Small Amazonian fish

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Onglets

Description

Distinguishing features

Small fish from the Amazon come in a remarkable variety of shapes and colours. These features help us identify them and better understand their way of life.

Grouped under the common name “tetras,” these species in fact belong to different evolutionary lineages. Even so, these small fish share several distinctive traits that reflect useful adaptations to life in Amazonian waters.

Some have laterally compressed bodies, well suited to swimming in tight schools. Many of these fish, particularly characids, have a small adipose fin between the dorsal fin and the tail. Their bright colours, which form contrasting stripes, bold markings, or iridescent highlights, play a key role in communication between individuals, especially during movement or courtship displays.

Other small Amazonian fish are distinguished by a long, slender silhouette. They often remain almost motionless in the water, adopting a characteristic posture. Their longitudinal lines, often symmetrical, help confuse predators when the fish gather in schools.

Reproduction

In the wild, reproduction in small river fish generally begins with the arrival of the rainy season, when softer, slightly cooler water spreads into forested areas.

These new conditions, created by rising water levels, trigger hormonal activity in the adults. The males then develop brighter colours and perform brief courtship displays around the females, guiding them toward densely vegetated areas. Once ready to mate, the female releases small clusters of translucent eggs among submerged vegetation, roots, or leaf litter, while the male fertilizes them immediately.

The eggs are sticky and adhere to the substrate, which maximizes their chances of remaining hidden. There is no parental care, and the adults leave right away. Only eggs that are well enough hidden escape predation.

Within a few days, the larvae hatch and feed on microorganisms that are naturally abundant in these waters, which are rich in organic matter. This allows them to begin their development in a favourable environment.

Diet

As opportunistic feeders, small freshwater fish from the Amazon eat invertebrates such as mosquito larvae, small crustaceans, zooplankton, and floating organic matter. For example, golden pencilfish glean tiny insects from the surface, while rosy tetras may form small hunting groups to capture mobile prey.

Some species also eat fruit or seeds that have fallen into the water, a common occurrence in floodplains.

Predators

Their small size makes them vulnerable to many predators, including carnivorous fish such as cichlids and catfish, piscivorous birds, and certain amphibians.

To protect themselves from these predators, small Amazonian fish use several defence strategies:

tight schooling behaviour;
disruptive colouring, which makes body outlines harder to detect;
near-motionless swimming, particularly in pencilfish, which reduces the risk of detection.

Even today, fish are still collected from the wild in some parts of the Amazon Basin to meet demand from aquarium hobbyists. This is usually done on a small, artisanal scale to obtain species that are more difficult to breed in captivity. Some Brazilian programs regulate the practice, as it can provide a sustainable source of income for local communities. Most fish commonly sold, however, come from aquaculture rather than from the wild.

Habitat

Small Amazonian fish are found mainly in calm tributaries, seasonally flooded areas, and blackwater or clearwater streams of the Amazon Basin. They may form loose or tight schools among vegetation or around the roots of floating aquatic plants.

Ecology, behaviour

These fish play a central role in the food chain: they feed on invertebrates and are themselves essential prey for larger fish, such as the yellow peacock bass.

Several species are strictly gregarious, including the ornate tetra and rummy-nose tetra, relying on group cohesion to reduce stress and increase their chances of survival. Pencilfish, by contrast, adopt a still, oblique posture that helps them go unnoticed in areas with little current.

French name

Tétra rosé, Jupiaba anterior, Poisson-crayon doré, Poisson-crayon brun, Tétra nez rouge

Scientific name

Hyphessobrycon bentosi, Jupiaba anterior, Nannostomus beckfordi, Nannostomus eques, Petitella rhodostoma

Phylum

Chordata

Class

Actinopterygii

Order

Characiformes

Family

Characidae

Size

From 2 to 10 cm

Weight

A few grams

Life span

From 3 to 7 years

Status

Stable

At the Biodôme

At the Biodôme, small Amazonian fish are all found in the river habitat of the Tropical Rainforest ecosystem.

Ornate tetras, Jupiaba anterior, golden pencilfish, brown pencilfish, and rummy-nose tetras share the aquarium with the red-finned cactus pleco, Tapajos red head, and emerald catfish. Each of these species occupies its own place at varying depths.

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