Common Hatchetfish

The common hatchetfish owes its name to its profile: a laterally compressed body with a perfectly straight back and a deep, keeled chest shaped like an axe blade. That keel is not decoration — it houses the oversized muscles that drive the large, wing-like pectoral fins. A member of the freshwater hatchetfish family Gasteropelecidae, it wears a polished silver-grey livery crossed by a fine dark line. Seriously Fish measures 35–40 mm standard length, though adults commonly reach about 6.5 cm including the tail. The species ranges widely across South America, through the Amazon, Orinoco, Essequibo, Tocantins-Araguaia and upper Paraguay basins, plus the coastal drainages of the Guianas. It favours the slow-flowing water of creeks and swamps, hanging in loose shoals within the top few centimetres, often under overhanging vegetation, watching for insects that fall or fly past. Everything happens at the surface. Seriously Fish requires a water surface of at least 120 x 30 cm, and that length matters far more than the litre count. Keep six at an absolute minimum, eight or more ideally: alone, the fish stays nervous and stops feeding. A tightly fitting lid is vital, as it clears several metres in a single leap. Offer 23–27 °C, gentle flow, floating plants for cover, and surface foods such as fruit flies and mosquito larvae — it ignores anything that sinks. Shy by nature, it will not compete for food against boisterous tankmates. Breeding in aquaria is all but unknown.