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SnailsCardinal Tetra Care & Info | Paracheirodon axelrodi
If you're looking for a colorful schooling fish for your aquarium, why not go for one of the classics? Paracheirodon axelrodi, better known as the cardinal tetra, is one of the most commonly kept freshwater fish. And there's a reason for that: this species isn't just colorful, but also peaceful and easy enough to care for.
Keep reading for everything you need to know about cardinal tetra care!
| Scientific name | Paracheirodon axelrodi |
| Common names | Cardinal tetra |
| Difficulty level | Easy |
| Origin | South America (Orinoco & Negro rivers) |
Table of Contents
Cardinal tetra appearance & natural habitat
Appearance
It's not difficult to see why the cardinal tetra took the aquarium hobby by storm after it was first formally described in 1956. These fish may be small, but they're absolute gems! Their bodies are horizontally divided into two different colors: bright blue at the top and vivid cardinal red on the belly, with an iridescent blue line in between.
If that description sounds a lot like the ever-popular neon tetra, you're right. Along with one other very similar fish, the false neon tetra (P. simulans), they make up the only species in the genus Paracheirodon. It is possible to tell neons and cardinals apart, though:
- Neon tetras grow to a maximum size of 1.5". At max. 2", cardinal tetras are a bit larger.
- On neon tetras, the red coloration only runs halfway across the lower body. The other half is silver.
If you have a school of adult cardinal tetras, it's usually possible to tell the females from the males based on size. The ladies are significantly bigger and also tend to be rounder when viewed from above.
Did you know? Like many species, the cardinal tetra has had a few different scientific names over the past. Cheirodon axelrodi, Hyphessobrycon cardinalis... and now, Paracheirodon axelrodi. Herbert R. Axelrod, who the species was named for, was a bit of a legend in the aquarium hobby. He founded Tropical Fish Hobbyist magazine and wrote many books on freshwater fishkeeping.
Natural habitat
The cardinal tetra is naturally found in the middle and upper Orinoco and Rio Negro river systems in South America, specifically Brazil, Venezuela and Colombia. Here, it mostly inhabits the middle water layer, usually shoaling in the upper reaches of slow-moving swampy river side arms.
These streams are small and shallow (generally under 2ft deep), with dark, stained water, not too much direct sun and a thick layer of leaf litter on the bottom. There tends to be plenty of vegetation around the edges, particularly palm trees.
The natural palm swamp habitat of this fish is characterized by seasonal fluctuations. During the dry season, shoals can end up in small pools in areas that maintain some water year-round. When the rainy season rolls around, they're thrust into the igapós: seasonally flooded forests full of food and safe opportunities to reproduce.
In the state of Amazonas in Brazil in particular, the catching and export of cardinal tetras is actually a big contributor to the local economy. One 2006 study notes 30-40 million of these little fish exported yearly from the Rio Negro region, with profits up to $3 million every year (although those numbers may have fallen since then, as cardinals can now finally be captive bred on a commercial scale).
Setting up a cardinal tetra aquarium
Requirements
If you'd like to keep a group of cardinal tetras, it's a good idea to go for an aquarium of at least 20 gallons (long, not high; as we've discussed, they prefer shallow water anyway). This should offer plenty of swimming room.
Although you don't have to, our favorite option is to turn the aquarium into a bit of a biotope, recreating the species' natural habitat as best as you can. The Rio Negro is a blackwater river whose side arms are full of leaf litter and plant roots. Your cardinal tetras will appreciate something similar in the aquarium: dark water (stained using a layer of leaves on the bottom), relatively dim lighting, and plenty of wood and leaves scattered about.
The substrate doesn't matter much, as it'll be covered anyway, although we like the look of river sand.
Water parameters
The water in this species' natural habitat is characterized by its very low mineral content and high acidity. Research has shown the cardinal tetra can withstand pH levels under 4! They're not fussy, though: one study noted them surviving in water with a pH up to 8.8, although we would personally try to keep it under 7.5.
Although it can be difficult to maintain a stable nitrogen cycle in an aquarium with low pH, you should still try. Avoid introducing cardinal tetras or other livestock into tanks that aren't fully cycled, and be sure to perform regular maintenance in the form of weekly small water changes in order to keep the water quality high.
As for temperature, a 2011 study noted that the temperatures in one specific locality where cardinal tetras are naturally found fluctuated between around 77-86 °F during a five-month period, which gives us some pretty good info. They're absolutely tropical fish, so a temperature of 73 °F or higher is a must.
pH: 4.5-7.5
Temperature: 73-86 °F
Hardness: 4 dGH max
Tankmates
When i tcomes to compatibility, first and foremost, you should remember that these fish naturally occur in shoals of a few dozen individuals. In the aquarium, it's best to keep at least 10 cardinal tetras. In smaller groups, they can begin to feel stressed, which may affect their coloring, behavior, and even their lifespan.
As for other tankmates, you won't have much trouble choosing. One of the reasons these tetras became so popular in the first place is that they're peaceful and will leave almost all fish and invertebrates alone. On the other hand, they're also quick enough to avoid many predatory fish. Their size (they're a bit larger than the ubiquitous neon tetra) also helps in that department.
As mentioned, we like a biotope set-up for cardinal tetras. There are many, many suitable tankmates for this species, but you could consider species that hail from the same natural habitat, or at least close:
- Top water layer: Carnegiella (hatchetfishes), killifish (like Apterolebias)
- Middle water layer: Hemigrammus tetras (such as rummynoses), Nannostomus (pencilfish), Hyphessobrycon tetras, Apistogramma dwarf cichlids
- Bottom water layer: Otocinclus sp.
Cardinal tetras and shrimp
If you'd like to get a school of cardinal tetras to keep your (dwarf) shrimp company, that should work. Many shrimp also do well in the conditions that cardinals like; they share a love for leaf litter, for example. However, you do need to keep something in mind: research has conclusively shown that these little tetras are predators.
Because a freshly hatched baby shrimp is unfortunately the perfect size for a cardinal tetra snack, you should refrain from keeping them with slow-breeding or expensive shrimp. They're fine for something like a colony of cherry shrimp, though, especially if you provide plenty of hiding places like aquatic moss for the fry to hide in until they're big enough to evade the tetras.
Cardinal tetra diet
The cardinal tetra is considered a micropredator. A 2004 study analyzing the species' gut content found mostly microcrustaceans like daphnia and copepods. There were also other small insects and (midge) larvae, rotifers, insect eggs, algae, bits of carrion, and plant detritus.
In the aquarium, you can offer your cardinals a high-quality floating micropellet for carnivores, or go for small flake food. They will also really appreciate regular portions of (thawed) frozen fish foods like bloodworms and mosquito larvae, or even the occasional serving of live food.
Breeding cardinal tetra
In the wild, cardinal tetras breed in large groups during the rainy season, when food and space are abundant. The females can lay over 500 tiny eggs at a time.
In the aquarium, successful breeding of cardinal tetras used to be a rarity. This has changed in recent years, particularly after a 2006 study in which Brazilian researchers managed to pin down the water parameters required to get the species to spawn. Notably, they lowered water conductivity and pH (to 5.5) by adding rainwater.
If you'd like to try your hand at breeding cardinals in your own tank, here's what you'll need to provide:
- Very soft and acidic (and clean!) water
- Plenty of plants for the eggs to be deposited on
- Dimmed lighting
- Live foods
Once the parents have spawned, you can remove them from the breeding tank to protect the fry. Unfortunately, the larvae are absolutely tiny, meaning it's difficult to find foods that are small enough for them to eat. Extra-small Artemia or cyclops nauplii should work, but don't leave them for more than a few hours after hatching or they'll outgrow the baby cardinals.
Be sure to keep the water quality high as the fry grow. Avoid overfeeding them. For more details about cardinal breeding, we found this article to be quite informative.
Buying cardinal tetra
Thanks in part to the recent advancements in captive cardinal tetra breeding, this species has dropped in price and can be found at any aquarium store. You can also buy yours online: get your cardinal tetras at The Shrimp Farm and have them shipped right to your doorstep!
FAQ
Although cardinals are definitely not the most fragile microfish out there, they don't respond well to low water quality. Most aquarists are of the opinion that neon tetras are the hardier option.
Wild cardinal tetras rarely live for more than a year. In the safety of the aquarium, they can survive for up to five.
Although cardinals are considered peaceful fish, they can be nippy as well. This is one of the reasons they don't make suitable Betta fish tankmates.
