
Source: Wikimedia Commons
Knodus borki
A small characin whose flanks shine an intense blue, so vivid that newcomers often assume the fish has been dyed. Small but constantly on the move, it will nip fins at feeding time or in cramped quarters. A dark substrate and floating plants set it off best.
Knodus borki is a small characin whose flanks shine an intense blue, so strong that people seeing it for the first time in a shop often take it for a dyed fish. Seriously Fish gives 5.0cm SL, 22-26C, pH 5.5-7.0, 5-12 dGH and a base of at least 75 by 38cm. FishBase records only the distribution, Iquitos in Peru, without size or water figures, while Seriously Fish gives rivers, streams and tributaries in Colombia and Brazil. Small though it is, it swims a great deal, and its true colour comes out in a densely planted tank with a dark substrate and floating plants to soften the light; in sparse surroundings it stays dull. It is broadly peaceful but will nip the fins of its own kind and of long-finned species, which settles when eight to ten or more are kept together in a roomy tank. Do not pair it with slow or retiring fish.
Source: Wikipedia (CC BY-SA 4.0)
The Blue Tetra lives 3-5 years.
The Blue Tetra grows to About 5cm.
The ideal temperature for the Blue Tetra is 22〜26℃.
Origin
South America (sources differ: FishBase gives Iquitos in Peru, Seriously Fish gives Colombia and Brazil)
Lifespan
3-5 years
Sources: Seriously Fish / FishBase
Edited & verified by: BreederDirect editorial team
The taxonomic, regulatory, and husbandry data on this page are compiled and verified against the authoritative primary sources below.
Sources: CITES Appendices (species not listed) / IUCN Red List
Regulations may change. Always verify the latest information with the relevant authorities.
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Size
About 5cm
Temperature
22〜26℃
Dried foods, frozen bloodworm, Daphnia, brine shrimp and some plant matter
Seriously Fish suggests a base of at least 75 by 38cm, about 86 litres at 30cm depth. The fish is small but swims a great deal, so a nano tank will not do. Plant densely and soften the light with a dark substrate and floating plants to bring out the blue; an Amazon layout of driftwood and leaf litter suits it as well.
Seriously Fish gives 22-26C, pH 5.5-7.0 and 5-12 dGH. The FishBase page carries no water figures for this species, so these come from that one source. It settles best in soft, slightly acidic water.
Broadly peaceful, but it will nip the fins of its own kind and of long-finned species, most noticeably at feeding time or in cramped quarters. Keeping eight to ten or more in a roomy tank spreads the aggression among themselves and settles it. Avoid slow or retiring tank mates, which are overwhelmed by its constant movement, and do not use it as a dither fish for dwarf cichlids.
It eats almost anything and is especially keen on small live and frozen foods such as bloodworm, Daphnia and brine shrimp. Include some plant matter, blanched spinach or a good algae-based flake.
It has been bred, but little is documented. Set up a bare-bottomed tank of about 30 by 20cm with a small air-driven filter and a couple of potted broad-leaved plants such as Amazon swords, since the female is said to lay under a wide leaf. Remove the adults once eggs are seen. Mature females are rounder in the belly, and males are more strongly coloured with the anal fin flushing red in spawning condition.
FishBase lists it as IUCN Data Deficient, not on the CITES appendices and harmless to people. The trade name blue tetra was long attached to Boehlkea fredcochui, but FishBase and GBIF treat the two as separate species, so expect the scientific name on the label to vary between shops.
Intermediate. This is an intermediate-level species. Some prior experience and knowledge of environmental management are recommended.
The ideal temperature for Blue Tetra is 22〜26℃. Avoid sudden temperature changes and maintain a stable environment.
The average lifespan of Blue Tetra is 3-5 years. With proper care and nutrition, they can live a long and healthy life.
Blue Tetra typically reaches About 5cm as an adult. Size may vary depending on care conditions and individual genetics.
Blue Tetra feeds on: Dried foods, frozen bloodworm, Daphnia, brine shrimp and some plant matter. Aim for a balanced diet with appropriate feeding frequency.
The price of Blue Tetra varies significantly depending on morph, size, and lineage. Check our market price page for the latest pricing information.
Last updated: September 17, 2026