Back to top

Emperor Tetra – Nematobrycon palmeri

Emperor Tetra

Tetras are amongst the most popular aquarium fishes. There are probably more than 150 distinct species of tetra from which the aquarist may choose and this includes a large number of visually stunning fishes that are bound to enhance any home aquarium.

Is the Emperor Tetra a good community fish? The Emperor Tetra is an excellent community fish and gets on with most small to medium-sized species. It is an ideal species for relatively inexperienced aquarists.  The Emperor Tetra has a blue/black band running beneath the eye-line into the tail. The male has a three-pronged caudal fin whilst that of the female is the normal two-pronged tail. The male has metallic blue eyes whilst the females’ are metallic green.

Key Facts

CategoryKey Facts
Common name(s)Emperor Tetra – also known as:
Imperial Blue Rainbow Tetra
Rainbow Tetra
Scientific nameNematobrycon palmeri
Originate fromAtrato and San Juan river basins in western Colombia in South America
Care requiredEasy to care for, truly impressive and hugely popular
TemperamentPlacid, shoaling fish
Colour & FormPearlescent scales with blue/black cental, horisontal stripe. Elegant, three-pronged tail, elongated dorsal fin and larger anal fin in males
LifespanUp to 6 years
Adult size2 inches
DietOmnivorous – eat aquatic insect larvae in nature
Aquarium size24 inches in length or greater
Compatible withMost other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches
Avoid keeping withLarge and/or aggressive species and fin-nippers
BreedingEasy if you put the fish in the right environment.
Water temp73 – 81 Fahrenheit
Water pH5.0 to 7.8
Water hardness (dGH or dH)Up to 25 dGH

Origins of the Emperor Tetra

Tetras, as a “family” of fishes belonging to the biological family Characidae are found in nature in Africa, Central America and South America.

The Emperor Tetra originates in the Atrato and San Juan river basins in western Colombia in South America where it shoals in thousands. The vast majority of Emperor Tetras available to aquarists are captive-bred.

Characteristics of the Emperor Tetra

As you can see, the Emperor Tetra is characterized by its almost pearlescent body which has a blue/black stripe running below the line of the eye towards and into the caudal fin. The Emperor Tetra will grow to up to 2 inches in the aquarium and live for around six years. 

Emperor Tetras prefer fairly neutral water with a pH of 5.0 to 7.8 with a temperature range between 73 and 82 degrees Fahrenheit and up to 25 dGH.

The Emperor Tetra is a shoaling fish and should be kept as a group of at least six fish, though a shoal of, say, ten or more fish is highly recommended. Having plenty of vegetation to break up lines of sight will also help to protect your Emperor Tetras from predation but it is obviously advised that Emperor Tetras are not kept with predatory species.

The eyes of the male are typically a metallic blue in colour whilst those of the female tend to be a metallic green.

The caudal fin of the male (above) has an additional, central prong not present in the female (below) but note that this could be nipped off in the hurly-burly of aquarium life. The dorsal fin of the male is somewhat elongated when compared with that of the female. The anal fin of the male is also deeper than that of the female along its length. All of the fins are more-or-less clear (hyaline), perhaps with a slightly yellow/ochre hue, except for the caudal fin which carries the blue/black line part or all of the way along its centre.

Emperor Tetra - Female
Emperor Tetra – Female

When the female is gravid (carrying eggs), her abdomen will be swollen, this is also a reliable way of sexing the fishes. 

The Emperor Tetra has a deeper body than, for example, a Neon Tetra, being more rhomboid in shape but remains quite streamlined when compared with other Tetras. 

The Emperor Tetra tends to inhabit the middle and upper areas of the aquarium (top to bottom). That said, it is a vigorous fish when breeding and will readily traverse the entire aquarium.

The Emperor Tetra is, by nature, a shoaling fish and it is generally recommended to purchase six or more fish, as their nature is to swim together as a shoal and they will tend to thrive much better as a shoal. Emperor Tetras are excellent community fish and are ideal for aquarists with moderate experience, as they don’t tend to have aggressive tendencies towards other species. It is advised not to include Emperor Tetras in an aquarium containing predatory species, as their wellbeing will rapidly deteriorate.

Emperor Tetras, like most rainforest species, prefer a shaded and well-planted tank, as they can hide from predation, so consider including floating leaves and/or allowing vegetation to grow so that it floats on the surface of the water to provide shade.

It is generally advised that the minimum tank size for Emperor Tetras should be one of 24 inches in length or more due to the shoaling nature of the species, which will enable a small shoal to move around freely. The tank should be well-planted but with clear areas where the fish can swim freely. The water should only have gentle movement.

The general rule for Tetras is that by keeping six or more of the same species in an aquarium they will be fully aware of which is male and which is female and they will act accordingly.

Most (but not all) Tetras have an additional fin which identifies them as being Tetras and the Emperor Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the Emperor Tetra you will observe a tiny, additional fin, known as the adipose fin. The purpose of this fin is not fully understood but, if it is present on a freshwater tropical fish then you can be pretty certain that the fish is a Tetra.

Tetra comes from the Greek word “Tetragonopterus” which means square-finned and appears to relate to the four fins on vertical plane of the fish (dorsal, adipose, caudal and anal fins) which span the central line of the fish (when viewed from above or below, front or rear) and are not present as a pair (e.g. the pectoral or pelvic fins).

Emperor Tetras – Video

How do Emperor Tetras breed?

Tetras, in general, will scatter eggs by laying them over fine plants such as Cabomba, Fontanalis or Java Moss.

Emperor Tetras, like most species, are noted to leap above the water surface during breeding and in general, so it is advised that the tank should be covered to mitigate the risk of losing fish.

As the female Emperor Tetra becomes ripe with eggs, the difference between the sexes becomes even more evident. If you plan to attempt to breed Emperor Tetras then it is recommended that you have a breeding tank prepared. Such a tank can be empty but you may wish to include a mesh or grid under which the fertilized eggs will fall and/or a sterilized breeding mop.

That said, Emperor Tetras will breed in a community tank and, if the tank is well planted, it is likely that at least a few fry may survive to reach adulthood.

Some say that a novice may find it difficult to breed Emperor Tetras but, in my experience, by understanding the conditions that are ideal for breeding, most species will breed quite readily, as it is natural for them so to do and, in general, nature finds a way.

I have observed Emperor Tetras breeding readily and vigorously in quite soft, neutral water (pH 7.0) and the general recommendation is a temperature of 80 to 82 degrees Fahrenheit

The female will swim vigorously around the tank and, if you include two males then they will encourage her to lay her eggs by bumping into her. She will lay her non-adhesive eggs which will immediately be fertilized by the male(s) and will fall to the bottom of the tank (preferably through the mesh or trap). Once spawning is complete, remove the adults, as they are likely to consume the eggs, given the chance, and take no further parental responsibility. A mature female may lay up to 50 eggs.

Spawning usually takes place in the early morning. In nature, Emperor Tetras spawn at the start of the rainy season.

Breeding tank for Emperor Tetras

You should prepare a tank of around 20 gallons in size with mature water. The water should be at a pH of around 7.0, ideally, around 80 to 82 degrees Fahrenheit with a low level of light.

You may wish to introduce mosquito larvae or bloodworm as an inducement to reproduction.

The female will swim amongst the plants, laying her eggs whilst the male will swim alongside or behind her and fertilize the eggs as they are laid. Typically, the female can lay around about 50 eggs during a spawning, which may adhere to plants or will sink to the bottom of the tank.

Once the female has scattered her eggs and the male has fertilized at least some of them then the adults should be removed carefully from the breeding tank because they will have nothing more to do with the eggs but they may simply eat them.

Keep the lights off and the tank dark because Tetra eggs and fry are particularly sensitive to the light.

The eggs will hatch typically in around three days or so depending on tank temperature and conditions and the fry will become free-swimming after around five to seven days after hatching. Keep the tank unlit for the first week or so then gradually increase the lighting.

The newly hatched fry will firstly feed on their yolk sac but, once free-swimming, can be fed infusoria (particularly rotifers) and will also thrive on egg yolk during the first two to four weeks. It is worth mentioning that immediately after hatching, fry seem quite vigorous but will soon go into a resting state before they become free-swimming so please don’t mistake this initial stage as being free-swimming.

After around four days or so add baby brine shrimp. Once the fry are sufficient in size not to be treated as a snack then they can be introduced into the community tank where they will join the existing shoal. Before moving the adolescent fish into the community tank ensure that you have balanced the water temperatures to mitigate the risk of White Spot or other diseases being triggered.

Should your Emperor Tetras have a special diet for breeding?

Adult Emperor Tetras don’t need any particular inducement to breed. That said, it has been suggested that adding mosquito larva may encourage them, presumably because the addition of a new food may “fool” the fish into thinking that it is breeding time. From my own experience, I would always recommend keeping all of your fish in the best possible condition at all times, as this is good for the wellbeing of your fish.

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

Recent Posts