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X-Ray Tetra – Pristella maxillaris


X-ray Tetra

Tetras are amongst the most popular aquarium fishes. There are probably more than 150 distinct species of tetra from which the aquarist may choose and this includes a large number of visually stunning fishes that are bound to enhance any home aquarium.

Is the X-Ray Tetra a good community fish? The X-Ray Tetra should be considered to be an excellent community fish and gets on with most species. It is tolerant of a wide range of water chemistry and should also be considered to be an ideal species for novice aquarists. 

Key Facts

CategoryKey Facts
Common name(s)X-Ray Tetra
Scientific namePristella maxillaris
FamilyCharacidae
Originate fromAmazon and Orinoco basins, as well as coastal rivers in the Guianas in both acidic and alkaline waters in northern South America
Care requiredEasy to care for and hugely popular
TemperamentPlacid, shoaling fish
Colour & FormTransparent body with yellow, black and white stripes on leading edges of fins
LifespanUp to 5 years
Adult sizeUp to 2 inches
DietOmnivorous – eat aquatic insect larvae in nature
Aquarium size24 inches in length or greater
Compatible withMost other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches
Avoid keeping withLarge and/or aggressive species
BreedingEasy if you put the fish in the right environment.
Water temp75 – 82 Fahrenheit
Water pH6.0 to 8.0 (can tolerate slightly brackish water)
Water hardness (dGH or dH)Up to 20 dGH (some aquarists report up to 25 dGH)

Origins of the X-Ray Tetra

Tetras, as a “family” of fishes belonging to the biological family Characidae are found in nature in Africa, Central America and South America.

The X-Ray Tetra originates in the Amazon and Orinoco basins, as well as coastal rivers in the Guianas in both acidic and alkaline waters in northern South America. The vast majority of X-Ray Tetras available to aquarists are captive-bred. 

Characteristics of the X-Ray Tetra

As you can see, the X-Ray Tetra is characterized by its almost transparent body, from which its common name is derived. It will grow to up to 2 inches in the aquarium and live for around five years.  The X-Ray Tetra is also known by the following names:

  • X-Ray Fish
  • Water Goldfinch
  • Golden Pristella Tetra

The X-Ray Tetra is a very adaptable little fish because it can tolerate both acidic and alkaline water and also thrives well in brackish (slightly salty) water, being that in nature it lives in river estuaries (as well as in other areas).

The X-Ray Tetra is a shoaling fish and should be kept as a group of at least six fish, though a shoal of, say, ten or more fish is highly recommended. Having plenty of vegetation to break up lines of sight will also help to protect your X-Ray Tetras from predation but it is obviously advised that X-Ray Tetras are not kept with predatory species.

The body of the X-Ray Tetra is virtually transparent and you can see its spine through its body. Behind the gills, level with the spine you will frequently observe a black spot approximately the same size as the eye of the X-Ray Tetra. The dorsal and anal fins have leading edges that, starting closest to the body, include a yellow, black and white stripe. These three stripes are variable in how far back they extend on both fins.

The adipose fin can show signs of a yellow stripe at the root, closest to the body. The caudal fin can show an orange/red tinge to it. The pectoral fins are generally transparent whilst the pelvic fins can display the same yellow, black and white stripes as the dorsal and anal fins.

The female has a slightly deeper body than the male and also a rounder body, especially when gravid (carrying eggs). The colouring (such as it is) of the male tends to be fuller and richer than that of the female, especially as spawning approaches.

The X-Ray Tetra tends to inhabit the middle area of the aquarium (top to bottom). That said, it is a vigorous fish when breeding and will readily traverse the entire aquarium.

The X-Ray Tetra is, by nature, a shoaling fish and it is generally recommended to purchase six or more fish, as their nature is to swim together as a shoal and they will tend to thrive much better as a shoal. X-Ray Tetras are excellent community fish and are ideal for novice aquarists, as they don’t tend to have aggressive tendencies towards other species. It is advised not to include X-Ray Tetras in an aquarium containing predatory species, as their wellbeing will rapidly deteriorate.

The X-Ray Tetra has an enhanced, amplified hearing system known as a Weberian Apparatus. Essentially, its hearing is enhanced by being connected through bones connected with the first four vertebrae through to its swim bladder, which serves to amplify any sounds significantly so that the X-Ray Tetra is ideally adapted to hearing potential predators and making their escape before the potential predator is aware of their presence.

X-Ray Tetras, like most species, prefer a shaded tank, as they can hide from predation, so consider including floating leaves and/or allowing vegetation to grow so that it floats on the surface of the water to provide shade.

It is generally advised that the minimum tank size for X-Ray Tetras should be one of 24 inches in length or more due to the shoaling nature of the species, which will enable a small shoal to move around freely. The tank should be well-planted but with clear areas where the fish can swim freely. The water should have gentle movement.

X-Ray Tetras prefer fairly neutral water with a pH of 6.0 to 8.0 but can also tolerate slightly brackish (salty) water, with a temperature range between 75 and 82 degrees Fahrenheit and up to 20 dGH (though some aquarists report up to 25 dGH).

The general rule for Tetras is that by keeping six or more of the same species in an aquarium they will be fully aware of which is male and which is female and they will act accordingly.

Most (but not all) Tetras have an additional fin which identifies them as being Tetras and the X-Ray Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the X-Ray Tetra you will observe a tiny, additional fin, known as the adipose fin. The purpose of this fin is not fully understood but, if it is present on a freshwater tropical fish then you can be pretty certain that the fish is a Tetra.

Tetra comes from the Greek word “Tetragonopterus” which means square-finned and appears to relate to the four fins on vertical plane of the fish (dorsal, adipose, caudal and anal fins) which span the central line of the fish (when viewed from above or below, front or rear) and are not present as a pair (e.g. the pectoral or pelvic fins).

X-Ray Tetra – Video

How do X-Ray Tetras breed?

Tetras, in general, will scatter eggs by laying them over fine plants such as Cabomba, Fontanalis or Java Moss.

X-Ray Tetras, like most species, are noted to leap above the water surface during breeding and in general, so it is advised that the tank should be covered to mitigate the risk of losing fish.

As the female X-Ray Tetra becomes ripe with eggs, the difference between the sexes becomes even more evident. If you plan to attempt to breed X-Ray Tetras then it is recommended that you have a breeding tank prepared. Such a tank can be empty but you may wish to include a mesh or grid under which the fertilized eggs will fall and/or a sterilized breeding mop.

That said, X-Ray Tetras will breed in a community tank and, if the tank is well planted, it is likely that at least a few fry may survive to reach adulthood.

I have observed X-Ray Tetras breeding readily and vigorously in quite neutral water but soft, slightly acidic water is the general recommendation

The female will swim vigorously around the tank and, if you include two males then they will encourage her to lay her eggs by bumping into her. She will lay her slightly adhesive eggs which will immediately be fertilized by the male(s) and will either stick to plants or spawning mop or will fall to the bottom of the tank (preferably through the mesh or trap). Once spawning is complete, remove the adults, as they are likely to consume the eggs, given the chance, and take no further parental responsibility.

Spawning usually takes place in the early morning. In nature, X-Ray Tetras spawn at the start of the rainy season.

Breeding tank for X-Ray Tetras

You should prepare a tank of around 20 gallons in size with mature water. The water should be at a pH of around 6.0 to 6.8, a dGH of 18 and, ideally around 78 degrees Fahrenheit with a low level of light.

You may wish to introduce mosquito larvae or bloodworm as an inducement to reproduction.

The female will swim amongst the plants, laying her eggs whilst the male will swim alongside or behind her and fertilize the eggs as they are laid. Typically, the female can lay as many as 300 to 400 eggs during spawning, which may adhere to plants or will sink to the bottom of the tank.

Once the female has scattered her eggs and the male has fertilized at least some of them then the adults should be removed carefully from the breeding tank because they will have nothing more to do with the eggs but they may simply eat them.

Keep the lights off and the tank dark because Tetra eggs and fry are particularly sensitive to the light.

The eggs will hatch typically in a day or so depending on tank temperature and conditions and the fry will become free-swimming after around three to four days after hatching. Keep the tank unlit for the first week or so then gradually increase the lighting.

The newly hatched fry will firstly feed on their yolk sac but, once free-swimming, can be fed infusoria (particularly rotifers) and will also thrive on egg yolk during the first two to four weeks. It is worth mentioning that immediately after hatching, fry seem quite vigorous but will soon go into a resting state before they become free-swimming so please don’t mistake this initial stage as being free-swimming.

After around four days or so add baby brine shrimp. Once the fry are sufficient in size not to be treated as a snack then they can be introduced into the community tank where they will join the existing shoal. Before moving the adolescent fish into the community tank ensure that you have balanced the water temperatures to mitigate the risk of White Spot or other diseases being triggered.

Should your X-Ray Tetras have a special diet for breeding?

Adult X-Ray Tetras don’t need any particular inducement to breed. That said, it has been suggested that adding mosquito larva may encourage them, presumably because the addition of a new food may “fool” the fish into thinking that it is breeding time. From my own experience, I would always recommend keeping all of your fish in the best possible condition at all times, as this is good for the wellbeing of your fish.

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

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