The Red Eye Tetra, Moenkhausia sanctaefilomenae, has a number of other common names, these include: Yellowhead Characin, Lamp Eye, Yellow back Moenkhausia, Yellowhead Tetra, and Yellow-banded moenkhausia. The Red Eye Tetra comes from eastern Bolivia, western Brazil, eastern Peru and Paraguay in South America. The maximum length of the Red Eye Tetra is about 3 inches (8cm) although most are much less than this. The likely life span is about 5 years.
The preferred temperature range of this species is 23 – 28 degrees C (73 – 82 degrees F) although they will survive a little outside this. I would note that their natural range actually goes outside the tropics, so there might be some populations that are more cold resistant, but I have never tried the Red Eye Tetra in an unheated tank, and I do not recommend this.
In the wild they mainly come from soft, slightly acid water, but they can adapt even to hard alkaline water, so they are happy in a normal community aquarium of mixed fish with a temperature of 24 degrees C (75 degrees F), neutral acidity and some hardness.
The Red Eye Tetra is an omnivore and readily eats all normal aquarium foods. They will benefit from a variety, including live food like mosquito larvae and Daphnia as well as frozen food like Blood worms.
Most sources list the Red Eye Tetra as being peaceful. This is not quite my experience and I regard it as often being a problem to some fish. I would not put Red Eye Tetras with Siamese Fighting Fish, Guppies, Endlers Guppies, Neon Tetras or Cardinal Tetras.
More suitable companions include Silvertip Tetras, Gold Barbs, Cherry Barbs, Pristella Tetras, Rummy Nose Tetras, Harlequin Rasboras, Scissortail Rasboras, Lemon Tetras, Emperor Tetras, Head and Tail Light Tetras, Glass Bloodfin Tetras, Swordtails, Platies, Mollies, Zebra Danios, Glowlight Tetras, White Cloud Mountain Minnows, Black Widow Tetras, Rosy Barbs, Tiger Barbs, Paraguay Tetras, Buenos Aires Tetras and Colombian Tetras; as well as the Corydoras catfish like the Peppered Catfish.
However, even with these fish, I would be cautious in matching the sizes of the fish in the aquarium. Remember that the Red Eye Tetra grows bigger than some of these other fish.
The Red Eye Tetra is a schooling fish, and I would always try to keep at least 6, and preferably more together. This should reduce their fin nipping tendencies.
There is not a big difference in appearance between the sexes of the Red EyeTetra. When the females have eggs, they will appear fatter with a more rounded, and, perhaps, lighter belly.
To breed the Red Eye Tetra it is necessary to have very soft, slightly acidic water with floating plants. They will lay their eggs among the roots of the floating plants, although many of the eggs may still end up on the bottom of the tank. The parents will eat their eggs and babies, so they are normally removed after spawning.
The eggs should hatch in about one or two days, and the fry should be free swimming a few days later. The baby Red Eye Tetras are slightly bigger than the babies of most tetras and they are vigorous and not as hard to raise as some egg laying fish babies are.
They will eat fine live food and commercial fry foods as soon as they are free swimming. Although protozoa (infusoria) are certainly eaten at first, the babies are big enough to not be totally dependent on these.
The Red Eye Tetra has the potential to damage fragile aquatic ecosystems and care should be taken to prevent their release.