Iguanodectes polylepis is a small fish, measuring a maximum of 8.4 cm (3.3 in) standard length (SL).

It has a patch of pigmentation on its caudal fin that occupies a great deal of the junction between lobes, and its lateral stripe is generally dark, with a pinkish band on top.

[11] The type locality is a tributary of the Rio Ipixuna, specifically a point located to the west of the city Hamaitá, in Amazonas, Brazil.

Other members of the genus are usually herbivorous,[4] some with omnivorous traits observed in captivity,[13][14] and it is likely that I. polylepis displays similar habits, especially given its native range.

The Purus and Maderia basins are dense with wetlands and flooded forests, establishing plentiful riparian vegetation upon which native fish species can feed.

[17] Overall, the wide range and the lack of interest in wild-caught specimens of I. polylepis speaks to a generally stable population.

[16] Rivers surrounded by farmland are noted to have decreased water quality, including factors like contamination from pesticides and animal feces.