巴西后臀丽鱼

Overview

Retroculus xinguensis requires warm, exceptionally clean, oxygen-rich flowing water and is unsuitable for an ordinary community aquarium. Sand feeding and its unusual pebble-covered breeding nests make extensive floor space and an appropriate substrate especially valuable.

Distribution & habitat

Most records concern the lower Xingu and middle to lower Iriri in Brazil, although the type locality lies much farther upstream in Mato Grosso. The full range remains unclear, with additional scattered records from neighboring systems including the Jamanxim, Arapiuns and Maués Açu. Rapids and fast clearwater reaches contain boulders of many sizes, with quieter sandy or gravelly pools near the margins.

Aquarium setup

Provide at least approximately 210 × 60 cm of floor space in a river-style aquarium. Use soft sand, adding small pebbles if breeding is intended, together with rocks, roots and branches. Robust plants attached to furnishings can be used. The fish needs warmth and does not thrive in cool conditions.

Strong oxygenation and substantial circulation may require additional pumps. Replace roughly 30–70% of the water weekly and prevent organic waste accumulation; current alone is not maintenance. Newly imported wild fish may be delicate and susceptible to ich, making an extended observation and quarantine period appropriate.

Diet & feeding

Wild feeding centers on bottom-dwelling aquatic invertebrates, particularly midge, caddisfly and mayfly larvae. Offer fine prepared foods alongside suitably sized live and frozen items, including some plant-containing dry food. Gel foods can also work. Three to five small meals daily support condition better than one large feeding.

Behaviour & compatibility

The fish is relatively peaceful outside reproduction, though smaller companions may be eaten. Unless the aquarium is exceptionally large, prefer peaceful open-water fishes over additional bottom dwellers. Start with five to eight individuals. A hierarchy develops, and undersized groups can leave weak fish repeatedly targeted or the whole group unsettled.

Sexual dimorphism

Mature males are leaner, with a straighter underside between the pelvic and anal fins. Females are rounder there. Male pelvic fins become larger and redder and can support the body during territorial displays. Breeding fish intensify red on the head and fins; juveniles and subadults lack reliable external differences.

Breeding

Both parents care for offspring after substrate spawning, which has occurred in aquaria. Raise juveniles together for natural pairing and expect at least a year, often two or more, before maturity. Good food and rigorous maintenance with substantial weekly water changes matter more than any single established trigger.

The pair excavates pits and deposits eggs in batches, producing 200 or more. Very adhesive eggs collect sand and are covered with small pebbles, wood fragments or other material, or moved into a prepared pile. The nest may be relocated repeatedly during incubation. Hatching begins after about three to four days. Once the yolk is absorbed and fry swim freely, brine-shrimp nauplii are suitable. Some parents guide young back before dark and disturb the bottom, possibly to expose food for them.

Notes

Conspicuous dark tail bars are useful identification features. A resemblance to some earth-eating cichlids does not mean that sand-sifting behavior alone establishes close taxonomic relationship.