Red Eye Tetra: Species Overview

Category: Tetra

Common Names: Red Eye Tetra

Scientific Name: Moenkhausia sanctaefilomene

Family: Characidae

Minimum Tank Size: 30 Gallons

Care Level: Easy

Temperament: Peaceful

Max Size: 3 Inches

Temperature: 72-80 F

pH: 6.0-8.0

Tank Level: All

Colors: Silver, Black, Red

Diet: Omnivore

Breeding: Moderate

Red Eye Tetra with Plants in Background

Red Eye Tetra: Species Overview

Red eye tetras are on the large side for the tetra species, showcasing their classy metallic silver appearance and red highlight around their eye as they swim around the tank.

These peaceful fish are popular because they have lots of energy and are schooling fish, so they’re always up to something in the tank instead of staying hidden out of sight.

Unlike many species of tropical fish, red eye tetras have an excellent tolerance for changing water parameters. So, they’re a good fit for beginners.

Nevertheless, you’ll need to ensure the parameters stay within specific numbers to maximize your red eye tetra’s health and longevity.

Distinguishing Features

The most distinguishing feature of the red eye tetra is the bright red that circles the topmost part of the iris. It stands out beautifully against the silver color of the rest of its body, including the lower part of its eye.

Red eye tetras have an oval body. Although they’re primarily a metallic silver color, certain varieties have a yellow hue on the sides of their heads.

Many—but not all—red eye tetras also have an iridescent color on their gills and fins, depending on the lighting.

Despite having primarily transparent fins, red eye tetras feature a thick black mark at the start of their forked tail with a thin white highlight, making their tail appear smaller than it is.

Red eye tetras also have an anal fin that runs along their lower body, an abnormal feature for the tetra family.

School of Red Eye Tetras


Red eye tetras hail from freshwater rivers in several South American countries, including:

  • Eastern Bolivia
  • Eastern Peru
  • Western Brazil
  • Paraguay

They gravitate towards clear water, although it isn’t unheard of to encounter them living in cloudier water in the Amazon River.

The natural habitat of red eye tetras contains a combination of sand, pebbles, and mud. But these fish rarely visit the bottom of the river, given that they prefer to live in the middle to the upper portion of the water.

It’s common for red eye tetras to live in densely vegetative areas. River grass and giant water lilies are some of the plants they may encounter.


As adults, red eye tetras average 2.75 inches long. However, this species can sometimes grow as long as three inches if they have lots of space and high-quality food.

It’s common for females to grow slightly longer than males. But the difference in length is so minimal that it’s easier to notice males having a slightly thinner appearance than females.


Many red eye tetras live up to five years in captivity if you give them ideal living conditions.

That’s a higher-than-average lifespan compared to many tropical fish species.

The best way to help your red eye tetras live as long as possible is to keep their tank clean, be mindful of quarantining new fish, and maintain their ideal water parameters.


It isn’t always easy to tell the difference between male and female red eye tetras.

However, females have slightly thicker bodies than males. These fish get an even girthier appearance as they grow eggs in preparation for spawning.

In contrast, males have thinner bodies. They also develop deeper colors when they’re getting ready to mate to help them attract females.


Red eye tetras have an excellent temperament. They’re peaceful fish that get along well with many other species of a similar size.

Because these fish are so sociable, placing a minimum of six red eye tetras in one tank is vital. They don’t always school together, so it’s common to find them individually exploring other parts of the tank and greeting tank mates of different species.

Should you have fewer than six red eye tetras together, or worse, a single fish by itself, it’ll develop anxiety and stay in hiding.

There aren’t any noticeable differences between male and female red eye tetra temperaments.

Although red eye tetras are overall friendly, peaceful fish, they’re notorious for enjoying nipping at long fins on slow-moving fish.

Red Eye Tetra from the Side

Tank Parameters

If you’re ready to bring home a group of red eye tetras, follow the advice below for setting up their tank and water.

Minimum Tank Size

You should purchase a minimum 20-gallon tank for six red eye tetras.

That means you should increase the tank size by about 3.5 gallons for every additional tetra you want to add.

But the larger the tank you can offer your fish, the happier they’ll be.

Water Parameters

Below are the water parameters your aquarium must remain within for your red eye tetras to thrive.


Red eye tetras enjoy warm conditions, with 79°F to 80°F as their ideal temperature. However, they can handle water that ranges from 72°F to 84°F.

A tank heater is the best way to ensure the water remains at a temperature that your red eye tetras are comfortable with.


Your red eye tetras will be happy if your tank water has a pH of 5.5 to 8.5. That means they have an excellent tolerance for slightly acidic and basic water properties.

That said, keeping their water pH around neutral (7.0) is ideal.

You can use testing strips to monitor the water’s pH level.


As a freshwater species, there’s no need to add salt to your red eye tetra’s tank. But if you’d like to boost their immune system, adding a small amount of salt on occasion is safe.

Should you choose to add salt, ensure that it’s in the form of high-quality aquarium freshwater salt. The iodine in table salt can be deadly for your fish.

Tank Setup

Arranging your tank in a conducive way for your red eye tetra fish is equally as important as their water parameters. Below are tips on setting up your tank for success.


Your red eye tetras will spend little time at the bottom of their tank. So, the type of substrate you choose isn’t too important.

Nevertheless, we recommend selecting a dark substrate for two reasons: Red eye tetras are used to dark substrates in the wild, and it’ll help their metallic silver stand out even more in your tank.

Since we recommend using live plants in a red eye tetra trank, using sand or fine gravel substrate they can grow in is ideal.


When it comes to caring for red eye tetras, decorations are often more appealing to the owner than these fish.

Feel free to decorate the bottom of the tank however you’d like. Your red eye tetras won’t spend much time there.

But adding some floating driftwood or decoration that comes into the middle of the water column is an excellent option for giving your tetras some additional places to hide aside from plants.


Keeping plants in a red eye tetra’s tank is the most important type of “decoration” you can give them. These fish can get skittish at times, so they’ll feel comforted having a place to hide.

Red eye tetras are also accustomed to many aquatic plants in their natural habitat.

The best types of plants for red eye tetras are those that grow from the ground all the way to the top of the tank. Including plants that float at the top of the tank is also an excellent option.

Plants also help reduce light, which is something that these fish prefer.

Some of the best types of plants for red eye tetras include:

  • Java moss
  • Red lugwidia
  • Duckweed
  • Water wisteria
  • Tiger lotus

We recommend placing a thick layer of plants around the sides and back of your aquarium to ensure your red eye tetras have enough space for swimming.

By Jhartshorn [CC BY-SA 4.0]


Red eye tetras don’t live in places with lots of sunlight in nature. So, while a tank light is a good idea to help these fish maintain their circadian rhythm, keeping it lit on a dim setting is ideal.

If you have other fish in the tank that prefer a brighter light, the next best option is to section off a portion of your tank with a thick top plant cover.

That way, your red eye tetras can escape the brighter light.


A filter designed to manage the size of your fish tank is vital for keeping red eye tetras in good health.

The most common filters have mechanical and biological functions, helping to remove larger debris and toxins that are too small for the eye to see.

When setting up your filter, point it away from the area where your red eye tetras will swim (the middle of the tank). These fish live in areas with little water movement in the wild, so they’ll feel more comfortable without a filter generating a lot of turbulence.


We encourage you to purchase a heater for your red eye tetras, even if your home normally stays at or above 72°F.

That’s because these fish thrive in water with a consistent temperature. Furthermore, the red eye tetra’s preferred water temperature is around 80°F.

Be sure to buy a thermometer with your heater so that you’ll know if it starts to malfunction.


Red eye tetras are omnivores and require a varied diet to stay healthy. Some of the best foods to give them include:

  • Spinach
  • Daphnia
  • Tubifex
  • Brine shrimp
  • Flake food

You should feed your red eye tetra a minimum of two times per day, although three times per day is ideal.

These fish will gladly overeat, with some fish even being known for binge eating. So, allow them to eat as much as possible in three minutes before removing excess food.


It’s easy to breed red eye tetras, as these fish are prolific spawners.

You’ll first need a breeding tank with floating plants and a slightly acidic pH, and a water temperature between 80°F and 84°F. Then, choose about six males and six females that you’d like to mate.

Place these fish in separate tanks and prepare them for breeding by feeding them lots of high-quality protein.

Once the females get heavy with eggs and the males turn a more brilliant color, place them together in the breeding tank.

These fish have an interesting spawning behavior, with the male wrapping its body around the female as she releases about twelve eggs.

After this occurs, move the parents back to the original tank. Otherwise, they’ll eat the eggs and baby fish.

Common Diseases

No matter how careful you care for your red eye tetras, they can still have issues with diseases. But more often than not, a lack of proper water conditions or not quarantining new fish are the most common instigators of illness.

Some of the most frequent diseases that red eye tetras face include:

  • Ich
  • Fin rot
  • Red velvet disease
  • Bacterial infections
  • Skin flukes

Of these diseases, ich is among the most common. Ich is a parasite that rapidly transmits between tropical fish without direct contact because it gets into the water system.

While you can treat the water with ich medication, you’ll need to be persistent, as it’ll only kill ich during one phase of this parasite’s life cycle.

Red velvet disease and skin flukes are other parasitic infections caused by an infected fish arriving in an aquarium.

For this reason, we recommend quarantining any new fish—including your red eye tetras—before introducing them to a tank with others.

Finally, fin rot and bacterial infections most commonly plague red eye tetras living in tanks with dirty water. So, it’s vital to switch the filter media regularly and perform frequent partial water changes.

Potential Tank Mates

Many fish make excellent tank mates for red eye tetras. That said, you should keep long-finned fish like guppies and angelfish in a separate tank.

Some of the key features to look for when choosing tank mates is that the fish are of a similar size and are community-friendly.

Top and bottom-dwelling fish are especially ideal, given that your red eye tetras will rarely cross paths with them.

Some of the best potential tank mates for red eye tetras include:

  • Danios
  • Rainbowfish
  • Other tetras

Remember, you should keep a minimum of red eye tetras in your tank before adding tank mates.