Moenkhausia sanctaefilomenae (Red-eye tetra)

Moenkhausia sanctaefilomenae or the Red-eye tetra belongs to the Characidae family and Characiformes order. The species may also be known as Tetragonopterus sanctaefilomenae. Other common names of the species are Lamp-eye tetra and yellow-banded Moenkhausia. The Moencausia genus consists of about 50 species or more that have many similarities with some of them difficult to distinguish from Moenkhausia sanctaefilomenae by aquarists. However, in the aquarium industry, the Red-eye tetra is mainly M. sanctaefilomenae and captive bred in Asia.
The species is native of South America (Peru, Bolivia, Brazil, Paraguay, Argentina). The Red-eye tetra inhibits clear water rivers that are slightly acidic to neutral with minimum vegetation. Furthermore, the species occurs also in slow-moving waters of jungle streams and tributaries, as well as filtered lighting, dense vegetation, driftwoods, and submerged roots of trees. The water parameters of the natural habitat of the Red-eye tetra, as with other tetra species’ habitat usually are low in minerals and nutrients and rich in humic acids due to the decay of organic matter such as woods and leaves which indicates that the water parameters are soft and acidic.
Red-eye tetra has a flat, silver body with a vertically elongated black patch on the base of the caudal fin that sometimes fades when the species are stressed. Furthermore, near the black spot, there is a yellow band. Above the eye, the iris has a red pigmentation which is the reason for the famous common name of M. Sanctaefilomenae, the Red-eye tetra. There is also a balloon belly Red eye tetra form due to the selective breeding.
An interesting fact about the red-eye tetra is you can recognize it from its relative, the Glass tetra (M.oligolepsis) from its yellow band in the caudal peduncle.
In general, tetras are difficult to sex but, male tetras are thinner and sometimes smaller while mature female tetras have a round abdomen that is more apparent when female tetras are ready to spawn. Furthermore, males are more colorful sometimes than females during mating.
Red-eye tetras are slightly larger than the usual size of tetras and grow up to 7.5 cm (3 inches) and have a lifespan of 4 years.
Red-eye tetra like Glowlight and Serpae tetra is an excellent choice for beginners because of his hardiness and easiness of reproduction. They are schooling fish that should be kept in groups of 8 individuals (minimum) and more.
The species are known to be highly energetic, somewhat peaceful tetra and a good choice for community tanks. However, Red-eye tetras are not as aggressive as Serpae tetras, but in smaller numbers and tanks their aggression intensifies. They also bully one another to establish a pecking order. You can decrease their aggressiveness by increasing their numbers and place them in bigger tanks with lots of plants and hiding spots.
On the other hand, other species or tetras may pick on Red-eye tetras at a time. I remember when I was working in a pet shop, the Serpae tetras were fin nipping a lonely red-eye tetra which I removed and placed on a different tank. It could also be the opposite as every individual has a different personality and the ”rules” do not apply every time. For that exact reason, I recommend keeping an eye on Red-eye tetras. They are compatible with corydoras, other tetras, barbs, danios, larger rasboras, etc. They are not compatible with boisterous or aggressive tank mates.
It is normal for a few days the old Red-eye tetras to bully the new ones to form a new hierarchy. It’s also common when you add new individuals to a new tank to get stressed (hiding behind objects, inactive, lose vividness of the color) for a few days until they adjust to the new environment. Other reasons (environmental issues) that may stress the fish and get inactive are other fish, small space to swim and high temperature.
Although Red-eye tetras can survive in a wide range of water parameters because of the natural habitat should be kept in soft acidic water. A pH between 6.0-7.5, with a temperature between 23-27 Celsius, and hardness between 100-150 mg/l, suits the species. An aquarium of 113 liters (30 gallons) could be enough for a group of 8-10 Red-eye tetras.
You may decorate the aquarium with sand or fine gravel, rocks, leaves, woods, and many plants to create hiding spots. Although Moenchausia Sanctaefilomenae may nibble some plants most of the aquarists never had that problem. Furthermore, they need plenty of space to swim freely.
Red-eye tetras are omnivorous and can eat prepared food (plant and animal based food) and small live-foods. You may also give some lettuce or similar plants food. In nature, their diet consists of crustaceans, insects’ larvae, worms, and plant matter, e.t.c.
Several tetra species are difficult to reproduce, but that is not the case with Red-eye tetras that spawn better at 26-27 Celcius dGH lower than 4 and 6,0-6,5 pH. Furthermore, you may cover the tank to create darkness with papers or other materials because tetras’ eggs and fry are sensitive to daylight. After twelve days the young are not susceptible to the light. A mixed diet with live food prior spawning attempt may help (5-7 days). Woods and leaves (almond leaves) benefit the process as they provide tannins and humic acids. The tank needs good aeration for the optimal health of the eggs. An air-powered sponge filter does the work. You may use a breeding tank of 40 liters (10 gallons) for better results for a pair or three females with three males in the tank.
Usually, the spawn begins the next day and lasts for 3-4 hours. Replace the individuals if no eggs have appeared for 2-3 days. Remove the adults If the spawning is successful to protect the eggs. Furthermore, you may use plants or/and cover the bottom of the tank with a net to protect the eggs from the adults. The female lays up to 100 eggs, which hatch in about 24-48 hours. Keep in mind that the temperature affects the eggs’ hatching period. For 3-5 days the young feed on the yolk sac, so in that period they don’t need food. After the consumption of the yolk sac, you can feed the young three times per day with newly hatched brine shrimp, infusoria, daphnia, crushed flake food, etc.

Red eye tetra Moenkhausia sanctaefilomenae Monk Tetra aquarium fish


  1. David Alderton 2005, 2008, Encyclopedia of aquarium and pond fish, Published in the United States by DK Publishing, ISBN 978-0-7566-3678-4
  2. Angela Beck 2014, Fish: keeping and care for your pet, Enslow Publishers Inc, ISBN 9780766041851
  3. Geoffrey Rogers 1985, Tropical fish, Multimedia publications (UK) LTD, ISBN 0831788569
  4. Moenkhausia sanctaefilomenae. Retrieved from
  5. Moenkhausia sanctaefilomenae TSN 162990.
    Retrieved from:

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