Fish of the Rio Sucuri

Though the Amazon is South America’s best-known river, the Rio Sucuri better reflects an ideal freshwater habitat.

The Amazon is not the only habitat in South America that is home to our aquarium fish and plants. Actually, the regions to the south of the great Amazon basin have been the sources of most of the popular aquarium plants from South America. The Brazilian Pantanal (one of the world’s largest wetland regions) and the region to the south (known as the Mato Grosso del Sul) both have incredibly clear rivers and swampy wetlands, and are home to hundreds of aquatic plant species and several popular aquarium fish.


The rivers (Rios) Sucuri, Bonito and Da Prata are among the clearest freshwater habitats in the world. No other place, except perhaps Africa’s Lake Malawi, offers such an incredible opportunity to observe our aquarium fish in their natural habitat. The Brazilian government has long recognized the unique region, and today many of the most striking natural wonders are protected areas or national parks. 

The water of the Río Sucuri is medium hard, with a pH of neutral or slightly alkaline. The water temperatures range from 65 to 74 degrees Fahrenheit. For us, swimming in the river for any length of time requires a wet suit, as well as a guide to ensure the sensitive habitat is not harmed.

The amazing water clarity is easily explained because the river originates from artesian wells and literally springs out of the ground. The water is so clear there that the the entire pool (which is more than 60 feet long) is visible under water. The pool is home to a small number of juveniles of the larger species of fish and some impressive schools of the smaller tetras. The shallow, clear water allows for a lush growth of plants of many species, particularly fantastic forests of Amazon sword plants (Echinodorus).

Cool water erupts from the ground where the wells break the substrate, creating fountains of fine sand — like submerged geysers. The pool overflows to form a narrow river that is quickly joined by other small streams from hundreds of other smaller wells. Eventually, a rapidly flowing river is formed that is up to 7 feet deep in the center channel and spreads out to flood the surrounding forest.

Biotope Tank

In terms of a biotope tank, few habitats are more interesting to recreate than this one. Although the fish of the Amazon are wonderful, the Amazon underwater is not the image many of us have in mind. It is an underwater landscape of fallen trees and leaf litter, with few rocks and almost no aquatic plants. The Mato Grosso Del Sul region offers the habitat many of us imagine the South American home of our fish to be like. This biotope would be an aquarium filled with many species of aquatic plants, along with a number of interesting, colorful fish that are commonly available in stores. A Río Sucuri habitat tank with some rocks, small pieces of driftwood and many aquatic plants is relatively easy to recreate. It can include schools of the common serpae tetra (Hyphessobrycon callistus) and Aphycharax paraguayensis, perhaps some Cichlasoma  perhaps some Cichlasoma bimaculatum (a less aggressive cichlid) and the bristlenose pleco (Ancistrus sp.). More difficult to find — but excellent tankmates for this biotope setup — would be Characidium fasciatum and Apeirodon affinis

Brycon Hilari

Brycon Hilari. Youtube

A Río Sucuri habitat tank with some rocks, small pieces of driftwood and many aquatic plants is relatively easy to recreate. It can include schools of the common serpae tetra (Hyphessobrycon callistus

The Real Deal

Within the natural habitats of this river, the popular serpae tetra is the most striking species in the shallows. The bright sun makes its intense red color visible, even from a great distance. The small tetras closely follow the larger, peaceful characins as they forage for food in the substrate. These larger characins include pacu (Collossoma macropomum), Leporinus frederici, Curimata curimata and Leporellus vittatus. Schools of up to several hundred smaller tetras will follow these larger gentle fish around to feed on the small crustaceans and other matter stirred up as they dig in the substrate. Smaller individuals of the large predators crowd the shallows, hunting the smaller fish, shrimp and small worms in the leaf litter. 

Larger fish occupy the plant thickets, boulders and areas with stronger current. Small fish rarely enter these zones, where they would be easy prey for Crenicichla and predatory characins. The current is stronger there, and the substrate moves constantly. The fine sand shifts, leaf litter is blown around as if there were wind, and the plants in this area are always moving. Bristlenose plecos (Ancistrus teminicki or A. dolichopterus) are very common, living in nearly every crevasse between rocks and in the holes of sunken driftwood and trees. 

The main channel is safe only for the largest fish. The large predators ensure that few fish less than 1 foot in length can be seen here. The largest, fastest fish is the dorado (Salminus maxillosus). At more than 40 inches, the largest individuals are, without doubt, the kings of this domain. At the surface, schools of Brycon hilari crowd to feed on insects and the fallen fruits and leaves of the trees above. Small troops of black pacu and Leporinus frederici are too large to be threatened by the predators, so they spend their time feeding off of aquatic plants and tree branches whose leaves touch the surface.

Perhaps most impressive are the gigantic schools of Curimata curimata. These large herbivorous characins form schools of up to several hundred individuals, foraging on the plants and leaves of trees.
After sunset, the nocturnal predators emerge. These include tiger shovelnose catfish (Pseudoplatystoma tigrinum) and swamp eels (Symbranchus marmoratus), as well as anaconda. More surprising is the nocturnal activity of the piranhas (Pygocentrus nattereri), which are never seen during the day — they quietly sit deep under the riverbanks. 

Aquarists cannot completely mimic the río Sucuri in a biotope aquarium; there is no way we could track down many of the aquatic plant species found there or adequately care for large fish such as the pacu and the dorado. We can bring a small slice of this Brazillian wonder into our homes by recreating parts of this South American habitat. Our home aquariums are suitable for smaller South American fish and several species of plants that are sold at our local fish stores. The río Sucuri — with its cool, clear water, abundant plants and dazzling fish — is a great source of inspiration when creating a lifelike biotope for our farm-raised aquarium fish.

Residents of Río Sucuri

Large species

  • Curimata curimata 
  • Brycon hilari
  • Leporinus frederici
  • Tiger shovelnose (Pseudoplatysoma tigrinum
  • Black pacu (Collosoma macropomum)
  • Dorado (Salminus maxillosus)
  • Swamp eel (Symbranchus marmoratus)
Mid-size fish and smaller predators
  • Crenicichla vittata
  • Pike cichlid (Crenicichla aff. lepidota)  
  • Leporellus vittatus
  • Leporinus striatus
  • Cochliodon species
  • Hypostomus species
  • Barracuda (Acesterohynchus species)
Small fish
  • Darter tetra (Characidium fasciatum)
  • Astyanax bimaculatus
  • Hyphessobrycon sp.
  • Serpae tetra (H. callistus)
  • Hemigrammus species
  • Apeirodon affinis
  • Bristlenose catfish (Ancistrus dolichopterus)
  • Aphyocharax paraguayensis
  • Cichlasoma bimaculatum

Water in the Rio Sucuri is medium hard, and has a neutral or slightly alkaline pH. The river comes from artesian wells, literally springing out of the ground.

The Rio Sucuri is one of the clearest freshwater habitats on earth —and it is a great place to observe aquarium fish in their natural world.
The Rio Sucuri habitat can be interesting to recreate. Many species of aquatic plants and fish, such as Astyanax bimaculatus, live in its waters.
Brycon hilari is one of the larger fish that makes its home in the Rio Sucuri.
Article Categories:
Fish · Freshwater Fish