Moenkhausia sanctaefilomenae

The Red-eye Tetra is a hardy and active shoaling fish from South America, making it an excellent and popular choice for community aquariums and beginner keepers. They are known for their peaceful temperament and constant activity, primarily occupying the top and middle levels of the water column. As schooling fish, they thrive in groups and should be kept with several of their own kind to feel secure and display their most natural behaviors. A larger group helps them build confidence and creates a dazzling display as they swim together.

This species is not a picky eater and has an omnivorous diet. They will readily accept a variety of commercially available foods, including flakes and pellets, and will also appreciate occasional treats of frozen or live foods. Their adaptability to a wide range of water parameters makes them relatively easy to care for, provided the aquarium environment is kept stable and clean. With their energetic nature and peaceful disposition, they make a fantastic addition to a properly-sized community tank filled with other similarly-sized and tempered fish.

Native to the river basins of South America, the Red-eye Tetra is an adaptable and resilient species well-suited for the home aquarium. In its natural habitat, it inhabits slow-moving streams and tributaries, often with dense aquatic vegetation that provides cover from predators. To replicate this, an ideal aquarium setup should include both open swimming areas and heavily planted sections with driftwood or other decor. This mimics their environment and provides a sense of security, encouraging them to be more active. Gentle water flow is preferred, as they are not adapted to strong currents. As highly active and fast swimmers, ample horizontal swimming space is crucial to accommodate their energetic nature.

This species is a quintessential shoaling fish that defines its social structure by group dynamics. Keeping them in a sizeable school is not just a recommendation but a necessity for their well-being. A larger group dilutes aggression within the shoal, reduces stress, and promotes impressive, synchronized swimming behaviors. While generally peaceful, their boisterous activity can sometimes intimidate very timid or slow-moving tank mates. They are best housed with other active, robust fish of a similar size.

As omnivores, their dietary needs are straightforward but benefit immensely from variety. A high-quality flake or pellet food should form the staple of their diet, supplemented regularly with frozen or live foods like daphnia, brine shrimp, and bloodworms. This varied diet ensures they receive all necessary nutrients for robust health, strong immune function, and a long lifespan. Maintaining stable water quality is key, and due to their medium bioload and metabolism, a regular schedule of water changes and effective filtration is essential to manage waste and keep the environment healthy. Given proper care in a suitable environment, these fish can be a long-lived and dynamic centerpiece in a community aquarium.

Moenkhausia sanctaefilomenae is a freshwater fish belonging to the family Characidae, a large and highly diverse group within the order Characiformes. Its fusiform body shape is a classic morphological adaptation for sustained, active swimming in the water column, a characteristic trait of many species in its genus. This streamlined form minimizes drag, allowing for the efficient, fast-paced movement observed in aquarium settings. One of its most notable features is its large eyes, which may be an adaptation for foraging in the often dimly lit, vegetated waters of its native South American habitats, as well as for intraspecific communication and predator detection.

Ecologically, M. sanctaefilomenae occupies a niche as a mid-to-top water-dwelling omnivore. In the wild, its diet is likely varied, consisting of small insects, crustaceans, algae, and detritus found within its environment. This dietary flexibility contributes to its resilience and adaptability. The species exhibits a preference for low-flow aquatic environments, typical of floodplain lakes and slow-moving tributaries. Its physiological tolerance for a broad spectrum of pH levels and water hardness suggests an evolutionary history in habitats with fluctuating seasonal conditions. This adaptability is a key factor in its success and popularity in the aquarium trade.

From a conservation standpoint, the species is currently listed as Not Evaluated (NE) by the IUCN, indicating that its population status in the wild has not been formally assessed. While it is widespread and commonly bred in captivity, the lack of data highlights a gap in the scientific understanding of its wild populations and any potential threats they may face from habitat degradation or other environmental pressures. Its moderate metabolism, oxygen consumption, and waste production are consistent with a fish of its size and activity level.

Breeding the Red-eye Tetra is considered moderately difficult but is an achievable project for a dedicated aquarist. These fish are egg-scatterers and exhibit no parental care, often consuming their own eggs if given the chance. Success requires a separate, dedicated breeding aquarium.

To begin, a group of well-conditioned adult fish is needed. Conditioning involves feeding the potential parents a diet rich in live and frozen foods for several weeks to encourage egg and milt production. It is best to use a ratio of two or more females for every male to prevent a single female from bearing the full intensity of the male's spawning pursuits. Distinguishing between sexes can be subtle; females are typically larger and have a more rounded, robust body shape, especially when gravid (full of eggs), while males are generally more slender and streamlined.

The breeding tank should be equipped with soft, slightly acidic water. Subdued lighting is critical, as both the eggs and fry are light-sensitive. The tank floor should be covered with a mesh guard or a layer of marbles to allow eggs to fall through and be protected from the parents. Alternatively, dense clumps of fine-leaved plants like Java moss or synthetic spawning mops can be used to catch the adhesive eggs. A gentle, air-driven sponge filter is ideal to maintain water quality without creating a current that could harm the eggs or fry.

Spawning is often triggered by a small, gradual increase in water temperature followed by a significant water change with cooler, soft water to simulate natural rainfall. Spawning activity typically occurs in the early morning. Once spawning is complete and eggs are visible, the adult fish must be removed promptly. The eggs will hatch in approximately 24-36 hours. For the first few days, the newly hatched fry will feed on their yolk sacs. Once they are free-swimming, they must be provided with microscopic foods like infusoria or a commercial liquid fry food, progressing to baby brine shrimp and crushed flakes as they grow larger.