As for many other wildlife groups, it is safe to assume that plenty of other species remain to be discovered.

What fish populate the Amazon rivers

Of the Amazon fish described so far by science, 40% are catfish and characines², including the neon tetra (Hyphessobrycon innesi), pearl headstander (Chilodus punctatus), silver hatchetfish (Gasteropelecus levis), bronze corydoras (Corydoras geneus) and the oscar (Astronotus ocellatus).
 

Vegetarian fish?

Many Amazon fish have adapted to frugivory, a diet based on fruits and seeds. About 200 species of fish feed show this habit, more than in tropical Africa and Asia³.

This is probably due to the presence of river galleries (river banks with low hanging trees), which make it easy for fish to eat fruit and seed that float on the surface of the water.

Some of the vegetarian fish include the giant  tambaqui (Colossoma macropomum), a bass-like fish that can weigh up to 30 kg. Its specialized, powerful teeth allow it to crush and grind hard fruit such as palm nuts and rubber tree seeds.

The fat stored in the food allows the fish to survive during periods of low water, while seeds, which are swallowed but not digested, are dispersed through the river network.

In varzea forests, plankton – a group that includes tiny aquatic plant and animal organisms, which drift with the currents - is abundant, which make these forests ideal grounds for fish that are growing, especially after flooding when zooplankton (or animal plankton) is particularly abundant.
 

Piranha (Sarrasalmus species)

A fearsome reputation precedes the piranha around the world, but this species is actually much less aggressive than commonly believed. At a respectable length of 35 cm, the red piranha (Sarrasalmus nattereri) is widely distributed and abundant in the Amazon rivers. Only when water levels and food supplies are low is it advisable to stay away from them. Otherwise, they are of no danger to swimmers. Of the 20 piranha species, most are vegetarian.³

Electric eels (Electrophorus electris)

Not to be underestimated, electric eels can reach 1.8 m and deliver electric shocks of up to 650 volts. Understandably, they are much feared, as they are also quite common. To make up for their blindness, eels have an electric field, which is used to detect and stun prey.⁴