X-Ray Tetra Care Guide: Tank Setup, Diet & Tank Mates

Species Overview#

The X-Ray Tetra (Pristella maxillaris) is one of the few freshwater fish you can almost see through. Its translucent body lets light pass right past the swim bladder and skeleton, which is exactly where the common name comes from. The species ranges from the Orinoco basin in Venezuela down through the coastal Amazon rivers of Brazil and the Guianas, where it lives in soft, tannin-stained blackwater near vegetated banks.

What makes the X-Ray Tetra notable in the hobby is how forgiving it is. Most tetras demand soft, acidic water, but Pristella maxillaris tolerates a wider hardness range and even handles slightly brackish conditions in the wild. Pair that with a peaceful temperament and a willingness to eat anything you drop in the tank, and you have one of the best beginner schooling fish on the market.

Adult size

1.75 in (4.5 cm)

Lifespan

4-5 years

Min tank

20 gallons (school of 6+)

Temperament

Peaceful

Difficulty

Beginner

Diet

Omnivore

Appearance & the Transparent Body#

X-Ray Tetras get their name from a body wall that is genuinely see-through. Look closely at one in good light and you can pick out the spinal column and the silver swim bladder running through the middle of the fish. This translucency is not a defect — it is the species' camouflage strategy in tannin-stained blackwater, where a transparent fish is much harder to spot from above.

The fish is not entirely colorless. The dorsal and anal fins carry a striking three-band pattern of yellow, black, and white, and the caudal peduncle often shows a faint silvery flush. Selectively bred Golden X-Ray Tetras (sometimes labeled as the "albino" variant) drop most of the body pigment, producing a pale gold cast that exaggerates the see-through effect.

Natural Habitat#

In the wild, X-Ray Tetras occupy slow-moving coastal rivers, flooded forests, and seasonally inundated swamps from the Orinoco delta down through Brazil's coastal Amazon drainages. The water is typically soft, acidic, and stained dark brown by leaf litter, but the species also tolerates the brackish conditions that develop where these rivers meet the sea. That dual tolerance is unusual among South American tetras.

Replicating the look of this habitat at home is straightforward. Use floating plants to dim the light, add a handful of dried Indian almond leaves for a tea-colored tint, and you have a tank that mirrors the species' natural environment without forcing the water chemistry to extremes.

Size & Lifespan#

Adult X-Ray Tetras top out at about 1.75 inches (4.5 cm), which makes them a true nano-tank candidate. Females tend to be slightly larger and rounder once they fill with eggs, but the size difference is subtle.

With clean water, a varied diet, and a stable tank, expect a healthy school to live 4-5 years. Individual fish in pristine setups occasionally push closer to 6 years, but premature deaths almost always trace back to chronic ammonia exposure, single-fish loneliness in a too-small group, or shipping-related stress that never fully resolves.

Water Parameters & Tank Requirements#

Pristella maxillaris is one of the more forgiving tetras when it comes to water chemistry, but "forgiving" is not the same as "indestructible." Get the basics right and the fish will reward you with bright colors and active schooling behavior.

Ideal Water Parameters#

Aim for 72-82°F (22-28°C), a pH of 6.0-7.5, and general hardness anywhere from 4-12 dGH. That hardness ceiling is the headline number — most South American tetras start showing stress above 8 dGH, but X-Ray Tetras handle the harder water that comes out of many municipal taps without issue.

Stability matters more than hitting the exact center of these ranges. A tank that swings between 75°F and 80°F over the course of a day is fine. A tank that sits at 78°F most days but spikes to 85°F when the heater fails is not. Use a digital thermometer and an inline backup heater on systems above 20 gallons.

Minimum Tank Size & Schooling Space#

Ten gallons is the absolute floor for a school of six, and even that is tight once the fish hit adult size. A 20-gallon long is the size most experienced keepers settle on — the extra horizontal footprint gives the school room to spread out, school properly, and stay out of any aggression from bottom-dwelling tank mates.

If you want a larger group (10 or more X-Ray Tetras alongside corydoras and a few small rasboras, for example), step up to a 29 or 33-gallon long. Tank length matters more than tank height for any schooling tetra; a 20-gallon high actually gives the school less usable swimming space than a 20-gallon long despite the identical water volume.

Filtration, Flow & Lighting#

A sponge filter rated for the tank size handles biological filtration cleanly and produces the gentle current X-Ray Tetras prefer. A small hang-on-back filter works just as well, but baffle the output with a piece of filter sponge or aim it at the back glass — these fish do not enjoy fighting strong currents.

Lighting should be dim to moderate. Pair a low-output LED fixture with a layer of floating plants (frogbit, dwarf water lettuce, red root floaters) to break up the surface and shade the column below. The fish color up better in dim conditions and they spawn more readily under a leaf-littered, shadowed setup that mimics their blackwater home.

Diet & Feeding#

X-Ray Tetras are omnivores with mouths small enough to handle micro-pellets but big enough to take adult brine shrimp. Feeding them is genuinely simple — they accept practically anything you offer.

Staple Foods#

A high-quality micro-pellet or a finely crushed flake formulated for tropical community fish covers the daily nutritional base. Brands like Hikari Micro Wafers, New Life Spectrum AlgaeMax 0.5mm, and Bug Bites Micro Granules all sink slowly enough that the school can pick them off mid-water rather than racing to the surface.

Rotate between two or three staple brands rather than relying on a single one for years. Different formulas use different protein sources (insect meal, krill, salmon, spirulina) and rotating them broadens the nutrient profile your fish receive.

Live & Frozen Enrichment#

Two or three times a week, swap a staple feeding for live or frozen baby brine shrimp, daphnia, micro worms, or finely chopped bloodworms. Live foods trigger the natural pursuit and flash-strike behavior X-Ray Tetras display in the wild, which gives the school visible color and conditions adults for spawning.

Daphnia in particular is worth offering regularly — it acts as a mild laxative and helps prevent the constipation issues that crop up in tetras fed exclusively on dry foods.

Feeding Schedule & Quantity#

Twice daily is the right rhythm for adults. Drop in only what the school can clear in two minutes, then wait. If food is sitting on the substrate after that window, you fed too much. Uneaten food rots, ammonia spikes, and small tanks tip into trouble fast.

Skip a feeding once a week. A planned fast day mimics the boom-and-bust feeding patterns wild fish experience and gives the digestive tract a chance to clear out completely.

Tank Mates & Compatibility#

The X-Ray Tetra was practically engineered for community tanks. It is too small to bully anything, too peaceful to fight back hard, and fast enough to dodge most threats — but those same traits mean stocking decisions still matter.

Ideal Community Companions#

The best tank mates are similarly peaceful, similarly sized, and occupy different parts of the water column. Pygmy and panda corydoras handle the substrate. Ember tetras and harlequin rasboras share the mid-water with the X-Ray school without competing for territory. Otocinclus catfish quietly graze algae from the glass and plant leaves.

Peaceful dwarf cichlids — Apistogramma cacatuoides, Bolivian rams, or German blue rams — work well in a larger tank (29 gallons or more) where the cichlids have territory and the tetras have open swimming space above. Just confirm the cichlid is not in active spawning mode before adding the school, since even peaceful dwarf cichlids defend a clutch hard.

Species to Avoid#

Tiger barbs are the obvious mistake — they nip flowing fins and bully smaller schooling fish until the tank turns into a stress incubator. Larger cichlids (oscars, jack dempseys, full-size angelfish) view 1.75-inch tetras as feeder fish. Aggressive bettas can also injure or kill X-Ray Tetras, though community-bred females in a planted 20-gallon often coexist fine.

Avoid pairing X-Ray Tetras with any large semi-aggressive species in tanks under 40 gallons. The tetras will spend their lives hiding and you will rarely see them.

Keeping Them in Schools#

A school of six is the absolute minimum. Eight to ten is better. The fish display tighter, more synchronized swimming patterns at higher counts, and the dominant individuals stop singling out the smallest fish for harassment.

Add the entire school at once if you can. Introducing a few stragglers weeks later forces the established group to absorb newcomers, and the integration is rougher than just stocking the full count on day one.

Breeding#

X-Ray Tetras spawn readily in the home aquarium if you give them the right triggers. The species is an egg-scatterer with no parental care, which means you need a dedicated breeding setup rather than relying on the community tank.

Sexing X-Ray Tetras#

Females are noticeably rounder when viewed from above, especially once they are conditioned with live foods. Males are slimmer and slightly more pointed at the anal fin. The differences are subtle in juveniles and only become reliable once the fish hit 12 weeks or so.

In a school of eight or more, you will almost certainly have both sexes, so most keepers do not bother sexing individually — they just condition the whole group and move the rounded females and a couple of slim males into the breeding tank.

Breeding Tank Setup#

Set up a separate 10-gallon with very soft water (4 dGH or below), pH around 6.5, and temperature raised to 80°F (27°C). Light the tank dimly and fill the bottom with a spawning mop or a thick mat of fine-leaf plants like java moss — eggs need somewhere to fall where adults cannot easily eat them.

A sponge filter run gently is the only filtration you need. Strong flow blows eggs around and stresses the breeding pair. Condition the breeders for a week with twice-daily live food feedings before introducing them to the spawning tank in the evening.

Egg Care & Fry#

Spawning typically happens at first light. Females scatter 200-400 small adhesive eggs through the plants over the course of a few hours, with males following behind to fertilize. Pull the adults the moment spawning ends — they will eat eggs and fry without hesitation.

Eggs hatch in 24-36 hours. Fry remain attached to surfaces for another 3-4 days while they absorb their yolk sacs, then become free-swimming around day 5. Feed infusoria or commercial fry powder for the first week, then switch to newly hatched baby brine shrimp. Growth is steady — fry reach juvenile size at about 6-8 weeks and full adult color around 4 months.

Common Health Issues#

X-Ray Tetras are hardy, but they share the same disease vulnerabilities as most small schooling fish. The good news is that their transparent body makes early detection easier than with most species.

Ich & Velvet#

Ich (Ichthyophthirius multifiliis) shows up as discrete white spots roughly the size of grains of sand on the body and fins. Treat by raising the tank temperature to 82-86°F over 48 hours and dosing a copper-free ich medication like Ich-X or Hikari Ich-X — copper is rough on small tetras and on any invertebrates in the tank.

Velvet (Oodinium) presents as a fine gold or rust-colored dust coating, easier to see in side lighting than overhead light. Velvet kills faster than ich and requires immediate treatment with a velvet-specific medication. Both diseases almost always trace back to a stressed new addition or a temperature drop, so quarantine new fish for two weeks before adding them to an established tank.

Fin Rot & Bacterial Infections#

Frayed or whitening fin edges, especially on the dorsal and tail, indicate bacterial fin rot. The root cause is almost always poor water quality — a single ammonia spike or chronically high nitrate slowly erodes the tissue. Test the tank, perform a 30% water change with dechlorinated water matched for temperature, and the early-stage rot will heal on its own within a week or two.

Persistent or systemic infections need an antibiotic like Maracyn 2 or Kanaplex dosed in a hospital tank. Do not medicate a planted display tank unless you have to; antibiotics destroy the beneficial bacteria your filter relies on.

Where to Buy & What to Look For#

X-Ray Tetras are inexpensive and widely available, which makes it tempting to grab the first school you see. Don't. Healthy stock from a reputable local store is the difference between a thriving five-year school and a tank full of slow attrition.

Selecting Healthy Specimens at Your Local Fish Store#

Watch the school in the dealer tank for two minutes before you buy. The fish should be swimming actively as a tight group at mid-water, not hanging at the surface or hiding in the corners. Fins should be erect and undamaged, eyes clear and proportional to the head, and bellies visibly rounded but not swollen.

Pay close attention to the body cavity itself, which is where the species' transparency pays off. Cloudy patches inside the body, internal redness around the spine, or a visibly thin (sunken) belly profile all indicate trouble. Skip any tank where you see dead or dying fish, white-spotted individuals, or visible flashing (rubbing on rocks or substrate).

Aquacultured vs. Wild-Caught#

The vast majority of X-Ray Tetras in the trade are tank-raised in commercial hatcheries, mostly in the Czech Republic and Southeast Asia. Captive-bred stock is hardier, adapts faster to a wider range of water chemistry, and arrives at the store in noticeably better condition than wild-collected fish.

Wild-caught Pristella maxillaris does occasionally show up at specialty stores, usually labeled with origin information. The wild fish are sometimes more vibrant in color but require softer, more acidic water to thrive long-term. For a community tank or a beginner-friendly setup, captive-bred is the right call.

Quick Reference#

• Tank size: 20 gallons minimum for a school of 6+
• Temperature: 72-82°F (22-28°C)
• pH: 6.0-7.5
• Hardness: 4-12 dGH (more flexible than most tetras)
• School size: 6 minimum, 8-10 ideal
• Adult size: 1.75 in (4.5 cm)
• Lifespan: 4-5 years
• Diet: Omnivore — micro-pellets, flake, frozen and live foods
• Tankmates: Corydoras, ember tetras, harlequin rasboras, otocinclus, peaceful dwarf cichlids
• Avoid: Tiger barbs, large cichlids, aggressive bettas
• Difficulty: Beginner

Pair the X-Ray Tetra with a pristella tetra school (same species, alternate common name) or compare it against the more demanding neon tetra and the larger Congo tetra. For broader stocking ideas, see the freshwater fish overview, and for a tank-size primer, the 20-gallon fish tank guide covers everything you need to set up a proper home for a school of six or more.