Geophagus megasema

Overview

An upper Madeira sand-sifting cichlid, Geophagus megasema has a relatively large rounded flank spot without vertical bars. It is social, requires soft sand and stable water, and begins mouthbrooding during the egg stage.

Distribution & habitat

Records come from the Mamoré and Guaporé drainages of Bolivia and Brazil; the Guaporé is called the Iténez in Bolivia. The species appears restricted to the upper Madeira system.

Detailed habitat evidence is limited. By comparison with relatives, gently sloping margins over sand or mud, with scattered rocks, roots, and leaves, are considered likely settings.

Aquarium setup

Provide at least a 180 by 60 cm footprint. Soft sand supports natural feeding, while coarse gravel risks gill injury or harmful ingestion. Low light, wood, roots, and occasional flat stones provide shelter and potential spawning surfaces.

Excess decaying leaves become suspended particles during sifting. Mature biological filtration, fine-particle removal, and protection of pumps from sand are important. Change at least 50–70% weekly, maintaining stability without excessive direct flow.

Diet & feeding

The genus obtains small invertebrates, seeds, and organic debris by sifting substrate. Use fine prepared foods, including plant-rich products, alongside bloodworms, tubifex, brine shrimp, and similar fare.

Even adults benefit from small particles and three or four modest daily feedings rather than a single large meal.

Behaviour & compatibility

Keep at least five to eight in a loose social hierarchy. Inadequate groups can leave fish nervous or expose weaker individuals to persistent harassment. Select peaceful companions with matching needs, avoiding territorial bottom dwellers and harder-water species.

Sexual dimorphism

Juvenile external sexing is unreliable. Mature males tend to be slightly larger and longer-finned, while the female ovipositor is conspicuous during spawning.

Breeding

Captive reproduction is known, with eggs laid on solid surfaces before biparental oral incubation. Young groups can form pairs naturally, taking at least about a year to mature.

Pairs clean and defend rock, wood, or glass. Females lay successive batches for fertilization, with up to about 200 eggs. The female usually collects first while the male guards, but male participation may begin earlier or become dominant.

Later care can involve simultaneous carrying or exchange of the whole brood. Young become free-swimming at about seven to fourteen days of age, gaining progressively longer feeding periods outside before retreating when threatened. Fine prepared foods, brine-shrimp nauplii, and microworms are suitable. Separate rearing arrangements reduce predation by companions and conspecifics.

Notes

The combination of no dark preopercular or suborbital marks, no flank bars, and a large rounded side spot assists identification. Reliable provenance is preferable to borrowing trade names from similar eartheaters.