Red eyed tetra - Moenkhausia sanctaefilomenae

Scientific name: Moenkhausia sanctaefilomenae

Common name: Red eyed tetra

Family: Characidae

Usual size in fish tanks: 5 - 7 cm (1.97 - 2.76 inch)

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Recommended pH range: 6 - 7.5

Recommended water hardness: 5 - 12°N (89.29 - 214.29ppm)

0°C 32°F30°C 86°F

Recommended temperature range: 22 - 28 °C (71.6 - 82.4°F)

The way how these fish reproduce: Spawning

Where the species comes from: South America

Temperament to its own species: peaceful

Temperament toward other fish species: peaceful

Usual place in the tank: Middle levels

General Information

The Red-eyed tetra (Moenkhausia sanctaefilomenae) is a hardy, active characin native to the São Francisco and upper Paraná–Paraguay–Uruguay (La Plata) basins of eastern & central South America. Adults typically reach 5–7 cm and show a silver body, red eye ring, and a black-white tail band. Keep them in shoals of 8–10 for best behavior and color.

Food & Feeding

Omnivorous micro-predator/grazer. Use quality flakes or small sinking granules as staple; rotate frozen/live foods (baby brine shrimp, daphnia, cyclops, finely chopped bloodworms). Include some vegetable matter (spirulina, blanched greens). Feed small portions 1–2× daily.

Sexing

Females are deeper-bodied and fuller when gravid; males slimmer. Color pattern is otherwise similar.

Breeding

An egg-scattering free-spawner with no parental care. Use a separate, dim tank with very soft, slightly acidic water, fine plants/spawning mops or marbles, and remove adults post-spawn (they eat eggs). Eggs generally hatch in ~24 hours; fry free-swim after a few days. Start with infusoria/green-water or commercial liquid fry food, then Artemia nauplii.

Lifespan

Typically ~5 years with clean, stable water and good diet.

Tank Requirements & Water Parameters

Tank size: long tank, at least 80–90 cm (32–36″) for a group; provide open mid-water lanes.
Water: pH ~6.0–7.5, hardness ~5–12 °dH (tolerates a bit harder), temperature 22–28 °C (72–82 °F). Keep nitrate low and parameters stable.
Aquascape: robust planting (edges/back), wood/roots, darker substrate and some floating plants to diffuse light; moderate flow and good oxygenation.
Maintenance: weekly water changes; avoid abrupt parameter swings.

Compatibility & Tank Mates

Peaceful but lively shoaler. Best with other robust, similarly sized community fish (larger tetras/rasboras, peaceful barbs/rainbows, Corydoras, small loricariids). Avoid very slow or long-finned species if the shoal is small—occasional nipping can occur when under-stocked or cramped.

Behaviour & Usual Place in the Tank

Spends most time in the middle levels, schooling in open water and diving into cover when startled. Provide both swimming space and shade.

Short Description

Red-eyed tetras are hardy, active community characins from the São Francisco and La Plata drainages. Keep them in sizeable groups in clean, well-oxygenated aquaria with mixed omnivorous fare. Breeding is achievable in very soft, slightly acidic, dim setups; eggs hatch in about a day.

Q&A

Where are they from? São Francisco and upper Paraná–Paraguay–Uruguay basins (Brazil, Paraguay, Argentina; also reported from Bolivia/Uruguay in the La Plata system).
How many should I keep? At least 8–10 to minimize nipping and show proper schooling.
Are they plant-safe? Generally yes with robust plants; grazing is mild compared to true plant-nippers.
Do the eggs need darkness? As with many tetras, low light improves hatch, but water softness/acidity and removing adults are the main keys.