Pristella maxillaris – What Are X ray Fish?
How many species do you think exist on our planet? Hundreds of thousands? A million? Maybe a billion? Well, even scientists can’t seem to agree on how many there are. Some studies suggest there are 2 million or fewer, others estimate there are 12 million, with even one recent study suggesting the earth is home to a trillion species! Wait until you hear about the x ray fish!
Scientists, however, generally agree that there are many more species than those formally described in the scientific literature, which are about 1.5 million. The latest estimate of biodiversity was by researchers from the University of Arizona who put the number at 2 billion.
According to National Geographic, there are more fish species than mammals, reptiles, and birds combined. More than 32,000 species of fish exist, with Australia having 4400. But as a radiologic technologist, only one of them piqued my curiosity, X ray fish. And you can imagine why.
Personal Discovery of the X ray fish
When I learned of their existence, my first thought was, why are they called X ray fish? Did it have anything to do with medical imaging and if so, what? Here’s what I learned.
X ray fish are small characins whose name comes from the fact that their silvery to yellowish skin is translucent, allowing you to see their spine. Scientists believe their see-through skin is an anti-predator adaptation that developed over time. Having translucent skin makes these fish particularly hard to spot as they swim in the clear waters and spawn in dense vegetation.
Aside from their backbone, a bony structure called the Weberian apparatus is also visible through the skin. Said structure helps pick up sound waves and transmits them to the vertebrae, giving X ray fish impressive hearing abilities. The sound waves are received by the swim bladder, before traveling to the inner ear. This keen sense of hearing also helps them avoid predators.
X ray fish are scientifically known as Pristella maxillaris and are the only species in the Pristella genus. They also go by other names depending on their description. These names include X ray Tetra, Water Goldfinch, Golden Pristella Tetra, and Albino Pristella Tetra.
Habitat and Distribution
Pristella maxillaris were formally described in 1984 by Albert Ulrey. Ulrey was an American marine biologist who died in 1932. X ray tetras are native to South America, specifically in Venezuela, Amazon, Orinoco, and coastal river drainages of the Guianas in both acidic and alkaline waters.
They occur in calm coastal waters that are often brackish. Unlike other characins, they are tolerant of brackish water, which is water that is saltier than freshwater, but not as salty as seawater. These tetras live in clearwater streams and tributaries during the dry season. But when the rainy season comes, they migrate into densely vegetated swamps to spawn.
Pristella tetras swim in schools when in swamps with thick vegetation. Schooling puts them at a reduced risk of predation, improves their foraging, and helps them swim more efficiently. The species is not listed or evaluated on the IUCN Red List of Threatened Species. The IUCN Red List was established in 1964 and is to date identified as the world’s most comprehensive source of information in regards to the global conservation status of fungi, plants, and animal species.
Description
X ray fish grow up to around 1.8 inches in length and live for 4 to 5 years or longer. These fish have a silver or yellow appearance. Additionally, Pristella tetras have a small, round humeral spot that’s about the size of the pupil. The dorsal and anal fins start with a yellow stripe, followed by a black one, then end with a white tip. The tail appears reddish inspiring the name Pink Tailed Tetra.
X ray fish with a stronger golden cast inspired the common names Golden Pristella Tetra, Water Goldfinch, and Goldfinch Tetra. There is also a popular albino variety known as Golden X-ray Tetra or Albino Pristella Tetra. These fish have pink eyes and pink spots and a more washed out body coloration. Albino Pristella Tetras are much easier to breed than normal X ray tetras, which could explain their popularity.
Gender
There are various ways to distinguish the males from the females. For starters, the males are smaller and thinner than the females. They also have a sharply-pointed swim bladder, while that of the females is more rounded. Lastly, it’s possible to see the eggs in adult females.
Diet/Foods
As an omnivorous species, X ray tetras eat the vegetation that surrounds them during the rainy season, as well as insects, small crustaceans and worms. In a home aquarium, give them high-quality flake food every day. Feed them live foods such as bloodworms and brine shrimp as a treat. Additionally, feed them several times a day but give them only what they can consume in 3 minutes or less at each serving.
Reproduction
Pristella tetras are egg layers and are relatively easy to breed. The hardest part, however, is in finding a compatible breeding pair as they are rather picky about their partners. The females lay 300 to 400 eggs in a process referred to as spawning. However, commercially-bred specimens may spawn fewer eggs since the application of growth hormones in fish feed can result in low fertility.
A 10-gallon spawning tank is suitable. The ideal breeding temperature should be between 75° F (24° C) and 78.8° F (26° C). The water should be soft and slightly acidic with a pH of 6.5 to 7 and hardness of 4° dGH or less. There also needs to be fine-leaved plants such as Myriophyllum (watermilfoil), java moss, or artificial spawning grass so that the female has a place to deposit the eggs.
A layer of mesh that is wide enough for the eggs to pass through but small enough to keep the parents out would also do. The tank should be dimly lit, adding floating plants can help block out light. An air-pump-driven sponge filter is also needed for filtration as well as orchestrating water flow. Filtering the water through aquarium-safe peat is also helpful as it reduces pH and water hardness values.
Xray Tetras
X ray tetras can be made to spawn in groups of six, three males and three females. But for optimal fecundity, single-pair spawning is best. It’s also advisable to condition the males and females in separate tanks before breeding. Feed them a rich diet of live foods for several days then choose a spawning pair or group and transfer them into the breeding tank in the evening. When adult females are full of eggs, their bellies become nicely rounded. Go for males that appear more colorful.
They will usually spawn the following morning. If no eggs appear within a day or two, remove them and select a different pair or group. Following a successful spawn, remove the parents lest they eat the eggs. The eggs will hatch within the next 24 to 36 hours, and the fry will be free-swimming in 3 to 4 days. Since fry are quite tiny, rearing them can prove to be rather challenging. For the first few days, feed them infusoria until they are large enough to start eating other foods, such as brine shrimp nauplii.
Temperament/Behaviour
X ray fish have a peaceful character. They are a shoaling species, meaning they stay together for social reasons. For this reason, they should be kept in groups of at least six individuals. They are ideal for a community tank but can be skittish around larger tankmates. The best tankmates for Pristella tetras are other small tetras, Corydoras, pencil fish, small rasboras, loaches, and most livebearers.
If the aquarium has slightly brackish water, they can share the habitat with Pelvicachromis pulcher (kribensis), Etroplus maculatus (orange chromide), small gobies and other small non-predatory fish. In a nutshell, you should not place them with large, aggressive, and or predatory tankmates. Pristella tetras pose no threat to humans.
Care level
Pristella tetras are hardy fish. Hardy fish are ironically any fish that are easy to maintain in a home aquarium due to their ability to adapt to a range of water quality parameters. These tetras are, therefore, ideal for beginner fish keepers. All available specimens are commercially bred and will do well in most tank setups, within reason. If you maintain proper water quality and optimize the water flow rate, the fish and aquarium plants will do well.
Aquarium setup
A school of 6 Pristella maxillaris will do best in about a 15 to 20-gallon aquarium. The aquarium should be densely planted around the sides and back and have plenty of water for swimming in the front. Create a few hiding places as well. Add a canister filter or powerhead to create a gentle current. Ensure the aquarium has moderate to dim lighting.
A biotype setup is an ideal choice for Pristella tetras and is quite easy to put together. Use river sand with some driftwood and twisted roots as the substrate. Add a few handfuls of dried leaves, which you will require to remove and replace every few weeks. Add some aquarium-safe peat to the filter to simulate the black waters of their natural environment. Peat achieves this by changing the color of the water from clear to brown.
Characins do not tolerate salty water, but Pristella maxillaris are an exception. They are the only characins that naturally inhabit a variety of water environments, including brackish water. Brackish water is mineral-rich and has an alkaline pH. Nonetheless, their tolerance for salt is not high. They can only tolerate a salinity that is around 10% of a regular saltwater tank with a specific gravity of 1.0002. If the specific gravity reaches 1.003, they will die.
Aquarium care
X ray fish are easy to care for so long as their water is kept clean. Aquariums are closed systems and as such, require regular, routine maintenance. Over time, decomposing organic matter, nitrates, and phosphates build up in the tank. Moreover, water hardness increases due to evaporation. Water should, therefore, be replaced regularly, particularly so for a densely stocked tank. Doing so will ensure proper water quality is maintained and the fish remain healthy. At least 25 to 50% of the tank water should be replaced every two weeks.
Fish Diseases
For X ray fish in a well-maintained aquarium, diseases are hardly a problem. That is not to say you won’t ever have to deal with sick fish. Anything you add to your tank, be it other fish, plants, substrate, or decoration, can introduce diseases. To prevent this, properly clean or quarantine anything that you add to an established tank so as not to upset the balance.
Since Pristella tetras are resilient, an outbreak of disease can often be limited to one or a few fish if it’s dealt with at an early stage. With sensitive fish, it is common for all fishes to be infected even before the first symptoms show. The best way to proactively prevent the fish from falling sick is by maintaining the proper environment and feeding them a balanced diet.
The closer the aquarium environment resembles their natural habitat, the less stress the fish will have. Stressed fish are more likely to contract diseases. The most common diseases seen in home aquaria are usually either bacterial or parasitic.
Here’s a list of some of the most common pet fish diseases according to the American Veterinary Medical Association (AVMA):
- Physical injury
- Parasites such as white spot disease (Ich), nematodes, monogenean flukes, fish lice, anchor worms, and gill maggots
- Bacterial infections such as columnaris (cottonmouth) and mycobacterial infections
- Fungal infections such as Saprolegnia, Branchiomyces, and Fusarium
- Fin Rot or ulcer disease, which is rotting of the fins caused by bacterial or fungal infections
- Hole-in-the-head (HITH), a disease characterized by holes in the front or side of a fish’s head
- Fish pox, which is caused by a fish herpes virus resulting in gray, pink, or white wart-like growths
- Velvet or coral fish disease, which is a parasitic disease that results in dusty and slimy scales
- Ammonia or chlorine poisoning resulting from poor water quality
Some of the common signs diseased fish will show include:
- Appearing disoriented, such as swimming upside down
- Leaving food uneaten
- White spots on fins or body
- Discolored gills
- Trouble breathing such as gasping at the surface of the water
- Bulging eyes (one or both)
- Mucus accumulation on the body
- Rubbing on hard surfaces
- Unusual isolation from the group of fish (if housed with others)
- Skin lesions/sores anywhere on the body
- Bloating
- Crooked back or other changes in fish shape or size
Availability
X ray fish are readily available and affordably priced. They are also commonly sold as X ray Tetra, Golden Pristella Tetra, and Pristella Tetra.
However, the survival of the Pristella maxillaris is dependent upon their environment and the seasonal relationship they have developed with rainy and dry seasons. The biggest threats to X ray tetras are, therefore, are water pollution and climate change. Increasing industrial activity in South America’s coastal waters has caused a decrease in water quality, which has contributed to their population decline. Additionally, climate change threatens to compromise the delicate balance the X ray fish have created between the rainy and dry seasons of the Amazon.
Quick facts about X ray fish
- X ray fish are also known as Pristella maxillaris, Golden Pristella Tetra, X ray Tetra, Pristella Tetra, and Water Goldfinch.
- Their name comes from the fact that their skin is usually translucent, allowing you to see their spine.
- They grow up to about 1.8 inches in length.
- They have a lifespan of 4 to 5 years or longer.
- There is an albino variety known as the Golden X-ray Tetra.
- They are native to South America.
- They are omnivorous.
- The female lays 300 to 400 eggs.
- They are popular among aquarists because of their peaceful nature and striking colors.
- They are community fish and should be kept in groups of at least six specimens.
Conclusion
X ray fish are small, hardy fish with translucent skin. They are commonly kept as pet fish and serve no function in medical imaging (surprise!) I love to look around the internet and see what things are similar in any fashion to our world of x rays. In this particular case, it has to do with the transparency of the fish or the ability to see right through it… as if x raying the fishie. Eh, gave me a break from the usual anyway.
References
http://animal-world.com/encyclo/fresh/characins/pristella.php
