Knodus borki

Blue Tetra

Classification

Characidae

Distribution

Colombia and Brazil.

Habitat

Rivers, streams and tributaries.

Maximum Standard Length

2″ (5cm).

Aquarium SizeTop ↑

Despite it’s diminutive size, this is a very active species and is not really suitable for tanks smaller than 30″ x 15″ x 12″ (75cm x 37.5cm x 30cm) – 88.5 litres.

Maintenance

Best kept in a heavily-planted arrangement with a dark substrate and floating plants to diffuse the lighting. If maintained in sparse surroundings it will not develop its best colours. Alternatively, it can look very effective in an Amazon-type biotope setup. Use sand as substrate and add some twisted beech branches and roots. Complete the effect by scattering a few handfuls of dried oak, beech or Indian almond leaves around the tank. You might also wish to add a net bag containing aquarium-safe peat or peat moss to the filter. This will release humic acids and tannins into the water, giving it a similar stained effect to the natural waters of the fish. The water should also contain plenty of dissolved oxygen.

Water Conditions

Temperature: 72-78°F (22-26°C)

pH: 5.5-7.0. Will not do well in alkaline conditions.

Hardness: 5-12°H

Diet

Omnivorous and will accept most foods offered. It particularly relishes small live and frozen foods such as bloodworm, daphnia and brineshrimp. Some vegetable matter such as blanched spinach or a good quality Spirulina flake should also be included in the diet.

Behaviour and CompatibilityTop ↑

Although generally peaceful, it may occasionally nip at the fins of conspecifics and other species with elongated fins. This behaviour becomes more apparent at feeding time or if the fish are kept in cramped conditions. It can be limited by buying at least 8-10 specimens and maintaining them in a larger tank. Under these conditions any aggression is more often directed towards conspecifics.

Avoid any particularly quiet or slow-moving tankmates as they might be intimidated by the species‘ constant movements and vigorous nature. It’s certainly not a good dither species for dwarf cichlids such as Apistogramma. Possible choices include other tetras, Loricariids and smaller catfish such as Corydoras sp.

Sexual Dimorphism

Mature females are clearly rounder in the belly than males. Males are a little more intensely coloured than females, and their anal fin is supposed to become suffused with a reddish colour when in spawning condition.

Reproduction

Has been achieved but little information is available. A separate spawning tank will certainly be required. Something around 12″ x 8″ would be suitable. Set this up very simply, with no substrate, a small air-powered sponge filter. Add a couple of pots containing Amazon swords or similar, as the female is supposed to lay her eggs under a broad plant leaf. Fill the tank with soft, acidic, aged water.

Meanwhile, condition the fish in a group with plenty of high quality live and frozen foods. When the female are noticeably round with eggs and the males are showing their best colours, select the best-looking pair and place them in the spawning tank in the evening. Once eggs are noticed (hopefully the following morning), remove the adults as they will probably make a meal of them given the chance. The fry are very small indeed and require infusoria or Paramecium as a first food.

NotesTop ↑

The colour of this species is often so intense that many who first see it for sale assume it to be artificially coloured. It is currently the only representative of the genus known.