X-Ray Fish Care & Keeping: Size, Diet, and Tank Setup

X-ray fish (lat. Pristella maxillaris) is a fish kind of Characidae family. This is the only species of Pristella kind. The fish is a perfect choice for beginner aquarists, it is very undemanding and it can live in water with various parameters.

Habitat in the wild

Pristella maxillaris, commonly known as the X-ray Tetra or X-ray Fish, belongs to the Characidae family. The Characidae family is a large and diverse group of freshwater fish, commonly referred to as characids or characins. It includes many popular aquarium fish, such as tetras, hatchetfish, and pencilfish, among others.

This x-ray fish species is widespread in South America. It inhabits in Amazon and Orinoco rive basins and in rivers of Guyana. It can be found in various countries within this region, including Brazil, Colombia, and Venezuela. These fish inhabit slow-moving or still waters, particularly in areas with dense vegetation, such as flooded forests, tributaries, and flooded meadows during the wet season.

In their natural habitat, X-ray Tetras are usually found in water bodies with soft, acidic water conditions. Quite often the fish can be encountered in inshore waters with brackish water. During rain season the fish migrates to flooded areas of fluvial plain (savanna, forest canopy) for spawning. They tend to inhabit the middle to upper levels of the water column, often swimming among plants and seeking cover in areas with submerged vegetation. These fish are accustomed to a tropical climate with warm water temperatures.



X-ray tetra typically grows to a size of about 2 inches (5 cm) in length when fully mature. This size makes them well-suited for community aquariums, and their attractive appearance, featuring a translucent body, makes them a popular choice among aquarium hobbyists.


The typical lifespan of the Pristella maxillaris, or X-ray tetra, can vary based on factors such as water quality, diet, genetics, and overall care conditions. On average, in a well-maintained aquarium with suitable conditions, X-ray tetras can live for approximately 3 to 5 years. Some individuals might live slightly shorter or longer depending on the specific circumstances.


The fish body coloring is semitransparent, its skeleton and some internal parts of the body are clearly seen through its skin. Due to this distinctive feature the fish got its name.

The fish body is moderately long and flattened from sides with high back; this fish has a fatty fin. The fish translucent body coloring varies from olive to olive green with silvery tint; there is a black spot on the fish forebody. The x-ray fish has the same black spots on its lemon-yellow dorsal, anal and abdominal fins; dorsal and anal fins have white ends.

There are also albino fish species with red eyes and paler colored body, but it is quite seldom encountered on sale.

Scientific NamePristella maxillaris
Common NameX-ray Tetra, pristella tetra
OriginAmazon River Basin (South America)
SizeAbout 2 inches (5 cm)
Lifespan3 to 5 years (in proper care)
Aquarium Size15 gallons or larger for a small group
Temperature Range75°F to 82°F (24°C to 28°C)
pH Range6.0 to 7.5
HardnessSoft to slightly hard (2-15 dGH)
BehaviorPeaceful, schooling
DietOmnivorous, accepts flake and live foods
Tank DecorPlants, driftwood, hiding spots
Water FlowGentle to moderate
Breeding DifficultyModerate (requires separate breeding tank)

Difficulties in keeping

X-ray fish is easy both to keep and to breed. It is peaceful and suitable for any company of small fishes as well as it is rather enduring. The fish is undemanding in terms of food and it wasn’t observed when eating tank plants.

Care and keeping in a tank

Tank size

The recommended tank size for X-ray tetras, depends on the number of tetras you plan to keep and the overall setup of the aquarium. These fish are relatively small, reaching about 2 inches (5 cm) in length, and they are peaceful schooling fish, which means they should be kept in groups.

A general guideline for tank size when keeping X-ray tetras is to provide at least a 15-gallon (56.8 liters) tank for a small group of these tetras. However, larger tanks can offer more space for the fish to swim, provide better water stability, and allow for a larger school of tetras if desired.

Keep in mind that while a 15-gallon tank can accommodate a small group of X-ray tetras, it’s crucial to maintain good water quality. Regular water changes and proper filtration are essential for the health and well-being of your fish. Additionally, providing a well-planted tank with hiding spots and swimming spaces can make the environment more comfortable for these tetras.

As with any fish, the more space you can provide, the better, so consider the size of the aquarium in relation to the number of X-ray tetras you plan to keep and their need for swimming space and social interaction.

Water parameters

The fish is plain and enduring, it can adapt to quite various water parameters. There are no special requirements as for tank decorations, it depends only on financial possibilities and imagination of its owner or on its tank mates demands. Tank water parameters should be the following:

  1. Temperature: X-ray tetras prefer a tropical water temperature range of about 75°F to 82°F (24°C to 28°C). Keep the temperature stable within this range to prevent stress and fluctuations.
  2. pH Level: Aim for a slightly acidic to neutral pH level. The ideal range is around 6.0 to 7.5. It’s essential to avoid extreme pH swings, as stable pH levels are vital for fish health.
  3. Water Hardness: X-ray tetras come from soft water habitats in their native Amazon River Basin. Aim for a relatively low to moderate water hardness, with a general range of 2 to 15 dGH (German degrees of hardness). Soft water conditions are more suitable, but a slightly harder range can be tolerated.
  4. Ammonia and Nitrite: These toxic substances should be kept at zero. Regular water changes, proper filtration, and not overfeeding are essential to maintain low ammonia and nitrite levels.
  5. Nitrate: While nitrate is less toxic than ammonia and nitrite, it should be kept at a reasonable level. Aim for nitrate levels below 40 ppm (parts per million), with lower levels being preferable.
  6. Water Movement: X-ray tetras do not require strong water flow. A gentle to moderate water movement is sufficient. Provide areas with calmer water for the fish to rest.
  7. Tank Decor: Adding live or artificial plants can help stabilize water parameters, especially pH, by providing natural buffering. A well-planted tank also provides hiding spots and makes the fish feel more comfortable.

Remember to monitor water parameters regularly, especially when setting up a new aquarium or introducing new fish. Regular water changes, good filtration, and maintaining stable conditions will go a long way in ensuring the health and longevity of your x-ray Tetras. The tank maintenance consists of regular bottom substrate cleaning from organic waste (food leftovers, excrement) and weekly water renew (15–20% from the total tank volume) with fresh one.


X-ray fish is omnivorous and eats all type of live, frozen or artificial food.

Pristella maxillaris are omnivorous fish that have a varied diet in their natural habitat, feeding on a combination of small aquatic insects, zooplankton, and plant matter. In captivity, it’s essential to provide a well-rounded diet to ensure their health and vitality. You can feed the fish with high quality flakes and give it bloodworm and brine shrimp to make the fish diet more balanced. But keep in mind, that tetra species have small mouth and you have to choose food as small as possible.

Here’s a suitable diet for X-ray tetras:

  1. High-Quality Flake Food: A good quality tropical fish flake food can serve as a staple diet for X-ray Tetras. Choose a brand that includes a mix of ingredients to provide balanced nutrition.
  2. Live and Frozen Foods: X-ray Tetras enjoy live or frozen foods such as daphnia, brine shrimp, bloodworms, and other small aquatic invertebrates. These foods should be offered occasionally to provide additional protein.

Remember to feed X-ray tetras in small amounts multiple times a day rather than a large quantity in a single feeding. This approach mimics their natural feeding behavior and helps prevent overeating, which can lead to water pollution. Providing a diverse diet ensures that your X-ray tetras receive essential nutrients, and it also helps keep them active and vibrant.

Tank mates

X-ray tetras (Pristella maxillaris) are generally peaceful and social fish, making them suitable for community aquariums. When choosing tank mates for X-ray tetras, it’s essential to consider fish that share similar water parameters and temperament to ensure a harmonious environment.

Here are some compatible tank mates for X-ray tetras:

  1. Other Small Tetras: Since X-ray tetras are tetras themselves, they generally get along well with other small tetra species. Examples include Neon Tetras, Cardinal Tetras, Rummy Nose Tetras, and Glowlight Tetras. These species are of similar size and share similar water requirements.
  2. Corydoras Catfish: Corydoras catfish are peaceful bottom-dwelling fish that can make great tank mates for X-ray tetras. They help keep the substrate clean and are generally compatible in terms of temperament and water preferences.
  3. Small Rasboras: Many rasbora species, such as Harlequin Rasboras, are suitable companions for X-ray tetras. They are peaceful, colorful, and occupy different levels in the tank.
  4. Dwarf Gouramis: Certain species of dwarf gouramis, like the Honey Gourami or Sparkling Gourami, can work well as tank mates, especially in larger aquariums with ample hiding spots. Make sure the tank is adequately sized to prevent territorial issues.
  5. Small Livebearers: Some small livebearers, such as Endler’s Livebearers, can be compatible with X-ray tetras. However, avoid larger or more aggressive livebearers, as they may stress out the tetras.
  6. Peaceful Bottom Dwellers: Species like Otocinclus catfish (for algae control), small shrimp (e.g., Cherry Shrimp), or peaceful snails can coexist with X-ray Tetras, adding diversity to the tank.

Always monitor the tank for signs of aggression or stress, and ensure that the tank mates are not overly aggressive or fin nippers. A well-planted aquarium with hiding spots and sufficient swimming space can help reduce stress and provide a more natural environment for your X-ray tetras and their tank mates.

Gender differences: male vs female

Determining the sex of X-ray tetras can be a bit challenging, especially in juvenile fish. However, there are some subtle differences that become more apparent as the fish mature.

Here are some general characteristics that can help differentiate between male and female X-ray tetras:

  1. Body Size: In some cases, females may be slightly larger and rounder than males, especially when they are carrying eggs.
  2. Fins: There may be slight differences in the shape and size of the dorsal fin between males and females. Males might have slightly more elongated or pointed dorsal fins, but this difference can be subtle.
  3. Coloration: In mature females, the belly area might appear more rounded and fuller, especially when they are carrying eggs. The intensity of coloration can also vary among individuals, making it a less reliable indicator.
  4. Egg Carrying: Females that are ready to spawn may have a more noticeable bulge in the abdomen, indicating the presence of eggs. This sign is most apparent when the fish are well-fed and approaching the breeding season.
  5. Behavior: During the breeding season, males might exhibit more intense coloration and may display courtship behaviors, such as chasing and fin displays, to attract females. This behavior can be an indicator, especially in a breeding setup.

Keep in mind that these differences might not be easily noticeable in all individual X-ray tetras, and there can be variations among different fish. It’s often easier to differentiate between sexes when the fish are in a breeding condition or when you have a group of mature fish to observe. If you’re interested in breeding X-ray tetras, it’s best to observe their behavior and monitor any signs of spawning activity.


Any change of tank conditions (of course, a favorable one) triggers X-ray fish spawning. Water of average hardness and with neutral pH is good for the fish breeding. Tank water temperature should be 25 – 26 °C. A tank of 5-6 liters capacity and less can be used as a spawning tank.

The fish couple put in the tank will start spawning in the morning of the next day. If spawning process is delayed, keep the fish in a spawning tank for 1-2 days more. If you want you can feed the fish a little, for example, give it 3-4 bloodworms or coretra for each fish.

The eggs are small, transparent and not sticky. After spawning is over, you should put the breeders back to the community tank and leave the eggs for 5-6 days.

The juveniles require standard feeding. On the 6th day give them their first food. In spring, summer and autumn these will be pond microorganisms (daphnia, cyclop nauplii) and in winter – you should prepare infusorians in advance.

In a week you can feed the juveniles with larger live food: brine shrimp nauplii, cyclops and daphnia. The juveniles also eat Vinegar eels. Later on you can make the food size larger.

Juveniles grow comparatively slow. At the age of 6 month old they become 2.5-3 cm long and reproductive.