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Glass Tetra – Prionobrama filigera


Glass 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 Glass Tetra a good community fish? The Glass Tetra should be considered to be an excellent community fish and gets on with most species. Being captive-bred it will thrive in a wide range of water chemistry. The Glass Tetra is suitable for novice aquarists and is relatively easy to breed.

Key Facts

CategoryKey Facts
Common name(s)Glass Tetra
Scientific namePrionobrama filigera
FamilyCharacidae
Originate fromAmazon drainage in Ecuador, Colombia, Peru, Bolivia and Brazil in South America
Care requiredEasy to care for and hugely popular
TemperamentPlacid, shoaling fish
Colour & FormSilver, streamlined body with red caudal fin. Adult female is fuller-bodied.
LifespanUp to 7 years
Adult size2.5 inches
DietOmnivorous – eat aquatic insect larvae in nature
Aquarium size24 inches in length or greater
Compatible withMost other Tetras, Barbs, Danios and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches
Avoid keeping withLarge and/or aggressive species
BreedingEasy if you put the fish in the right environment.
Water temp73 to 80 Fahrenheit
Water pH6.0 to 7.5
Water hardness (dGH or dH)Up to 30 dGH

Origins of the Glass 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 Glass Tetra originates in the Amazon drainage in Ecuador, Colombia, Peru, Bolivia and Brazil in South America.

Characteristics of the Glass Tetra

As you can see, the Glass Tetra is an impressive little fish. It has a slender body – often described as being “torpedo-shaped”. It will grow to up to 2.5 inches in the aquarium and lives for up to seven years.

The Glass 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 Glass Tetras from predation but it is obviously advised that Glass Tetras are not kept with predatory species, as they are quite small fish and may be seen as a snack.

The body of the Glass Tetra is silver with iridescent, pale green reflecting from the scales behind the fill plates along the central, lateral area to the root of the caudal fin, which is blood-red in colour. The other fins are clear (hyaline). The caudal peduncle (the trailing end of the body leading to the caudal fin) begins to take on the blood-red colouration just ahead of the blood-red caudal fin.

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

The Glass 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. Glass Tetras are excellent community fish and are ideal for novice aquarists.

Glass Tetras, like most rainforest species, prefer a shaded 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. They are used to habitats in nature that include decomposing wood and vegetation, which tends to make the water brown (the effects of tannins) and acidic but seem equally happy in clear water, particularly since you are only likely to obtain captive-bred specimens.

It is generally advised that the minimum tank size for Glass Tetras should be one of at least 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 have gentle movement.

Glass Tetras prefer fairly acidic water with a pH of 6.0 to 7.5 with a temperature range between 73 and 80 degrees Fahrenheit and up to 30 dGH. 

Glass Tetras are fairly difficult to sex until they are mature, where the female has a slightly fuller body than the male. 

Glass Tetras are also susceptible to elevated nitrate levels so it is advised that you monitor the water on a regular basis. Overfeeding is the most common cause of elevated nitrate levels. Firstly, fish which are overfed produce more waste, which increases water toxins, including nitrates. Secondly, uneaten food rots down and also increases water toxins, again including nitrates.

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 Glass Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the Glass 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).

Glass Tetra – Video

How do Glass Tetras breed?

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

Glass 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 Glass Tetra becomes ripe with eggs, the difference between the sexes may become more evident, as the body expands because it is carrying eggs. If you plan to attempt to breed Glass 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, Glass Tetras may 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. Having a good covering of Willow Moss on the floor of the aquarium seems to provide a safe haven for fry, which can help them to survive predation in a community or single-species tank.

Some say that a novice may find it difficult to breed Glass 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 will find a way.

The female will swim more 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 slightly adhesive eggs which will immediately be fertilized by the male(s) and will either stick to plants or spawning mop or 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.

Spawning usually takes place in the early morning. 

Breeding tank for Glass Tetras

You should prepare a tank of around 20 gallons in size with mature, soft, acidic water. The water should have 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 several hundred eggs during a spawning. The male(s) will swim alongside or behind her and fertilize the eggs as they are laid. Once the female has laid all her eggs the adults should be removed from the breeding tank.

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 a day 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 Glass Tetras have a special diet for breeding?

Adult Glass 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.

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