Knodus borki (Blue Peru Tetra)

09 June 2026

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The Blue Peru Tetra (Knodus borki) is a stunning, highly active schooling fish native to the Peruvian Amazon. Known for its brilliant iridescent blue lateral stripe, this peaceful yet energetic species has gained immense popularity among aquarists seeking vibrant colors and lively movement for their planted community aquariums.

Overview

The Blue Peru Tetra, scientifically known as Knodus borki, is a beautiful and energetic freshwater fish. Often misidentified in the past as Boehlkea fredcochui, this species has carved out its own well-deserved reputation in the aquarium hobby. They are prized for the striking iridescent blue stripe that runs down their sides, which shines brilliantly under proper aquarium lighting.

Image of blue perusal tetra knodus borki

Distribution and Habitat

This species is endemic to South America, specifically found in the upper Amazon River basin in Peru. They inhabit slow to moderately flowing streams and tributaries, often swimming among submerged vegetation, tree roots, and leaf litter where the water is slightly acidic and stained with tannins.

Description of Blue Peru Tetra

Body shape:

They possess a streamlined, torpedo-like body shape that is characteristic of highly active, fast-swimming tetras. This aerodynamic profile allows them to dart quickly through the water.

Color:

The base body color is a translucent silver or clear hue, but their defining feature is a bold, iridescent blue lateral band that stretches from the mid-body to the base of the tail. The gill covers often show a slight reddish or pinkish flush.

Barbels:

Like other characins, the Blue Peru Tetra does not possess any barbels.

Snout:

They feature a relatively short snout with a terminal mouth, perfectly adapted for snatching small insects and zooplankton from the water column.

Eyes:

The eyes are proportionately large with a dark central pupil surrounded by a reflective silver and slightly golden iris.

Fins:

The fins are mostly translucent with a very faint bluish or whitish tint. They possess a small adipose fin between the dorsal and caudal fins, a hallmark of the Characidae family.

The Tail:

The caudal fin (tail) is deeply forked and transparent. The brilliant blue lateral line extends slightly into the central base of the tail.

Temper

While generally peaceful, they are incredibly boisterous and fast-moving. They do not typically nip fins, but their sheer speed and constant darting can easily stress out slow-moving or shy tank mates.

Sociality

This is a strict schooling species. They must be kept in groups of at least 6 to 8 individuals, though a school of 10 or more is highly recommended to bring out their best colors and most natural behaviors.

Activity

They are exceptionally active swimmers. They spend the majority of their time in the middle to upper levels of the aquarium, constantly on the move and exploring their environment.

Keeping and Caring for Blue Peru Tetra

Tank size:

Because of their high activity levels, a minimum tank size of 20 gallons (approx. 80 liters) is required. A longer footprint is preferred to give them ample horizontal swimming space.

Water Parameters:

Temperature

They thrive in tropical temperatures ranging from 22-26°C (71-79°F).

pH

Keep the water slightly acidic to neutral, ideally between 6.0 and 7.5.

Hardness

They prefer soft to moderately hard water, ranging from 2 to 15 dGH.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always be at 0 ppm. Nitrates should be kept below 20 ppm through regular water changes and good filtration.

Lighting

Moderate lighting is best. If the lighting is too bright, floating plants can be used to diffuse it, which will also help their blue stripe stand out more vibrantly.

Water flow

They appreciate a moderate water flow that mimics their natural stream habitats, providing them with a current to swim against.

Decorations and Plants

A densely planted aquarium with plenty of open swimming space in the center is ideal. Driftwood and dried botanicals (like almond leaves) can recreate their natural Amazonian environment.

Diet

Blue Peru Tetras are omnivorous micro-predators. In the aquarium, they will readily accept high-quality dry foods such as micro-pellets and crushed flakes. To ensure optimal health and coloration, supplement their diet with live or frozen foods like daphnia, brine shrimp, and bloodworms.

Some Feeding Tips

Feed them small amounts once or twice a day—only what they can consume in a couple of minutes. Because they are fast mid-water feeders, ensure the food sinks slowly so they can catch it before it reaches the bottom.

Breeding

Breeding is similar to other egg-scattering tetras. Set up a separate, dimly lit breeding tank with soft, slightly acidic water and fine-leaved plants like Java Moss. Introduce a conditioned pair or small group. After spawning, the adults must be removed immediately as they will eat their own eggs. The fry will hatch in a few days and require infusoria or specialized liquid fry food until they are large enough to eat baby brine shrimp.

Conclusion

The Blue Peru Tetra is a fantastic choice for aquarists looking for a hardy, dynamic, and visually striking schooling fish. As long as they are provided with adequate swimming space and kept in a properly sized school, their energetic antics and neon-blue flashes will bring any planted community tank to life.

Fish info

Care level: Easy - Moderate
Temperament: Peaceful
Adult size: 5 cm
Life expectancy: 3-5 years
Fish type: Tetra
Temperature : 22-26°C
pH: 6.0-7.5
Color Form: Blue, Clear, Silver

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