The x-ray tetra is one of two species in the Pristella genus and was first identified in 1894.
True to its name, this fish has a transparent body that lets you see straight through to its spine and internal organs.
You will find it online under various names. Its scientific name is Pristella maxillaris, but it is also known as the pristella tetra, golden pristella tetra, or water goldfinch.
This fish is an excellent addition to a home aquarium. Not only do they present a look that is a sure conversation starter, but they are also amazingly hardy and incredibly easy to care for.
Their tiny size and gentle nature allow them to live in a single species, smaller aquarium.
They can just as easily pair with numerous other species of fish in a larger community tank.
We love them and think you will, too! Read on for more information on the care and feeding of this tetra species.
At a Glance
| Tank Size: | 15 – 20 gallons |
| Group Size: | 6 or more |
| Water Temperature: | 74 – 82°F (23 to 28°C) |
| pH: | 6.0 – 7.5 |
| Hardness: | 4 – 18 dGH |
| Lifespan: | 4 – 5 years |
| Breeding: | Egg layer |
| Adult Size: | 1.75 inches (4.4 cm) |
| Usual Place in the Tank: | Middle to upper levels |
In this article
Natural Habitat
This highly adaptable fish inhabits a wide range of environments in South America, including areas in Brazil, French Guiana, Guyana, Suriname, and Venezuela.
Their migration patterns take them from clear, inland streams during the dry season to marshlands and flooded plains during the rainy season.
These tetras live in both rapidly moving and still waters and can be found in tributaries, swamps, and coastal regions.
They tolerate both fresh and slightly brackish water and love areas with dense aquatic vegetation, especially when they are spawning.
While the IUCN Red List notes that this species is “stable,” there are areas where the wild population of x-ray tetras is sporadic or in extensive decline.
Threats to this species’ natural habitat include overdevelopment, agricultural runoff, and other forms of pollution.
No protection plans are in place; however, this species exists in protected areas of Venezuela, Guyana, and Suriname.
Appearance and Biology
This member of the family Characidae is well known for its unique appearance.
The first thing that catches your eye with the x-ray tetra is its translucent skin.
In fact, the common name of “x-ray” comes from its visible backbone and organs.
The scales on its body have a slight yellow tint, which lends to its other common nickname: “goldfinch.”
The dorsal and anal fins are striped with bright yellow, white, and black and these fish have a forked, red-colored caudal fin.
X-ray tetras have an excellent hearing in the water. A bony structure called the Weberian apparatus helps to detect sound waves.
Size
X-rays reach an adult size of 1.75 inches (4.4 cm). Occasionally, they may reach two inches (5 cm), but not often.
Lifespan
A well-cared-for x-ray tetra can live from four to five years. While these fish are hardy, their lifespan depends on the care you provide.
Behavior
Aside from their incredible looks, another draw for the x-ray is its wonderfully peaceful nature.
These schooling fish enjoy exploring their environment and pair well with numerous other species in a community aquarium.
X-ray tetras are most comfortable in groups of at least six.
Keeping them as a solitary fish or in too small of a group can result in a fish that is constantly stressed. As a result, they may hide most of the time and can be prone to illness.
X-rays are active swimmers that benefit from a little extra space in the tank. They tend to stay in the middle to upper levels of the water column.
There may be the occasional fight within the school to establish dominance, but these squabbles usually do not last long or result in severe injury.
X-rays can be easily spooked, so make sure there are enough hiding spaces in the tank that the fish can duck into if frightened.
How many per gallon?
Plan on a 15-to-20-gallon tank size to accommodate a group of six x-ray tetras.
Tank Setup
Setting up a tank for your x-ray tetras is easy. They are incredibly adaptable and tolerate a wide range of conditions.
That said, once you set the tank conditions, they need to remain stable for the optimal health of your fish.
Decorations
Line the tank bottom with a sandy substrate, which will mimic the river bottoms in their natural habitat.
Set up driftwood or rocks for hiding spaces. This species is good with aquatic plants, so feel free to add some.
Consider Java fern and Amazon sword plants for a great look and to help keep up water conditions.
Water Conditions
Although these fish tolerate a range of water conditions, they do best in the following parameters:
- Temperature: 74 to 82°F (23 to 28°C)
- pH: 6.0 to 7.5
- Hardness: 4 to 18 dGH
Change out 10 percent of the water every week to keep the tank clean. Add a few Indian almond leaves to bump up the acidity and release natural tannins into the water.
Equipment
This species does not have unique equipment needs. Install a quality canister filter and clean it once a month.
A water heater and thermometer are also good investments, especially for a smaller tank that can be prone to rapid temperature fluctuations due to the lower water volume.
Keep the lighting at a moderate to dim level and have test kits on hand to ensure the nitrate and ammonia levels are in check.
Tank Mates
This is one species that absolutely needs a peaceful tank. Any tank mates you select should be gentle in nature and similar in size.
X-ray tetras get along well with other small South American species as well as peaceful bottom dwellers that occupy a different level of the tank.
Consider these species to pair with your x-ray tetra:
- Other peaceful tetras such as neons, cardinals
- Small, South American species
- Hatchet fish
- Pencil fish
- Smaller dwarf cichlids
- Peaceful bottom dwellers
Avoid the following:
- Larger or more aggressive species
Food and Diet
In the wild, this omnivorous species feeds on algae, plant material, and small invertebrates.
In an aquarium, they will eat commercial flake foods, pellets, and granules.
Supplement their diet with the occasional treat of live or frozen daphnia, artemia, or bloodworms.
Feed your fish several times a day (two to three feedings are enough) and only as much as your fish can finish in three minutes.
Clean out any leftovers and adjust the amount you are giving if you find your fish are consistently leaving uneaten food.
Breeding
X-ray tetras are ready to breed when they are between five and eight months old.
These egg layers will breed in a captive setting if placed in the right environment.
Remember that in the wild, these fish migrate to floodplains and marshes during the rainy season to breed, so creating a breeding tank with a similar setup is ideal.
Setting up a Breeding Tank
Set the water temperature a little warmer than in the community tank, around 80 to 85°F (27 to 29°C).
The pH should be between 5.5 and 6.5 and the hardness between 1 and 5 dGH.
Install a sponge filter to keep the water clean while protecting the tiny new fry. Keep the lighting dim.
Add some plants, such as Java moss, on which the female tetra can deposit eggs. Alternatively, you could use a spawning mop with equal success.
Determining Male or Female
Males have slender, pointed bodies. Females tend to be rounder in the body and reach a larger adult size.
In addition, when they are ready to spawn, you can see the developing eggs within the female’s body.
Spawning
It can be challenging to get these tetras to pair up naturally. Starting with a good-sized group gives you better odds.
Females will appear more rounded when carrying eggs. Males that are ready to spawn will display vivid colors.
If selecting your breeding fish from a group, select the stoutest female and most brightly colored male to move to the breeding tank.
Feed the breeding pair twice a day and add in more live protein sources, such as bloodworms.
The female will lay up to 300 eggs on plants or the spawning mop.
After the male fertilizes the eggs, remove the parents immediately, as they may eat the eggs.
Caring for the Fry
The eggs should hatch within 24 to 36 hours after spawning occurs.
The fry will stay with and get nutrients from their egg sacs for three to four days. After that, they will become free-swimming.
At this time, you can start feeding them infusoria or powdered fry food. As they grow, transition to flake foods and baby brine shrimp.
Hardiness and Diseases
X-ray tetras are hardy fish by nature. Considering that they live their natural lives in a wide range of water conditions and habitats, they are a resilient species and not prone to any specific ailments.
That said, they can develop typical freshwater tank diseases if they are in a state of stress, are not well fed, or are kept in sub-standard water conditions.
Fortunately, you can treat most freshwater ailments if you spot them quickly. Learn to recognize the signs of common diseases, such as ich and fin rot.
Treatments for most diseases include quarantining sick fish, correcting any poor water conditions, and adding medication to the water.
Closing Thoughts
If you are looking for a fish that will add dimension, activity, and beauty to your tank, the x-ray tetra is the one for you.
So easy to care for, hardy, and peaceful, they can be part of a smaller species-only tank or a larger community tank.
You can find these fish online at prices ranging from $4 to $6 a fish.
Keep in mind that you will need a group of at least six fish for them to be comfortable. Set up a stable tank and you will enjoy your tetras for many years to come!
We would love to hear from you!
How many x-ray tetras do you keep in a school?
What fish do you like to pair them with in your community tank?