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Disk Tetra – Myleus schomburgkii

Disk 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 Disk Tetra a good community fish? The Disk Tetra could be an excellent community fish and gets on with most species and is most peaceful, bordering on timid. The issue is that the Disk Tetra will be around 16 inches long as an adult so small fish are likely to be seen as food.  The Disk Tetra is a rhomboid Tetra in shape. The Disk Tetra is quite easy to sex because the male extended rays on the leading edge of the dorsal fin.

Key Facts

CategoryKey Facts
Common name(s)Disk Tetra – also known as:
Disk pacu
Black-ear pacu
Black-band myleus
Black-barred myleus
Scientific nameMyleus schomburgkii
Originate fromMiddle and lower Amazon River basin, Nanay River, upper Orinoco River basin in Brazil, Peru, Venezuela and possibly in Suriname in South America
Care requiredEasy to care for by experienced aquarists
TemperamentVery placid, shoaling fish
Colour & FormSilver, almost circular body with, in mature adults, distinct, black, vertical stripe between pelvic and adal fin leading almost up to dorsal fin and generall gold finnage
LifespanUp to 10 years
Adult size16 inches
DietOmnivorous – eat aquatic insect larvae in nature but enjoy sald vegetables
Aquarium size72 inches in length (200 gallons) or greater
Compatible withLarge, peaceful species
Avoid keeping withSmall species (might be eaten) and any aggressive species
BreedingNot appropriate for the amateur but technically the same process as for any Tetra
Water temp73 – 81 Fahrenheit
Water pH5.0 to 7.0
Water hardness (dGH or dH)1 to 12 dGH

Origins of the Disk 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 Disk Tetra is found in the middle and lower Amazon River basin, Nanay River, upper Orinoco River basin in Brazil, Peru, Venezuela and possibly in Suriname in South America. The vast majority of Disk Tetras available to aquarists are captive-bred and the species is hugely popular. At the time of writing it is believed that the Disk Tetra has not been bred by the hobbyist mainly because the adult fish requires a tank of six feet in length and Tetras almost always consume their own eggs.

Characteristics of the Disk Tetra

As you can see, the Disk Tetra is characterized by its beautifully coloured silver body with gold fins. The Disk Tetra will grow to up to 16 inches (males) or 2.75 inches (females) in the aquarium and live for around ten years.

Being that the adult Disk Tetra is a very large fish, take extreme care when handling them, as they have extremely sharp teeth which can inflict injury. This Disk Tetra is closely related to another Tetra, namely the Piranha family. You have been warned!

Disk Tetras prefer fairly neutral water with a pH of 5.0 to 7.0 with a temperature range between 73 and 81 degrees Fahrenheit and up to 12 dGH.

It is generally recommended that Disk Tetras are kept in peat-filtered aquariums and either as a single species or with companions of a similar size.

The Disk 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 Disk Tetras from predation but it is obviously advised that Disk Tetras are not kept with predatory species as they are very timid. Avoid having anything with sharp edges in the aquarium, as such objects can damage the body of the Disk Tetra.

The adult Disk Tetra shows a blue/black stripe, top to bottom between the pelvic and anal fins. In younger specimens, the stripe is less distinct but develops as the fish matures.

The sheer size of the Disk Tetra is the hallmark of this species. It is fairly easy to distinguish between the sexes of the adult Disk Tetras, as the male has longer rays on the leading edge of the dorsal fin and, when ready to breed, its colouring becomes much more intense. When the female is carrying eggs (gravid), as her lower abdomen will become more distended than the male. 

The Disk Tetra has a much deeper body than most Tetras, being much more rhomboid in shape to the point of being almost circular. 

The Disk Tetra tends to inhabit all areas of the aquarium simply because of its size. You should also ensure that there is a close-fitting top on the aquarium because the Disk Tetra will otherwise probably jump out, as jumping clear of the water is in its nature.

The Disk 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. Disk 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 Disk Tetras in an aquarium containing small species, as they may consider them to be food. Aquarists also note that Disk Tetras are very conscious of movement outside the aquarium and tend to be very nervous so please ensure that there are plenty of densely clustered plants behind which they may hide.

Disk 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. Bearing in mind the lower pH levels preferred by Disk Tetras, they should be kept is an aquatic peat-filtered aquarium

It is generally advised that the minimum tank size for Disk Tetras should be one of 72 inches in length or more due to the size, levels of activity and 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 Disk Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the Disk 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).

Disk Tetra – Video

How do Disk Tetras breed?

Here’s the thing about breeding Disk Tetras…

Tetras eat their eggs and because Disk Tetras are so large it could be very risky moving a breeding pair into a breeding tank, as there is a distinct risk of harming the fishes. A female will lay around 200 eggs which, if laid in a community tank or a tank with a shoal of Disk Tetras in, those eggs are unlikely ever to hatch but highly likely to be eaten. It can be argued that it is unkind simply to keep a male and female Disk Tetra because the species is a shoaling species and the natural timidity of the species may leave it feeling very vulnerable. In any event, you will still need to remove the eggs once laid and fertilized.

With all of the above noted then the following may be helpful for those considering breeding this fine specimen.

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

Disk 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 Disk Tetra becomes ripe with eggs, the difference between the sexes becomes even more evident. If you plan to attempt to breed Disk 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, Disk Tetras will breed in a community tank and, if the tank is well planted, it is possible that at least a few fry may survive to reach adulthood.

Some say that a novice may find it difficult to breed Disk 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 Disk Tetras breeding readily and vigorously in quite soft, acidic water (pH 5.5 to 6.0) and less than 12 dGH.

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 (though with this species, just a mature male and female is advised. She will lay her 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 in the order of 200 eggs.

Spawning usually takes place in the early morning.

Breeding tank for Disk Tetras

You should prepare a tank of around 100 gallons in size with mature water. The water should be at a pH of around 5.0 to 6.0, maintained using an aquatic peat filter and 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 200 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 two days or so depending on tank temperature and conditions and the fry will become free-swimming after a further two 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 Disk Tetras have a special diet for breeding?

Adult Disk 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.

Being a large fish, they will enjoy feeding on cucumber, lettuce and other vegetables.

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.

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