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Care guide · Freshwater · fish

Congo tetra

Phenacogrammus interruptus

Congo tetra (Phenacogrammus interruptus)
Photo: NasserHalaweh · Source · CC BY-SA 4.0Resized and compressed; no cropping or colour changes.

The Congo tetra (Phenacogrammus interruptus) develops from a fairly plain juvenile into a striking African shoaling fish. Adult males in particular acquire a blue-green sheen, warm colours along the upper body and gracefully extended fins. This development needs more than attractive lighting: a generous group, open swimming water and a calm environment are essential. The species is peaceful but quite active, so it is not automatically a good neighbour for every small, timid fish. Equally, boisterous or fin-nipping companions can stress the Congo tetras themselves. Plan for adult fish from the moment of purchase and provide a long aquarium where the group can turn without constantly encountering plants, wood or other fish.

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At a glance

Temperature
23–26 °C
pH
6.0–7.5
GH
5–18 °dGH
Aquarium length
At least 120 cm
Adult size
Approximately 6–8 cm
Group size
At least 8 individuals
Temperament
Peaceful

About this species

This species belongs to the African tetra family Alestidae. Its scientific name distinguishes it from other fish also sold as Congo tetras. Males grow larger and develop longer dorsal and tail fins than females. Their iridescent flanks change with the angle of light; less sheen from another viewpoint does not automatically indicate illness. Juveniles do not yet display the final male fin shape.

FishBase records approximately 8 cm total length for males and 6 cm for females. Care sources sometimes use a different length measurement or mention larger aquarium specimens. Treat 8 cm as a planning size rather than an absolute growth limit. The spreading fins and movement of an entire group also need more clear space than body length alone suggests. A small shop juvenile cannot be housed permanently according to its purchase size.

Natural habitat

The natural distribution lies in the Congo drainage in Central Africa, including the Democratic Republic of the Congo and the Republic of the Congo. A country name is not a complete habitat description. This enormous drainage contains different water types, so it does not establish a compulsory strong current or fixed extreme acidity. Most fish in the trade are now captive-bred, but ask the supplier about the actual origin of the group offered.

A planted aquarium with sheltered edges, wood and open swimming water provides a useful practical arrangement. Anubias can grow on wood or stone without taking much substrate space. This leaves a clear central area where fish can pass one another. We do not automatically describe a combination with a particular plant as an exact natural biotope. Lighting that reveals the colours must never come at the expense of shade and security for the fish.

Aquarium and layout

Use at least 120 cm aquarium length as the starting point for adult Congo tetras. Some sources mention 100 cm, but the more generous guideline better accommodates a group of mature fish. Also assess width, layout and the entire population. We do not automatically convert one published tank size into a universal minimum in litres. A broad, well-arranged aquarium offers more usable swimming space than a narrow tank of the same volume.

Keep a long swimming route clear and concentrate plants at the sides and rear. Do not let floating plants cover the whole surface. Provide good circulation and gas exchange, with quiet areas away from the direct outlet. A suitable cover reduces risk during a startle response. Avoid sharp projecting decorations along the swimming route. Long fins are not a reason to eliminate all water movement; distribute the flow so that fish can choose a quieter area.

Water conditions

For everyday care we use 23–26 °C, pH 6–7.5 and GH 5–18 as a jointly supported range. Sources also report broader temperature and hardness limits. Choose a stable setting within the range that suits the fish's origin and companions. Softer, slightly acidic water is often recommended, but a rapid chemical adjustment is not an improvement when fish are already accustomed to other suitable water.

Congo tetras require attention to water quality. Check ammonia/ammonium and nitrite, remove food remains and tailor partial changes to measurements and stocking load. Use replacement water of suitable temperature and composition. No separate KH target has been inserted without sufficient support. Poor fin development or loss of colour may relate to conditions but is not a diagnosis on its own. Also examine damage from other fish, appetite and breathing before choosing treatment.

Behaviour and group size

Keep at least eight individuals, preferably including both sexes. Several males display to one another when sufficient space is available. An adult male alone among other species lacks that social setting. A group does not guarantee freedom from fright: bare surroundings, sudden movements in front of the glass or restless companions can still disturb the fish.

Avoid fin-nippers and species that continually chase Congo tetras. Conversely, their active swimming can overwhelm small, timid fish. Bronze corys are conditionally suitable because they mainly use the bottom, but need their own group, clear floor space and targeted sinking food. Do not regard them as cleaners that automatically find enough leftovers. Adding more species because they use different water layers still increases the overall load. Check that every group feeds calmly and has somewhere to retreat.

Feeding

Wild Congo tetras eat insects, worm-like prey, small crustaceans and plant material, among other foods. In aquaria they generally accept flakes, suitably sized granules and live or frozen food. Use a complete food as the foundation and provide variety. Fish enthusiastically approaching the surface do not need unlimited food. Watch body condition and actual intake rather than begging behaviour alone.

Distribute food so that the fastest individuals do not take everything. Juveniles may need crushed pieces; adults do not need to be fed powdered fry food. The linked complete Supervit flakes and supplementary dried Daphnia serve different purposes. Water fleas alone do not constitute a complete diet. Feed bottom-dwelling companions separately with appropriate sinking foods. Fish losing weight despite sufficient food need assessment of competition and health, rather than an automatic increase in the daily ration for the whole tank.

Breeding

The Congo tetra scatters eggs and provides no parental care. Deliberate breeding requires a separate quiet setup with suitable soft, acidic water and protection of the eggs from the parents. Fine-leaved plants or a safe spawning substrate provide structure. A mesh floor must allow eggs through without injuring or trapping fish. Adults are separated from the eggs after spawning.

Breeding accounts describe spawning over several days. Eggs and fry at different developmental stages can therefore be present together. Remove spoiled eggs carefully and prevent food for swimming fry from fouling the remaining eggs. Sources differ over first foods: prepare very small starter foods and move to Artemia only when fry actually take them. A fixed timetable or guaranteed number of offspring is not a reliable recipe. This attention to hygiene and food size makes breeding considerably more demanding than routine care.

Sources & review

This care guide draws on several specialist sources and was last checked on .

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