Congo Tetra, Phenacogrammus interruptus
Phenacogrammus interruptus

The Congo Tetra has opalescent scales that shine in all the colors of the rainbow!

The Congo Tetra Phenacogrammus interruptusis a timid but incredibly beautiful fish. They are often overlooked when seen in the pet store however, as they are generally adolescents that have not yet attained their full size and adult coloration. As adults, they are the most gorgeous of the true African Characins. They have luminescent rainbow colors in the body and their dorsal, anal, and tail fins develop into the most beautiful feathery appendages.

These are a peaceful schooling fish, but get nervous if not housed with a group of their own kind. They need to be kept in schools of 6 or more fish to thrive. The males can reach up to over 3 inches (8.5 cm) in length, so a group of these good-sized fish need a large aquarium. A 40 gallon tank or larger, planted aquarium with open space in the middle, will give them plenty of room to swim and develop their full beauty.

Congo Tetras are best kept by aquarists with some experience. Their water quality must be maintained or they will loose their beautiful color, and the males’ fins may become impaired. They are most comfortable in an aquarium with lower light levels, which can be provided by floating plants. However, they sometimes do like to nibble on softer plants and young shoots.They prefer soft, peat filtered water and a dark substrate. The beautiful rainbow colors of this fish will show off best with a dark substrate and lower light levels, too.

They are generally a good community fish with other peaceful, similar sized companions, but they may try to bite smaller fish. These fish are easily frightened by aggressive tankmates and loud noises. Do not tap on the glass! Congo Tetras are also timid eaters and may wait for you to leave the aquarium before they will feed.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Characiformes
  • Family: Alestiidae
  • Genus: Phenacogrammus
  • Species: interruptus
Congo Tetra – Quick Aquarium Care
  • Aquarist Experience Level: Intermediate
  • Size of fish – inches: 3.4 inches (8.51 cm)
  • Minimum Tank Size: 40 gal (151 L)
  • Temperament: Peaceful
  • Aquarium Hardiness: Moderately hardy
  • Temperature: 73.0 to 82.0° F (22.8 to 27.8&deg C)
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Habitat: Distribution / Background

The Congo Tetra Phenacogrammus interruptus was described by Boulenger in 1899. This species is listed on the IUCN Red List as Least Concern (LC) because it has a large population and no major widespread threats. They are found in Africa in the Zaire River region of the upper Congo Basin.

They are found in streams, tributaries, pools, and marshes with slightly acidic and murky waters. These habitats have tall vegetation around the margins and sandy bottoms, or in slow-moving pools the substrate can be thickly layered with silt and mud. There are few rocks in these areas and no branches or wood. The Congo Tetras swim in schools and feed on worms, crustaceans, insects, plant matter, algae, and other zooplankton.

  • Scientific Name: Phenacogrammus interruptus
  • Social Grouping: Groups
  • IUCN Red List: LC – Least Concern


The Congo Tetra has a full-bodied typical tetra shape with rather large scales. Males have lush fins, with the dorsal, anal, and tail fins sporting long veiled edges, and the middle portion of the tail fin becomes extended. Males will reach about 3 1/3 inches (8.5 cm) in length, and females will reach about 2 1/3 inches (6 cm). They have a lifespan of between 3 to 5 years in the home aquarium.

Congo Tetra, Phenacogrammus interruptus
Photo © Animal-World

When mature, the Congo Tetra has a palette of rich opalescent colors runing along the body from front to back. They are blue on top, changing to red down through the middle into a yellow-gold, and then back to blue just above the belly. The fins are grayish violet with white edges.

  • Size of fish – inches: 3.4 inches (8.51 cm) – The males get up to 3.5 inches (8.9 cm) while females reach up to 2.75 inches (6 cm).
  • Lifespan: 5 years – They have a lifespan of about 3 to 5 years in the aquarium.

Fish Keeping Difficulty

Congo Tetras are moderately hardy, but due to their care requirements, are suggested for hobbyists with some experience. They are sensitive to the quality of the water. Diligent tank maintenance is necessary or they will loose color and the male’s fins may become impaired. Be careful picking tankmates as these peaceful, long-finned tetras are often a target for attacks by aggressive tankmates. These attacks can stress them out and injuries can lead to disease and possibly death.

  • Aquarium Hardiness: Moderately hardy
  • Aquarist Experience Level: Intermediate

Foods and Feeding

The Congo Tetras are omnivorous. In the wild these fish are insectivores, feeding primarily on insects, but also eat small worms, crustaceans, plant matter, algae, and other zooplankton. In the aquarium the Congo Tetra will generally eat all kinds of live, fresh, and flake foods. To keep a good balance, give them a high quality flake food every day. Feed brine shrimp (either live or frozen) or blood worms as a treat. Feed them several times a day and only what they can consume in 3 minutes or less at each feeding.

  • Diet Type: Omnivore – In the wild, these fish are primarily insectivores, but they can usually be trained to take live foods, large flakes, and pelleted foods.
  • Flake Food: Yes – Provide large flakes.
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Some of Diet
  • Vegetable Food: Some of Diet
  • Meaty Food: Some of Diet
  • Feeding Frequency: Several feedings per day

Aquarium Care

Congo Tetras are not exceptionally difficult to care for provided their water is kept clean. They will loose their color and the male’s fins may become impaired in less than optimal conditions. Aquariums are closed systems and regardless of size, all need some maintenance. Over time, decomposing organic matter, nitrates, and phosphate build up and water hardness increases due to evaporation. The water needs to be replaced on a regular basis. At least 25% of the tank water should be replaced every other week, and up to to 50% if the tank is densely stocked.

  • Water Changes: Bi-weekly

Aquarium Setup

The Congo Tetra has been successfully kept and even bred in aquariums as small as 20 gallons. This fish is commercially bred in huge numbers, so it is adaptable and will thrive in most well-maintained tanks. However, because they really need to be kept in schools of at least 6 fish, an aquarium of at least 40 gallons or larger is recommended. For a larger school or when the become adults, 55 to 75 gallons or more is best for them to thrive. Water should be on the acidic side and soft with good circulation. Dim lighting will develop the tetra’s best coloring.

To get the best out of this fish, set up a biotype tank. These fish prefer some plant cover and a dark gravel. The Congo Tetra looks particularly effective in a heavily-planted setup, but with some open space in the center for swimming. It can appear a little washed out if the decor is too sparse. For the substrate, use a river sand with some drift wood and twisted roots. Add some dried leaves to the tank, which will stain the water a light brown, and then replace the leaves every few weeks.

  • Minimum Tank Size: 40 gal (151 L) – This fish should be kept in groups of at least 6 and requires plenty of swimming space.
  • Suitable for Nano Tank: Sometimes
  • Substrate Type: Any
  • Lighting Needs: Low – subdued lighting – Low lighting and a shadowy tank setup will bring out this tetra’s best coloration.
  • Temperature: 73.0 to 82.0° F (22.8 to 27.8&deg C)
  • Breeding Temperature: 77.0° F – These fish will spawn at 77 to 82.4° F (25 to 28° C).
  • Range ph: 6.0-7.5
  • Hardness Range: 4 – 18 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: All – These fish will swim in all areas of the aquarium.

Social Behaviors

The Congo Tetra has a very timid temperament and should be kept in a school with at least 6 individuals. They get easily frightened and need a school of their own kind to be comfortable and thrive. Keeping them in a species tank with up to 20 individuals is ideal, but with smaller groups, keep a mix of 2 or 3 females to 1 male or keep all males. That will help avert any aggression that may arise when in breeding mode or establishing a social group dominance.

They are generally a good community fish as well, but they may try to bite smaller fish. These shy fish should not be housed with any of the more aggressive fish. The best tankmates are other tetras, rainbowfish, Corydoras, Loricariids, Synodontis, and some peaceful dwarf cichlids. Do not keep Congo Tetras with fish that are known to be fin nippers as male Congos will sustain injuries. Rasboras and Barbs (except for extremely nippy species like the Tiger Barb) may also work, but keep an eye out for any aggression. Also, they sometimes like to nibble on softer plants and young shoots.

  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species – conspecifics: Yes
    • Peaceful fish (): Safe – This fish has a very timid temperament and should not be housed with aggressive or fin-nipping fish.
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Monitor – Tetras can out compete them for food.
    • Shrimps, Crabs, Snails: Safe – not aggressive
    • Plants: Monitor – They may snack on soft plant matter and new shoots.

Sex: Sexual differences

The male is larger and more colorful, and the tail fin and dorsal fin are more extended. In the picture above, you can see the extension at the center of the tail fin. A mature female will be more rounded.

Breeding / Reproduction

Congo Tetras are egg layers and have been bred in captivity. They are bred commercially for the aquarium trade, with most available species originating from Eastern Europe and the Far East. Breeding these fish in the home aquarium, however, can be a bit of a challenge. Their spawning is seasonal and getting a pair to spawn in the aquarium is somewhat difficult.

To breed them, provide a large aquarium with peat-filtered water and bright lighting. A 20-gallon spawning tank is adequate. The water should be soft and acidic with a pH of 6.5 to 6.8, a hardness around 1.5 to 3° dGH, and a temperature of 77 to 82.4° F (25 to 28° C). Provide bunches of live plants, java moss, or artificial spawning grass to give the female a place to deposit the eggs. A layer of mesh works, too, if it is wide enough for eggs to pass through but small enough to keep the parents out. A small, air-powered sponge filter is needed for filtration and water flow. Filtering the water through aquarium-safe peat will encourage this fish to spawn.

They can be spawned in pairs or in a group, with 2 males for every female. To optimize breeding success, condition the males and females in separate tanks prior to breeding. Feed them a rich diet that includes plenty of small, live foods for about 14 days. Select a breeding pair or group and transfer them into the breeding tank in the evening. A mature female’s belly will become nicely rounded when she is full of eggs. Choose males that are the most colorful.

The tank should be brightly lit to induce spawning. They may spawn immediately, or it may take a day or two, even up to 6, to start. The male will chase the female through the plants, then they will sink down in the tank and spawn side-by-side with a quivering motion. The females will scatter up to 300 round, transparent eggs, which will sink to the bottom.

Once a successful spawn has been achieved, remove the parents, so they don’t eat the eggs. At this point, keep the tank very dim as the eggs are sensitive to light. Any eggs that whiten and start to look fuzzy are developing a fungal growth. Remove these to prevent fungus from spreading. The fertilized eggs will hatch in about 6 to 7 days, and the fry will be free-swimming right away. The newly hatched fry are large enough to eat freshly-hatched brine shrimp, rotifers, or finely crushed flake food. See Breeding Freshwater Fish: Characins for a general description of breeding processes, and see Fish Food for Fry for information about types of foods for raising the young.

  • Ease of Breeding: Moderate – Getting a pair to spawn is moderately difficult. Peat-filtered water and morning sunlight conditions can help initiate a spawn.

Fish Diseases

The Congo Tetras are fairly hardy and disease is not usually a problem in a well-maintained aquarium. However, they are prone to developing ich if kept in colder temperatures. Also, remember that anything you add to your tank can introduce disease. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so as not to upset the balance.

A good thing about Congo Tetra is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if dealt with at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your fish the proper environment and a well-balanced diet. The more closely their environment resembles their natural habitat, the less stress the fish will have, making them healthier and happier. A stressed fish is more likely to acquire disease.

As with most fish, Congo Tetras are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


The Congo Tetra is readily available but more expensive than many tetras.


 Phenacogrammus interruptus (Image Credit: André Karwath aka Aka, Wikimedia Commons CC BY-SA 2.5 Generic)