Penguin tetra

Geographical Origin and Habitat: Thayeria obliqua is native to South America, specifically inhabiting the Tocantins River basin and the upper Amazon River in Brazil. It populates slow-flowing forest streams, clearwater or blackwater creeks, and flooded margins rich in submerged vegetation, fallen branches, and roots, where the water is soft, slightly acidic, and shaded by the rainforest canopy.

Taxonomy and Morphology: Belonging to the family Characidae and subfamily Tetragonopterinae. Described by Eigenmann in 1908, this species is famous for its head-up swimming posture, holding its body at a 30-to-45-degree angle. It features a slender, laterally compressed body and an asymmetrical caudal fin with a longer lower lobe. Adults reach about 5 to 6 centimeters.

Social Behavior: A peaceful, active, and schooling fish that must be kept in groups of at least 6 to 8 individuals. If kept in too small a group, they will become stressed and hide. They swim in the upper and middle levels of the aquarium, maintaining their unique tilted posture. School cohesion is spectacular to observe during rapid turns.

Coloration and Sexual Dimorphism: The body color is translucent silvery-gold. Its most prominent feature is a black longitudinal stripe running from the gill cover to the caudal fin, curving downward to completely cover the longer lower lobe of the tail. Sexual dimorphism is minimal; mature females are slightly rounder and larger than the slimmer males.

Aquarium Setup: Requires a freshwater aquarium of at least 80 liters with plenty of open swimming space in the center. The layout should include dense plantings along the sides and back (using Echinodorus, Vallisneria, or Cabomba) and driftwood roots for shelter. Dark substrate and floating plants help dim the lighting to showcase their silver coloration.

Diet and Feeding: An omnivorous species that feeds on insects falling onto the water surface, small crustaceans, and zooplankton in the wild. In captivity, it readily accepts high-quality flakes, micro-pellets, and frozen foods such as daphnia, brine shrimp, and bloodworms. Feed once or twice daily in small amounts.

Water Quality: Demands clean, well-filtered water with regular 20% partial changes every two weeks. Ideal parameters are: temperature between 22°C and 28°C, pH between 6.0 and 7.2, and water hardness (dGH) of 4 to 15. Avoid sudden parameter changes and maintain ammonia/nitrite at zero, with nitrates below 25 mg/l.

Compatibility and Cohabitation: An excellent addition to any peaceful community aquarium. It lives comfortably with other small tetras, rasboras, Corydoras catfish, peaceful dwarf cichlids (like Apistogramma), and small bottom-dwellers. Avoid housing with large, predatory, or aggressive fish that might view it as prey.

Aquarium Breeding: Breeding is possible but requires a separate spawning tank with very soft water (dGH < 4), acidic pH (5.5-6.0), dim lighting, and fine-leaved plants or spawning grates to protect the eggs. The pair deposits adhesive eggs among the plants. Remove parents immediately after spawning to prevent egg predation.

Risks and Diseases: While robust, they can contract Ichthyophthirius multifiliis (white spot disease) if exposed to sudden temperature drops or stress during water changes. High nitrate levels weaken their immune system, leading to fin rot or fungal infections. Routine filter maintenance is key to prevention.