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Silver Dollar Tetra – Metynnis argenteus


Silver Dollar 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 Silver Dollar Tetra a good community fish? The Silver Dollar Tetra is not really a good community fish. Whilst it is very peaceful and herbivorous it is also very large and related to the Piranha. The Silver Dollar Tetra is the ultimate rhomboid Tetra in shape, being that it is almost round. The Silver Dollar Tetra is possible to sex because the adult male as an elongated anal fin which may be tinged red.

Key Facts

CategoryKey Facts
Common name(s)Silver Dollar Tetra
Scientific nameMetynnis argenteus
FamilyCharacidae
Originate fromTapajós River Basin in Brazil in South America
Care requiredEasy to care for and hugely popular
TemperamentPlacid but very large, shoaling fish
Colour & FormSilver, almost circular fish. The male may have a larger anal fin tinged with red.
LifespanUp to 10 years
Adult sizeUp to 10 inches
DietOmnivorous – eat aquatic insect larvae in nature. Mainly herbovorous and enjoys a salad (the green parts).
Aquarium size48 inches in length or greater – 60 inches recommended
Compatible withMost other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches
Avoid keeping withAggressive species
BreedingEasy if you put the fish in the right environment.
Water temp75 – 82 Fahrenheit
Water pH5.5 to 7.5
Water hardness (dGH or dH)4 to 18 dGH

Origins of the Silver Dollar Tetra

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

This Silver Dollar Tetra is found in the Tapajós River Basin in Brazil in South America. The vast majority of Silver Dollar Tetras available to aquarists are captive-bred. There are at least four distinct species of Silver Dollar Tetra and each will be covered in separate articles.

Characteristics of the Silver Dollar Tetra

As you can see, the Silver Dollar Tetra is characterized by its almost round, silver body. The fins are all generally clear (hyaline) with the exception that the anal fin of the male tends to be longer than that of the female and may also be tinged with red.

The Silver Dollar Tetra will grow to up to 10 inches in the aquarium and live for around ten years. For this reason, it is not advised for the novice aquarist but only for aquarists that can invest in a suitably large aquarium.

Silver Dollar Tetras prefer fairly neutral or acidic water with a pH of 5.5 to 7.5 with a temperature range between 75 and 82 degrees Fahrenheit and up to  4 to 18 dGH.

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

The Silver Dollar Tetra in nature is more often found in slightly “blackwater” conditions. It is a timid fish so should certainly have plenty of plant cover and limited light.

In order to maintain the softness and acidity of the water to simulate a “blackwater” environment, it is recommended that the aquarium is filtered using aquatic peat. In addition, floating and naturally decomposing Indian Almond leaves are highly recommended. 

The floating leaves provide the shaded area that the Silver Dollar Tetra will dwell beneath and the decomposing vegetation provides the tannins that will effectively synthesize the “blackwater” conditions found in the natural habitat of the Silver Dollar Tetra.

The Silver Dollar 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 Silver Dollar Tetras from predation but it is obviously advised that Silver Dollar Tetras are not kept with predatory species as they are very timid.

It is possible to distinguish between the sexes of the adult Silver Dollar Tetras, as the male has an extended anal fin which can be tinged in red whilst the female is rounder and, when ready to breed, the colouring of the male becomes much more intense. When the female is carrying eggs (gravid), as her lower abdomen will become more distended than the male.

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

The Silver Dollar Tetra tends to inhabit the lower to middle area of the aquarium. You should also ensure that there is a close-fitting top on the aquarium because the Silver Dollar Tetra will otherwise probably jump out, as jumping clear of the water is in its nature – including when feeding.

The Silver Dollar 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. Silver Dollar Tetras are a great community fish but are only ideal for aquarists with, at least, moderate experience, as the sheer size of the species will require a significant investment in a suitable aquarium. Silver Dollar Tetras enjoy plenty of densely clustered plants behind and amongst which they may hide.

Silver Dollar Tetras, like most rainforest species, prefer a shaded and well-planted tank with open areas for free-swimming, as they can hide from predation or strong light, 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 Silver Dollar Tetras, they should be kept is an aquatic peat-filtered aquarium

It is generally advised that the minimum tank size for Silver Dollar Tetras should be one of 48 inches in length or more due to the shoaling nature of the species, which will enable a small (or even quite a large) shoal to move around freely. My personal recommendation is for a tank of around 60 inches with a front to back depth of at least 18 inches and a height of around 24 inches. 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 when the time comes for breeding.

Most (but not all) Tetras have an additional fin which identifies them as being Tetras and the Silver Dollar Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the Silver Dollar 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).

Silver Dollar Tetra – Videos

How do Silver Dollar Tetras breed?

Here’s the thing about breeding Silver Dollar Tetras…

Tetras eat their eggs and because Silver Dollar Tetras are no exception, they should not be left in the tank once the eggs are laid. A female will lay up to 2,000 eggs which, if laid in a community tank or a tank with a shoal of Silver Dollar Tetras in, those eggs are unlikely ever to hatch but highly likely to be eaten.

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

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

Silver Dollar 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 Silver Dollar Tetra becomes ripe with eggs, the difference between the sexes becomes even more evident. If you plan to attempt to breed Silver Dollar 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, Silver Dollar 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 Silver Dollar 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 Silver Dollar Tetras breeding readily and vigorously in quite soft, acidic water (pH 6.0 7.0) and less than 8 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 2,000 eggs.

Spawning usually takes place in the early morning and is triggered by the rising of the sun.

Breeding tank for Silver Dollar Tetras

You should prepare a tank of around 40 gallons in size with mature water. The water should be at a pH of around 6.0 to 7.0, and a dGH of around 8 and with a low level of light.

You may wish to introduce baby brine shrimp, 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 up to 2,000 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.

A useful tip would be to consider keeping your Silver Dollar Tetras in an aquarium that has reasonable-sized marbles as the substrate because the eggs will fall between the marbles where the adults cannot get at 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 thirty-six hours or so depending on tank temperature and conditions and the fry will become free-swimming after a further six to nine days after hatching. Keep the tank unlit for the first fortnight or so then gradually increase the lighting.

The newly hatched fry will feed firstly 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 Silver Dollar Tetras have a special diet for breeding?

Adult Silver Dollar Tetras don’t need any particular inducement to breed. That said, it has been suggested that adding baby brine shrimp and 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.

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