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Glofish Tetra – Gymnocorymbus ternetzi

Blue Glofish 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 Glofish Tetra a good community fish? The Glofish Tetra should be considered to be an excellent community fish because it can live quite happily amongst a wide variety of other species. It is best to avoid keeping Glofish Tetras with large, aggressive species and fin-nippers, which may bully or even eat the Glofish Tetra.

Key Facts

CategoryKey Facts
Common name(s)Glofish Tetra
Scientific nameGymnocorymbus ternetzi
Originate fromNot found in nature – a genetically modified species derived from the Black Skirt Tetra which originates in the Paraguay River basin of south-central Brazil (mainly the Pantanal region), Paraguay and northeast Argentina in South America
Care requiredEasy to care for and hugely popular
TemperamentPlacid, shoaling fish
Colour & FormThe same form as the Black Skirt Tetra but available in a range of genetically modified, fluorescent colours
LifespanUp to 5 years
Adult sizeUp to 3 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 temp72 – 82 Fahrenheit
Water pH6.0 to 7.5
Water hardness (dGH or dH)1 to 8 dGH

Origins of the Glofish 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 Glofish Tetra originates as the Black Skirt Tetra from the Paraguay River basin of south-central Brazil (mainly the Pantanal region), Paraguay and northeast Argentina in South America. Glofish Tetras, being genetically modified, are not found in nature but (subject to applicable laws) may be bred in captivity. Already available in a range of stunning colours, more colour choices are sure to be available over time.

Please note that Glofish Tetras are patented and whilst they may breed it is a breach of law to sell, trade, barter or give away any fry (though I am unclear as to how this would be policed).

Characteristics of the Glofish Tetra

As you can see, the Glofish Tetra is a beautiful, little fish which will grow to around 3 inches in the aquarium and lives for around five years. 

The Glofish Tetra will thrive in water of between 72 to 82 degrees Fahrenheit, with a pH range between 6.0 to 7.5 and up to 8 dGH.

The genetically modified Glofish Tetra includes DNA from a jellyfish to make it glow in the dark.

Since the Glofish Tetra is genetically modified it may not be available for purchase (or legal to import) in your country so please ensure that you are familiar with your applicable legislation.

The Glofish Tetra is a deep-bodied fish and takes the form of a tetragonal shape. The female, once gravid (carrying eggs) will become even more rounded and, at that stage, is easily distinguished from the male.

Bearing in mind the slightly elongated finnage of the Glofish Tetra, it may be appropriate to avoid keeping them with species prone to fin-nipping.

The featured image above shows the Blue Glofish Tetra, which is one of a variety of Glofish Tetras that are available. Below are further images of Glofish Tetras showing different colouring and finnage development.

Orange Glofish Tetra
Orange Glofish Tetra
Pink Glofish Tetra
Pink Glofish Tetra
Purple Glofish Tetra
Purple Glofish Tetra
Yellow Glofish Tetra
Yellow Glofish Tetra

The Glofish Tetra is omnivorous in the aquarium though it generally eats small, live aquatic insect larvae but also eats plants. In the aquarium, as well as consuming small flake food the Glofish Tetra will enjoy brine shrimp, freeze-dried bloodworms, daphnia and tubifex worms. In addition, the Glofish Tetra will benefit from pellet food, as most of these commercial foods include nutrients designed to enhance the vibrant colours of the fish. That said, the Glofish Tetra rarely ventures to the bottom of the aquarium.

The Glofish Tetra tends to inhabit the upper half of the aquarium so it is worthwhile including some Corydoras in the tank as they will eat any food that falls down. That said, it is a vigorous fish, especially when breeding and will readily traverse the entire aquarium.

The Glofish 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. Glofish Tetras do have a reputation for squabbling amongst themselves initially, apparently to establish a hierarchy but once this is established they are extremely peaceable and, in any event, do not bully other species.

Glofish Tetras are ideal to be kept in a mixed aquarium (or in a single-species aquarium) as a shoal and are both graceful and beautiful to observe. These smaller Tetras are quite timid fish so should not be kept with large, aggressive species which may bully or even eat them.

Glofish Tetras mix well with most other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches. It is strongly recommended not to include fin-nipping fish (such as male Bettas) with Glofish Tetras.

It is generally advised that the minimum tank size for Glofish Tetras should be one of 24 inches in length or more, which will enable a small shoal to move around freely. The tank should be well-planted, preferably including dense foliage, in order to enable them to find cover and open space to enable them freely to swim.

Glofish Tetras prefer slightly acidic water in nature because, in the wild, this is the natural habitat of the Black Skirt Tetra (from which the Glofish is created) which is under the canopy of the Amazon rainforest. In nature, the water will get relatively little light and will also tend to be tannin-stained due to the decomposition of leaf matter and this causes the water to be quite acidic. That said and because you are only likely to obtain tank-bred specimens, they are acclimated to neutral water so water condition is less critical than one might otherwise expect.

LED lighting of different colours will make the modified DNA of the Glofish fluoresce in different ways so you may wish to try colour-changeable LED lighting to find out how your particular Glofish show to best advantage. You may wish to bear in mind that these are living creatures and may not take too kindly to living in a “disco inferno” of multi-colour, strobing lights 

It is best to ensure that the aquarium is well planted, possibly with floating plants included to provide shade from the tank illumination and thus mimic the blackwater environment found in the natural habitat of the Glofish Tetra, despite the fact that you cannot obtain anything other than tank-bred specimens.

It is somewhat difficult to determine with certainty the sex of most Tetras. It is, however, easy to determine the sex of Glofish Tetras once a female is gravid (carrying eggs), as her belly becomes much more rounded.

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

Glofish Tetras – Videos

How do Glofish Tetras breed?

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

As the female Glofish Tetra becomes ripe with eggs, the difference between the sexes is even more evident. If you plan to attempt to breed Glofish Tetras then it is recommended that you have a breeding tank prepared which will be unlit and well planted.

Whilst you can keep Glofish Tetras in community tanks with fairly neutral water, in order to optimize for breeding conditions it is far better to create an environment much closer to that of its natural habitat (i.e. fairly dark with soft, somewhat acidic and very soft water). That said, I have observed Glofish Tetras breeding readily and vigorously in quite neutral water. Nature finds a way!

The female will swim amongst the plants in which she will lay her eggs which will stick to the plants and the male will follow her or swim alongside her and fertilize (at least some of) the eggs as they are laid. Once spawning is complete, remove the adults, as they are likely to consume the eggs and take no further parental responsibility.

Breeding tank for Glofish Tetras

You should prepare an unlit tank of around 20 gallons in size with mature water. You may wish to consider covering most, if not all of the aquarium glass with card to maintain the dark conditions requires (perhaps including a viewing port which can be closed when not in use).

Ensure that there is plenty of fine vegetation (e.g. Cabomba, Fontanalis or Java Moss) in the tank. Glofish Tetras tend to breed in the early morning. The water should be at a pH of around 5.0 to 5.5, a dGH of 1 to 2 and, ideally around 69 to 78 degrees Fahrenheit. I would add that, as stated above, I have observed Glofish Tetras breeding successfully in fairly neutral water.

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 several hundred eggs, which will stick onto the plants or fall to the bottom of the tank.

Once the female has scattered her eggs (perhaps 300 or more in a single spawning) and the male has fertilized at least some of them then both should be removed carefully from the breeding tank because neither will have anything more to do with the eggs but they may simply eat them.

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

The eggs will hatch typically in around 24 hours depending on tank temperature and conditions. 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.

Cross-breeding Glofish Tetras of different colours

You can breed a Glofish Tetra of one colour with a Glofish Tetra of another colour. Thus far, when this cross-breeding has been performed, the offspring are roughly 50% the colour of the male and 50% the colour of the female and there is currently no record of cross-breeding the genetically modified species to take on the colour characteristics of both parents.

Doubtless, in time, further research and development will alter this, perhaps in a range of aspects.

Should your Glofish Tetras have a special diet for breeding?

Adult Glofish 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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