Silver Mylossoma

Fascinating facts about the Silver Mylossoma

• A fish that barely reaches a foot long, about 25 cm, can weigh up to a kilogram.
• When the Amazon floods between December and March, silver mylossoma leave lake pools and surge upstream into big rivers, then ride the rising waters onto the forest floor as the flood peaks.
• DNA and shape studies in 2018 trimmed its known range to the Río de la Plata Basin, Paraguay, lower Paraná and Uruguay rivers, while splitting off two look-alikes into separate species.
• In parts of its home, the fish is listed as vulnerable because farms, mines, dams and tourism are affecting the flood-dependent forests that its larvae need to survive.

At a glance

About the Silver Mylossoma

The silver mylossoma, Mylossoma duriventre, glides through South America’s tropical and subtropical rivers with a sleek, silvery sheen that catches the dappled light of nutrient-rich floodplains. Reaching up to 25 cm (10 in) and weighing about 1 kg (2.2 lb), its streamlined body is built for the relentless journeys of a potamodromous fish, migrating entirely within freshwater. In the Amazon’s flood season, from December to March, the species erupts from lakes and pools onto the swollen rivers, moving upstream in massive shoals toward mysterious spawning grounds. Adults then disperse onto the forest floor as floodwaters inundate the várzea, while larvae are swept downstream, later finding refuge in nursery areas where planktonic food abounds. A striking, often overlooked habit is its close association with the catfish Potamorhina altamazonica, a partnership that hints at shared ecological niches in the seasonally-flooded forest. Juveniles switch diets, snapping up insects, whereas mature fish become frugivores, swallowing fruits and seeds that float downstream, inadvertently sowing the very trees that sustain their habitat.

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