X-ray (Pristella) Tetra Care Guide

The X-ray, or Pristella, tetra is one of the hardiest, most forgiving tetras in the hobby — a see-through shoaler that shrugs off a wide range of water chemistry and tolerates harder, more alkaline water than almost any other tetra. That tolerance, plus a peaceful temperament and a translucent body, makes it a genuinely excellent beginner schooling fish. The one thing it still needs is numbers: it is a shoaling species and suffers kept in twos and threes.

X-ray (Pristella) Tetra at a glance

The sourced figures the welfare engine uses to judge X-ray (Pristella) Tetra — the parseable key facts.

Where it comes from

It comes from northern South America — the coastal river drainages of the Guianas and northern Brazil, plus the lower Amazon and Orinoco. In the dry season it lives in clearwater streams and tributaries, then moves into flooded savannah to spawn among submerged plants in the rains. The standout origin fact is that its heartland is the coastal floodplain belt where rivers meet the sea, so many wild populations sit in soft freshwater that turns slightly brackish near estuaries. That variable coastal habitat is the accepted explanation for the species' unusually wide chemistry tolerance — it does not demand the soft, acidic blackwater that cardinals do, and it copes with the harder, more alkaline tap water many keepers actually have. The brackish trait is a wild resilience legacy, not a keeping recommendation: keep this fish in freshwater.

Did you know?

• It is named for being see-through: the translucent body lets you see the spine and swim bladder straight through the fish — the "X-ray" trait — while the golden sheen and bright tricolor fins earned it the nickname "water goldfinch."
• Its single best ID feature is the tricolor fin flag: yellow base, black middle and white tip on the dorsal and anal fins, plus a red tail — unique among commonly kept tetras.
• It is a genus of one: Pristella is monotypic, with P. maxillaris the only species in it, named by Ulrey in 1894.
• It is the rare salt-tolerant tetra: almost no popular tetra copes with any salinity, but this one does, a legacy of its coastal Guiana habitat where rivers meet the sea.
• It is the see-through tetra that survives the tap water that kills cardinals — the hardiest, hardest-water-tolerant common tetra in the hobby.

Tank size — and why

A 15 US gallon footprint (around 60 cm) is the sensible floor for a proper school, with 20 gallons or more better for the group of ten-plus it really wants. The driver is not bioload — this is a small, low-waste fish — but swimming room and group size. A longer footprint gives the active mid-water school room to shoal confidently, so prioritise length over height for the swimming lane. There is no territorial or oxygen-demand reason for a big tank here, only the welfare of the school.

As a guide, a 20-gallon tank comfortably suits about 8–11 X-ray (Pristella) Tetra as a single-species display, leaving room for tankmates.

How big does it really get?

Full-grown X-ray (Pristella) Tetra reach about 4.5 cm (1.8 in) long, but they are usually sold at only about 2.5 cm (1 in) — a typical shop size (estimate). At full size, X-ray (Pristella) Tetra needs roughly a 15-gallon tank, about 51 cm long; a common 10-gallon starter kit is only about 51 cm.

Adult size is sourced; the shop size is a typical-juvenile estimate; tank length is approximate for a standard 15-gallon aquarium.

Water parameters in practice

This is where the Pristella earns its reputation. Aim for around 24–27 °C, comfortable anywhere across 22–28 °C. On pH it is genuinely wide: prefer near-neutral around 6.5–7.5, but it is safe up to pH 8 — FishBase rates it to 8.0 and well into hard water (to roughly 35 dGH), which is the trait that separates it from the soft-water-only tetras and lets it thrive in moderately hard, mildly alkaline tap water. That wide envelope is the whole selling point, but it buys forgiveness, not neglect: the fish still needs a cycled, stable tank and regular water changes. The brackish tolerance is real in the wild, but don't oversell it — default to freshwater, since standing salted water is reported to shorten its life.

Will it thrive in your water?

The comfortable range for X-ray (Pristella) Tetra is about 22–28 °C (72–82 °F) and pH 6–8. Test your own tap water against it below.

These are the sourced comfortable ranges. Stable water matters more than chasing an exact number — a steady reading inside the band beats a "perfect" one that drifts. Some fish also need a particular water hardness (GH); where that applies, the prose above covers it.

Diet & feeding

An omnivorous micropredator. In the wild it takes small invertebrates, worms, small crustaceans and insects. In the tank it readily accepts a good-quality micro flake, small pellet or granule as the staple, varied with small live or frozen foods — daphnia, brine shrimp, bloodworm, cyclops — to boost colour and condition, and essential when conditioning for breeding. Feed small amounts once or twice a day, sparingly, to protect water quality. It is an active, unfussy mid-water feeder.

Gear & setup

A heater to hold a stable mid-20s temperature and a gentle-to-moderate filter suit this slow-water, vegetated-stream fish. It does well in a planted tank with cover; a darker substrate and some shade deepen its colour and reduce skittishness, while open mid-water space gives the school room to move. A lid is sensible for any active small fish, though it is not a notorious jumper.

Temperament & behaviour

Peaceful and gregarious — FishBase calls it "gregarious and non-aggressive." This is a non-territorial mid-water shoaler with no meaningful same-species aggression and no habitual fin-nipping in a proper group. The behaviour only appears in numbers: a confident, colourful, active shoal in a good-sized group versus skittish, washed-out fish kept in ones and twos. It asks nothing of its tankmates beyond being left in peace by anything larger or pushier.

Group & social needs

Keep a real group: six is the bare minimum, ten or more is the real target. Larger groups reduce stress, produce confident shoaling and better colour, and dilute any nipping. Seriously Fish notes it will "fare much better when in the company of its own kind," and under-stocked fish hide and lose confidence. There is no special sex-ratio requirement for general keeping.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with X-ray (Pristella) Tetra and that suit its size and temperament best. Tap a name for its care guide, or use + to load the pairing in the planner.

• Amano Shrimp+Peaceful temperament, similar adult size
• Black Neon Tetra+Peaceful temperament, similar adult size
• Black Phantom Tetra+Peaceful temperament, similar adult size
• Bolivian Ram+Uses the bottom zone, peaceful temperament, similar adult size
• Brilliant Rasbora+Peaceful temperament, similar adult size
• Bronze Corydoras+Uses the bottom zone, peaceful temperament, similar adult size
• Cardinal Tetra+Peaceful temperament, similar adult size
• Checker Barb+Peaceful temperament, similar adult size

A note on the shrimp and snails here: X-ray (Pristella) Tetra is peaceful and generally invertebrate-safe — but almost any fish will take very small shrimplets given the chance, so give shrimp dense cover (moss, leaf litter) if you want a colony to grow, rather than expecting every baby to survive.

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

Breeding & sexing

Sexing is straightforward: mature females are larger, deeper-bodied and noticeably stockier, especially when gravid, while males are slimmer and more streamlined. Breeding is comparatively easy for a tetra — FishBase notes "reproduction is easily carried out, 300 to 400 eggs are obtained per spawn." Note that the spawning water is narrower than the day-to-day tolerance: use a separate, dimly-lit tank with fine-leaved plants or spawning mops, a gentle sponge filter, and soft, slightly acidic water (around pH 5.5–6.5, GH 1–5) at roughly 27–29 °C, conditioning the group on small live foods first. It is a prolific egg-scatterer; parents eat the eggs, so remove the adults after spawning. Eggs hatch in about 24–36 hours and fry are free-swimming a few days later, started on infusoria and microscopic foods, then microworm and baby brine shrimp.

Lifespan

Four to five years in a well-maintained tank, with some hobbyists reporting longer in ideal conditions; wild fish live perhaps three to four years. What shortens it is chronic poor water quality, being kept in too small a group, and — per several care guides — keeping it in standing brackish or salted water long-term, which is said to reduce lifespan even though the fish tolerates short exposure.

Common mistakes

• Keeping too few. Two to four fish become skittish, faded and stressed — buy six minimum, ten or more ideally.
• Assuming hardy means no cycling. "Bulletproof" still needs a cycled, maintained tank; the wide tolerance buys forgiveness, not neglect.
• Over-reading the brackish trait. Don't add salt as a default — this is a freshwater fish that can cope with mild brackish water, not a brackish fish, and standing salted water can shorten its life.
• Housing it with boisterous or predatory tankmates. Tiger barbs, rainbow/red-tail sharks and large cichlids will bully or eat a bite-sized tetra.
• Buying poor stock. Skip any tank holding faded, clamped, white-spotted or lethargic fish.

Signs of trouble

• Fading or dulling of the gold sheen and a fish dropping out of the shoal — usually water quality, an immature tank, or too small a group.
• Clamped fins, hiding and loss of appetite — general stress cues worth investigating.
• Flicking and scratching against decor — early ich (white spot), the most common disease in this otherwise robust fish.
• Skittish, washed-out behaviour in a small group — a husbandry signal the school is too small rather than an illness.

Is this fish right for you?

Don't buy Pristellas if you can only house a couple of them, if your tank is uncycled, or if your community contains large or aggressive fish such as tiger barbs, red-tail sharks or big cichlids. Hard or mildly alkaline tap water is fine here — that is the species' selling point, not a problem — so this is the tetra to choose when you can't soften your water. On stock quality, the gold or golden semi-albino strain is a legitimate selectively-bred line, not a dyed fish; the dyed or injected "painted" fish to avoid are glassfish, not Pristellas.

Bringing one home

It forgives more than most tetras, but still acclimate properly: float the bag to equalise temperature, then add tank water gradually over fifteen to twenty minutes before netting the fish into a mature, cycled tank and leaving the transport water behind. Quarantine new arrivals to protect the rest of the shoal.

Common questions

Are X-ray (Pristella) tetras good for beginners?

Yes — they are among the hardiest, most forgiving tetras in the hobby, explicitly recommended for beginners. They tolerate a wide range of water chemistry, including harder and mildly alkaline tap water, and ask mainly for a cycled tank and a proper group.

What pH and water hardness do Pristella tetras need?

Near-neutral, around pH 6.5–7.5, is ideal, but they are safe up to pH 8 and well into hard water (FishBase rates them to roughly 35 dGH). This wide tolerance is their defining trait and the reason they suit hard-water tap that cardinals can't handle.

Can Pristella tetras live in brackish water?

Their wild coastal populations tolerate slightly brackish water, and they cope at the low end of a molly setup better than most tetras — but they are a freshwater fish. Don't add salt as a default; standing brackish water is reported to shorten their lifespan.

How many X-ray tetras should I keep?

Six is the bare minimum and ten or more is the real target. They are shoaling fish — small groups stay skittish and faded, while a larger school is confident, active and more colourful.

How do you tell a Pristella from a glass catfish or glassfish?

Look for the tricolor dorsal/anal fins and red tail: that's a Pristella. Whiskers and a near-invisible elongated body mean a glass catfish; a deep, perch-like body that's often dyed means an Indian glassfish.

Sources & confidence

Sources & confidence (9 species)

These back the X-ray (Pristella) 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.

• X-ray (Pristella) Tetra Pristella maxillaris — Seriously Fish (seriouslyfish.com/species/pristella-maxillaris) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction 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
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Brilliant Rasbora Rasbora einthovenii — Seriously Fish (seriouslyfish.com/species/rasbora-einthovenii) 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
• Checker Barb Oliotius oligolepis — Seriously Fish — Oliotius oligolepis (https://www.seriouslyfish.com/species/oliotius-oligolepis/) high confidence

Care-guide sources (6)

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.

• FishBase — Pristella maxillaris — authority/year (Ulrey 1894), family (Acestrorhamphidae), max 4.5 cm TL, freshwater/pelagic classification, temp 24–28 °C, pH 6.0–8.0, dH up to ~35, range (Amazon/Orinoco/Guiana coastal drainages), diet, trophic level 3.2, IUCN Least Concern, resilience High, "gregarious and non-aggressive," "groups of 5 or more / 60 cm," "300 to 400 eggs… per spawn"
• Seriously Fish — Pristella maxillaris — family (Characidae), synonym P. riddlei, "water goldfinch" name, coastal Guiana/N-Brazil range, dry-season streams / flooded-savannah biotope, 40–45 mm, temp 22–28 °C, pH 6.0–7.5, GH 2–20 (breeding 1–5), 60×30 cm tank, micropredator diet, group 6 (10+ preferred), sexing (females bigger/stockier), breeding setup, gold strain, "won't compete well with very boisterous or much larger tankmates"
• Wikipedia — X-ray tetra — Ulrey 1894, monotypic genus Pristella (Eigenmann 1908), translucent body / visible spine, "yellowish-silver, almost golden" scales, red caudal fin, black-yellow-white dorsal/anal markings, max 4.5 cm TL, IUCN Least Concern, "hardy and easy to maintain, a good fish for beginners"
• Aquadiction — X-ray Tetra profile — temp ~23–27 °C, pH 6.0–8.0, GH 4–18, ~5 cm size, lifespan up to 5 yrs, group 6+, brackish-tolerance framing, beginner difficulty, peaceful, tankmates, egg-scatterer (~300 eggs, 24–36 h hatch), gold/albino colour forms
• AquariumStoreDepot — Pristella Tetra care — hardiness / "bulletproof" / "most adaptable tetra" framing, brackish-tolerance note, beginner suitability, temp/pH/GH corroboration, group 6 (10+), tankmates
• Fishkeeping World — Pristella Tetra — beginner/hardy framing, temp 75–82 °F, pH 6.0–8.0, ~2 in size, lifespan 3–4 wild / up to 5 captive, group 6+, tankmates incl. mollies/livebearers, diet, sexing, breeding triggers, brackish caveat ("not recommended… reduces lifespan")

More on X-ray (Pristella) 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 →