Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Pristella maxillaris

X ray tetra

X ray tetra, Pristella maxillarisX ray tetra, Pristella maxillaris
Photos by Andy Rapson


Pristella: Greek, pristis = saw, diminutive

General Notes:

X-ray tetras are cheap to buy, peaceful, lively and hardy which makes them very popular aquarium fishes. Keep them in groups of at least five individuals with other small peaceful fish. They show their best colours when kept under subdued lighting in an aquarium with lots of decor such as bogwood and plants (real or artificial). Young fish in a sparse dealers tank won't be seen at their best but don't over look them because of this.


Wild x ray tetras feed on on worms, small crustaceans and insects.


Adult female x-ray tetras are larger and plumper than adult males.


One of the easier tetras to breed using a standard tetra breeding set up:

Use a separate aquarium filled with soft acidic aged water and containing a small air powered sponge filter and something to act as a spawning mop such as a bunch of fine leaved plants tied in to a bunch for example. Keep the tank away from direct light and in very dim conditions because both eggs and fry of this species are light sensitive. Introduce a well conditioned pair in the evening and they will probably spawn at dawn. After spawning remove the parents to prevent them from eating all their eggs. The eggs hatch after about 30 hours but it will be another three or four days before the fry become free swimming. Add a commercially available liquid fry food to the tank about a day or so before the fry become free swimming as this will encourage the growth of infusoria which the fry can eat but don't add to much and pollute the water. Carry on using the liquid food or similar until the fry are large enough to take micro worms or newly hatched brine shrimps. X ray tetras can be bred as a pair or in a group. If you breed them in a group be aware that you will have a very large number of fry which will require a great deal of space to raise and dealers won't thank you if you flood the local market with these fish and they end up stuck with them.

Note: commercially bred fish may produce small broods due to low fertility if the fry have been fed food containing hormones in order to force a faster maturity so that they can be sold on faster. Fish which have been bred by hobbyists without the use of hormones will produce better broods.

Wild status

Wild populations of P. maxillaris have not been evaluated. The species is commercially bred on a large scale due to its popularity. All specimens offered for sale will have been bred in captivity so the aquatic industry is not a threat to the species.

Information at a glance

pH: 6 - 7.5
dGH: 5 - 20
Temperature: 24 - 28°C (76 - 82°F)
Diet: Omnivore
Size: 4.5cm (1.8in)
Min tank size: 60 litres
Difficulty level: Easy
Aquarium type: Community
Swimming level: All levels

Distribution and habitat

distribution map for X ray tetra, Pristella maxillaris

Origin: South America: Amazon, Orinoco, and coastal river drainages of the Guianas.

Habitat: Found in calm coastal waters in densely vegetated swamps


Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Characidae
Genus: Pristella
Species: P. maxillaris (Ulrey, 1894)

Common name:
X ray tetra

Synonyms: Aphyocarax maxillaris, Holopristis riddlei, Pristella riddlei