Phenacogrammus interruptus

The Congo Tetra, Phenacogrammus interruptus, is a distinguished member of the Alestidae family, often referred to as African Tetras. Originating from the fast-flowing tributaries and pools of the Congo River basin in Africa, its natural habitat shapes its aquarium requirements. These environments are typically characterized by soft, slightly acidic water with a moderate current, which should be replicated in captivity through good filtration and water movement. A well-oxygenated environment is crucial for this active species. Its streamlined, fusiform body is an evolutionary adaptation for navigating these currents, making it a graceful and energetic swimmer.

In an aquarium setting, recreating their natural social structure is paramount for their well-being. They are a shoaling species that relies on the presence of its own kind for security. A group of at least six is the minimum, though larger groups are highly recommended. In a proper shoal, they will exhibit more confidence and fascinating group dynamics. Without a group, they can become shy, stressed, and prone to illness. Their active nature means they spend most of their time in the top and middle regions of the tank, requiring a setup that provides substantial open space for swimming. A longer tank is preferable to a taller one to accommodate their horizontal swimming patterns. While open space is key, they also appreciate planted areas along the sides and back of the aquarium, which provide security and a place to retreat. Dim lighting can also help to mimic their natural environment and encourage more active behavior.

As omnivores, their diet in the wild consists of insects, crustaceans, and plant matter. In captivity, they are not particularly fussy eaters but thrive on variety. A high-quality flake or pellet food can form their dietary base, but it should be regularly supplemented with frozen and live foods such as daphnia, brine shrimp, and bloodworms. This varied diet is essential for maintaining their health and vitality. Due to their medium metabolism and waste production, a robust filtration system is necessary to manage the bioload and maintain the stable, clean water conditions they require. They are sensitive to poor water quality and sudden changes in parameters, making them better suited for aquarists with some experience in maintaining a stable aquatic environment.

Phenacogrammus interruptus is a species of characiform fish belonging to the family Alestidae, a group commonly known as African tetras. Its classification places it within the order Characiformes, which it shares with its more numerous South American cousins, the characins. However, its origin from the Congo River basin in Africa distinguishes it phylogenetically and ecologically. The species name 'interruptus' refers to the broken or incomplete lateral line, a morphological characteristic of the species.

Its body plan is fusiform, a classic torpedo-like shape that is hydrodynamically efficient for life in habitats with moderate water flow. This morphology, combined with a medium metabolic rate, supports its classification as an active swimmer. Physiologically, it has a moderate oxygen consumption rate, underscoring the need for well-aerated water, a condition typical of its native riverine environment. Water chemistry in its natural habitat is soft and slightly acidic to neutral. The species exhibits a moderate tolerance range for pH and water hardness, though it thrives in conditions that mimic the dark, tannin-stained waters of its origin.

Ecologically, P. interruptus is an omnivore, occupying a trophic level where it feeds on a wide range of available food sources, including small invertebrates, zooplankton, and phytoplanktons. This dietary flexibility contributes to its success in its natural ecosystem. In terms of social structure, it is a shoaling species, a behavior that serves as a defense mechanism against predation and facilitates foraging and reproduction. Sexual dimorphism is pronounced in mature specimens. Males are distinguished by the significant elongation of the fin rays, particularly in the dorsal, caudal, and anal fins, a trait driven by sexual selection. Its current IUCN Red List status is Least Concern (LC), indicating that the species is not currently at high risk of extinction in the wild, with widespread and stable populations.

Successfully breeding this species is considered a moderately difficult but achievable endeavor for the dedicated hobbyist. To begin, a separate breeding aquarium should be established. This tank should feature soft, acidic water and be kept at the warmer end of the species' preferred temperature range. Subdued lighting is critical, as bright light can inhibit spawning behavior. The tank should be furnished with fine-leaved plants, such as Java moss, or artificial spawning mops. These provide a suitable medium for the female to deposit her adhesive eggs and offer some protection from the parents.

Sexual dimorphism is quite pronounced, making it easy to select a breeding group. Males are larger and develop spectacular, flowing extensions on their dorsal and caudal fins, which are absent in females. Females are typically smaller and have a rounder, fuller body shape, especially when conditioned for breeding. For a successful attempt, condition the fish separately or in the main tank with a rich diet of live and frozen foods for several weeks. A good ratio for a spawning group is one male to two or three females, which helps prevent any single female from bearing the full brunt of a male's persistent courtship.

Once conditioned and introduced to the breeding tank, spawning often occurs in the early morning. The male will chase and display to the female, guiding her into the plants where they will release eggs and milt simultaneously. They are egg-scatterers and exhibit no parental care; in fact, they will readily consume their own eggs. Therefore, the adult fish must be removed from the tank immediately after spawning is complete. The eggs will hatch in approximately six days. The fry will initially sustain themselves by absorbing their yolk sac. Once they become free-swimming, they are extremely small and must be fed infusoria or a commercially available liquid fry food. As they grow over the first week, they can be transitioned to larger foods like newly hatched brine shrimp and microworms. Maintaining pristine water quality through small, frequent water changes is crucial for the survival and healthy development of the delicate fry.