Biotope 101: An authentic upper Rio Araçá biotope for Rummynose and Cardinal tetras

Jeroen Vanhooren Biotope, Uncategorised Leave a Comment

The Rio Araçá is an affluent of the Demini River, which is a tributary of the Rio Negro. The Araçá is a 390 km long blackwater river originating high up on the Serra Tapirapeco Mountain in the forests of the Guianas and flows through the Serra do Araçá, a state conservation unit near to the border between Amazonas and Roraima states.  The river is also situated in the wider area of the Yanomami Indigenous Territory, within which the indigenous Yanomami and Ye’kuana (The Canoe People) reside. In the centre of the Serra do Araca can be found the Cachoeira do El Dorado or the El Dorado Waterfall, it is Brasil’s highest waterfall at 353m! 

Davi Kopenawa, a Yanomami leader and shaman surrounded by children (Rio Demini, Brazil). © Fiona Watson/Survival International

  The waters of the Rio Negro and many of the rivers and streams in its drainage basin are extremely dark in colour and epitomise the term black-water. They are arguably the darkest waters in the entire Amazon and have extremely low conductivity, yet despite the poor mineral content the region is home to a vast richness of biodiversity; more can be read about this in the 1989 publication “Rio Negro, rich life in poor water” by Goulding et al. 

The dark tea-coloured waters of the Rio Negro region underpinned with fine white sand and leaf litter. © N. Rezeq 2007

As can be expected the wet/dry seasons have a huge influence on these surroundings and are the driver for a great deal of the behaviour of fishes and plant life, especially with regard to reproduction. Although nutrients in this area are poor and only restricted light penetrates through the forest canopy or even the water, one can find some very special places including some instances of less tannin-stained clear water habitats.   This tank simulates a planted area in a small Igarapé in the upper parts of the Rio Araçá and is a tribute to the two most popular ornamental fishes: Paracheirodon axelrodi and Hemigrammus bleheri. Smaller fishes use these areas for protection against predation and to feed on periphyton (organic matter) that was caught by the leaves.  Substrate is made of fine white sand, that covers the entire region. Tree branches, twigs and leaves. Plants in the background that provide shade and food complete this landscape. pH is very low (4-6) with very low conductivity. Temperature 25-29°C. In this specific habitat the water is tea-coloured.

Fallen trees and their branches provide important refugia for many aquatic species in this igarape along the Rio Araca. © N. Rezeq 2007

In these igarapé habitats numerous fish species can be found including Paracheirodon axelrodi, Paracheirodon simulans, Hemigrammus bleheri, Apistogramma cf. gibbiceps, Apistogramma cf. paucisquamis, Apistogramma cf. pertensis, several Nannostomus sp., Carnegiella marthae, Copella cf. nattereri, Rivulus ornatus, Pyrrhullina sp. Brittanichthys sp., Iguanodectes geisleri, Crenicichla sp., different Loricariidae… In this specific biotope many Nymphaea sp., mostly small under water (red coloured), Eleocharis sp., Mayaca sp. and Hydrocotyle sp. In the broader region Utricularia, Sagittaria, Cyperus, Nymphoides, Salvinia, Najas, Nitella and many, many more. A very special sight along the Rio Negro, the Pink River Dolphin (Inia geoffrensis) also known as the “Boto” in Portuguese or “Delfin Rosado” in Spanish – © N.

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