpae Tetra Care Guide

The serpae tetra is a hardy, cheap, brilliant blood-red tetra marketed as the 'Jewel' or 'Blood' tetra — and simultaneously one of the most notorious fin-nippers in the hobby. Keep it only as a large, tight shoal in a long planted tank, and never mix it with bettas, guppies, angelfish, gouramis or any slow, long-finned fish, which it will harass relentlessly. Its challenge is behaviour, not fragility.

Serpae Tetra at a glance

The sourced figures the welfare engine uses to judge Serpae Tetra — the parseable key facts.

Where it comes from

Serpae are widespread across tropical South America — the Amazon drainage (Brazil, Peru, Bolivia), the Guaporé and Madeira, and the Río Paraguay and upper La Plata basin. The wild habitat is telling: still and sluggish waters — backwaters, oxbows, floodplain lakes and ponds — among marginal vegetation, submerged roots and dense plants, where the fish is gregarious near the surface among plant stems. Two care lessons follow. First, dense planting, driftwood and broken sight-lines are functional, not just decorative: cover breaks up the aggression the species aims at tankmates and at each other. Second, this is a warm-water lowland fish — its comfortable floor is about 22 °C, not the low-20s some charts imply. The water is soft and slightly acidic to neutral in the wild, but tank-bred stock (which is almost all of it) is very adaptable.

Did you know?

• A jewel with a mean streak: marketed as the gorgeous 'Jewel' or 'Blood' tetra, it is at the same time one of the most infamous fin-nippers in the hobby — beauty and the beast in one fish.
• The name eques is Latin for 'horseman' or 'rider', after the saddle- or comma-shaped black humeral mark behind the gill cover.
• It is a taxonomic shape-shifter: sold for a century under callistus, serpae and eques as a confusing 'blood-tetra complex' of look-alikes, now mostly lumped as Hyphessobrycon eques — while FishBase has moved it to a resurrected genus, Megalamphodus eques (family Acestrorhamphidae). Hobby copy uses Hyphessobrycon eques / Characidae; the reclassification is recorded as a fact, not an error.
• The fin-nipper sold with long fins: breeders have created a long-finned 'Longfin / Super Serpae' strain (plus metallic, balloon and fairy-fin forms) — a notorious nipper deliberately bred into the very fin shape it loves to nip.
• Kept correctly, its aggression is part of the appeal: in a big shoal the constant male sparring and flaring is a dynamic, watchable display.
• IUCN Least Concern (assessed 2021); abundant, widespread, and the trade is overwhelmingly tank-bred.

Tank size — and why

A 20 US gallon tank with roughly an 80 cm footprint is the practical floor, and longer is better. Seriously Fish stocks that footprint with 12-15 serpae as the only upper-water species. The driver is not bioload — they are small, medium-waste fish — but length and footprint to spread aggression: a longer tank lets the shoal disperse and chase within the group rather than cornering tankmates or a single weak conspecific. Prioritise length over height; horizontal swimming and sight-line distance are part of how you keep the nipping internal. An active surface-oriented fish, so fit a lid.

As a guide, a 20-gallon tank comfortably suits about 7–10 Serpae Tetra as a single-species display, leaving room for tankmates.

See it to scale

Adult Serpae Tetra reach only about 4 cm (1.6 in) long — close to the size they are sold at, so what you see is roughly what you get. The catch is the group: a proper shoal still needs about a 20-gallon tank, around 76 cm long.

Adult size is sourced; tank length is approximate for a standard 20-gallon aquarium.

Water parameters in practice

Hardy and forgiving on chemistry. Tank-bred serpae accept pH from about 5.0 to 7.8 and soft-to-medium hardness, happiest soft and slightly acidic but undemanding in practice. On temperature, aim for about 24-26 °C and treat roughly 22 °C as the practical comfort floor — FishBase and most hobby sources give a 22-26 °C band, and only Seriously Fish stretches to 20 °C as a wild-tolerance extreme rather than a recommended setpoint. Running the tank too cool stresses a warm-water fish. As with the other tetras, a mature, cycled, stable tank matters far more than chasing a precise number; the serpae's real difficulty is never the water, it is the behaviour.

Diet & feeding

An omnivorous micro-predator taking small invertebrates, crustaceans, insects, algae and fallen plant matter in the wild. A good-quality dried flake or micro-pellet makes the base, varied with small live or frozen foods — bloodworm, mosquito larvae, daphnia, moina, brine shrimp — to deepen the red and condition for breeding. Feed small amounts once or twice a day. Feeding behaviour matters here: the serpae is an eager, competitive feeder, and FishBase notes fin-nipping intensifies during competitive feeding — so spread the food and feed adequately so squabbling does not concentrate on tankmates.

Gear & setup

A heater to hold the warm setpoint, a filter giving gentle to moderate turnover (a still-water fish — avoid strong current), dark substrate to intensify the red, and crucially a densely planted layout with driftwood and broken sight-lines. That cover is one of the main tools for keeping intra-group chasing harmless, alongside the long footprint. Keep it covered.

Temperament & behaviour

This is the headline. The serpae is one of the most notorious fin-nippers in the hobby — Seriously Fish calls it 'notorious as an aggressive community inhabitant with a reputation for nipping the fins of tankmates', and Wikipedia that it is 'notoriously and widely known to be aggressive both to conspecifics and community aquarium tankmates'. Within the shoal, rival males form loose hierarchies and continually spar and flare; in a healthy large group that sparring stays mostly inside the group and is normal display, not damage. A genuinely contested point is whether a big group cures the nipping: the dominant model (Seriously Fish, AquariumStoreDepot) is that larger groups, length and planting reduce but never eliminate it — 'a group of 6+ reduces it, but never eliminates it' — while Wikipedia flags a real dissent, that 'copious anecdotal reports say [larger school or tank] does not help.' The honest synthesis: a big tight shoal in a long planted tank is the best mitigation and clearly helps, but no group size makes a serpae safe with long-finned or slow fish — plan tankmates around the nipping as a permanent trait, not a problem you can manage away.

Group & social needs

An obligate shoaler and the group size is the primary aggression-control lever, not a nice-to-have. Seriously Fish recommends a minimum of 12; hobby consensus is at least 8, ideally 12 or more. In a school of 8 to 12 the nipping stays mostly within the group; in a group of four or five, one or two fish take the brunt and it gets ugly. A minority of care sources still suggest 5-7, but the sourced welfare best-practice is 8-12+. Sexing: males are slimmer and more intensely coloured, females rounder-bodied, plumper and a little larger, especially in spawning condition.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Serpae Tetra and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Amano Shrimp — Peaceful temperament, similar adult size.
• Assassin Snail — Uses the bottom zone, peaceful temperament, similar adult size.
• Black Neon Tetra — Peaceful temperament, similar adult size.

One caveat on the shrimp and snails here: engine-cleared means a size, temperament and water-needs fit — it is not a guarantee of safety. An individual Serpae Tetra may still hunt shrimp or pick at small snails, and temperament varies from fish to fish, so add invertebrates cautiously, give them cover, and watch the first encounters.

This engine-cleared shortlist is Serpae Tetra's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Sexing is moderate (females rounder and larger, males slimmer and redder), and breeding is easy-to-moderate — serpae are willing egg-scatterers that spawn readily in mature tanks, with spawning preceded by male driving and display. Use a separate, dimly lit breeding tank with fine-leaved plants, spawning mops or a mesh grid so the eggs fall out of reach, soft slightly acidic-to-neutral water at the upper end of the temperature range, and condition the pair or group on live and frozen foods first. They eat their own eggs and give no parental care, so remove the adults immediately after spawning; eggs hatch in roughly 24-48 hours, fry free-swimming a few days later, raised on infusoria then microworm and baby brine shrimp.

Lifespan

Five to seven years with good care is the common hobby figure, with a wider 3-7 year range across sources (neither FishBase nor Seriously Fish states a hard figure, so treat this as care-blog consensus). What shortens it is chronic stress in too small a group, poor or unstable water, overfeeding, and injury from being housed with fish it cannot dominate or that out-compete it.

Common mistakes

• Buying too few. The number-one mistake — a group of one to six turns into a bully and victims and concentrates the nipping on tankmates. Buy eight to twelve or more, with twelve-plus the target.
• Adding them to an existing peaceful community. The serpae is a fish you build the tank around, not a late addition to a tank with bettas, angels, guppies or gouramis.
• Pairing with long-finned or slow fish — bettas, fancy guppies, angelfish, gouramis and fancy livebearers will have their fins shredded. This is why those species are excluded from this fish's recommended tankmates outright, even when a coarse size match would clear them.
• Trusting that 'a big group fixes it'. A large shoal reduces the nipping but does not eliminate it, and there is a real dissenting view that group size doesn't help much at all — so never rely on numbers to make long-finned tankmates safe.
• Running the tank too cool. Treat about 22 °C as the floor; the low-20s and below stress a warm-water fish.
• Buying the long-finned or balloon strain naively. The long-fin 'Super Serpae' is more vulnerable to its own group's nipping, and the balloon morph is a deformity-based fancy strain — a welfare red flag for buyers who care about ethical stock.

Signs of trouble

• Frayed or nipped fins on one individual — check for a scapegoated fish; the group is probably too small to diffuse the aggression, and the wounds invite secondary fin rot.
• Faded colour, clamped fins and hiding — chronic stress, often from too few fish or being out-competed.
• Nipping concentrated on a tankmate's fins rather than internal sparring — a sign of insufficient numbers, an unsuitable long-finned or slow tankmate, or too little planted cover.
• White spots with flashing or scratching — ich, typically after a chill or poor water.

Is this fish right for you?

Don't buy serpae if you want a peaceful community centrepiece, if you keep or want bettas, guppies, angelfish, gouramis or any long-finned fish, if you can't house a shoal of at least eight (ideally twelve-plus), or if you only have a short or small tank that can't disperse the aggression. On stock quality, the long-finned 'Super Serpae' and especially the balloon morph are welfare-questionable fancy strains; the wild-type short-finned fish is the ethical pick. Most serpae are hardy, cheap and tank-bred — the fish itself is forgiving; the buying decision is what goes wrong.

Bringing one home

Add serpae only to a mature, cycled, stable tank, acclimating gently before netting them across, and quarantine new stock. Add the full shoal at once rather than building the group up slowly, and stock the serpae early — as the fish the community is designed around — rather than dropping them into an established peaceful tank.

Common questions

Are serpae tetras fin nippers?

Yes — the serpae is one of the most notorious fin-nippers in the hobby, described by Seriously Fish as 'notorious as an aggressive community inhabitant with a reputation for nipping the fins of tankmates' and confirmed by FishBase and Wikipedia. The behaviour is its single defining trait and dictates how it must be kept and what it can live with.

Does keeping a big group stop serpae tetras nipping?

It helps but doesn't cure it. The mainstream view is that a large shoal in a long planted tank reduces nipping by directing the aggression inward — 'a group of 6+ reduces it, but never eliminates it' — but Wikipedia notes copious anecdotal reports that larger schools don't help much. Treat a big shoal as essential mitigation, never as a licence to add long-finned tankmates.

Can serpae tetras live with bettas, guppies or angelfish?

No. Bettas, fancy guppies, angelfish, gouramis and any slow or long-finned fish are the serpae's prime targets — their fins will be nipped and shredded and they can't escape. Those species are excluded from this fish's recommended tankmates. Pair serpae only with fast, robust, short-finned fish of similar size.

How many serpae tetras should I keep?

Eight to twelve or more, with twelve-plus the ideal — Seriously Fish recommends a minimum of 12. In a school of 8 to 12 the nipping stays mostly within the group; in a group of four or five, one or two fish take the brunt and it gets ugly. Six is a bare minimum, not a goal.

What is the scientific name of the serpae tetra?

Hobby usage is Hyphessobrycon eques (Steindachner, 1882), family Characidae. FishBase now lists it as Megalamphodus eques in the family Acestrorhamphidae after a recent reclassification. It has long been sold under the synonyms callistus and serpae as part of a 'blood-tetra complex' of look-alikes.

What temperature do serpae tetras need?

Aim for about 24-26 °C and treat roughly 22 °C as the practical floor. It is a warm-water lowland fish, so don't run it cool — FishBase and most hobby sources give a 22-26 °C band, with only Seriously Fish stretching to 20 °C as a wild-tolerance extreme.

Are serpae tetras good for beginners?

The fish itself is hardy and forgiving, so as an organism it is beginner-friendly — but the stocking decision is not. A beginner who buys six and adds them to a betta or guppy tank will have a bad time. Serpae suit a keeper willing to build a large shoal in a long planted tank with fast, short-finned tankmates.

Sources & confidence

Sources & confidence (9 species)

These back the Serpae Tetra figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Serpae Tetra Hyphessobrycon eques — Seriously Fish (seriouslyfish.com/species/hyphessobrycon-eques) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Assassin Snail Clea helena (Anentome helena) — The Shrimp Farm (theshrimpfarm.com/posts/assassin-snail-care) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Bleeding Heart Tetra Hyphessobrycon erythrostigma — Seriously Fish (Hyphessobrycon erythrostigma) high confidence
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Bronze Corydoras Corydoras aeneus — Seriously Fish (seriouslyfish.com/species/corydoras-aeneus) high confidence
• Cardinal Tetra Paracheirodon axelrodi — Seriously Fish (seriouslyfish.com/species/paracheirodon-axelrodi) high confidence

Care-guide sources (7)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• Seriously Fish — Hyphessobrycon eques (Serpae Tetra) — authority (Steindachner 1882), family Characidae, synonyms (callistus, serpae), Amazon/Paraguay range, still-water habitat, max 30-40 mm SL, temp 20-28 °C, pH 5.0-7.5, GH 18-268 ppm, 80×30 cm min tank, group of 12-15, 'notorious... nipping the fins of tankmates' quote, male hierarchies, unsuitable (shy/slow/long-finned/livebearers/cichlids/anabantoids) vs suitable tankmates, diet, sexing, breeding
• FishBase — Megalamphodus eques (= Hyphessobrycon eques) — current name Megalamphodus eques, family Acestrorhamphidae, Steindachner 1882, Amazon/Guaporé/Paraguay range, max 4.0 cm SL, temp 22-26 °C, pH 5.0-7.8, dH 10-25, trophic 3.1, IUCN Least Concern (2021), gregarious/stagnant-water/surface biology, fin-nipping during competitive feeding, oviparous with male driving
• Wikipedia — Serpae tetra — Megalamphodus eques, synonyms, common names, distribution, 4 cm SL, etymology (eques = horseman, saddle mark), 'notoriously and widely known to be aggressive... to conspecifics and community... tankmates' quote, the contrarian 'copious anecdotal reports say [larger school/tank] does not help' quote, captive-bred status
• AquariumStoreDepot — Serpae Tetra Care Guide — size ~1.75-2 in, lifespan 5-7 yr, temp 72-79 °F, pH 6.0-7.8, hardness 5-20 dGH, min 20 gal for 6, 'persistent fin nippers... reduces it, but never eliminates it' and 'in a school of 8 to 12 the nipping stays mostly within the group' quotes, avoid bettas/angelfish/guppies/gouramis, good tankmates, diet, breeding
• Aquarium Source — Serpae Tetra 101 — size 1.75-2 in, temp 72-79 °F, pH 5-7.8, GH 5-25 dGH, min 20 gal, group 5-7 (minority view), lifespan 5-7 yr, 'for the most part peaceful... fast-moving' + 'slight aggression toward slow-moving long-finned' (the softer-temperament dissent), good tankmates, diet, breeding, sexing
• Virtual Aquarium — Serpae Tetra Care Guide — temp 72-79 °F, pH 6.0-7.5, size 4.5-5 cm, min tank 64 L, group minimum 8 / ideally 12+, 'well-known fin-nippers — especially when kept in small groups or with slow, long-finned tankmates', 'social hierarchy behavior without serious damage' in well-structured tanks, lifespan 3-7 yr, planted setup
• Aquadiction / Aqua Imports / PetSmart — Longfin Serpae strains — confirms the long-finned 'Longfin / Super Serpae' ornamental variety is widely traded, plus metallic/balloon/fairy-fin strains (retail corroboration of the variety's existence, cross-ref Seriously Fish)

More on Serpae Tetra

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →