Rainbow Tetra (Nematobrycon lacortei): Full Care Guide

Rainbow Tetras are stunning freshwater fish that many aquarists are interested in owning. 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 tank.

Species Summary

The Rainbow Tetra (Nematobrycon lacortei) is a gorgeous freshwater fish that you don’t see too often in the pet trade. It’s on the rarer side and is more difficult to source. But if you’re lucky enough to own one, keeping these fish can be a rewarding experience.

A Rainbow Tetra swimming in a freshwater aquarium

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

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

Author Note: Because their natural environments are so distinct, caring for these fish in captivity can be tricky. They’re a favorite among skilled aquarists, as their needs are often too complex for newer enthusiasts to manage.

No Spam, Subscribe for Cool Fish Stuff!

* indicates required


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

A darker line of color stretches from the eye to the tailfin. You may also see darker stripes on the fanned-out anal fin and dorsal fin.

Like other types of tetras, the Rainbow Tetra has a torpedo-shaped body with a rounded head and large, beady eyes. Males usually have vibrant red eyes, while females may have bluish-green eyes.

Author Note: Sexual dimorphism is pretty easy to spot thanks to the variation in eye color. Males are also usually more colorful and have more prominent fins. Meanwhile, females are plumper.

Average Rainbow Tetra Size

These fish aren’t big at all. Pair their small size with their shoaling nature, and this species is ideal for small tanks (more on that later). As groups, they can create tons of stunning shimmer as they swim around the tank.

The average size of an adult Rainbow Tetra is about one and a half inches 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 that’s a typical lifespan for species of this size.

As always, there are no guarantees with life expectancy. Many factors can affect a fish’s health. Lackluster care and inadequate tank conditions could lead to disease and early 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 best for experienced aquarists in the pet trade. They have distinct needs to cover. Follow these care guidelines, and you can appreciate their hardy nature and beautiful color for years to come.

Tank Size

Thanks to the freshwater fish’s small stature, you don’t need a massive tank to keep them happy. However, you will need several of them (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 veer too far from that recommended size unless you plan on caring for a large group of fish.

Water Parameters

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

Failing to do so could cause unnecessary stress and illness. Test the water frequently and stick within 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 8 GH

Author Note: Getting an accurate aquarium water test kit will make it easy for you to keep an eye on these parameters and make adjustments when needed.

What To Put In Their Tank

Here’s where you can have a little fun creating your Rainbow Tetra home. However, it’s also where you need to be vigilant about meeting your fish’s needs.

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

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

Once the substrate is ready, you can set your sights on recreating that thick vegetation these fish are used to living among in the wild. You have plenty of flexibility in the types of plants you use, but you must ensure that you use live vegetation and cultivars with abundant foliage.

Live plants can turn a tank into a living, breathing ecosystem. The plants improve the health of your fish and act as hiding spaces. These fish love to swim in and out of plants as they explore the environment in a group.

Any plant that fits the accepted water conditions of the Rainbow Tetra will do. Mix and match varieties and focus on creating density. The plants should provide ample coverage and plenty of shade.

Author Note: With live plants comes a need for strong lighting. Rainbow Tetras can also benefit from a regular light schedule to maintain their circadian rhythm. Around nine to ten hours of light daily is ideal for this species.

Common Possible Diseases

Don’t let the tiny Rainbow Tetra fool you. It’s a tough little fish with plenty of grit!

But even still, these freshwater fish aren’t immune to health problems. They can suffer from all the usual issues.

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

Fortunately, it’s easy to treat with quarantine and over-the-counter medications.

Other potential health issues include fin rot and parasitic infections. The former problem is another one caused by bad water conditions. 

To avoid health complications, experts recommend changing roughly 10 percent of the water volume weekly. Doing so can keep ammonia and nitrate levels low and maintain water conditions.

Food & Diet

Feeding Rainbow Tetras is a straightforward process. These fish aren’t picky eaters by any means. They take what they can get and will appreciate it either way. Thanks to their small size, Rainbow Tetras don’t eat much either.

Daily feedings are more than enough to support a group. Provide as much food as the fish can eat in two or three minutes, and they will do fine.

What food should you feed them? Most aquarists recommend providing a balanced commercial fish food as a diet staple. Floating flakes and pellets are best.

Author Note: If you want to treat your fish, you can offer the occasional high-value snack. The Rainbow Tetra loves bloodworms, daphnia, and mosquito larvae.

Behavior & Temperament

Rainbow Tetras are a joy to watch. They spend most of their days swimming around as a group and exploring the vegetation in the tank. As the light dances over their bodies, you can enjoy a shimmer of sparkling color.

Rainbow Tetras are a shoaling species, so you’ll need to keep several in one tank. Between eight and ten fish are a good start. However, you can keep even more if you invest in a more voluminous tank.

Don’t ignore the group rule. These fish are notorious for being semi-aggressive and territorial when they don’t have the distraction of a shoal around. They can nip at more vulnerable fish, targeting those with long flowing fins.

The nips are more than just a nuisance. They can lead to infection and eventual death of the target fish. Because Rainbow Tetras are small and agile, they’re usually quicker than the species they bully.

Avoid that nightmare and keep a group of Rainbow Tetras. When shoaling, 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 similarly-sized Tetra species in the same tank. They usually get along fine and cohabitate in peace.

To avoid trouble, don’t keep any long-finned or slow-moving fish in the same tank as the Rainbow Tetra. Also, avoid incompatible mates like Oscar fish, Angelfish, or cichlids.

Instead, you can try similarly sized Tetras, fish that fall into the characidae or callichthyidae family, and Apistogramma.


Breeding Rainbow Tetras isn’t too challenging. Many times, the fish will spawn naturally without intervention. However, you can follow some steps to encourage adults to lay eggs.

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

Condition the fish with plenty of live food, and you’ll notice the female plump up with eggs. When this happens, add spawning mops or plants with ample foliage. Unfortunately, Rainbow Tetras don’t have parental instincts, so they often eat the eggs and are young.

The plants and mops give the babies a fighting chance of survival.

When ready, the female will scatter her eggs around the tank. This is a slow process. The fish will lay eggs sporadically over several hours.

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

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

Closing Thoughts

Rainbow Tetras are beautiful fish that we recommend to anyone. As long as you have the proper experience and can provide them with the conditions they need, we think they’re a great choice!

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

You May Also Like