Finding the right fish for a nano tank can be a real challenge. So, today I will be talking about Ruby tetras (Axelrodia riesei) a lesser-known species of fish that could be the perfect choice for your small aquarium.
Ruby tetras are tiny, peaceful, and relatively easy-to-care-for fish. The behavior and swimming style of these fish in an aquarium significantly distinguish them from most other fish species and can make them one of the most interesting characins.
In this article, I will take a closer look at Axelrodia riesei, exploring their natural habitat, behavior, and care requirements. So if you are curious about learning more about this intriguing species, read on!
Quick Notes about Ruby Tetra
| Name | Ruby tetra |
| Scientific Name | Axelrodia riesei |
| Water type | Freshwater |
| Tank size | 10 gallons (~40 liters) |
| Keeping | Easy-Medium |
| Breeding | Medium-Difficult |
| Size | 0.8 – 1.2 inches (2 – 3 cm) |
| Optimal Temperature | 75 – 82°F (24 – 28°С) |
| Optimal PH | 6.0 – 7.0 |
| Optimal GH | 1 – 8 |
| Dwellers | Mid to bottom-dwelling |
| Nitrate | Less than 60 |
| Diet | Omnivore |
| Temperament | Peaceful |
| Life span | up to 3 years |
| Color Form | From bright red to pinkish |
Taxonomy of Ruby Tetra
In 1965, Jacques Géry (1917–2007), a renowned French ichthyologist specializing in the ecology of the Amazon basin, established the genus Axelrodia.
At that time, he was only aware of one of the three species that now belong to the genus, with Axelrodia fowleri later recognized as a junior synonym of Hyphessobrycon stigmatia.
In 1966, he described Axelrodia riesei.
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Characidae
Genus: Axelrodia
Species: Axelrodia riesei
Etymology of Ruby Tetra
This species (Axelrodia riesei) was named in honor of Dr. Herbert R. Axelrod (1927 – 2017), a well-known tropical fish expert, and a publisher of pet books, and Mr. William Riese, a tropical-fish exporter, who helped collect this species.
Distribution of Ruby Tetra
Axelrodia riesei has a very narrow natural distribution and can only be found in the basin of the left tributary of the Orinoco River, the Meta River, in Colombia, South America.
Habitat of Ruby Tetra
The Ruby tetras inhabit stagnant or slow-moving blackwater rivers and streams that flow under the dense cover of the tropical forest.
Its natural habitat also consists of the bottom which is littered with fallen leaves and driftwood. The water is rich in tannins from decomposing organic matter, giving it a brownish color.
Description of Ruby Tetra
The Ruby tetra is one of the smallest fish in the aquarium hobby and probably the smallest in the Tetra family. The adult size ranges from 0.8 – 1.2 inches (2 – 3 cm).
Distinguishing characteristics of Ruby Tetra:
- Shape. Their body is elongated and slightly compressed laterally, with a pointed snout.
- Eyes. The eyes are large compared to their size.
- Color. Their coloration can range from bright red to pinkish, with the color typically becoming slightly paler towards the belly.
- Fins. The fins are short and transparent. The caudal fin is forked and has a conspicuous black spot.
Note: The genus Axelrodia is characterized by a very small size, an incomplete lateral line, the naked caudal lobes, the mouth terminal, the teeth strictly conicals, rather numerous, the maxilla toothed and not thickened, the mandible with a single series of teeth and the sides not much elevated, the fontanels broad and the circumorbital bones reduced.
Lifespan of Ruby Tetra
Currently, there is no data available on the maximum lifespan for Axelrodia riesei in the wild.
However, in captivity, Ruby tetras can live up to 2 – 3 years, if appropriately cared for.
Their lifespan will greatly depend on the conditions they are kept in, how well you feed them, and how stressful your aquarium environment is for them. These tiny fish will live most in an aquarium containing low food competition and the absence of various larger or aggressive animals.
Typical Behavior of Ruby Tetra
Temper:
Ruby tetras are peaceful and harmless fish. They will not annoy anyone in the community tank. On the contrary, they are more likely to be bullied by other fish.
They do not nip other fish.
The males may engage in a dominance competition but nothing serious, they usually do not do any visible damage to each other.
Note: Ruby tetras can sometimes be confused with Serpae tetras (Hyphessobrycon eques), especially when they are still young. However, the problem is that this species can be classified as semi-aggressive and nippy.
Sociality:
This is a social species. Although Ruby tetras like to be in a group, they do not stay in close proximity all the time. Occasionally, you will see them hanging out with each other. Thus, it is not schooling but rather a shoaling fish.
In the aquarium, you need at least 8 (bare minimum) of them to start. Large groups make them happier and they should get more confident over time too.
These fish must be kept in groups in order for them to establish a hierarchy, which is necessary for them to emulate their natural behavior in the wild. Keeping them in small group or leaving them alone can make them feel stressed.
Activity:
Ruby tetras are incredibly shy and skittish. They often hide in the plants or stay behind the driftwood and rarely come out unless it is a feeding time.
They are jumpers.
The behavior of these fish is truly captivating and unique among Tetras. Ruby tetras move like dragonflies. They remain motionless for periods of time, only to suddenly dart forward 1 – 2 inches (2 – 5 cm) before coming to a halt once again. Even if they happen to be slightly angled downward after their forward movement, they will maintain that position until their next dart forward.
This is a diurnal species. These fish rely significantly on their vision to detect predators and find food or conspecifics.
Placement in Tank:
Ruby tetras tend to prefer staying in the middle and bottom areas of the tank.
Features:
- Social: Yes
- Activity: Medium
- Placement: middle and bottom dwellers
- Peaceful: Yes
- Nippers:No
- Jumpers:No
Feeding Ruby Tetras
In the wild, this fish is a micropredator that feeds on small invertebrates and other types of zooplankton.
In an aquarium, they will usually accept dry or freeze-dried food of all kinds as long as it is adapted to their small mouth size. A varied and balanced diet will result in healthier, more active, lively, and colorful fish.
Ruby tetras will eat live food:
- brine shrimp (artemia salina),
- artemia nauplii,
- cyclops,
- daphnia,
- fruit flies,
- mosquito larvae,
- moina,
- detritus worms
- vinegar eels,
- grindal worms, etc.
Ruby tetras will have no problem taking any small live or frozen food as far as it is small enough to fit into its mouth for mastication and digestion. Therefore, for example, large worms (grindal worms, etc.) should be chopped into small pieces and flake food should be crumbled.
They also accept frozen and commercial food as well, such as (links to Amazon):
- Fluval bug bites,
- Hikari first bites,
- TetraMin Crisps,
- any kind of really small crushed-up tiny flake food.
Features:
- Diet Type: Omnivore
- Food Preference: Meat
- Feeding Frequency: Daily
How to Feed Ruby Tetras If They are Hiding?
If your Ruby tetras are too afraid to go in the open, you can use this trick:
- Take a small pot and crush a pill or flake there.
- Add water until the mixture reaches a liquid consistency.
- Take a syringe or turkey baster and suck up the mixture.
- Use it in the place or general direction of the fish.
Are Ruby Tetras Plants Safe?
Yes, Ruby tetras can be kept in planted tanks. They do not eat live plants. Even more, planted tanks are highly recommended for them.
Keeping and Housing Ruby Tetras
Maintaining a clean and healthy aquatic environment is crucial for the well-being of Ruby Tetras.
It was noticed that high levels of ammonia, nitrites, and nitrates can be detrimental to their health, making it essential to cycle and fully establish your aquarium before introducing them.
Tank size:
Due to their small size and extremely interesting swimming style, Ruby tetras can be successfully kept even in nano aquariums. An aquarium of 10 gallons (10 liters) would be suitable for a group of 8-10 individuals, provided that there are no other fish species in the tank.
Keeping this species in excessively large tanks would be counterproductive, in my opinion.
While it is true that it is easier to maintain a particular level of water quality in larger tanks, however, because these fish dislike swimming in open water, they will simply “disappear” in larger aquariums.
Water parameters:
Temperature: The recommended temperature for Ruby tetras ranges between 75 – 82°F (24 – 28°C).
pH: The ideal pH range is 6.0 to 7.0. Keep in mind that in their natural habitat, they are found in blackwater environments with acidic water.
Hardness: The recommended general hardness (GH) range for these fish is 1 to 8 dGH. The recommended carbonate hardness (KH) range is 1 to 4 dKH.
Note: Many aquarists noticed that in hard water Axelrodia riesei loses his colors.
Ammonia, Nitrite, Nitrate: It is important to maintain the ammonia, nitrite, and nitrate levels at 0 ppm, 0 ppm, and below 60 ppm, respectively.
Blackwater: Water with a natural dark or tea-colored tint, resembling the water in many rivers and streams in tropical rainforests, is referred to as “blackwater” in aquariums.
It is typically brought on by the release of tannins and other organic chemicals into the water from decaying plant material, such as leaves and wood.
Many fish species, including Axelrodia riesei, find this natural setting to be very favorable.
| Blackwater is frequently produced in aquariums by adding plants like Indian almond leaves, driftwood, and other organic items to the tank or by employing specialized water conditioners that are intended to replicate the habitat-specific characteristics of blackwater. |
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Lighting:
Ideally, Ruby tetras prefer subdued lighting.
However, if you decide to keep these fish in planted tanks, lighting should be adapted to the needs of plants.
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Water flow:
In the natural environment, Ruby tetras are found in stagnant or slow-moving blackwater with little to no water flow. Therefore, we need to do the same in our tank.
Still or very slow water currents are recommended for tanks housing this species
Substrate:
Ruby tetras spend lots of time close to the substrate, so it is important to provide them with a substrate that will not harm them (such as sand or smooth gravel).
In planted tanks you can use an active substrate, besides boosting plants’ growth rate it will also help you to maintain a low pH level in the water.
Avoid coarse gravel. Its sharp edges can injure/scratch the body of the fish as they swim in the lower regions of the tank.
Filtration:
Since Ruby tetras are sensitive to the composition and cleanliness of the water, a powerful filtration system with filtering materials that increase acidity is desirable.
Soft water can be achieved using a reverse osmosis system.
Water changes:
Ruby tetras are very sensitive to the accumulation of organic decomposition products in the water.
Therefore, it is essential to perform weekly water changes (at least 20%), remove leftover food and vac clean the bottom from excrement.
Decorations:
This species is very shy and prefer to hide. Therefore, for the Ruby tetras setup, a natural look with dim lighting, incorporating elements such as driftwood, leaves, shade-tolerant aquatic plants, floating plants, dark ground, and background, and lots of hiding places is highly recommended.
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Acclimation:
Before putting Ruby tetras into the tank, you need to at least temperature acclimate them.
Give them time to acclimatize before adding to the tank. Do not rush the process! Sudden changes in habitat can harm them.
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Breeding Ruby Tetras
Unfortunately, Ruby tetras do not breed very infrequently in captivity. There is currently no established breeding protocol for their reproduction. In addition, little is known about this species’ wild reproduction in the scholarly literature as well.
Basically, all information regarding the breeding Axelrodia riesei is based on observations made by aquarists.
Sexing:
Although Ruby tetras are sexually dimorphic, their small size makes it challenging to differentiate between males and females.
- Body shape and size: Females are generally slightly larger and plumper than males, especially when they are carrying eggs. Male Axelrodia riesei have a slimmer and more streamlined body shape.
- Coloration: The males tend to exhibit slightly more color than the females.
- Fins: In males, the dorsal fin tends to be more pointed and elongated than in females, while the anal fin is more pointed and narrow.
Maturity:
The Ruby tetra reaches sexual maturity at the age of 5-7 months.
Eggs:
Ruby tetras are egg scatterers. They do not exhibit any parental care and will readily eat their own eggs given the chance.
Therefore, to ensure the survival of the eggs, parents should be transferred to a separate tank a few days before mating. After that, they must be removed.
Note: A small breeding tank should have lots of various hiding places such as rocks, driftwood, and plants.
| One of the reasons for the lack of success in breeding this fish species is also related to their diet. Many aquarium hobbyists start to feed their fish heavily when the spawning period is approaching.
Unfortunately, it has been observed that this is not enough! Ruby tetras require constant good feeding with high-quality foods to ensure successful breeding, not just before the spawning period. |
Fry:
Generally, the fry hatch in 2-3 days. The newly hatched fry are very small and require microscopic food such as infusoria or specialized liquid or powdered products.
Unfortunately, adult shrimp may eat the fry. Thus, the fry should stay in a separate tank for at least a month.
Ruby Tetras and Suitable Tankmates
It is important to take into account Ruby tetras’ small size and skittish behavior when choosing their tankmates. For example, if you have very active, boisterous and/or territorial fish, it is strongly recommended to avoid cohabiting with such species.
Fish:
Its tank mates should be all small fish species that are not big enough to eat or harass them such as:
- Pygmy Cory,
- Clown Killifish,
- Least Killifish,
- Guppies,
- Peacock Gudgeon,
- Ghost Glass Catfish,
- Harlequin Rasboras,
- Sparkling Gourami,
- Otocinclus, etc.
Shrimp:
Keeping Ruby tetras and dwarf shrimp will be very risky for shrimplets
While adult dwarf shrimp may generally be safe, the same cannot be said for baby shrimp, which are highly susceptible to predation by this fish.
Even heavily planted tanks may not provide sufficient hiding places for baby shrimp. Therefore, if you are serious about maintaining a thriving shrimp population, the safest course of action is to keep the shrimp separate from Ruby tetras.
Freshwater snails:
Ruby tetras can share the same tank with any type of freshwater snails.
However, it is important to note that the majority of snails prefer hard water and do not tolerate acidic water well in long term as it can have a negative effect on their shells over time. Meanwhile, this fish species actually prefers soft and acidic water.
Avoid:
Keep Ruby tetras away from most types of crayfish and freshwater crabs.
Even small African Dwarf Frogs can and will try to catch them whenever it is possible.
In Conclusion
Ruby tetras are not as well-known as some other popular aquarium fish. As a result, many people may miss out on the opportunity to enjoy the unique beauty and personality of this fascinating species.
This small, colorful fish can be a highlight in many peaceful community aquariums, especially in a planted tank.
References:
- Axelrodia riesei, a new characoid fish from upper Rio Méta in Columbia (with remarks concerning the genus Axelrodia and description of a similar, sympatric Hyphessobrycon-species). Ichthyologica-The Aquarium Journ., 37 (3) new ser.: 111- 120.
- Axelrodia riesei in Morales-Betancourt D (2022). Especies acuáticas y semiacuáticas de humedales interiores de Colombia derivado de información secundaria. Instituto de Investigación de Recursos Biológicos Alexander von Humboldt.
- Bührnheim, Cristina Motta. “Sistemática de Odontostilbe Cope, 1870 com a proposição de uma nova tribo Odontostilbini e redefinição dos gêneros incertae sedis de Cheirodontinae (Ostariophysi: Characiformes: Characidae).” (2006).
- Géry, J., 1977. Characoids of the world. Neptune City ; Reigate : T.F.H. [etc.]; 672 p. : ill. (chiefly col.) ; 23 cm. (Ref. 598)
- Christopher Scharpf & Kenneth J. Lazara (22 September 2018). “Order CHARACIFORMES: Family CHARACIDAE: Subfamily STEVARDIINAE + Incertae sedis”. The ETYFish Project Fish Name Etymology Database. Christopher Scharpf and Kenneth J. Lazara. Retrieved 27 March 2021.
- Weitzman, Stanley H., and William L. Fink. Relationships of the neon tetras, a group of South American freshwater fishes (Teleostei, Characidae), with comments on the phylogeny of New World characiforms. Museum of Comparative Zoology, Harvard University, 1983.