Red eye tetra (Moenkhausia sanctaefilomenae)

Red eye tetra (lat. Moenkhausia sanctaefilomenae) once was the most spread and common tetras in a tank. A school of these characins can make any tank look nice and lively, but nowadays the fish has yielded the palm to other fishes. Is a peaceful active fish, quite easy in care. This fish needs to be in the school much more unlike it’s relative redeye tetra. Regardless of how many of them are in a tank: three, eight or twenty species – they always swim in a school.

Habitat in the wild

Moenkhausia sanctaefilomenae was first described in 1907. It inhabits in South America, Paraguay, Bolivia, Peru and Brazil. In the wild the fish lives in pure, flowing waters of big rivers, but sometimes it may swim to tributaries to search for feed in thick plants there. This is a schooling fish and it feeds on insects.


Max size is up to 7,5 cm (3 in) and its lifespan is about 3-5 years. Despite that there are a lot of species and subspecies of the fish, there are only two known to aquarists:

  • red eye tetra
  • balloon red eye tetra

The first one is a less schooling fish and it prefers to swim alone.

Compared to balloon tetra it is much smaller and it has more wide than long body, so it looks more rounded. Tetra has a very social behavior and it prefers swimming in schools of 5-6 fishes.

Difficulties in keeping

Care is easy since it’s not a demanding fish, so it’s good for beginner. As we’ve already mentioned – the fish is active, peaceful and if it is a balloon species, it also keeps the school well.

Care and keeping in a tank

Scientific NameMoenkhausia sanctaefilomenae
Common NameRed eye tetra, lamp eye tetra, red eyed fish, blood eye tetra, red eye monk tetra
Tank size15 gallon/65 litre
Temperature75–81 °F (24–27 °C)
pHpH around 6.5–7.0
Length2 3/4 inches (7 cm)

Fish prefers lower and middle water layers. It’s desirable to keep a school of 5-6 fishes or more in a tank of 15 gallons capacity minimum.

In the wild the fish habitat doesn’t have a lot of light, because the shores of the rivers have lots of greenery. It’s better if the tank has soft lighting which can be achieved by putting some fluctuants on the water.

Since the fish can jump, you should keep it in closed community tank (more than 40 cm long) with some shaded by the plants areas. Red eye tetra doesn’t like strong water flow, so make sure that the filter doesn’t create one.

Each week renew up to 20-25% of total water amount.

Compatibility and tank mates

The fish is good for community tanks at the condition that it’s kept in a school.

However, they may scare more calm fishes, since it’s very active, so you just have to choose the same active tank mates for it.

For example, it can be black skirt tetra, emperor tetra, cardinal tetra.

Also tetra may nip other fishes fins, so don’t keep them with long-finned fishes or other slow fishes with large fins, for example, with angelfishes.

If there’s no such possibility, you may smooth this kind of the fish behavior by keeping it in a school where the fishes have an hierarchy and they become busy with the species of their kind.


Fish is omnivorous and in a tank it feeds on all kinds of live, frozen or artificial feed. If you add some plant feed into the diet it’ll make the fish more healthy and brightly colored.

Gender differences: male vs female

The only real difference between male and the female is that the latter is more rounded and fat.


Become reproductive approximately at the age of 10 month. Breeding should take place in a separate tank from 2 gallons capacity, covered from top.

It should also have some Javan moss or Thai fern and a separating grid on the bottom. The tank water should be warmer (24-28 °C), acidic (6-6,8) and soft (до 6°). Before spawning you should prepare the fishes: put them is a separate tanks, feed well and add some plant food into the diet.

The fishes that were put into spawning tank in the evening start their mating game within the tank plants in the morning. The female lays up to 1000 sticky eggs that lay on the tank bottom or get stuck on the plants leaves.

At the end of spawning period the fishes are removed from the tank and you should start light aeration in it. The fish is very fruitful.

The eggs incubation time is about 1-2 days. On the 5-6th day larva become juveniles and they start feeding on small nauplii of brine shrimp.

The juveniles are very small from the beginning, therefore the brine shrimp should be small correspondingly, the same concerns cyclops nauplii, rotifers or infusorian (Paramecium). Juveniles grow slowly even despite well balanced and high diet.

About author: Sergey Schulz

Sergey is a founder and author of He’s been fond of aquarium husbandry since his early childhood. His favorite aquariums are biotopes (Amazon River), with Echinodorus and freshwater angelfish. However, through the years he’s had experience of keeping almost all types of freshwater fish and shrimps.