Red-Eyed Tetra 101: Everything You Need to Know

Red-Eyed Tetra is a freshwater fish that’s famous for its striking red eyes and metallic silver bodies.

As schooling fish, they add dynamic movement and a touch of brilliance to any well-planned community tank. 

In this guide, I will explore the history, behavior, care requirements, and other essential aspects of keeping Red-Eyed Tetras, setting you on the path to creating a thriving underwater habitat for these enchanting fish.

Red-Eyed Tetra Summary

Common NamesRed-Eyed Tetra
Scientific NameMoenkhausia sanctaefilomenae
SpeciesM. sanctaefilomenae
ColorSilver body with a black band running across the eyes and a red patch on the upper half of the eye
SizeUp to 2 inches (5 cm)
LifespanUp to 5 years
pH Level6.0-7.5
Water Temperature72-79°F (22-26°C)
Water HardnessSoft to moderately hard (5-15 dGH)
Water TypeFreshwater
Minimum Tank Size20 gallons (76 liters)
Community TankYes
Care LevelEasy
CompatibilityPeaceful community fish such as other tetras, corydoras, rasboras, and peaceful livebearers

Red-Eyed Tetra History

Red-Eyed Tetras (Moenkhausia sanctaefilomenae) have a rich history that can be traced back to their native regions in South America. 

The Austrian ichthyologist Steindachner first discovered these tetras in 1907. 

The scientific name Moenkhausia sanctaefilomenae is derived from the combination of the genus Moenkhausia, which is named in honor of American zoologist William J. Moenkhaus.

The species name sanctaefilomenae, which is Latin for “St. Philomena,” is a Catholic saint. 

The fish were named after Saint Philomena, as they were first discovered in the vicinity of the Saint Philomena Church in Brazil.

The striking appearance and active, social behavior of these guys have made them a favorite among fish enthusiasts. 

They were introduced to the aquarium hobby in the early 20th century, quickly gaining popularity due to their hardy nature and compatibility with other peaceful fish species.

Over the years, breeders have successfully bred them in captivity, making them readily available in the aquarium trade. 

This has further contributed to their widespread popularity, as more people have had the opportunity to keep these fascinating fish in their home aquariums.

Red-Eyed Tetra Origin & Habitat

Red-Eyed Tetras are native to the Amazon River Basin, which spans multiple South American countries, including Brazil, Argentina, Paraguay, and Peru. 

The fish predominantly inhabit slow-moving rivers and streams, as well as flooded forests and swamps in these regions. 

Their natural environment is also characterized by soft, acidic waters with plenty of submerged vegetation and leaf litter, which provides them with ample hiding spots and food sources.

Red-Eyed Tetra Behavior

One of the most notable aspects of Red-Eyed Tetra’s behavior is their strong schooling instinct. 

These fish prefer to live in groups of at least 6 or more, and larger groups are even more beneficial for their well-being. 

In the wild, schooling offers numerous advantages, such as increased protection from predators, improved foraging opportunities, and more efficient use of energy while swimming.

In an aquarium setting, Red-Eyed Tetras maintain their schooling behavior, swimming together in a coordinated fashion. 

This group dynamic not only provides the fish with a sense of security but also creates an impressive visual display for aquarists.

They are also most active during the daytime when you can see them darting around the aquarium in search of food or interacting with their tank mates. 

These fish tend to occupy the middle to upper regions of the tank, which allows them to easily access both the surface and lower areas.

Although their active swimming patterns are not only visually appealing, they serve a functional purpose. 

By constantly moving, Red-Eyed Tetras are better able to evade potential predators and maintain their position within the school.

What Are the Features of Red-Eyed Tetra?

1. Appearance

Red-Eyed Tetras have a compressed, elongated body shape that is typical of many Tetra species. 

This streamlined form allows them to move quickly and efficiently through the water, making them highly adept at maneuvering in their natural habitats and aquariums alike. 

Their body is also relatively slender, with a prominent dorsal fin and a forked caudal (tail) fin that contributes to their agile swimming capabilities.

When it comes to coloration, they’ve predominantly silver bodies, with an iridescent sheen that can reflect a variety of colors under different lighting conditions. 

This shimmering effect gives the fish a captivating appearance as they move through the water.

But one of the most striking features of the Red-Eyed Tetra is the bright red coloration around their eyes, which gives them their common name. 

This vivid red ring stands in stark contrast to the rest of their body, making it an easily recognizable characteristic of the species.

Running along the midline of their body, from the gill cover to the base of the caudal fin, is a bold black stripe. 

This dark stripe further accentuates the tetra’s vibrant appearance and creates an eye-catching contrast against the silver and red colors on their body.

Their fins are generally transparent, with a slight yellow or orange tint in some individuals. 

Their anal and dorsal fins may also display subtle black markings, adding to the overall visual appeal of these fish.

2. Body Size

Red-Eyed Tetras are small fish, with adults typically reaching a length of 1.5 to 2 inches (3.8 to 5 cm). 

Their small size makes them well-suited for community aquariums, where they can coexist with other similarly-sized, non-aggressive fish species.

Red-Eyed Tetra Lifespan

With proper care and optimal living conditions, Red-Eyed Tetras can live for up to 5 years in captivity.

Red-Eyed Tetra Life Cycle

Stage 1: Egg

The life cycle of Red-Eyed Tetras begins with the fertilized eggs, which are scattered by the female among plants or other submerged surfaces in their environment. 

The eggs are small, transparent, and adhesive, allowing them to stick to the chosen surfaces. 

After fertilization, the eggs develop for 24 to 36 hours before hatching.

Stage 2: Fry (Larval Stage)

Once the eggs hatch, the Red-Eyed Tetra fry emerge as tiny, fragile larvae with a yolk sac attached to their bodies. 

This yolk sac provides essential nutrients for the first few days of their lives. 

During this stage, the fry are highly vulnerable and require a safe, stable environment to ensure their survival.

Stage 3: Fry (Free-Swimming Stage)

As the Red-Eyed Tetra fry grow and absorb their yolk sacs, they transition into the free-swimming stage. 

At this point, they will begin to actively search for food, consuming microscopic organisms like infusoria or newly hatched brine shrimp. 

The fry gradually develop the characteristic body shape and coloration of adult Red-Eyed Tetras during this stage, which lasts for several weeks.

Stage 4: Juvenile

After the fry stage, Red-Eyed Tetras enter the juvenile phase, characterized by rapid growth and maturation. 

During this time, the fish continue to develop their adult coloration and body shape, becoming more adept at swimming and interacting with their environment. 

You should feed them a varied diet of high-quality, appropriately sized foods to support their growth and development.

Stage 5: Adult

Once Red-Eyed Tetras reach full maturity at around 6 months of age, they enter the adult stage of their life cycle. 

At this point, they will display their vibrant colors and distinctive body shape, as well as exhibit their social and schooling behaviors. 

These guys are now capable of reproduction and require proper care, including a suitable environment and a balanced diet, to ensure their health and longevity.

Stage 6: Senescence

As Red-Eyed Tetras age, they enter the senescence stage of their life cycle. 

During this time, their energy levels, growth rate, and reproductive capabilities may decline. 

But providing optimal care, including a well-maintained environment and a balanced diet, can help support the health and well-being of Red-Eyed Tetras during their senior years.

Is Red-Eyed Tetra Hardy?

Red-Eyed Tetras are hardy fish that can adapt well to various water conditions. However, they still require proper care and a stable environment to thrive.

How to Care for Red-Eyed Tetra?

a.Water Requirements

1. Water Quality

Water quality is a crucial factor in maintaining the health and well-being of aquarium fish, including Red-Eyed Tetras. 

And performing regular water changes is a key component of maintaining good water quality. 

For Red-Eyed Tetras, you should change about 25-30% of the tank water every 1-2 weeks. 

Here’s a basic guide to performing water changes:

  • Fill a clean container with tap water and treat it with a water conditioner to neutralize chlorine and chloramines
  • Adjust the temperature, pH, and hardness to match the existing aquarium water
  • Before starting the water change, switch off the heater, filter, and any other equipment to prevent damage or injury
  • Use a siphon or gravel vacuum to remove 25-30% of the tank water. The gravel vacuum will also help clean the substrate by removing debris and uneaten food
  • If needed, clean any algae buildup or debris from decorations, filter media, and other equipment
  • Avoid using any chemicals or soap, as they can be harmful to your fish
  • Slowly pour the prepared water into the tank, ensuring the temperature and other parameters remain stable. This will help prevent stress and shock to your fish
  • Once the water change is complete, turn the heater, filter, and other equipment back on
  • Test the water to ensure that the temperature, pH, hardness, and levels of ammonia, nitrite, and nitrate are within the appropriate range for Red-Eyed Tetras

2. Water Temperature

Red-Eyed Tetras thrive in water temperatures between 72-79°F (22-26°C). 

To maintain the appropriate water temperature for Red-Eyed Tetras, you should select a reliable and adjustable aquarium heater with the appropriate wattage for your tank size. 

Generally, 3-5 watts per gallon of water is ideal. For example, a 20-gallon tank would require a 60-100 watt heater.

You can also place a thermometer in the tank, preferably at the opposite end of the heater, to monitor the water temperature accurately. 

This will help you make any necessary adjustments to the heater settings.

Don’t forget to make sure the room where your aquarium is located has a stable temperature, avoiding any drafts or direct sunlight that may cause sudden changes in the water temperature.

3. pH Level

The pH level indicates the acidity or alkalinity of the water, with a pH of 7 being neutral, below 7 being acidic and above 7 being alkaline.

Red-Eyed Tetras prefer a slightly acidic to neutral pH, with an optimal range of 6.0-7.5. 

To regularly test the pH of your aquarium water, you can use a pH test kit or digital pH meter. 

This will help you monitor the pH level and make necessary adjustments.

If the pH is outside the optimal range, you can use pH buffers or natural solutions to adjust it. 

To lower the pH, you can use commercial pH reducers, peat moss, or driftwood. 

On the other hand, if you want to raise the pH, you can use commercial pH increasers or add crushed coral or limestone to the aquarium.

You should also know that some substrates and decorations can affect the pH of your aquarium water. 

So, you should use a neutral or slightly acidic substrate, such as sand or fine gravel, and avoid using materials that can significantly raise the pH, such as coral sand or limestone.

4. Water Hardness

Water hardness is a measure of the concentration of minerals, primarily calcium and magnesium, dissolved in water. 

There are two types of water hardness: general hardness (GH) and carbonate hardness (KH). 

General hardness refers to the total amount of calcium and magnesium in the water, while carbonate hardness refers to the concentration of carbonate and bicarbonate ions.

Red-Eyed Tetras prefer soft to moderately hard water, with a general hardness (GH) range of 5-15 degrees of hardness (dGH). 

So, you need to keep track of these levels in the aquarium water by testing the hardness of your aquarium water using a GH and KH test kit. 

This will help you determine if adjustments are necessary to maintain the appropriate hardness level for your buddies.

If you need to soften the water, you can dilute the aquarium water with distilled water or reverse osmosis (RO) water, which has a lower mineral content. 

Alternatively, you can use peat moss or specialized water-softening resins in your aquarium filter, which can help reduce the mineral content of the water.

If you need to increase the water hardness, you can add crushed coral, limestone, or commercial products designed to raise GH and KH levels. 

But be sure to add these materials gradually and monitor the water hardness to avoid sudden fluctuations, which can stress your fish.

b.Tank Requirements

1. Tank Size

Tank size is an essential aspect of keeping Red-Eyed Tetras healthy and happy, as it directly impacts their swimming space, water quality, and overall well-being. 

These guys are schooling fish, which means they prefer to be in groups of at least 6-8 individuals. 

When they’re in a group, they exhibit more natural behaviors and feel less stressed.

For a group of 6-8 Red-Eyed Tetras, the minimum tank size should be 20 gallons. This size provides adequate space for the fish to swim freely and comfortably. 

But if you plan to keep a larger group or house them with other compatible fish species, you should consider a larger tank size. 

As a general rule, the larger the tank, the better, as it allows for greater swimming space and more stable water parameters.

When selecting a tank for your tetras, I prefer to choose a tank with a larger surface area rather than a tall, narrow tank.

2. Decorations

Decorations play a significant role in creating a comfortable and visually appealing environment for your Red-Eyed Tetras. 

They provide hiding spots, mimic their natural habitat, and contribute to the overall aesthetics of the aquarium. 

ed-Eyed Tetras come from densely planted habitats in the wild, and they appreciate the presence of live plants in the aquarium. 

So, you can provide them with plants like Java Fern, Anubias, Amazon Sword, and Cryptocoryne, as they can thrive in the same water conditions as these tetras. 

In fact, live plants also offer additional benefits, such as oxygenating the water, providing cover, and reducing stress.

Another thing you can add is driftwood. It can create a natural-looking environment, offer hiding spots, and contribute to the water’s slight acidity. 

But ensure the driftwood is aquarium-safe and you’ve been properly cleaned and soaked it to remove any tannins or contaminants.

Red-Eyed Tetras also appreciate having hiding spots to retreat to when they feel stressed or threatened. 

You can create caves and shelters using rocks, such as slate or river rocks, ensuring they are aquarium-safe and have no sharp edges that could injure the fish.

3. Lighting

Just like humans, Red-Eyed Tetras need a proper balance of light and darkness to thrive. 

Providing moderate intensity lighting with a full spectrum and maintaining a consistent 10-12 hour photoperiod will ensure a comfortable environment for your fish.

I actually prefer using LED lights as they’re an energy-efficient and adjustable option to achieve the ideal lighting conditions.

Red-Eyed Tetra Compatibility

Red-Eyed Tetras (Moenkhausia sanctaefilomenae) are peaceful, schooling fish that thrive in community aquariums with other similarly-sized, non-aggressive species. 

When selecting tank mates for them, you should consider their compatibility to ensure a harmonious environment for all inhabitants. 

Here is a table outlining good and bad tank mates for these guys:

Good Tank MatesCompatibility ReasonBad Tank MatesIncompatibility Reason
Neon TetrasPeaceful, schooling fish with similar environmental needsCichlidsAggressive and territorial fish that may harass Red-Eyed Tetras
Cardinal TetrasNon-aggressive, schooling fish that share similar preferencesOscarsLarge, predatory fish that may consume smaller tank mates
Rummy Nose Tetras Peaceful, shoaling fish that coexist well with Red-Eyed TetrasArowanasPredatory fish with the potential to prey on Red-Eyed Tetras
Harlequin RasborasGentle temperament and similar sizeJack DempseysAggressive cichlids that may attack peaceful fish
Galaxy RasborasSmall, non-aggressive fish that thrive in community tanksRedtail CatfishLarge, predatory fish unsuitable for community aquariums
GuppiesPeaceful livebearers that can coexist with Red-Eyed TetrasFlowerhorn CichlidsTerritorial and aggressive fish incompatible with Red-Eyed Tetras
MolliesNon-aggressive fish with a similar size and disposition
PlatiesPeaceful tank mates suitable for community aquariums
Cherry BarbsCalm, community-oriented fish with a similar size
Gold BarbsNon-aggressive fish that can coexist in a community tank
Corydoras CatfishPeaceful bottom dwellers that won’t compete for space

Red-Eyed Tetra Feeding & Diet

In their natural habitat, Red-Eyed Tetras consume a variety of food sources, including small insects, crustaceans, and plant matter.

In captivity, you should provide them with a balanced diet to mimic their natural feeding habits. Some suitable food options for these tetras in captivity include:

  • High-quality flake or pellet food
  • Frozen brine shrimp
  • Frozen daphnia
  • Frozen bloodworms
  • Live foods, such as brine shrimp, daphnia, or mosquito larvae
  • Chopped vegetables, such as spinach, lettuce, or zucchini

When it comes to feeding frequency, you need to feed them small amounts of food 2-3 times per day, adjusting the quantity as needed to prevent overfeeding. 

Here’s an example feeding schedule for a week that I already use for my Red Eyed Tetras:

MonFlake foodFrozen brine shrimpLive daphnia
TuePellet foodFrozen bloodwormsFlake food
WedFlake foodChopped vegetablesFrozen brine shrimp
ThuPellet foodFrozen daphniaFlake food
FriFlake foodLive brine shrimpFrozen bloodworms
SatPellet foodChopped vegetablesFlake food
SunFlake foodLive mosquito larvaeFrozen daphnia

Red-Eyed Tetra Breeding

1. Preparing for Breeding

Before attempting to breed Red-Eyed Tetras, it’s crucial to provide them with an optimal environment that encourages spawning. 

First, you should provide a separate breeding tank, as it allows you to control the conditions and protect the eggs and fry from being eaten by other fish in the community tank.

The breeding tank should be around 10-20 gallons in size, with a sponge filter for gentle filtration and a heater to maintain a consistent temperature. 

You should also place fine-leaved plants or spawning mops in the tank to provide cover and a suitable location for the female to deposit her eggs. 

Further, maintain a water temperature of 77-82°F (25-28°C), with a pH of 6.0-7.0 and soft water hardness.

Before introducing your Red-Eyed Tetras to the breeding tank, condition them with high-quality, protein-rich foods like live or frozen brine shrimp, daphnia, or bloodworms. 

This will help improve their overall health and increase the chances of successful breeding.

2. Spawning

Introduce a pair of healthy, mature Red-Eyed Tetras (one male and one female) into the breeding tank. 

The male will typically display more vibrant coloration and have a more streamlined body, while the female will be rounder, particularly when filled with eggs.

Once they’re in the breeding tank, the male will court the female by swimming around her and displaying his colors. 

If the female is receptive, she will lay about 300 eggs on the fine-leaved plants or spawning mops. 

The male will then fertilize the eggs as they are being laid. 

3. Post-Spawning Care

After the eggs have been laid and fertilized, you should remove the adult Red-Eyed Tetras from the breeding tank, as they may consume the eggs or fry. 

The eggs will hatch within 24-48 hours, depending on the water temperature.

4. Raising the Fry

Once the eggs have hatched, the fry will initially feed on their yolk sacs for nourishment. 

After 3-4 days, when they consume the yolk sacs, start feeding the fry with infusoria or commercially available fry food. 

Gradually introduce larger foods, such as baby brine shrimp and microworms, as the fry grow.

Within 6-8 weeks, the fry will begin to resemble adult Red-Eyed Tetras and can be introduced to a community tank with compatible tank mates.

Red-Eyed Tetra Common Diseases

Like all fish, Red-Eyed Tetras are susceptible to various diseases that can impact their health and well-being.

Here is a table with the common diseases that might affect Red-Eyed Tetras, along with their causes, symptoms, treatments, and prevention strategies:

IchParasite (Ichthyophthirius multifiliis)White spots, increased mucus, rapid breathingAnti-parasitic medicationMaintain water quality, quarantine new fish
Fin RotBacterial infection (Aeromonas, Pseudomonas)Fins deteriorating, frayingAntibacterial medicationMaintain water quality, avoid overcrowding
Swim Bladder DiseaseBacterial infection, parasites, constipation, injuryDifficulty maintaining buoyancy, abnormal swimmingTreat underlying causeProvide a balanced diet, maintain water quality
VelvetParasite (Oodinium spp.)Gold or rust-colored dust, clamped fins, rapid breathingCopper-based medicationMaintain water quality, quarantine new fish
DropsyBacterial infection, kidney dysfunctionSwollen abdomen, raised scales, loss of appetiteAntibacterial medication, Epsom salt bathsMaintain water quality, provide balanced diet
Pop-EyeBacterial infection, injury, poor water qualityProtruding eyesAntibacterial medication, water changesMaintain water quality, provide suitable tank setup
Gill FlukesParasite (Dactylogyrus spp.)Rapid breathing, gasping, excess mucus productionPraziquantel or similar medicationMaintain water quality, quarantine new fish
Hole-in-the-HeadNutritional deficiency, poor water quality, parasitesPits or holes on the head and face, weight lossImprove diet, water changes, an anti-parasitic medicationProvide a balanced diet, maintain water quality


Is Red Eye Tetra Aggressive?

Red-Eyed Tetra is not an aggressive fish. It is a great addition to community tanks with other similarly-sized, peaceful species. 

How Big Do Red-Eyed Tetras Get?

Red-Eyed Tetras typically grow up to 2 inches (5 cm) in length. Their relatively small size makes them suitable for a variety of aquarium sizes, but it’s important to ensure they have enough space to swim and school comfortably. 

How Do You Take Care of a Red Eye Tetra?

To take care of Red-Eyed Tetras, you should do the following:

  • Maintain good water quality by performing regular water changes and testing the water parameters
  • Keep the water temperature between 72-79°F (22-26°C), with a pH range of 6.0-7.5 and a hardness level of 5-15 dGH
  • Provide a well-decorated tank with plenty of hiding spots, live plants, and moderate lighting
  • Feed them a balanced diet of high-quality flakes or pellets, supplemented with live or frozen foods like brine shrimp and bloodworms

Are Red Eye Tetras Hardy?

Red-Eyed Tetras are relatively hardy fish, making them suitable for both beginner and experienced aquarists. 

They can adapt to a variety of water parameters, but it’s essential to maintain stable conditions and avoid sudden fluctuations to keep them healthy. 


As promised, we’ve covered everything you need to know about Red-Eyed Tetras in this comprehensive guide. 

From their fascinating history and captivating behavior to their specific care requirements, you’re now equipped with the knowledge to create a thriving environment for these stunning fish. 

With dedication and a keen understanding of their needs, you’ll be able to appreciate the beauty and excitement these enchanting fish bring to your aquarium for years to come.

Do you still have questions? If so, leave a comment and I’ll be happy to answer them.

Leave a Reply

Your email address will not be published. Required fields are marked *