Penguin Tetra

Geographical Origin and Habitat: Amazon basin in Peru and Brazil, particularly the Araguaia river. Inhabits slow-moving tributaries, swamps, and floodplains filled with submerged branches and vegetation.

Taxonomy and Morphology: Elongated Characin (5-6 cm). The lower lobe of its caudal (tail) fin is noticeably longer and more developed than the upper lobe, an evolutionary adaptation tied directly to its unique swimming style.

Social Behavior: Peculiar and fascinating. Mid-to-top dwelling schooler. Its most famous trait is its posture: when resting, it hovers in the water with its head pointing UPWARD at a 30-degree angle. This is considered camouflage to mimic drifting organic debris or twigs. They are hyper-active, fast swimmers. If kept in small numbers (under 6), they become bored and will annoy or chase tankmates.

Coloration and Sexual Dimorphism: Bright platinum/silver base. Sliced longitudinally by a thick, velvety black 'hockey-stick' stripe: it starts at the gill, runs straight down the flank, and abruptly DIPS DOWN to fill the entire elongated lower lobe of the tail fin. No obvious sexual dimorphism, though gravid females are significantly rounder in the belly.

Aquarium Setup: A very strong swimmer requiring a long tank (minimum 100 cm / 40 inches). Needs plenty of open swimming space in the upper levels, combined with thick plant stands (Swords, Vallisneria) on the edges to retreat into when spooked. A tight-fitting lid is mandatory: they are frantic during feeding and easily jump out.

Diet and Feeding: Surface/mid-water omnivore. Extremely voracious (often outcompeting shy fish for food). Eats everything: flakes, floating pellets, bloodworms, daphnia, and especially small insects dropped on the surface (flightless fruit flies).

Water Quality: Very hardy and adaptable. Thrives in both soft, acidic water (pH 6.0) and moderate, slightly alkaline tap water (pH up to 7.5). Temp 23-28°C (73-82°F). Routine maintenance is all that is required.

Compatibility and Cohabitation: Excellent, BUT caution regarding their hyperactivity: their frantic swimming can deeply stress slow, shy fish like Dwarf Cichlids or Discus. Great with medium-sized peaceful cichlids (Severums, Geophagus), large armored catfish, and active Corydoras. MUST be kept in a large school (10-12+); if kept in groups of 3-4, they become nippy and aggressive out of hierarchical frustration.

Aquarium Breeding: Highly prolific egg-scatterers (laying over 1000 eggs among fine plants at dusk). In community tanks, eggs are eaten instantly. In breeding setups, parents must be removed. Fry hatch in just 24h and are microscopic, requiring infusoria.

Risks and Diseases: 1. Jumping out of open-top tanks during feeding frenzies. 2. Fin-nipping slow fish (like Angelfish) if the Penguin Tetra school is too small. 3. Ich outbreaks from sudden cold drafts.