Blue Tetra Care (Knodus borki): Diet, Tank Requirements & Breeding

The Blue tetra (Knodus borki) is a stunningly beautiful addition to an aquarium. The Blue tetra’s iridescent blue and silver coloration provides an amazing sight, especially in a dark-background planted aquarium.

Relatively speaking, the species is not as common as other tetras and is not typically found in pet stores or local fish stores. I thought it would be a good idea to write an article about this underrated species for which the world needs to know about. Having had these for over 5 years, I might be biased. But I have grown fond of my Blue tetras, having spent many hours starring in their aquarium.

Knodus borki, its scientific name, is from Greek. The first part of his name, Knodus = “knife” or, “sword.” The second, borki, refers to an aquarist and fish photographer, Dieter Bork.

For a long time, however, the Blue tetra was commonly misidentified with the Boehlkea fredcochui, also known as the Cochu’s blue tetra. 

The Knodus borki is endemic to tropical freshwater environments in Northeastern Peru, near Iquitos.


Knodus borki.
Knodus borki, CC BY-SA 3.0, via Wikimedia Commons.

The blue tetra’s appearance is quite beautiful. Their bodies show reflective blue coloration, with hues of pink and green. The deep-bodied, similarly to Cardinal or rummy nose tetras. Their lateral line generally shows deeper and shinier blue coloration than the rest of their bodies, especially in the rear half. Blue tetras can be slightly transparent, giving them a glass-like appearance.

Blue tetras are sexually dimorphic. Males will tend to be smaller than females, who are have much rounder bodies. Males however will show stronger coloration, especially during mating.

Blue tetras are small when compared to some other tetras like Diamond tetra or Congo tetra. Typically, Blue Tetras will be between 3.75 to 4.25 centimeters in size or 1.5 to 1.67 inches.

Habitat & Tank Condition

The Blue tetra is a schooling fish, so you will need at least 6 of them in the same aquarium. A 10 gallon or more aquarium will be adequate for that many fish. Make sure to add 2 gallons for each additional fish.

Blue tetras will thrive in an aquarium whose pH levels are between 6 and 7. To reduce pH levels, you may use peat moss, driftwood, pH buffers like the Seachem Acid buffer, or botanicals such as Indian almond leaves.

Eheim aquarium heater.
EHEIM aquarium heater.

Blues will require a warm-watered aquarium, with temperatures ranging between 22 and 26 degrees Celsius, or 72 to 80 degrees Fahrenheit. Depending on where you live, might need to use a heater during winter.

A good choice is the Fluval-E or the EHEIM Jager, both of which we live for their accuracy and durability.

Your fish will require proper filtration to remain healthy and full of life. A filter should be used to remove harmful chemicals, such as nitrates. 

The Blue Tetra Diet

Blue tetras are quite enthusiastic during feeding and will eat almost anything. As omnivores, you can feed them with a wide range of foods. It is recommended that you feed them a varied diet, as this will provide them with all the nutrients that they need to be healthy.

Their diet should consist primarily of dry foods. Good choices include flakes, crisps, pellets, algae wafers, and granules. 


To complement their diet, you may use live foods, freeze, or freeze-dried foods. Good examples include brine shrimps, daphnia, infusoria, bloodworms, tubifex, and earthworms.

Since tetras have small mouths, make sure to provide food that will fit into their mouth. If the food is too big, break it up into smaller pieces.

To avoid overfeeding, provide enough for the fish to eat in 5 minutes. If the fish are still eating 5 minutes after the start of feeding, then you have given them too much food. It is important that you do not overfeed, as it can lead to a wide range of issues, including indigestion and deteriorating water conditions.

Blue Tetra Compatibility

Blue Tetras are peaceful in a community tank. This delicate fish is evasive and will always avoid trouble. To make them feel more comfortable, make sure to add them to a group of 6 or more. As mentioned earlier, Blue tetras are schooling fish. If they are not part of a school, they will become stressed and thus more prone to aggressive behavior. By placing them in school, you reduce the chances of them showing aggression towards other fish. On the flip side, it also helps them avoid predation from other fish in the aquarium.

Breeding Blue Tetras

Blue tetra breeding pair.
Blue tetra breeding pair, CC BY-SA 3.0, via Wikimedia Commons

Blue tetras can be bred in an aquarium at home. Generally, patience is key as females may not be willing to spawn even when presented with a good opportunity. It will be easier to get the female to spawn once you have a confirmed breeding pair.

To increase your chances of success, prepare a separate breeding tank. This tank should have plenty of plants for the female to spawn onto. The eggs of Blue tetras are adhesive so they will stick to the plants, but also wood, rocks, and the glass of the aquarium.

Blue tetras will only breed in soft slightly acidic water. Technically, pH levels should be between 5.5 to 6, and water hardness lower than 1.5 dGH.

Once you have chosen a breeding pair, place them in the aquarium and close the aquarium light. If possible, cover the aquarium to keep the aquarium as dark as possible.

A day later, begin to increase the amount of light in the aquarium daily. This will encourage the female to spawn.

Once the eggs have spawned, make sure to remove the parents as soon as possible, otherwise the fish will eat their eggs.

The eggs will hatch approximately 24 hours, after which the fry will remain near the eggs, feeding on yolk sacks and gaining their strength. A day or so later, the fry will begin to swim about the aquarium

At this point, you will need to feed the fish with, preferably, small lives foods like infusoria. The fry will only be able to eat bigger foods, like brine shrimp, when they are 2 or 3 weeks old. If you do not have any small live foods, you can also feed them commercially available prepared foods specifically made for fish fry.

It is important that throughout this entire process, you keep the light of the aquarium as dim as possible. The eggs and the fry are hypersensitive to light.

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