A strikingly beautiful but notoriously boisterous schooling fish. Often misidentified in the trade as Boehlkea fredcochui. Known for their intense iridescent blue coloration, they are incredibly fast, hyperactive swimmers. They are infamous fin-nippers and require a long tank and a large group (8+) to prevent them from terrorizing slower or long-finned tank mates.
Blue Tetra At a Glance
Blue Tetra Tank Requirements
Will Blue Tetra fit in your tank?
Care guides tell you what Blue Tetra needs, the next question is whether your tank can safely provide it. Test Blue Tetra against your tank size, maintenance needs, and the fish you already keep before you buy.
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Blue Tetra Water Parameters
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Blue Tetra Temperament & Compatibility
Blue Tetra Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard
The standard wild-type coloration found in the trade. Must be kept in appropriately large schools to dissipate their aggressive, manic energy and minimize fin-nipping behavior towards other species.
Same care requirements as the base species
Also known as: Wild Type
Blue Tetra Care Guide Summary
The Blue Tetra, scientifically known as Knodus borki, belongs to the Characins family group. Adults reach a maximum size of approximately 5 cm and have a fusiform body shape with a moderate growth rate. Classified as semi-aggressive, this species primarily occupies the surface and mid-level zones of the aquarium and produces a low level of biological waste.
To thrive, the Blue Tetra requires a freshwater only aquarium with a minimum volume of 90 litres and a tank length of at least 90 cm. Water temperature should be maintained between 22°C and 26°C, with a pH range of 5.5–7.5 and a general hardness of 2–12 dGH. A moderate water flow is preferred.
The Blue Tetra is a rewarding species to keep, provided its core environmental needs are met. The Blue Tetra is typically available in one standard form.
Blue Tetra Habitat Setup
When setting up an aquarium for the Blue Tetra, a moderate water flow best suits their natural preferences. Because this species occupies the surface and mid-level zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include dense planting to provide cover, break sightlines, and reduce stress. Keepers should note that a tight-fitting lid is essential, as this species is a known jumper.
Blue Tetra Compatibility Notes
Classified as semi-aggressive, the Blue Tetra is a schooling species that feels most secure in a sizeable group, where natural shoaling behaviour reduces stress and brings out their best colours. When choosing tankmates, avoid housing with slow-moving or long-finned species that may become targets for fin nipping, conspecific aggression can be intense, especially in smaller tanks, and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the surface and mid-level zones can help reduce competition and territorial overlap.
Blue Tetra Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Blue Tetra.
30 Gallon Breeder
40 Gallon Breeder
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
Show 10 more tank sizes
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Frequently Asked Questions About Blue Tetra
How big does Blue Tetra get?
Blue Tetra (Knodus borki) typically reaches a maximum adult size of approximately 5 cm. They have a fusiform body shape and a moderate growth rate.
What tank size does Blue Tetra need?
A minimum aquarium volume of 90 litres and a tank length of at least 90 cm are recommended for Blue Tetra. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Blue Tetra need?
Blue Tetra thrives in freshwater only conditions with a temperature range of 22–26°C, a pH between 5.5 and 7.5, and a general hardness of 2–12 dGH. A moderate water flow is preferred.
Is Blue Tetra peaceful or aggressive?
Blue Tetra is classified as semi-aggressive with an aggression score of 5 out of 10. They can work in community setups but may clash with certain tankmates.
How many Blue Tetra should be kept together?
Blue Tetra is a schooling species and should be kept in groups of at least 8. Larger groups help distribute aggression and encourage natural schooling behaviour.
Does Blue Tetra have any special tank requirements?
Yes. Blue Tetra benefits from plants - densely covered in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Does Blue Tetra need a lid on the tank?
Yes. Blue Tetra is a known jumper, and a tight-fitting lid or cover is essential to prevent escape. Even a small gap can be enough for a determined fish to leap out.
Plants That Suit Blue Tetra
These plants pair well with Blue Tetra based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Afzel's Anubias
Anubias afzelii
Amazon Sword
Echinodorus amazonicus
Anacharis
Egeria densa
Anubias Barteri
Anubias barteri
Baby Tears
Lindernia rotundifolia
Balansae
Cryptocoryne crispatula
Fish Similar to Blue Tetra
Blue Emperor Tetra
Inpaichthys kerri
The Blue Emperor Tetra, also known as the Royal Tetra, is a stunning, active schooling fish native to the Aripuanã River basin in Brazil. They feature a bold dark lateral stripe and vibrant blue-purple iridescence that intensifies in planted aquariums with slightly acidic water. Males will actively spar and display to establish dominance, but are harmless to other species.
Cardinal Tetra
Paracheirodon axelrodi
A stunning schooling fish native to the upper Orinoco and Rio Negro basins in South America. Famous for its brilliant iridescent blue line and a vivid red stripe that extends the full length of its body (distinguishing it from the Neon Tetra). They are strictly schooling fish that thrive in warm, acidic blackwater environments.
Emperor Tetra
Nematobrycon palmeri
A striking, robust schooling fish from Colombia. Unlike many tetras, they do not swim in a tight shoal, preferring to loosely associate while males stake out small territories to display to females. They feature a bold black lateral line and iridescent purple/blue hues.
Lemon Tetra
Hyphessobrycon pulchripinnis
A peaceful, deep-bodied schooling tetra known for its translucent yellow coloration and striking black and yellow fins. They are robust and active, making them an excellent choice for planted community aquariums. Their colors intensify significantly in a well-established tank with a dark substrate and proper schooling numbers.
Serpae Tetra
Hyphessobrycon eques
A striking, deep-red schooling fish known for its highly active nature. While hardy and beautiful, Serpae Tetras are notorious fin-nippers. This behavior is usually localized within their own pecking order if kept in large enough schools (8+), but they should never be housed with slow-moving or long-finned tank mates like Bettas, Angelfish, or Gouramis.
Colombian Tetra
Hyphessobrycon columbianus
A larger, deep-bodied tetra known for its striking metallic blue body and bright red fins. They are very active and can be somewhat boisterous. They are known to occasionally nip fins if kept in groups that are too small or in tanks that lack adequate swimming space.