Thayeria obliqua

Penguin Tetra

Classification

Characidae

Distribution

Native to the central sections of the Amazon and Rio Tocantins basins and the Rio Guaporé, Brazil.

Habitat

Jungle streams and tributaries, presumably with dense marginal vegetation.

Maximum Standard Length

Fully grown at 3.2″/8cm.

Aquarium SizeTop ↑

A 24″ x 15″ x 12″/60cm x 37.5cm x 30cm/70 litre tank is just about suitable for a small group of these. Ideally keep it in higher numbers in a bigger tank though.

Maintenance

Makes a superb addition to the heavily-planted aquarium or well-maintained community. A planted tank can of course be further decorated with twisted roots, branches, smooth rocks and stones. A dark substrate is best, and consider the addition of some floating plants to provide the shady conditions preferred by the fish.

Alternatively, why not set up a jungle biotope-style tank? 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 (beech, oak or Ketapang almond leaves are suitable, and a mixture of all three looks really good) would complete the natural feel. Allow the wood and leaves to stain the water the colour of weak tea. A small net bag filled with aquarium-safe peat can be added to the filter to aid in the simulation of black water conditions. If you’re like us, you’ll just get hold of some real peat fibre and literally add a few handfuls to the tank. This will become completely soaked with water after a few days and sink to the bottom. Provided a good routine of water maintenance is practiced no adverse effects should occur.

In this kind of set-up slightly diffused or dimmed lighting is preferable. Aquatic plants will therefore not grow so well, but are generally not a feature of this species‘ natural waters anyway. You could add species that can survive under low lighting, such as Java fern (Microsorum pteropus), Java moss (Taxiphyllum barbieri), Anubias or Cryptocorynes. None of these are biotopically correct of course, but they can certainly be used to create an effective display.

Water Conditions

Temperature: 72° – 82° F/22 – 28°C

pH: Should be happy within the range 6.0 – 7.0.

Hardness: Up to 15°H.

Diet

Probably feeds on small insects, worms, crustaceans and other zooplankton in nature. For the best condition and colours offer regular meals of small live and frozen foods such as bloodworm, Daphnia and Artemia, although it should also accept dried flakes and granules.

Behaviour and CompatibilityTop ↑

A 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 or Hyphessobrycon tetras, pencil fish, Apistogramma and other small cichlids, Corydoras and 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’s a schooling species by nature, and will fare much better when in the company of its own kind. Any potential for fin-nipping is also limited when it is kept in sufficient numbers as the fish tend to concentrate on squabbling amongst themselves. Like most tetras it actually looks far more effective when maintained like this anyway.

Sexual Dimorphism

Adult females are more rounded in the belly and a little less intensely coloured than males.

Reproduction

We couldn’t find any reports of successful captive breeding of this species, although the strategy involved is likely to be similar to that of T. boehlkei.

NotesTop ↑

There are only three species in the genus Thayeria, of which Thayeria boehlkei is by far the most popular in the hobby. This is a shame, as T. obliqua is an equally attractive fish. It is the type species of the genus and was the original “penguin” fish or tetra, although Thayeria boehlkei is now usually sold under this name. T. sanctaemariae, described by Ladiges in 1951 is now classed as a synonym of T. obliqua.

The species are easy to tell apart, as in Thayeria boehlkei the thick black stripe extending from the lower lobe of the caudal fin travels laterally down the body to the opercle (gill flap). In T. obliqua this tapers upwards, fading out completely before it reaches the dorsal fin. The third species, T. ifati is a very pretty little fish that is rarely available in the hobby. In this one the black stripe is only present in the uppermost part of the lower caudal lobe, but it is much more clearly defined than in T. obliqua and extends upwards of the lateral line, beyond the dorsal fin. When in good condition the dorsal and anal fins develop attractive red tips, and the caudal lobes are edged in amber. All three species swim in an oblique, head-up style typical of the genus.

As with many genera of small characin, the taxonomic status of Thayeria species is currently Incertae Sedis, meaning uncertain. Most experts agree that a full revision is required, with the likely outcome that many species will be placed into new or different genera.