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Moenkhausia oligolepis

Glass Tetra




Ranges throughout much of northern South America, with populations in Venezuela, Guyana, Suriname, French Guiana, Peru and Brazil.


Slow moving rivers, tributaries and floodplain lakes.

Maximum Standard Length

2″ (5cm).

Aquarium SizeTop ↑

A 24″ x 15″ x 12″ (60cm x 37.5cm x 30cm) – 70 litre tank could house a small group of these comfortably.


A biotope setup would be very simple to arrange. Use a substrate of river sand and add a few driftwood branches (if you can’t find driftwood of the desired shape, common beech is safe to use if thoroughly dried and stripped of bark) and twisted roots. A few handfuls of dried leaves (again beech can be used, or oak leaves are also suitable) would complete the natural feel. Aquatic plants are not a feature of this species‘ natural waters. Allow the wood and leaves to stain the water the colour of weak tea, removing old leaves and replacing them every few weeks so they don’t rot and foul the water. A small net bag filled with aquarium-safe peat can be added to the filter to aid in the simulation of black water conditions. Use fairly dim lighting.

Alternatively it also does well in a well maintained, heavily planted tank.

Water Conditions

Temperature: 75 to 82°F (24 to 28°C)

pH: 5.5 to 7.2. Although it will survive in slightly alkaline water, it tends to be more colourful when kept in acidic conditions.

Hardness: 1 to 12°H


Easy to feed. It will readily accept just about anything offered. For the best condition and colours offer regular meals of small live and frozen foods such as bloodworm, Daphnia and brine shrimp, along with dried flakes and granules.

Behaviour and CompatibilityTop ↑

It’s a very peaceful species that won’t compete well with very boisterous or much larger tankmates. Ideally keep it with other South American species, such as Hemigrammus, Hyphessobrycon, other Moenkhausia, pencil fish, dwarf cichlids, Corydoras and small Loricariids. In a more general community it can be combined with smaller rasboras, barbs, Anabantoids and West African dwarf cichlids such as Pelvicachromis species.

Always buy a group of at least 6 of these, preferably 10 or more. It is a shoaling species by nature, and will fare much better when in the company of its own kind. Like most tetras it actually looks far more effective when maintained like this anyway.

Sexual Dimorphism

Adult females tend to be fuller bodied than males.


Can be bred in a similar way to other species in the genus. You’ll need to set up a separate tank if you want to raise decent numbers of fry. Something around 18″ x 10″ x 10″ in size is fine. Use very dimly lighting and add clumps of fine-leaved plants such as java moss or spawning mops, to give the fish somewhere to deposit their eggs. Alternatively you could cover the base of the tank with some kind of mesh. This should be of a large enough grade so that the eggs can fall through it, but small enough so that the adults cannot reach them. The water should be slightly soft and acidic in the range pH 6.0-7.0, gH 1-10, with a temperature of around 72-76°F. A small air-powered sponge filter bubbling away very gently is all that is needed in terms of filtration.

It can be spawned in a group, with half a dozen specimens of each sex being a good number. Condition these with plenty of small live foods and spawning should not present too many problems.

Alternatively, try spawning it in pairs. Under this technique the fish are conditioned in male and female groups in separate tanks. When the females are noticeably full of eggs and the males are displaying their best colours, select the fattest female and best-coloured male and transfer them to the spawning tank in the evening. They should spawn the following morning.

In either situation the adults will eat the eggs given the chance and should be removed as soon as eggs are noticed. These will hatch in 24-36 hours, with the fry becoming free swimming a 3-4 days later. They should be fed on an infusoriatype food for the first few days, until they are large enough to accept microworm or brine shrimp nauplii.

NotesTop ↑

This species is one of a handful that closely resemble the popular red-eyed tetra, M. sanctaefilomenae. This species is seen much less often in the hobby than its relative however and is also known as the glassy tetra.

The taxonomic status of all species in the genus Moenkhausia is currently Incertae Sedis, meaning uncertain. The genus is currently used as something of a catch-all for a large number of small characin species. Most experts agree that a full revision is required, with the likely outcome that many of these will be placed into new or different genera.

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