Black-winged Hatchetfish

Geographic Origin and Biotope: Endemic to the Rio Negro and upper Orinoco basins (Brazil, Venezuela). Inhabits almost exclusively still, heavily shaded, tannin-stained 'blackwater' swamps and flooded forests. The water is tea-dark, incredibly acidic, and devoid of minerals.

Taxonomy and Morphology: A miniature member of the Carnegiella genus. Rarely exceeds 3 cm (1.2 inches) in length. Possesses the classic flat-backed, axe-bellied shape, but the belly 'keel' is even sharper and deeper relative to its tiny body.

Social Behavior: Psychologically very fragile. An ultra-shy fish that lives constantly hiding among the roots of floating plants in schools of dozens. Its swimming motion is jerkier than the larger species. Very prone to panic and ballistic jumping if exposed to bright lights or sudden shadows crossing the tank.

Coloration and Sexual Dimorphism: Much darker than its cousins. The pale silver/olive body is dominated by a thick, continuous pitch-black line running along the entire lower edge of the axe-belly. The 'wings' (pectoral fins) have prominent dark rays, earning its common name. The center of the body features fine, dark horizontal stripes. Sexual dimorphism is negligible.

Tank Setup: Can be housed in a 60 cm (24-inch) tank due to its small size. A COMPLETELY SEALED LID IS MANDATORY. The setup must be a specialized biotope: very dim lighting, heavily shaded by a thick carpet of floating plants (Water Lettuce, Frogbit). The bottom should be covered in leaf litter and botanicals. Without overhead cover, they will panic and pace the glass frantically.

Feeding: Extreme micro-surface insectivore. Given their microscopic mouths, they cannot eat standard flakes. Requires finely powdered freeze-dried foods, 0.5mm floating micro-pellets, and critically, live tiny surface insects like springtails or small flightless fruit flies. They will not eat food that sinks below the surface.

Water Quality: THE MAIN HURDLE. In standard tap water (pH 7.0+), their slime coat degrades and they rapidly succumb to fungal infections ('cotton wool') or Ich. REQUIRES BLACKWATER: 100% RO water filtered over peat, pH 4.0 - 5.5, negligible hardness. Temp 24-28°C (75-82°F).

Compatibility: Best kept in a strict Species-Only tank. If tankmates are needed, they must be tiny, lethargic blackwater species: Green Neon Tetras (P. simulans), Chili Rasboras, or Otocinclus. Never house with frantic or large fish. Keep in massive schools (12-20+) so the 'swarm mentality' lowers their profound nervousness.

Reproduction: Extremely rare in captivity; parents aggressively consume the eggs scattered among floating plant roots.

Risks: 1. Fatal osmotic shock during acclimatization from store bags (drip acclimation of 2+ hours is mandatory). 2. Jumping to their death. 3. Immediate fungal outbreaks if the pH rises above 6.5.