Scoloplax dicra

Scoloplax dicra has the widest distribution in the family Scoloplacidae. Its range encompasses the Amazon and Paraguay River basins and several of their tributaries, particularly the Rio Maronon/Ucayali drainage of Peru, the Rio Mamore or Guaporé of Brazil, and the lower basin of the Rio Negro in its northernmost distribution. It is also present in the upper Rio Madeira and tributaries of the Rio Solimões, Rio Purus and Rio Juruá basins. Scoloplax dicra live in stagnant oxbow lagoons that are heavily shaded by lowland forests. Species of Scoloplax inhabit waters with slow currents, blackwater, muddy, silty, or sandy bottoms, and which have a presence of riparian and submerged vegetation. Their preferred habitat is acidic waters with settled organic detritus on the bottom.

The reproductive biology of Scoloplacids is poorly characterized by current studies. Scoloplacidae has exhibited marked sexual dimorphism, and Scoloplax dicra might be an inseminating species, based on the histological identification of spermatozoa within the ovaries. It is suggested that these fish reproduce early during the rainy season from November on, and most of the adult population dies afterwards. Not much is known about the longevity of this species. It is likely that Scoloplax dicra has an annual life cycle. There is a marked lack of living adults after the rainy season when they have reproduced.