Blue Tetra
Hyphessobrycon coelestinus
A small South American freshwater fish, highly valued in the hobby for its active behavior and beautiful metallic blue-violet body coloration. Looks stunning in groups.
Water Temperature
20 - 25 °C
pH Value
6.2 - 7.4
Water type
Freshwater
Tank level
Bottom and middle
Adult size
4.5 cm
Minimum tank volume
>= 80 L
Minimum group
>= 8
GH
3 - 12 dGH
KH
2 - 6 dKH
TDS
65 - 240 ppm
Conductivity
102 - 375 uS/cm
Species description
Geographical Origin and Habitat: Hyphessobrycon coelestinus, known as the blue tetra, is native to South America, specifically endemic to the upper Tocantins River basin in Brazil. It inhabits small inland streams, tributary creeks, and shallow margins with clear waters and slow to moderate currents, often characterized by dense riparian and submerged vegetation.
Taxonomy and Morphology: It belongs to the family Characidae. It features the classic laterally compressed and fusiform body shape typical of tetras, with a well-developed adipose fin located between the dorsal and caudal fins. In adulthood, it reaches a modest length of 3 to 4 centimeters. The mouth is equipped with small sharp teeth suitable for catching insects.
Social Behavior: It is a peaceful, extremely active, and lively schooling fish that must be kept in groups of at least 8-10 individuals to display its natural behavior and minimize stress. Within the school, a peaceful hierarchy is established, with males constantly displaying to impress females and establish territory.
Coloration and Sexual Dimorphism: The coloration is characterized by a beautiful metallic, iridescent blue-violet hue along the flanks, which stands out particularly under appropriate lighting. A dark longitudinal band runs from the operculum to the base of the caudal fin. Adult males are generally slenderer and exhibit much more intense colors than females.
Care, breeding and tankmates
Aquarium Setup: Requires a freshwater aquarium of at least 60-80 liters to allow adequate swimming space for the school. The ideal setup includes dense vegetation along the sides and background, leaving the central area open. A dark substrate and the presence of dry leaves or driftwood help highlight the blue coloration of the fish.
Diet and Feeding: It is an omnivorous and opportunistic species. In the aquarium, it readily accepts a wide variety of foods, including high-quality dry flakes or micro-granules. To keep the fish healthy and stimulate their colors, it is recommended to offer live or frozen foods such as daphnia, brine shrimp, cyclops, and bloodworms.
Water Quality: Water parameters should mirror its natural habitat: temperature between 22°C and 26°C, slightly acidic to neutral pH (6.0-7.2), and soft to moderate water hardness (GH 5-12). It is important to perform regular water changes and ensure efficient filtration without creating excessively strong currents.
Compatibility and Cohabitation: It is an ideal fish for community aquariums. It can coexist peacefully with other small characins, pencilfish, corydoras, loricariids, and small peaceful cichlids. Avoid keeping it with large fish that could easily view it as food, or with extremely timid species that might be stressed by its active swimming behavior.
Aquarium Breeding: Reproduction in the aquarium is possible and is typical of characins. It is an egg-scattering species that releases eggs among vegetation without providing parental care. It is best to set up a dedicated breeding tank with soft, acidic water and dense java moss, removing the parents immediately after spawning to prevent egg predation.
Risks and Diseases: It is a generally hardy and easy-to-keep species. However, if kept in water that is too hard or alkaline, its colors will fade and its immune system will weaken. It is sensitive to Ichthyophthirius (white spot disease) if sudden temperature drops occur during water changes. Always match the temperature of the new water.
Geographic Origin and Distribution
Hyphessobrycon coelestinus, known as the blue tetra, is native to South America, specifically endemic to the upper Tocantins River basin in Brazil. It inhabits small inland streams, tributary creeks, and shallow margins with clear waters and slow to moderate currents, often characterized by dense riparian and submerged vegetation.
Origin
Amazon, Orinoco, and Guianas
Fish profile
- Temperament
- Peaceful
- The temperament of Hyphessobrycon coelestinus is overwhelmingly peaceful, making them an exemplary model of a docile community fish. They are not prone to fin-nipping or aggressive territorial disputes, provided they are kept in appropriately sized schools that allow them to establish a natural hierarchy. While males may occasionally engage in harmless sparring displays to establish dominance or impress females, actual physical damage is exceedingly rare. Their gentle nature ensures they will not harass slower-moving tank mates, fostering a tranquil and harmonious aquatic environment.
- Diet
- Omnivore
- In their natural habitat, Hyphessobrycon coelestinus are micro-predators and foragers that feed on tiny insects, crustaceans, and various zooplankton. Within the aquarium environment, they readily accept high-quality dry foods such as micro pellets and crushed flakes designed for small tropical fish. To ensure their best coloration and overall health, their diet should be regularly supplemented with live or frozen foods like Daphnia, newly hatched brine shrimp, and bloodworms. A varied diet prevents nutritional deficiencies and mimics their diverse natural foraging behavior.
- Life expectancy
- 3-5 years
- In a mature and well-maintained aquarium, the Blueback Tetra has an average lifespan of 3 to 5 years. Being a species sensitive to nitrogenous waste buildup, stability in the chemical and physical parameters of the water is essential. Excellent biological filtration and regular water changes will significantly reduce stress, extending the lifespan of these fish.
- Adult size
- 4.5 cm
- The catalog's scalar value is 4.5 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 3.31 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Hyphessobrycon coelestinus (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- School
- While Hyphessobrycon coelestinus does not strictly require a specific male-to-female ratio, keeping a mixed group with a slight majority of females is generally recommended. Having more females helps distribute any amorous or territorial chasing behavior from the males, preventing individual females from becoming overly stressed. In larger schools of ten or more, the sex ratio becomes less critical as aggression and attention are widely dispersed throughout the group. Observing a healthy mix of both sexes also allows aquarists to enjoy the more intense, vibrant coloration that males display when showing off to the females.
- Feeding frequency
- Twice daily
- To maintain optimal health and vitality, Hyphessobrycon coelestinus should ideally be fed small portions one to two times per day. It is important to only offer an amount of food that the entire school can completely consume within two to three minutes. Overfeeding can lead to poor water quality, algae outbreaks, and potential health issues for these small fish. Providing a fasting day once a week can also be beneficial to clear their digestive tracts and replicate natural food scarcity.
- Bioload
- The bioload produced by Hyphessobrycon coelestinus is generally considered to be quite low due to their small adult size and active metabolism. These tiny fish do not generate significant amounts of waste, making them excellent candidates for densely planted setups or nano aquariums when kept in appropriate numbers. However, a proper filtration system and regular water changes are still essential to maintain optimal water quality. If kept in very large schools, their cumulative bioload can increase slightly, but it rarely overwhelms a standard, cycled aquarium filter.
- Flow
- Moderate
- Coming from environments ranging from sluggish tributaries to moderately flowing streams, Hyphessobrycon coelestinus appreciates a gentle to moderate water flow in the aquarium. They are not built to constantly battle strong, torrential currents, which would quickly exhaust them and induce significant stress. Employing a spray bar or directing the filter outflow towards the tank glass can help diffuse the water movement effectively. Providing calmer resting areas among dense vegetation allows them to retreat and conserve energy whenever needed.
- Jump risk
- Yes
- Like many small, active species, Hyphessobrycon coelestinus possesses a moderate risk of jumping out of the aquarium, especially when startled or during the initial acclimation period. Sudden changes in lighting, aggressive tank mates, or sudden movements outside the tank can easily spook them into a leaping reflex. It is highly recommended to keep the aquarium securely covered with a tight-fitting lid or a specialized mesh screen. Floating plants can also be added to the surface to help them feel more secure and deter jumping behaviors.
- Reproduction
- Oviparous
- Hyphessobrycon coelestinus belongs to the category of egg-scattering fish, meaning they broadcast their eggs freely without providing any subsequent parental care. In a dedicated breeding setup, dim lighting, very soft, acidic water, and an abundance of fine-leaved plants or spawning mops are required to encourage spawning. The adult fish are notorious egg-eaters and must be removed from the breeding tank immediately after the spawning event concludes. Once hatched, the microscopic fry require infusoria or specialized liquid fry food until they are large enough to accept baby brine shrimp.
- Compatibility & tankmates
- Community
- Hyphessobrycon coelestinus is an incredibly peaceful and sociable schooling fish that makes a fantastic addition to most community aquariums. They thrive when kept alongside similarly sized, non-aggressive species such as Corydoras catfish, small rasboras, and other docile tetras. It is crucial to avoid housing them with large or predatory fish that might view them as a quick snack, such as larger cichlids. Maintaining them in a group of at least six individuals will help them feel secure, significantly reducing any potential stress or shyness.
- Tank level
- Middle/Bottom
- In the aquarium, Hyphessobrycon coelestinus primarily inhabits the middle to upper levels of the water column, rarely venturing completely to the bottom unless searching for fallen food. They are enthusiastic swimmers that appreciate plenty of open swimming space in the center of the tank to dart around in their schooling formations. Providing tall background plants or floating vegetation will give them the upper-level cover they desire without encroaching on their preferred swimming zones. Their mid-water presence makes them an excellent choice for adding active, colorful movement to the central focal point of a planted setup.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 2.9 ± 0.3 se
- Resilience
- High (less than 15 months)
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.01318, b = 3.05
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
Related species
Recommendations grouped by close relatives, companion choices, and similar care.
