Emperor Tetra: A Guide to Keeping and Caring for These Vibrant Freshwater Fish

Species Snapshot

• Species Name: Nematobrycon palmeri

• Common Names: emperor tetra, rainbow tetra, imperial blue tetra

• Size: 2-3 inches

• Lifespan: 6 years

• Native Distribution: Colombia, South America

At first glance, the emperor tetra (Nematobrycon palmeri), is easily identifiable as a tetra. But the closer you look, the more apparent it becomes how different these stunning fish are from other characids. Keep reading to find out what makes the emperor tetra so unique and to learn how to care for them in the home aquarium.

Anatomy and Appearance

Members of the family Characidae, emperor tetras share many physical characteristics with other tetras. Their bodies are long, stocky, and laterally compressed with a slightly rounded back that tapers toward either end of the body. They also exhibit a horizontal band of dark color that runs along the body and through the caudal fin.

Speaking of fins, this is where the emperor’s uniqueness from other tetras starts to become apparent. Emperor tetras do not have adipose fins. The fins of male emperor tetras are particularly stunning, growing longer as the fish matures. They’re one of the only tetra species in which the central ray of the caudal fin becomes elongated.

Another characteristic that differentiates emperor tetras from other tetra species is their sexual dimorphism. In many tetra species, physical differences between male and female fish are often subtle and may not become apparent until the fish reach maturity. With emperor tetras, however, differences appear early.

Males of the species have metallic blue eyes while females have metallic green eyes. In females, the dark horizontal stripe only extends partway through the tail while, in males, it extends all the way through and into an elongated third prong.

Ideal Aquarium Setup

Like many tetras, the emperor tetra makes an excellent addition to freshwater community tanks. They’re best kept in densely planted tanks with a dark substrate and subdued lighting that mimics their native Colombian river habitat. Here’s what you should know about setting up and maintaining a tank for emperor tetras:

Tank Size

While emperor tetras remain fairly small—males growing up to 3 inches long and females average 2 inches in length—they need enough tank space to swim and school. A minimum tank volume of 20 gallons is recommended and long rather than tall tanks are preferred.

Water Parameters

In their South American habitats, emperor tetras are found in clear, slow-flowing streams. They tend to prefer cooler water temperatures in the 70s °F along with slightly acidic pH and a moderate level of hardness.

Here are the ideal water parameter ranges for this species:

• Temperature: 73-80°F
• pH Level: 5.0-7.5
• Water Hardness: 18-215 ppm

While it’s always recommended that you mimic a species’ native environment as much as possible, emperor tetras are fairly adaptable. The key is to keep your tank’s parameters as stable as possible, as significant fluctuations in water chemistry or quality can be stressful or even harmful to your fish.

Proper filtration is essential for an emperor tetra tank, as these fish are naturally found in very clean water. If your water is very soft, you may want to consider adding peat to your filter but clean water with consistent parameters is more important. Be sure to install an aquarium heater to keep the tank temperature stable and perform routine water changes to maintain high water quality.

Tank Décor

As previously mentioned, planted tanks are ideal for emperor tetras but not necessarily a requirement. When kept in sufficient numbers, these tetras will make use of open swimming space but will appreciate having some kind of cover within reach. To give your emperor tetra tank a natural appearance, utilize aquarium plants like driftwood or spider wood décor and floating plants to diffuse overhead lighting.

Diet and Feeding

In the wild, emperor tetras are considered micro-predators. They feed primarily on small crustaceans, insects, and worms but will also consume fish eggs and fry. In captivity, emperor tetras generally accept a wide variety of commercial foods as long as they’re of an appropriate size. Stick to flakes and pellets as a staple diet, supplemented with the occasional meaty food like frozen bloodworms, fresh brine shrimp, or freeze-dried tubifex worms.

Temperament and Tank Mates

Though docile by nature like other tetras, the emperor tetra is less skittish than some. They prefer to be kept in groups with at least 5 or 6 of their own kind and can often be seen swimming confidently in a group rather than darting around the tank. It’s best to keep emperor tetras with other peaceful, slow-moving species.

Emperor tetras will get along just fine with dwarf cichlids, danios, rasboras and other tetras. They’re also a good fit for tanks stocked with gentle bottom-feeders like Corydoras catfish. If you’re going to keep emperor tetras with other tetras, consider choosing a species with a contrasting color palette to maximize your tank’s aesthetic appeal.

Breeding Emperor Tetras

Emperor tetras are egg scatterers and may breed with little provocation in a suitable tank environment. If you plan to breed emperor tetras, however, it’s best to start with a group of 6-10 so they can pair off as they mature. Because emperor tetras are sexually dimorphic from a young age, you may be able to compose a group with an equal number of male and female fish.

When your emperor tetras are mature and ready for breeding, it’s wise to separate each breeding pair into its own tank for spawning. To improve the odds of successful mating, separate the male and female for a few days while feeding them live and frozen foods.

The breeding tank should have very soft water with a neutral pH and a slightly warmer temperature of around 80°F. Be sure to provide a spawning mop or some kind of moss for the fish to deposit their eggs on. Emperor tetras can produce up to 100 eggs per spawning, and it’s wise to remove the adults before they can eat the eggs. The eggs will hatch after 24-48 hours, and the fry can be raised on small foods like infusoria and baby brine shrimp.