Rainbow Tetra (Nematobrycon lacortei): Full Care Guide

Rainbow tetras are superb freshwater fish that many aquarists want to own. But like any fish, it’s important to do your homework first!

This guide will teach you how to care for rainbow tetras and see them thrive in your aquarium.

Species Summary

The rainbow tetra (Nematobrycon lacortei) is a beautiful freshwater fish that you don’t see too often in the pet trade. It’s rarer and harder to find. But if you are lucky enough to own one, keeping these fish can be a rewarding experience.

A Rainbow Tetra swimming in a freshwater aquarium

This colorful species of fish is native to Colombia’s Rio San Juan River system. Specifically, they are endemic to tributaries of the Rio Calima. Their natural habitat is quite isolated.

The fish reside in slow-moving waters full of vegetation. There they can easily hide from potential predators and feed on abundant natural food sources.

Author’s note: Because their natural environments are so distinct, caring for these fish in captivity can be tricky. They are a favorite of experienced aquarists, as their needs are often too complex for new enthusiasts to handle.


There is no doubt that the Rainbow Tetra is a beauty! The fish gets its name from its iridescent glow. When light bounces off the body, the scales produce all the colors of the rainbow! The most common colors you’ll see are red and pink, but flashes of blue, green, purple, and more will also occur.

A darker colored line extends from the eye to the caudal fin. You can also see darker stripes on the unfolded anal fin and dorsal fin.

Like other types of tetras, the Rainbow Tetra has a torpedo-shaped body with a rounded head and large, protruding eyes. Males usually have bright red eyes, while females can have blue-green eyes.

Author’s note: Sexual dimorphism is fairly easy to spot through variation in eye color. Males are also generally more colorful and have more prominent fins. Meanwhile, females are plumper.

Average size of the rainbow tetra

These fish are not big at all. Pair their small size with their wobbly nature, and this species is ideal for small tanks (more on that later). As a group, they can create tons of stunning reflections as they swim around the tank.

The average size of an adult Rainbow Tetra is about an inch and a half long.


On average, a healthy Rainbow Tetra has a lifespan of three to five years. It’s not as long as some other fish, but it’s a typical lifespan for species of this size.

As always, there is no guarantee of life expectancy. Many factors can affect the health of a fish. Poor care and improper tank conditions could lead to illness and premature death.

Rainbow Tetra Care

Think you’re up for the challenge of caring for a Rainbow Tetra? You have a lot of work ahead of you!

These fish are considered the best for experienced aquarists in the pet trade. They have distinct needs to cover. Follow these care guidelines and you can enjoy their rugged nature and beautiful color for years to come.

tank size

Thanks to the small size of freshwater fish, you don’t need a huge tank to keep them happy. However, you will need more than one (more on that later).

The recommended tank size for a group of Rainbow Tetras is 20 to 30 gallons. Bigger isn’t always better, so try not to stray too far from this recommended size unless you plan on caring for a large group of fish.

Water parameters

Like any species of fish, the best course of action in Rainbow Tetra care is to replicate its natural habitat as closely as possible. Water conditions are crucial. This fish is relatively hardy, but it should stay within accepted parameters.

Failure to do so could cause unnecessary stress and illness. Test the water frequently and adhere to the following ranges.

  • Water temperature: 72°F to 80°F (Aim for the middle of the range)
  • pH levels: 6.0 to 7.2
  • Water hardness: 5 to 8GH

Author’s note: Getting an accurate aquarium water test kit will allow you to keep an eye on these parameters and make adjustments if necessary.

What to put in their tank

Here’s where you can have a little fun creating your Rainbow Tetra home. However, this is also where you need to be vigilant to meet the needs of your fish.

Start with a layer of a soft sand substrate. Rainbow tetras typically dwell in the middle and upper parts of the water column. However, sand is what you will find in its natural habitat.

You can take this illusion further by adding a few stray tree branches and fallen leaves to the substrate layer. Leaf litter is particularly beneficial. The leaves can release tannins into the water and provide a valuable food source when they decay.

Once the medium is ready, you can aim to recreate that thick vegetation that these fish are used to living in in the wild. You have a lot of flexibility in the types of plants you use, but you need to make sure that you use living vegetation and cultivars with abundant foliage.

Live plants can transform a reservoir into a living, breathing ecosystem. Plants improve the health of your fish and act as hiding places. These fish love to swim in and out of plants as they explore the environment in groups.

Any plant that matches the accepted water conditions of the Rainbow Tetra will do. Mix and match varieties and focus on creating density. Plants should provide ample cover and plenty of shade.

Author’s note: Live plants need strong lighting. Rainbow tetras can also benefit from a regular lighting schedule to maintain their circadian rhythm. About nine to ten hours of light per day is ideal for this species.

Common possible illnesses

Don’t let the little Rainbow Tetra fool you. It’s a tough little fish with a lot of courage!

But even still, these freshwater fish are not immune to health problems. They can suffer from all the usual problems.

The Ich is one of the most common encountered by aquarists. The disease affects stressed fish living in poor conditions. It’s a highly contagious disease that can wipe out entire tanks if you’re not careful.

Fortunately, it is easily treated with quarantine and over-the-counter medications.

Other potential health issues include fin rot and parasitic infections. The first problem is another caused by poor water conditions.

To avoid health complications, experts recommend changing about 10% of the water volume per week. This can keep ammonia and nitrate levels low and maintain water conditions.

Food and diet

Feeding Rainbow Tetras is a simple process. These fish are by no means picky eaters. They take what they can get and will enjoy it anyway. Thanks to their small size, Rainbow Tetras don’t eat much either.

Daily feedings are more than enough to sustain a group. Provide as much food as the fish can eat in two or three minutes, and you’ll be fine.

What food should we give them? Most aquarists recommend providing balanced commercial fish food as the staple food. Floating flakes and pellets are best.

Author’s note: If you want to treat your fish, you can occasionally offer them a great value snack. The Rainbow Tetra likes bloodworms, daphnia and mosquito larvae.

Behavior and temperament

Rainbow Tetras are a joy to watch. They spend most of their days swimming in groups and exploring the vegetation in the reservoir. As the light dances across their bodies, you can enjoy a shimmering burst of color.

Rainbow tetras are a shoal species, so you will need to keep several in a single tank. Between eight and ten fish are a good start. However, you can keep even more if you invest in a larger tank.

Don’t ignore the group rule. These fish are known to be semi-aggressive and territorial when not distracted by a school. They can pinch the most vulnerable fish, targeting those with long, fluttering fins.

Pinches are more than just a nuisance. They can lead to infection and possibly death of the target fish. Because rainbow tetras are small and agile, they are generally faster than the species they bully.

Avoid this nightmare and keep a group of Rainbow Tetras. In school, these fish are much more peaceful.

tank mates

The best tank mates for the Rainbow Tetra are other Rainbow Tetras! You can also keep other Tetra species of similar size in the same tank. They generally get along well and live together peacefully.

To avoid trouble, do not keep long-finned or slow-moving fish in the same tank as the Rainbow Tetra. Also avoid incompatible partners like Oscar fish, angelfish, or cichlids.

Instead, you can try similar-sized Tetras, fish in the family Characidae or Callichthyidae, and Apistogramma.


Raising Rainbow Tetras is not too difficult. Many times the fish will reproduce naturally without intervention. However, there are steps you can take to encourage adults to lay eggs.

Start by preparing a breeding tank. The water should have a low pH and warmer water. Keep the lights off and present a paired male and female.

Condition the fish with plenty of live food, and you’ll notice the female swarming with eggs. When this happens, add spawn mops or plants with abundant foliage. Unfortunately, rainbow tetras do not have a parental instinct, so they often eat the eggs and are young.

Plants and mops give babies a fighting chance.

Once ready, the female will scatter her eggs around the tank. It’s a slow process. The fish will lay eggs sporadically for several hours.

After about 36 hours, the eggs hatch and the fry survive in their bags for another day.

Once the fish are free-swimming, you can provide freshly hatched daphnia or brine shrimp. Keep babies separate from adults until they reach maturity.

Final Thoughts

Rainbow tetras are beautiful fish that we recommend to everyone. As long as you have the appropriate experience and can provide them with the conditions they need, we think they are a great choice!

As always, send us your questions. We are more than happy to lend a hand.

Leave a Comment