All Hail the Emperor Tetras!

Mike Hellweg

Since the early days of the aquarium hobby, tetras have always been among the most popular of aquarium fishes. Many tetra species have just the right combination of traits to be perfect aquarium residents. They are attractive, easy to care for, hardy, adaptable, and colorful. Many of them also school, making a more impactful display by swimming or at least hanging around in a group, and they don’t harm tankmates. They also breed readily and are easily raised in large numbers by commercial fish farmers. Many tetras are so important to the hobby that they are considered “bread-and-butter” fishes—staples of the trade—and can be found in just about every pet shop in the world. In addition to these staple species, some tetra species are regularly available and have the same benefits mentioned above, but for some inexplicable reason just haven’t quite caught on to the same extent. This is where the so-called emperor tetras come in. 

Emperor tetras have a slightly more regal bearing than some of the smaller tetras. While capable of moving very quickly, they seem to swim with purpose, unlike the skittering of some of the smaller tetras. They like to be out in the open where all can see them. Their overall appearance, with their somewhat subdued but no less beautiful coloration, their slower, more stately swimming style, and the beautiful extensions of the dorsal and caudal fins really suit their imperial title.

Meet the Species

They are so different from the more common tetras that when the famed ichthyologist Carl Eigenmann described the first species in 1911, he created a new genus with one of the defining features being the triple extensions of the caudal fin on the males. Unlike most tetras, they lack an adipose fin. This was the emperor tetra, Nematobrycon palmeri, from western Colombia. 

Eigenmann described a second species in 1914, N. amphiloxus, but subsequent generations of ichthyologists decided that this is simply a color morph or locality variant of N. palmeri. In 1971, a third species was added to the genus, the rainbow emperor tetra (N. lacortei). Then, in 1977, a fourth emperor tetra was described, and it received its own genus. Smaller in size and lacking the caudal extensions of its imperial cousins, Inpaichthys kerri has several common names—blue emperor tetra, royal emperor, purple emperor, or just the kerri tetra. While the genus Nematobrycon comes from Colombia, Inpaichthys comes from Brazil. 

N. palmeri has a beautiful grayish-blue color above the lateral line and a wide, deep black band below it. In some populations (the former N. amphiloxus), the black extends into the lower half of the caudal fin and the anal fin. The anal fin in males of most populations is bordered with black and yellow. Even when young, it is easy to sex them, as males begin to develop extensions to the caudal fin rays when they are only about three months old. In addition, males have a blue iris and females have a gold iris. I have seen some males that are more greenish above the lateral line, and some that are more of a smoky gray in that area. They have a chunky or stocky body. The larger males reach about 3 inches (7.5 cm), and females reach just over 2 inches (5 cm). They have been bred into a solid black sport that doesn’t grow quite as large. An albino has been available in the past, but I have not seen them in quite a long time. 

N. lacortei is the rainbow emperor tetra, sometimes called simply the rainbow tetra. They have a thick dark-blue to black line just under the lateral line that extends through the central caudal extension with scattered reds, blues, and yellows on the body and fins. The spectacular adult males have a deep-purple coloration above the dark stripe that often covers the entire back. Males have bright-red irises, and females have a greenish-blue iris. Males can top 1¾ inches (4.5 cm), while females rarely top 1½ inches (4 cm), not including the tail. 

Inpaichthys kerri is the blue emperor tetra. They are the smallest of the emperor tetras, rarely topping 1½ inches (4 cm), and are a bit more slender overall. They have an adipose fin, which is blue in males and red in females, and a wide black band that runs from the nose to the base of the caudal fin. Male blue emperor tetras have a slate-blue coloration over much of the body that often somewhat overshadows the dark line. In some populations the male has a deep-red dorsal, anal, and caudal, while in other populations these fins are just pale orange. They do not have extensions on the caudal fin. There are a couple of sports that have shown up in the trade; one is deep, dark blue, and one is a solid slate-blue with bright-red fins. Unfortunately, both sports seem to be a bit sensitive to water quality and shipping, so they are rarely seen.

Water Parameters

In the wild, emperor tetras are lowland fishes found in slower-flowing clear water streams. Here they are found in small groups, in open water, near cover. Wild water parameters are described as pH around or just below neutral (7.0), total hardness up to just over 200 ppm, and temperatures from the low to upper 70s F (low to mid 20s C). In other words, they’re not that picky about water parameters. I have had great success with keeping and breeding all of them in both harder, more alkaline water with a pH around 7.5 and in softer, more acidic water with a pH around 6.5. All of my tanks in my fishroom are maintained without heaters, with those on higher rows being a bit warmer and those on lower rows a bit cooler. I have successfully kept and bred emperors on all three rows of my racks, so they don’t seem to be too demanding as to temperature.

Give Them a Home

Choose a longer, lower tank over a shorter, higher tank of the same volume. My favorite tank for emperors is a 20-gallon (76-liter) long. This can be a perfect home for a group of six to eight emperors, a few Corydoras, a pair of Apistogramma, and maybe a small Ancistrus or two. Plants aren’t necessary, as the emperors prefer the open water, but do give them someplace to hide. A tangle of spider wood and a big pile of oak leaves or similar leaves for aquaria will work just fine. Add a few floating plants like some of the larger Salvinia, water sprite, frogbit, or something similar to give them a sense of comfort. A single Echinodorus sp. swordplant or a small thicket of Cryptocoryne will satisfy your green thumb without filling the tank. Of course, if you want to keep them in a well-planted community tank, they will be happy there, too. 

Any type of commercial filter will work just fine. Just make sure to regularly maintain it. I don’t know how many times I have had people come to me asking for help with their fish only to find out they have not cleaned the filter in months. Water changes are also important. While many folks say one water change a month is sufficient, I strongly recommend at least one water change every week to 10 days.


In the wild, they are micropredators that consume small insects, crustaceans, and worms, and they are not above eating their own or other fish’s eggs or fry. In our tanks, they will eat all types of commercial foods, including flakes and pellets. They should get an occasional treat of meaty frozen foods like brine shrimp, small mysis shrimp, bloodworms, and similar fare. 

One of the foods they absolutely love is finely ground shrimp. I’m talking about the shrimp purchased in the grocery store. Buy a pound, pull a few shrimp out for your fish, and eat the rest yourself! Peel them and put them in a small sifter, use the back of a spoon to crush them, and then rinse the sifter into a container of dechlorinated water. Use a baster to feed them to your fish. You will be amazed—they are like a school of tiny piranhas going after the shrimp!


If you have both sexes and give them a lot of water changes and plenty of good food, especially meaty foods as described above, they will do what comes naturally and spawn. In a planted community tank, a youngster or two will occasionally appear. If you really want to try and get them to spawn for you, it is best to use a separate tank. There are two different methods for getting them to spawn, the permanent setup and the temporary setup.

Permanent Breeding Setup

The permanent setup is my preferred method, though it takes longer to get going and is less productive than the temporary setup. In my opinion, it is easier to maintain and produces just enough young to share with friends or trade to a local shop without producing hundreds of fry, which can become overwhelming to a casual hobbyist. 

It is fairly simple. Set up a 10-gallon (38-liter) tank with a mature sponge filter and a large (roughly football-size) pile of Java moss (Vesicularia dubyana). Unless you have liquid rock for water, try the setup first with your local water. Only start to modify parameters if you don’t have any success after a few months (more on how to do that below). Add a couple pairs of adult emperors and start feeding them daily with frozen foods like bloodworms, various shrimp, and shredded market shrimp. After about two weeks, start adding newly hatched baby brine shrimp.

If all goes well, you should start seeing baby emperors under the Java moss after about three weeks. Once you start seeing youngsters, remove the adults back to the community tank. You can leave the adults in the tank permanently, but production will be considerably lower. Continue feeding the fry baby brine shrimp, and after another 10 days or so start adding very finely shredded market shrimp. I also add a few snails to clean up any uneaten food at this time.  This method should produce a dozen or so young fish.

Temporary Breeding Setup

The temporary method requires a bit more work. Separate the males and females for a week or so and feed twice a day with meaty live and/or frozen foods. After a week to 10 days, add the adults to a 10-gallon (38-liter) tank set up as above late in the evening. They will spawn the next morning and should be done in a few hours.  Remove the adults and wait. After a week or so, you should see a large number of tiny fish swimming just above and just under the Java moss. 

At this time, you can start feeding them such items as microworms, newly hatched brine shrimp, and finely ground commercial foods. As before, add a few snails to help clean up any uneaten food. Depending on the age and size of the females, this method can produce several hundred youngsters. Be prepared with more food, more maintenance, and after a month or so, a larger tank to grow them out.

Modifying the Water

If you have really hard water or don’t have success with your tap water after a few tries, it is time to try and modify your water. The simplest method is to use RO water or collect rainwater or melted snow. Mix it about 50-50 with your local tap water and try that for a month or so. Another method is to use a 5-gallon (19-liter) bucket, fill it with dechlorinated tap water, and add a box filter filled with peat moss. After three days, change out the peat in the filter and run it for another three days. The water in the bucket should look like strong tea. Add this in a ratio of about 1:3 to your local water and try that for a month or so. One of these methods should provide you with good-quality spawning water without too much effort. As the fry grow, be sure to slowly change them over to your local tap water.

Regal Beauties

The emperor tetras are beautiful additions to our hobby. They are hardy, easy to keep, and easy to breed. I still can’t figure out why they aren’t as available in the hobby as some of the other tetras. If you want something to add a bit of regal beauty in your tank, they are worth seeking out. Even if you just want something different to add to your planted community tank, emperor tetras are a perfect choice. 

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