Beni

The pygmy hatchetfish, Carnegiella myersi, is a tiny freshwater hatchetfish from the Peruvian Amazon basin, with a second population in Bolivia. The smallest and most delicate of the nominal hatchetfishes, it has a shallower, rounded keel that gives it an elongate profile. It lives in small, shaded, shallow forest streams and must be kept in a group of at least six, away from active tankmates.

The Santa Cruz cory, Hoplisoma cruziense, long known as Corydoras cruziensis, is an armoured catfish from the Bolivian portion of the Río Madeira basin. The precise extent of its range is unclear and may include the Mamoré and Beni drainages. It is not well documented, but is said to differ from C. punctatus in having larger dark body markings, which form an irregular midlateral stripe in some specimens.

The black phantom tetra, Megalamphodus megalopterus, is a characid from the upper rio Madeira and upper rio Paraguai in Bolivia and Brazil. Most records are from the rio Guaporé (Río Iténez in Bolivia). Popular in the hobby and bred commercially in several countries, it is also available as a 'long-finned' strain. Adult males have black fins with the pelvic, dorsal and anal enlarged, while females are deeper-bodied with reddish pelvic, anal and adipose fins.