X-ray Tetra Care Guide: Tank Setup, Water Params, and What You Need to Know

The X-ray tetra (Pristella maxillaris) is one of the most underrated fish in the freshwater hobby. Its nearly transparent body reveals a visible spine — that's exactly where the name comes from. It's also one of the hardiest tetras available, making it a top pick for beginners and experienced keepers alike.

Quick Answer: X-ray tetras grow to 1.5–2 inches and need a school of 6 or more in a 15-gallon tank minimum. Keep water at 72–82°F and pH 6.0–7.5. They eat flakes and frozen foods, tolerate a wide range of water conditions, and live up to 5 years with proper care.

What Makes the X-ray Tetra Special

The X-ray tetra's translucent body is its defining feature — you can actually see its spine through its skin. This unique trait earned it nicknames like "water goldfinch," "golden pristella tetra," and simply "x-ray fish." No other common aquarium tetra looks quite like it.

It belongs to the family Characidae, alongside neon tetras and cardinal tetras. But unlike many of its cousins, the X-ray tetra comes from coastal rivers that sometimes blend with brackish water [1]. That background gives it a hardiness edge most tetras simply don't have.

Appearance and Size

X-ray tetras reach 1.5–2 inches at adulthood. Their bodies are pale gold or silver-white with a ghostly translucent quality. The dorsal and anal fins display bold black-and-white or black-and-yellow banding — the clearest visual ID marker for this species.

Females are slightly larger and noticeably rounder when carrying eggs. Males are slimmer and smaller. In a school of 8 or more, the difference between sexes becomes easy to spot.

Where They Come From

In the wild, X-ray tetras inhabit rivers and streams across Venezuela, Brazil, and the Guianas. They frequently live near coastal zones where freshwater rivers meet tidal saltwater influence. Most fishkeepers don't realize this at all.

That coastal origin explains their surprising tolerance for moderate hardness and even light salt. They handle water conditions that would stress neon tetras without any trouble.

Setting Up the Right Tank

X-ray tetras need a minimum of 15 gallons for a school of 6, but a 20-gallon long is the better starting point. More horizontal swimming space reduces stress and keeps the school active. These fish spend most of their time in the mid-water column.

A dark substrate makes a visual difference. Black sand or dark gravel makes their transparent bodies appear to glow. It also mimics the darker riverbeds of their natural habitat.

Water Parameters

Stable parameters matter more than hitting exact numbers. Run 25% water changes weekly to keep nitrates in check and conditions consistent.

Pro Tip: X-ray tetras handle light brackish conditions — up to 1 teaspoon of aquarium salt per 5 gallons. This low-salt approach can help prevent ich and ease stress during transport acclimation. Skip it if you have scaleless tankmates like corydoras.

Filtration and Flow

A sponge filter or hang-on-back filter with gentle output works best. Strong currents push these small fish around and cause chronic stress. Target a flow rate of 4–5x the tank volume per hour.

Dense planting along the sides and back gives the school places to retreat. Java fern, anubias, and hornwort all work well. Keep an open swimming lane in the front-center of the tank.

For more planted tank setup ideas, check out the neon tetra care guide — many of the same principles apply to X-ray tetra tanks.

Feeding X-ray Tetras

X-ray tetras eat almost any food, which is a big reason they're so easy to keep. A high-quality micro pellet or flake covers daily nutritional needs. Supplement with frozen or live foods 2–3 times per week for optimal health and color.

Good supplemental food choices include:

• Daphnia — supports digestion and prevents bloating
• Bloodworms — high protein, excellent for conditioning before breeding
• Brine shrimp — boosts color and encourages spawning behavior
• Micro worms — ideal for juveniles and small adults

Feed small amounts twice a day. Only offer what they'll eat in 2 minutes. Uneaten food decomposes fast and spikes ammonia levels.

The Northfin Community Formula on Amazon is a popular small-pellet option for schooling fish — quality ingredients, appropriate pellet size for tetras.

Pro Tip: Don't rely on dried flakes alone. Keeper community data shows that rotating in frozen daphnia or brine shrimp at least twice a week reduces bloating and supports a stronger immune response over time.

Tank Mates That Work (And Ones to Avoid)

X-ray tetras are peaceful community fish that get along with nearly any small, non-aggressive species. Their calm temperament makes them easy neighbors. The key rule: avoid known fin-nippers and anything large enough to eat them.

Compatible tankmate choices:

• Corydoras catfish — peaceful bottom dwellers, no overlap in territory
• Dwarf gourami — similar size and temperament
• Harlequin rasboras — nearly identical water preferences
• Otocinclus catfish — gentle algae grazers, fully non-aggressive
• Ember tetras or rummy-nose tetras — compatible schooling species

Species to avoid:

• Tiger barbs — relentless fin-nippers that stress smaller fish
• Most cichlids — too territorial and aggressive
• Large predatory fish (angelfish, oscars) — X-ray tetras become a snack

As of May 2026, keeper consensus on major fishkeeping forums consistently confirms X-ray tetras rarely trigger aggression when kept in schools of 6 or more.

Why School Size Matters

X-ray tetras are true schooling fish. In groups smaller than 6, they become timid, hide constantly, and stop displaying natural behavior. A school of 8–10 shows tight shoaling formations, active open-water swimming, and noticeably less skittishness.

Keeping fewer than 5 is one of the most common beginner mistakes. Stressed fish develop weakened immune systems and shorter lifespans.

See our full guide to the best fish to keep with tetras for a complete compatible species breakdown.

Common Mistakes New Keepers Make

The single biggest mistake with X-ray tetras is keeping too few fish. Under 6 causes chronic stress. Stressed X-ray tetras hide, refuse food, and become disease-prone within weeks.

Other frequent errors include:

• Skipping quarantine: New fish should spend 2 weeks in a separate quarantine tank. X-ray tetras can carry ich or internal parasites without showing obvious symptoms at first.
• Overfeeding: Uneaten food in a small tank creates ammonia spikes fast. Feed twice daily, two-minute rule only.
• Strong filtration flow: High-flow canister filters create current these fish struggle against. Match filter output to their gentle-water origins.
• Ignoring temperature drops: Sudden drops below 70°F commonly trigger ich outbreaks. Use a reliable heater with a built-in thermostat and check it weekly.

Pro Tip: Always run a nitrogen cycle before adding X-ray tetras. Even though they're hardy, uncycled water with ammonia spikes can kill an entire school within days.

Common Health Issues

X-ray tetras are resilient, but poor water quality causes most disease outbreaks in captivity. Prevention through regular maintenance beats any medication. Test water weekly during the first 3 months of a new tank.

Ich (White Spot Disease)

Ich looks like tiny white grains of salt scattered across the fins and body. It's caused by the parasite Ichthyophthirius multifiliis. Raising tank temperature to 82°F combined with treating using aquarium ich medication on Amazon clears most infections within 5–7 days [2].

According to SeriouslyFish, X-ray tetras are more resistant to ich than neon tetras, partly due to their brackish-water tolerance history.

Neon Tetra Disease

Despite the name, this bacterial and microsporidian disease affects X-ray tetras too. Symptoms include color fading, wasting, and visible cysts under the skin. There's no reliable cure — isolate affected fish immediately to prevent spread through the school.

Fin Rot

Fin rot starts as ragged or discolored fin edges. It's bacterial in most cases and triggered directly by poor water quality. A clean tank plus API Fin & Body Cure on Amazon resolves most early cases within a week.

Common Myth: "Adding salt always helps sick fish." Reality: Low-level salt (1 tsp per 5 gal) aids ich recovery and reduces stress. But higher concentrations harm scaleless fish like corydoras and some plecos. Always check every tankmate's salt tolerance before treating.

Breeding X-ray Tetras

X-ray tetras are one of the easier tetras to breed in captivity — egg scatterers that spawn readily with minimal coaxing. A dedicated breeding tank dramatically improves fry survival compared to spawning in the community display [3].

Setting Up a Breeding Tank

Use a 5–10 gallon bare-bottom tank. Add a clump of java moss or a spawning mop for eggs to sink into. Lower the water level to about 6 inches deep. Keep lighting dim — this species spawns more reliably in low-light conditions.

Condition the breeding pair with frozen bloodworms and brine shrimp for one week before moving them. Target pH 6.5, temperature 78–80°F, and soft water (dGH under 6).

Raising Fry

Eggs hatch in 24–36 hours. Free-swimming fry appear 2–3 days after hatching. Feed infusoria or liquid fry food for the first 5–7 days.

Introduce micro worms and baby brine shrimp after the first week. Once juveniles reach 0.5 inches, they can safely move into the main display tank.

Pro Tip: Remove adult X-ray tetras from the breeding tank immediately after spawning. They will eat their own eggs within hours if left together with the clutch.

X-ray Tetra vs. Similar Species: Which One Is Right for You?

Updated May 18, 2026: The X-ray tetra is frequently confused with neon tetras and glowlight tetras at fish stores. Here's a direct comparison to help you choose the right species for your setup.

The X-ray tetra wins for beginners whose tap water isn't perfectly soft. If your water is already soft and acidic and you want a showpiece planted tank, neons are stunning. For most community tank setups, the X-ray tetra is simply the more forgiving choice.

Also see the green neon tetra care guide if you're comparing smaller, more delicate tetra varieties.

Common Myth: "X-ray tetras need the same pure, soft water as neon tetras." Reality: X-ray tetras evolved in coastal rivers where water chemistry shifts regularly. They thrive at pH 6.0–7.5 with moderate hardness — far more adaptable than neons, which suffer in hard or alkaline tap water.

Ready to get started? Shop aquarium sponge filters on Amazon — quiet, gentle flow, and the ideal choice for X-ray tetra tanks of any size.