Tucanoichtys tucano

Endemic to the upper and middle Ro Orinoco watershed in Colombia (departments of Meta, Casanare, Arauca, Vichada, and Guaina) and Venezuela (states of Amazonas, Apure, Gurico, and Bolivar). It has been collected from severalmajor tributaries includingthe ros Atabapo, Guaviare, Inirida, Ventauri, Meta, Cinaruco, Arauca, Apure, Capanaparo, and Caura.

Apparentlyfavours minor tributaries, smaller rivers, oxbows, and flooded forests rather than main river channels.

It occurs throughout the vast llanos regions of Colombia and Venezuela, and in the latter country is often associated with habitats known as morichalswhich tend to contain transparent, clear water and sandy substrates, often with dense growth of aquatic plants or riparian vegetation among which the fish take shelter.

In other parts of its range it has been collected from both flowing blackwater habitats and still floodplain lakes, while the majority of rivers and wetlands across its range are subject to extreme floodingduring the annual rainy season.

One example of a natural habitat is the Ro Cinaruco, a low nutrient, blackwater tributary of the Orinoco in southwestern Venezuela which comprises a meandering river channel with numerous interconnected lagoons and floodplain lakes.

The latter two biotope-types feature reduced water flow, increased turbidity and temperature, a greater accumulation of leaf litter, and higher densities of zooplankton than the main channel.