In addition to harboring high levels of terrestrial biodiversity, the Amazon basin also contains the largest share of freshwater species in the world due to the immense size of the basin and the variety of aquatic habitat available . Freshwater species in the Amazon most commonly include fish, crustaceans, mollusks and insect larvae. These organisms are important to both riparian and terrestrial ecosystems as they are food sources for a number of aquatic animals and are also eaten by land-dwelling salamanders, mammals and birds. There are at least 3,000 species of freshwater fish species in the Amazon River basin. This includes hundreds of cichlid species, known for their diversity in body shape, coloration and life history patterns, as well as several species of freshwater stingrays. Though the inhabitants of the Amazon River are numerous and diverse, there is limited information on Amazonian aquatic species due to the difficulty of studying such an extensive river system.
The Amazon or pink river dolphin (Inia geoffrensis), commonly known as boto, is one of the few aquatic mammals found in the Amazon River. It is a pale pink color and different from other dolphins in that it has a flexible neck, allowing it to turn its head left and right . The river dolphin mostly feeds on crabs, turtles and bottom-feeding fish, putting it at risk for mercury poisoning due to bioaccumulation. The river dolphin is also threatened by water pollution, boating collisions and habitat fragmentation due to river development projects .
The arapaima (Arapaima gigas), commonly known as pirarucu, stands out among the many fish in the Amazon Rivers because it is one of the largest fish in South America, growing up to 15 feet long and 400 pounds. This fish is also remarkable because it has lungs in addition to gills, meaning it is able to breathe air . It is a top predator, consuming mostly fish, but sometimes propels itself out of the water to catch birds, lizards and even small primates. Though the arapaima is commercially important and has been traditionally fished by Amazonian communities, it may now be at risk for extinction due to insufficient fishing policies and regulation .
While rivers in western Amazonia are still relatively pristine, many are now threatened by the development of dams, roadways and other infrastructure. Pollution is also a significant threat, particularly due to runoff from nearby agricultural and industrial activities, as aquatic species are sensitive to changes in the biogeochemistry of their watershed. Mercury residue from illegal gold mining is an especially dangerous pollutant because it does not easily degrade, but instead accumulates in the sediments or is absorbed by algae and other plankton. When other organisms consume the plankton, the mercury is not excreted and is stored in their tissue . Therefore organisms higher up in the food chain tend to bioaccumulate mercury, and older, larger fish and predatory birds contain the greatest amounts of mercury. This is dangerous because mercury is a neurotoxin causing damage to the central nervous system, and poses a serious health threat to wildlife and humans that consume affected fish .
- Thieme, M. et al. (2007). Freshwater conservation planning in data-poor areas: An example from a remote Amazonian basin (Madre de Dios River, Peru and Bolivia). Biological Conservation, 135, 484-501.
- http://www.erie.buffalo.edu/2010 Summer Workshop/Week 2/Workshop 2/Fuhrmann/reference material/Thieme et al 2007FWconservationPlanningInDataPoorAreas.pdf