Have you ever visited an aquarium shop and seen fish that resembles a floating glass toy? Well, let us introduce you to X-ray fish. Also known as Pristella Tetras or X-ray Tetras, these are among the most unique-looking fish species you will come across in your lifetime.

 As you may have guessed from the name, they have a translucent, almost transparent body. This gives them a unique “see-through” look.

Another interesting fact about them is that you can directly see the ‘Weberian Apparatus’ present inside their body. It is pretty rare to see this organ from the outside of a fish.

Additionally, it is also considered Least Concern (LC) by The IUCN Red List of Threatened Species in 2020 (ref.). Thus, they are commonly sold all over the globe.

So, it is only valid that you get yourself a group of these fish if you ever see them on sale. Putting a few will definitely make your tank visually appealing.

Caring for them isn’t a hassle but you should always know the biology of a fish before adopting one. I have also covered the important things that you will need to understand if you ever decide to breed them at home. If you closely follow these steps, you will have numerous Pristella Tetras in no time.

A Brief Review of the Species

Quick Species Facts
Scientific Name Pristella maxillaris
Other Common Names Pristella Tetra, X-ray Tetra, Water Goldfinch
Family Characidae
Origin South America
Average Lifespan 2 to 5 years
Average Size 1.6 to 2.0 inches (3.2 to 5 cm)
Type Freshwater; Can tolerate slightly brackish waters

Origin & Habitat

Like many other Tetra species, X-ray Tetras also come from South America. They mostly occur in the Amazon and Orinoco basins. Some populations are also found in Brazil and Venezuela.

They like to inhabit coastal waters with lush vegetation. These waters are generally still or slow-moving.

They can also live in freshwaters such as shallow river streams, tributaries, and swampy wetlands, in addition to brackish waters. However, they migrate to swamps mostly during the monsoon season when the water flows into the marshes.

Size of X-ray Tetra

These are among the smaller Tetra varieties and grow to a size that varies between 1.6 to 2.0 inches, in the wild.

However, in captivity, they can grow to a size up to 2.2 to 2.4 inches, only if the optimal tank conditions are maintained.

What Do They Look Like?

The appearance of X-ray Tetras is what makes them quite unique among other Tetra varieties. As you may have guessed from the name, they have a translucent body. This gives them a unique “see-through” look.

You will be able to plainly see their internal organs through the naked eye. Even the vertebral column, along with the bones, is clearly visible.

But this is not the only thing that makes it attractive. Their bodies have a silvery shimmer, which glistens when light falls on them. Some species have a shiny golden hue, for which they have been given the name Golden Pristella Tetra or Water Goldfinch.

They have a transparent dorsal fin with a distinct black dot on top of a yellow base. Along with it, some species have a black dot on all their fins, except the caudal.

The caudal fins are generally transparent or translucent-orange. Some even have a hazy black spot right behind their eyes, which appears to be on the operculum.

A unique fact about X-Ray Tetra

One of the most prominent features that can be clearly seen in this species is the Weberian ossicles. It is present in other Tetras species as well, but it is only visible in this one.

This structure helps in better conduction of sound, which in turn, helps them detect vibrations in the water if a predator is nearby.

This Weberian ossicle connects the inner ear with the swim bladder, which enables the sound to travel through the spine and into the ear. Many bony fish species possess this auditory system.

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Varieties of X-ray fish

Balloon X-ray Tetra

These ones look exactly like regular X-ray Tetra except they are much rounder. These subspecies look like a balloon if we look at them from their tail point of view.

Albino X-ray tetra

Albino variants have the same size and features except they are almost completely white. Some have orange specs on the tail and the cheeks. They have the signature albino attribute- red eyes.

What’s Their Life Expectancy?

Like many other Tetras, you can expect them to have an average life span of 2 to 5 years. Although in the wild, it is usually 2 to 3 years. But they do live up to 5 years in captivity if proper care is taken.

Author Note– Their life expectancy also depends upon their genes. Some may have defects in their DNA, which greatly affects their lifespan.

Sexual Dimorphism

It is hard to determine the gender of X-ray fish because both the male and the female have identical appearances. However, the female seems to have a slightly rounder body than the male, but it is barely noticeable.

This is more prominent during the breeding season when the female carries eggs inside of her. This makes her body more fatty than usual, which can help to differentiate them from the males.

The mature female Pristella Tetras also tend to get a bit bigger than the male fish.

Availability & Sale Price of X-ray Tetra

X-ray fish are found worldwide and are quite cheap as well. They can be bought from local fish stores and even online stores, but the shipping charges will vary with your location.

It is sold for around $2.99 to $.99, which depends upon the size and fins. The all-transparent ones with black-dotted fins are a bit more expensive than the regular orange-tailed ones.

Complete Care Guide

Quick Care Facts
Care Level Easy
Breeding Easy; Egg Scatterers
Temperament/Behavior Peaceful; Gregarious; Non-invasive
Diet Omnivore
Hardiness Hardy

Best Food for Them

X-ray Tetras are not very selective when it comes to the choice of food. As omnivores, they consume all kinds of fish food. What’s surprising is that they eat a bit more than the other Tetra relatives, considering there are small fish species.

In their natural habitat, they generally eat tiny crustaceans, small aquatic insects, and worms (ref.) They can also be seen chewing on soft plant leaves and algae.

So, a good combination of both vegetable and meaty foods is an important factor in maintaining a good mood and health.

Here is a list of food items you can give to your X-ray Tetra-

  • Fish Flakes
  • Fish Pellets (smaller ones)
  • Brine shrimps (live or frozen)
  • Worms- Bloodworms, Blackworms, Tubifex worms, etc. (live or frozen)
  • Vegetables- Lettuce, Cabbage, Carrot, Banana, Plantain, etc. (boiled or blanched)
  • Smaller crustaceans- Artemia, Daphnia, etc.

Quick Tip– Keep consistency with feeding them food items that can easily be consumed in under 3 to 4 minutes, two to three times a day. This ensures low wastage of food, which, in turn, helps keep nitrogen levels low in the tank.

Temperament & Behavior

X-ray fish are quite peaceful, and gregarious, i.e., they like to stay in groups. It can be said that they are a shoaling variety, like many other Tetras.

If you want to keep them in school, make sure to keep at least five of them together. They are already very skittish, so they get even more if the group is small. Try to keep equal numbers of males and females.

In the aquarium, they are commonly seen swimming in the middle section or upper portion of the tank.

Breeding of X-Ray tetra

In the wild, Pristella Tetras like to spawn in the time of monsoon, in areas with thick, lush vegetation flooded by the water. However, mimicking these conditions is not that difficult.

Choosing a compatible pair

All you need is a separate tank with densely planted aquatic shrubs. Try to get at least a 10 to 15-gallon tank to give them enough space to move around during mating.

Now, it can be complicated sometimes when choosing the right pair for breeding. You can also put all the pairs together, but it is not advised. A good method is a trial and error method. You have to keep checking different combinations till you find a compatible pair.

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After you get yourself the right pair, put them together in the “breeding” tank and wait for them to spawn. Keep the pH of the water between 6.5 and 6.8 and the temperature between 75 and 78 °F.


The male and female will be around bumping each other, doing the mating ritual for a few days. The female will then spawn about 300 to 400 eggs, approximately (ref.). After 2 to 3 days of incubation, the eggs hatch into a small sac-fry.

Rearing of Baby X-ray fish

You can put the babies in a smaller tank of like 5 gallons if it’s possible. It will be easier to maintain the water parameters of a smaller tank than a bigger one.

At first, they will not move around much and will prefer to stay hidden in gaps and covers. You can feed them fish food like pellets and flakes, but give them in a powdered form. A better option would be microworms. They are small enough to fit in the baby’s mouth.

You can also feed them nauplii (larvae) of brine shrimps and even infusoria-type foods (tiny freshwater organisms) if you can get your hands on them. They are equally nourishing and a good source of protein.

After a few weeks, they will be big enough to be kept with their parents without the danger of getting eaten by them or any other fish.

Pro tip– After spawning, transfer the parents from the tank as a precaution because they sometimes eat their own eggs and even their own babies.

Common Diseases

They face dangers like any other freshwater fish species when it comes to the disease category. But X-ray tetras are much harder than usual because they migrate a lot.

So, they keep adapting to different environments throughout their lives. This phenomenon, in particular, has induced strong natural resistant characteristics in them.

However, that doesn’t mean they are not susceptible to diseases and parasites. There are a few diseases that the Pristella Tetra falls victim to-

Fin rot is a common disease that causes degradation of the fins, rendering the fish unable to swim. Both fungus and bacteria can be responsible for this.

The fungal infection can be detected as it leads to white borders around the fin ends. While the bacteria cause uneven decay of the fins.

Freshwater gill flukes can cause problems for these fish. They attach themselves to their gills, which causes issues with gaseous exchange. These can be treated using antibiotics such as Praziquantel.

Another rare disease is the Neon Tetra Disease. As you may have guessed, this was first discovered in Neon tetras. The microorganism responsible is a sporozoan known as Pleistophora hyphessobryconis. Unfortunately, there is no treatment for this disease and studies are still going on.

It forms cysts in the fish’s body and the color of the fish gets paler as the disease progresses. The fish loses the ability to swim properly, which ultimately leads to death.

However, a good diet and ideal tank conditions will ensure that your X-ray Tetra is healthy and develops good resistance to fight against any kind of sickness.

Tank Recommendations

Quick Tank Facts
Water Temperature 74°F – 82°F (24°C – 28°C)
Minimum Size 10 gallons (38 L)
Water Hardness 2 to 30 dGH
pH Level 6.0 to 8.5 (Between 6.0 to 7.5 is ideal)
Maximum Nitrate Content 35-40 ppm
Lighting Requirements Moderate
Specific Gravity or Salinity 1.002 (10%)

Tank Size Requirements

If you like to keep only a school of five to six X-ray Tetras, then a tank capacity of 15 gallons will suffice. But the minimum recommended size I would prefer is 20 gallons. Although, it is considering other small fishes along with a group of X-ray Fish.

Nonetheless, if you want to keep more fish alongside them, try to get at least a tank of double or more capacity.

You can also try to build a biotope tank. Biotope tanks are basically just normal tanks except they contain fish, other organisms, and plants that occur together in the same natural habitat.

But it might be a bit complicated for some to set it up at first because a lot of things go into it and also requires a lot of management.

What to Include When Setting Up a Tank


There are a lot of plants in their natural habitat. They are always hiding around and swimming between thick growth. So, it only makes sense to try and simulate the same environment in the tank.

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Some good options are-

  • Anacharis
  • Christmas moss
  • Java ferns
  • Water sprite
  • Ludwigia repens
  • Amazon sword
  • Brazilian pennywort

Quick tip– As mentioned before, they do eat plants as part of their diet. So, having lush vegetation can benefit you in terms of feeding them plant matter.


As you know, they have a translucent shiny body, so low light is not a good idea. Moderate to bright light is well and good, but try not to go too bright or the X-ray fish will be hard to spot.

The best options would be fluorescent tubes and bulbs, metal halide bulbs, or LED lights. Try to avoid incandescent bulbs as they can slightly increase water temperatures.


The best substrate for them is a soft sandy substrate like river sand. It can help simulate their natural environment. The color of the sand is a personal preference, but try to avoid Aragonite sand.

Aragonite sand contains calcium carbonate, which can increase the alkalinity of the water. And, evidently, X-ray fish prefer slightly acidic settings in the tank, like in the wild.


All kinds of décors can be put inside the tank. Ensure not to keep objects with fine edges as they might graze the fish when they are spurting around.

You can also put Indian almond leaves in the tank. It helps to create a natural aesthetic, as you would see in rivers and lakes. In addition to that, it can also serve as a hiding place for the young fish.

Tank apparatus

As the tank will have plenty of natural plants, oxygen deficiency won’t be an issue. But if you are still unsure about it, you can put in air-stones to help with the oxygen.

A good sponge filter will be useful as it won’t create turbulence in the water and will help maintain low nitrate levels.

Water Parameters

Water parameters are important even if the X-ray fish is hardy. Bad quality can result in the immune system getting compromised. This will make the fish more vulnerable to diseases.

  1. The water temperature should be between 74 and 82 °F. The ideal temperature would be around 78 °F.
  2. Pristella Tetras do not like hard waters and the pH is close to slightly acidic. It should lie in the 6.0 to 8.5 range.
  3. They can tolerate hardness up to 30 dGH, which is much higher than many smaller fish species.
  4. Nitrogen concentrations should be maintained close to zero, but should not exceed 35 to 40 ppm.
  5. If you are going for a brackish water setup, they will be able to tolerate a specific gravity up to 1.002.

X-ray Fish Tank Mates

As a result of their non-aggressive behavior, their range of compatible fish is wide. They can be kept with all kinds of non-aggressive fish.

As usual, try not to put bigger aggressive fishes like Cichlids, Oscars, etc. with them as they might end up on their food plate.

This is a list of perfectly compatible tank mates for your X-ray Tetra-

  1. Rasboras (like Chili Rasbora, etc.)
  2. Other Tetras (like Black Phantom Tetra, Neon Tetra, Bleeding Heart Tetra, etc.)
  3. Pencil fish
  4. Guppies
  5. Mollies (like common Molly, Dalmatian Molly, etc.)
  6. Loaches
  7. Plecos (like Royal Pleco, etc.)
  8. Platy fish

Frequently Asked Questions

Are Pristella tetra or X-ray fish fin-nippers?

No, Pristella Tetra is not known to nip fins, unlike its relatives such as Neon Tetras or Blue Tetras. They can be peacefully kept with long-finned fishes.

Can X-ray Tetra be kept in a 5-gallon tank?

They can be kept in a 5-gallon tank with  at most 2-3 fish. However, 5 gallons is too small of a swimming space for them and they might feel agitated. Additionally, they stay happier in a bigger group. So, in a smaller tank, with a small number of mates, they won’t be happy for long.

Can Pristella Tetra be kept with Angelfish?

Yes, they can be kept with Angelfish because they are not fin-nippers. So, if you decide to keep a few Angels with them, feel free to add them at your convenience.

Are X-ray fish aggressive?

They are actually the opposite of aggressive. They are a very friendly, social, peaceful fish species. They can stay peacefully with most fish and crustaceans. They also do not harm plants.

Final Conclusion: Should We Get Them?

If you own a community tank, then these X-ray fish will be a good addition to escalate the aesthetic level of your tank. The main redeeming qualities will be their unique appearance and how easily you can take care of them.

If you are familiar with Tetras, then taking care of them should not be of concern, even if you have no experience with them. In addition to that, if you ever decide to breed them, they can easily be carried out in a regular tank without needing to buy any additional equipment.

About the Author

Shelby Crosby

Shelby is a passionate fishkeeper who has been writing about fish for over 5 years. She is a pro aquarist and holds a BSc Honors Degree in Wildlife and Fisheries. She creates her own beautiful aquarium layouts and loves to share her knowledge of tropical fish with other hobbyists.

Career Highlights:

  • Has worked with several aquarium manufacturers as a consultant
  • Organized and hosted workshops on freshwater fish keeping at retail stores, educational facilities, and libraries
  • Released content for the amphibian community through her writings

Educational Highlights:

  • BSc Honors in Wildlife and Fisheries in 2011 (University of Northern British Columbia)
  • Completed her undergraduate thesis on the effects of zoochlorella supplementation on the growth and health of fish.

Writing Experience

Miss Crosby is a Freelance blogger; many of her articles are posted online on various blogs. She has also written a few short articles for "Tropical Fish Hobbyist Magazine" in the past. She is a regular contributor to FishParenting.com. Her education, first-hand experience with fishkeeping, and in-depth knowledge in aquaculture make her one of the most competent writers in the industry.

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