Pristella tetra

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

Eats anything. Flake, micro pellets, frozen bloodworm, frozen brine shrimp, frozen daphnia, live baby brine shrimp. Feeds in the midwater column. Not demanding, not competitive, not picky. A reliable feeder that will eat its share in any community. Twice daily in moderate amounts. Color in the fins improves with a varied diet that includes frozen food regularly. The yellow dorsal and anal fin markings are more vivid when the fish is well-fed and in good conditions.

Compatibility

• One of the most tolerant small tetras for varied water conditions. Pristella tetras handle hard alkaline water (up to pH 8, GH 20) without complaint, which makes them one of the few tetras suitable for keepers on hard tap water who don't want to run an RO unit.
• Peaceful schooling fish that works with any non-aggressive tankmate. Tetras, rasboras, corydoras, gouramis, and small cichlids are all fine. No nipping behavior.
• Groups of 6+ for proper schooling. In large groups (10+) the translucent body with yellow, black, and white fin markings is surprisingly attractive despite not having the flash of neons or cardinals.
• Also sold as the 'X-ray tetra' because the body is translucent enough to see the spinal column and swim bladder. The name oversells the transparency a bit but the effect is real under the right lighting.

Origin and habitat

Pristella maxillaris, the X-ray or pristella tetra, is the only species in its genus, a small, hardy characin from northern South America, ranging through the Amazon and Orinoco basins and the coastal rivers of Venezuela, Guyana, Suriname, French Guiana, and northern Brazil, one of the widest natural ranges of any common aquarium tetra. After years in the family Characidae it was placed in Acestrorhamphidae in the 2024 revision of the American characins. The X-ray name comes from the translucent body, through which the spine and swim bladder show, and the fish is also called the water goldfinch for its yellow-marked fins. The dorsal and anal fins carry neat bands of yellow, black, and white and the tail is reddish, with a golden colour form common in the trade. What sets the species apart from most tetras is its tolerance: it does fine in hard, alkaline water and even slightly brackish conditions, reflecting a wild life that runs from clearwater streams in the dry season into flooded savannah, and sometimes coastal estuarine water. It grows to about 4.5 cm, schools peacefully, and most trade fish are commercially bred.

Breeding

One of the more forgiving tetras to spawn, since it does not need the very soft, acidic water that many Amazon tetras demand and will breed in moderately hard water. A conditioned pair spawns at dawn in a planted breeding tank, scattering a large batch, on the order of a couple of hundred to four hundred non-adhesive eggs, that fall into the plants. The adults eat the eggs, so they should be removed afterward. The eggs hatch in a day or two, and the fry, a little larger than neon fry, take baby brine shrimp within a few days of becoming free-swimming. That tolerance of a range of water during breeding is the species' main appeal for hobbyist breeders.

Common problems

There is very little to go wrong; this is among the hardier small tetras and rarely runs into serious disease, tolerating a wide range of water and most medications. Ich on stressed new fish is about the only common ailment, and standard treatment clears it. The real complaint is cosmetic: over pale gravel under cool-white light the fish looks plain and the fin markings wash out, while a dark substrate, planted background, and warmer light bring it to life, which is why it is so often passed over in shop tanks. Older fish slowly lose fin-colour intensity.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size