Retroculus acherontos

Overview

From Brazil’s upper Tocantins drainage, Retroculus acherontos develops a nuchal hump in larger individuals of both sexes. Its less flattened body and blunter snout have prompted the suggestion that it is less specialized for strong currents than its relatives. This remains a morphological interpretation rather than a proven aquarium preference.

Distribution & habitat

Known sites are tributaries entering the Serra da Mesa reservoir in Goiás, including the Maranhão and das Almas systems. Collections come from small and medium rivers with either clear, lightly humic water or sediment-rich whitewater.

One documented habitat includes a fast rocky channel alongside still marginal pools over sand or gravel. Flow therefore differs within the same setting rather than being uniform.

Diet & feeding

Related members of the genus mainly exploit benthic animals, also taking suspended items and sifting substrate through the gills. A congener has a natural diet dominated by aquatic insect larvae. These observations provide context but do not establish the measured diet of R. acherontos.

Sexual dimorphism

Larger fish of both sexes can develop the nuchal hump, so its presence alone does not identify a male.

Notes

Other visible identification clues include a dark mark in the middle portion of the soft dorsal fin, faint narrow tail bars, and a relatively rounded ventral outline. Resemblance to eartheaters does not establish membership of the same group or identical care needs.