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Thayeria obliqua is a small South American characid with a distinctive profile. Its silvery body is crossed by a dark oblique marking, while its angled swimming posture recalls the well-known penguin tetra. Less frequently seen in the trade than [[FISH|Thayeria boehlkei]], this species is an appealing choice for aquarists who enjoy discreet, natural-looking schooling fish. It should be kept in a group, in clean, well-oxygenated water that is slightly acidic to neutral. Native to Brazil, it suits a peaceful community aquarium with open swimming space, planted areas and gentle water movement.

General species description

Thayeria obliqua belongs to the genus Thayeria and the family Characidae. This peaceful schooling fish shows its most natural behaviour when kept in a group of at least six, preferably more. Most activity takes place in the middle and upper levels of the aquarium, where the fish swim with a slightly inclined posture. It is less common in the aquarium trade than the better-known species of the genus, giving it an intermediate level of commercial rarity. Careful acclimation, stable water and calm tankmates are important. An overly turbulent, overcrowded or barren aquarium may make it shy. In suitable conditions, it becomes more confident and maintains its natural schooling behaviour.

Geographical origin and biotope

Country of reference: Brazil. Thayeria obliqua is associated with the Rio Araguaia basin in central-eastern Brazil. Its habitat includes calm or moderately flowing areas, including margins, side channels and places where riparian vegetation slows the current. The water is generally soft, warm and lightly mineralized, with a slightly acidic to neutral pH. To recreate this setting, provide plants, roots, areas of subdued lighting and good overall circulation without producing strong current throughout the aquarium. Open swimming space remains important because the species uses clear areas for schooling and movement.

Precise location and local name

The species is associated with the Rio Araguaia basin in Brazil. In the aquarium trade, it is mainly called the oblique penguin tetra or the oblique hockey-stick tetra. A traditional Brazilian local name is not commonly used in international aquarium keeping. It should not be confused with [[FISH|Thayeria boehlkei]], which is often sold as the penguin tetra or hockey-stick tetra. The most useful distinction is the shape and angle of the lateral dark stripe, together with the overall body profile. Fish may appear pale after transport and regain stronger colour after proper acclimation.

Appearance and physical characteristics

The body of Thayeria obliqua is elongated, laterally compressed and covered with silvery scales. Its most striking feature is the slanted black stripe extending toward the caudal region. The caudal fin is forked, while the other fins are relatively subtle, ranging from translucent to slightly yellowish depending on lighting and condition. Its angled swimming position enhances the unusual appearance of the fish. Adult size remains modest, allowing it to be kept in a reasonably sized community aquarium when adequate length is provided. Mature females may appear somewhat fuller than males, especially when in breeding condition. Sexual differences are otherwise discreet.

General diet

In the wild, Thayeria obliqua feeds on small prey and drifting organisms in the water column. In an aquarium, it generally accepts finely crushed flakes, small micro-pellets and appropriately sized frozen foods. Brine shrimp, daphnia and cyclops are useful additions and help maintain good condition. Offer small meals once or twice daily, with all food consumed within a few minutes. Because its mouth is small and it feeds mainly in midwater, food that is too large or sinks rapidly is less suitable. A varied diet also helps maintain colour and schooling activity.

Essential data

• River of origin: Rio Araguaia
• Local name used: Oblique penguin tetra; oblique hockey-stick tetra
• Origin of the scientific name: The genus Thayeria honours Nathaniel Thayer; obliqua refers to an oblique arrangement.
• Etymology of the full name: Thayeria, a genus name dedicated to Nathaniel Thayer; obliqua, from the Latin obliquus, meaning slanted or inclined.
• Common/vernacular names: Oblique penguin tetra; oblique hockey-stick tetra
• Family: Characidae
• Subfamily: Characinae
• Name pronunciation: thay-AIR-ee-ah ob-LIK-wah
• Discovery: Carl H. Eigenmann, 1908
• Maximum adult size: About 5 cm
• Water temperature and pH: 22 to 28 °C; pH 6.0 to 7.5
• Watercourse appearance and surrounding vegetation: Soft, warm water; calm to moderately flowing areas with riparian vegetation and shaded sections
• Typical tankmates: Thayeria boehlkei, Hyphessobrycon bentosi, Hemigrammus rhodostomus
• Temperament and behaviour: Peaceful, schooling and active; avoid boisterous tankmates
• Water depth: Shallow to intermediate areas near margins and vegetation
• Sexual dimorphism: Mature females are usually fuller-bodied; differences are subtle
• Bottom structure and flow: Sandy or fine substrate with plant debris; calm to moderate flow

In your aquarium, success depends mainly on keeping a sufficiently large group, providing stable water and offering small foods. Give Thayeria obliqua open swimming space, plants or roots to reduce stress, and peaceful companions. Regular water changes, efficient filtration and moderate flow support good health. This moderately uncommon species deserves careful handling, especially during acclimation and during the first weeks after arrival. With suitable conditions and a calm community, it can become a distinctive and active midwater schooler.