Taxonomy & naming
Phenacogrammus interruptus was originally described by George Albert Boulenger in 1899 on material from the Congo Basin, and the parenthetical authority notation in the valid name reflects a subsequent generic reassignment. Eschmeyer's Catalog of Fishes records the valid combination as Phenacogrammus interruptus (Boulenger, 1899), placing the species in the genus Phenacogrammus within the family Alestidae — the African tetras, sometimes called African characins.
The genus Phenacogrammus is native to equatorial Africa and belongs to a group of alestids characterised by a strongly iridescent lateral sheen and, in males, extravagantly elongated median fin rays. Alestidae as a family has undergone considerable revision since Boulenger's era; the Congo tetra was at times placed in Alestes or in the wastebasket genus Hemigrammopetersius, but the current Phenacogrammus placement is well supported by morphological and molecular work. The GBIF backbone records 176 georeferenced occurrence records for the species, confirming its presence across a broad swathe of the Congo drainage.
The species epithet interruptus refers to the interrupted lateral-line patterning apparent in the type specimens. In aquarium literature the fish is most often sold simply as the Congo tetra, though some sources — particularly in mainland Europe — use 'Congo salmon' for the reddish glint males show in certain lights.
Morphology
Adult males reach around 3 in total length; females are distinctly smaller, typically topping out near 2.5 in. The body is fusiform and laterally compressed in the typical characid manner, deep enough to give the fish a broad lateral surface that maximises the play of iridescent colour without appearing stocky. The scales are large and reflective, producing the species' hallmark iridescence: a broad horizontal band running from behind the operculum to the caudal peduncle that shifts between gold, blue, green, and violet depending on viewing angle and illumination.
The dorsal, anal, and caudal fins of dominant males develop greatly elongated central rays that extend well beyond the fin margin, giving the fish an ethereal, trailing appearance in calm water. This elongation intensifies with age and condition; subordinate males and females show far less exaggeration of the fin tips, and females are generally plainer overall, with a silvery-gold base colouration lacking the intense lateral band of males. The caudal fin is forked, the adipose fin is present as in all characids, and the lateral line is complete though the scale pattern along it creates the 'interrupted' appearance referenced in the name.
Habitat
Phenacogrammus interruptus is native to the Congo River Basin — one of the world's largest drainage systems, spanning the Democratic Republic of Congo and the Republic of Congo. Within that vast basin the species is associated with the Middle Congo and its tributaries, inhabiting slow-moving to standing waters including pools, backwaters, and marginal zones where current is reduced and aquatic or riparian vegetation provides cover.
Water conditions in the Middle Congo Basin are typically soft and slightly acidic to neutral, stained with humic acids from the surrounding rainforest catchment. Recorded parameters include temperatures of 73–79 °F, pH between 6.0 and 8.0, and hardness in the range of approximately 4–18°N (degrees of German hardness). The species is a mid-water schooler that occupies open water above substrate and vegetation rather than hugging the bottom, and in its natural habitat it forms large, sociable groups that provide anti-predator benefits through schooling coherence.
Feeding
In the wild, Congo tetras are opportunistic omnivores feeding on small aquatic and terrestrial invertebrates — worms, insect larvae, small crustaceans, and insects fallen to the water surface — as well as plant matter and algae grazed from submerged vegetation. This mixed diet reflects the food-web richness of Congo Basin backwaters, where both animal prey and plant material are seasonally abundant.
In the aquarium the species accepts virtually any appropriately sized food offered, making it straightforward to feed. High-quality flake and micro-pellets form a practical staple, but colour and breeding condition benefit significantly from regular supplements of live or frozen foods: bloodworm, Daphnia, brine shrimp, and small worms all elicit an enthusiastic response. Some vegetable matter — blanched spinach, algae wafers, or spirulina-based flake — rounds out the diet in a way that mirrors the omnivorous natural feeding. Because the fish is an active, constant feeder, small meals offered two or three times daily suit it better than a single large ration.
Mating
Phenacogrammus interruptus is an egg-scattering spawner. Males court females through persistent lateral displays, orienting alongside a receptive female and quivering while the fins are fully spread, showing off the trailing fin extensions to maximum effect. In a well-maintained group, dominant males will display near-continuously, and the intensity of courtship increases in the morning hours and after water changes that simulate the onset of rains.
Spawning pairs move into fine-leaved vegetation or among plant roots at the tank margins, where eggs are released and fertilised in small batches during each pass through the plants. Because spawning is loosely continuous rather than a discrete event, males maintain their courtship displays across extended periods, and a group with multiple competing males tends to show more vigorous colour and display behaviour than a single isolated pair. Females can lay up to approximately 300 eggs over a spawning session according to FishBase data, with eggs settling among or adhering lightly to fine plant material.
Breeding
Breeding Congo tetras in captivity is achievable but moderately demanding, requiring attention to water quality and the willingness to raise fry separately. Conditioning with live and frozen foods over several weeks before a planned spawning improves egg quality and the number of eggs produced. The breeding tank should be furnished with fine-leaved plants such as Java moss, or with synthetic spawning mops, to receive the adhesive eggs.
Spawning occurs in the morning; after the adults are removed or the eggs and plant material transferred to a separate container, the eggs hatch within approximately five to six days at 79 °F. Fry are initially large enough that first foods can include newly hatched brine shrimp nauplii as well as fine powder foods and infusoria; they are sensitive to poor water quality in the early weeks, so frequent small water changes and careful feeding management are important. Growth is steady under good conditions, but full male colouration and fin development take many months to express. Aquarium-bred stock is available from specialist retailers and hobbyists, and represents the overwhelming majority of Congo tetras traded today.
In the aquarium
Congo tetras are peaceful, active schooling fish that do best in groups of six or more. A school of at least eight allows the social hierarchy among males to develop naturally while providing adequate companionship for timid individuals. Given that males reach 3 in and are strong, continuous swimmers, a tank of at least 39.5–47 in in length gives the group the open mid-water swimming space they need to move comfortably in formation.
Water chemistry should broadly match the natural Congo Basin parameters: soft to moderately hard, slightly acidic to neutral (pH 6.0–7.5), and at temperatures between 23 and 79 °F. The species does not require extreme softness or high acidity to thrive, but hard alkaline water can dull the iridescent colouration and suppress breeding. A planted aquarium with dark substrate and subdued or indirect lighting brings out the lateral iridescence most effectively; a bare or brightly lit setup tends to bleach the colours. Tankmates should be peaceful, similarly sized, and not so nippy as to damage the trailing fin rays — other mid-water tetras, calm barbs, peaceful cichlids, and Corydoras catfish make compatible companions. Avoid large or aggressive species, and avoid fin-nippers such as tiger barbs.
Conservation
Phenacogrammus interruptus is assessed as Least Concern (LC) on the IUCN Red List, most recently under the 2025-2 assessment version. The species benefits from an expansive range across the Middle Congo Basin — one of the most biodiverse and hydrologically intact large river systems on Earth — and is not known to face acute threats at the population level. The Congo Basin's scale and relative inaccessibility have limited the habitat degradation and agricultural conversion that have affected other African river systems.
The Congo tetra has been an aquarium staple since the mid-twentieth century, and a substantial captive-breeding industry in Europe and Southeast Asia means that most commercially traded individuals are tank-bred rather than wild-caught. This reduces any collection pressure on wild populations and has established robust captive populations across the hobby. The species' combination of a large, resilient wild population and a well-established captive breeding base makes its conservation outlook among the most secure of any popular aquarium tetra.