Congo tetra

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: may nibble soft.

Feeding

Omnivore with a larger appetite than most community tetras. Flake, micro and small pellets, frozen bloodworm, frozen brine shrimp, frozen daphnia, and live food (microworms, brine shrimp, blackworms) are all taken eagerly. The natural diet is worms, small insects, crustaceans, and plant matter, so include occasional vegetable content (spirulina flake, blanched peas, blanched spinach) for a balanced rotation. The species feeds primarily in the midwater column and will not compete much for food sinking to the substrate, so a separate sinking-food drop for bottom-dwellers doesn't cost much. Feed twice daily. The iridescent sheen on male scales is noticeably brighter on fish maintained on varied frozen and live food than on a dry-food-only diet.

Compatibility

• A larger peaceful tetra (males to about 8 cm, females to 6 cm) that needs a longer tank than most tetras to swim properly. Minimum tank for a group of six is around 200 litres and 120 cm long
• Males develop dramatic flowing fin extensions over 8 to 12 months. Do not house with known nippers: tiger barbs, serpae tetras, ruby/odessa barbs, or other species that target trailing fins
• Good companions are medium-sized peaceful species: rainbow fish, denison barbs, larger rasboras, kribensis and other peaceful African cichlids, peaceful catfish, and other large tetras
• Schooling species; groups of eight or more, with a balanced sex ratio, produce the strongest visual display because males compete for female attention by flaring colour and finnage
• Tank too small or tankmates too active produces a hiding, washed-out group; congos need space and calm to show natural behaviour
• African Congo-basin biotope works particularly well: subdued lighting, driftwood, anubias, and African catfish (Synodontis species or kribensis) create a coherent display with appropriate water parameters

Origin and habitat

A large characin from the African-tetra family Alestidae, endemic to the lower and middle Congo River basin across the Democratic Republic of the Congo and the Republic of the Congo. George Albert Boulenger described the species in 1899 as Micralestes interruptus from Congo specimens; Eigenmann established the genus Phenacogrammus in 1907 and the species was transferred. The genus name Phenacogrammus combines Greek phenax (deceptive) with gramma (letter or signal), referring to the characteristic interrupted lateral line on the body (the species epithet interruptus reinforces the feature), which served as the diagnostic trait distinguishing the genus from related African tetras. Alestidae diverged from South American characins (Characidae and related families) roughly 100 million years ago when the South American and African plates split during the breakup of Gondwana, which is why congo tetras share the body plan and feeding niche of South American tetras while being a different evolutionary lineage. Adult males reach about 8 cm TL, females about 6 cm. Sexual dimorphism is dramatic. Males develop iridescent scales running through blue, green, gold, and orange across the flanks; the dorsal fin elongates into a flowing tip, the anal fin extends backward, and the central rays of the caudal fin grow into long filamentous extensions that often outline a violet edge with white margins. Full colour and finnage development takes eight to twelve months. Females are smaller, rounder when gravid, and noticeably more subdued in colour, with no fin extensions. Despite being scientifically described in 1899, the species did not become widely available in the aquarium trade until the 1970s, largely because early captive-breeding attempts repeatedly failed; most fish in the trade today are commercially bred in the Far East and Eastern Europe. A peer-reviewed paper by Pecio (2008, Folia Biologica 57(1-2):13-21) examined spermiogenesis and spermatozoon ultrastructure in this species. Wild habitat is slow-flowing or quiet sections of forest-shaded Congo tributaries. IUCN Least Concern (Snoeks et al. 2010 assessment). Released aquarium fish are established invasive in Puerto Rico (USGS NAS).

Breeding

An egg-scatterer that is moderately difficult to breed at home but produces respectable clutches once conditions are right. Captive breeding requires soft, acidic water (pH around 6.0 to 6.5, GH below 5 dGH), a sizeable breeding tank (roughly 100 litres or more because the male drives the female across open water), fine-leaved plants or spawning mops, and dim or shaded light. After a conditioning period of one to two weeks on live and frozen food, spawning typically happens at dawn after the male chases and drives the female vigorously through the plants; Records show up to 300 eggs per spawn (sometimes more), which sink to the bottom rather than sticking to vegetation. Eggs are light-sensitive and benefit from shaded conditions. Adults do not guard eggs and eat them readily, so remove the pair immediately after spawning. Hatching takes about six days at typical aquarium temperature, longer than most South American tetras. Fry are relatively large and accept baby brine shrimp within a few days of becoming free-swimming. Growth is initially slow; males begin showing fin extensions at three to four months and reach full adult colour and finnage by eight to twelve months.

Common problems

Fin damage in males is the most visible issue. The male's elongated dorsal, anal, and caudal-fin filaments tear easily on sharp objects and are prime targets for fin-nipping tankmates (tiger barbs, serpae tetras, and similar species). Damaged fins regrow but the process can take weeks, and severely damaged or repeatedly bitten fins sometimes do not recover fully. Use smooth decor and avoid known nippers. Water-quality sensitivity makes the species a useful indicator: congos clamp fins, lose iridescence, and pale out before most community species show stress, so faded colour or shy behaviour in an otherwise healthy-looking tank is worth investigating. Ich and columnaris are the usual disease responses to those stressors. Medications need to be dosed conservatively because the species is moderately sensitive; reduce copper-based treatments and watch for stress. Jumping is occasionally a problem in tanks without lids, particularly with startled or harassed fish; a snug cover is a good idea. The biggest non-medical issue is undersized tanks: adult congos at 8 to 10 cm with active swimming and flowing fins need substantially more space than a typical 75-litre tetra community provides.

Bioload

Further reading

• Why your angelfish ate your neons
• Biotope aquariums: matching fish to their natural habitat
• The schooling number matters more than you think