Ecology

This page describes the environment of Potamotrygon motoro and how it interacts with said environment and the other species within the ecosystem.

Habitat

Geographical Range

Potamotrygon motoro are found in a large distribution between Northern South America and Southeast Asia. The ocellate river stingray is native to the Amazon, Orinoco, Parana-Paraguay, and Uruguay river basins in Northern South America (Motoro Ray). Within the past 15 years, development of hydroelectric dams across the Amazon River have led to this species gaining access to previously unavailable regions in the upper Amazon (Spiegel 2013). This stingray is not only found in South America. There have been a number of reports of Potamotrygon motoro in the reservoirs of Singapore. This invasive population is thought to be a result of released aquarium specimens (Ng et al. 2010).

Temperature and Salinity

The distribution of Potamotrygon motoro is solely within the tropics. The water temperature of the species’ native range is between 24 and 26°C (Froese et al.) This species is a purely freshwater species. Due to the loss of the ability to retain urea, rays of the family Potamotrygonidae are unable to survive in salinities of more than 40% that of seawater. The family are considered to be stenohaline (Tresberg et al. 2006).

Depth

Ocellate river stingrays are largely benthic creatures with a preference for sandy and muddy substrates (Oliveira et al. 2017). The depths at which they are found vary, though they prefer to be near the edge of a given body of water. This species has been found at depths of 0.5 to 2.5 meters in the Paraná River as well as depths of 7 to 10 meters in the Uruguay River (Spiegel 2013).

Behavior

Migration and Aggregation

Ocellate river stingrays are migratory. Due to their stenohaline nature, this species is thought to be potamodromous. This means they migrate solely within rivers (Froese et al.). The species exhibits sexual segregation and is thought to be solitary outside of breeding seasons (Oliveira et al. 2017, Spiegel 2013).

Hunting

Potamotrygon motoro often buries itself under the soft substrate while waiting for prey to pass by (Motoro Ray). After prey moves close to the stingray, the ray undulates its disc to stir up sediment and block vision. The ray then ambushes the prey, using its spiracles to remove silt from its mouth while eating (Garrone-Neto & Sazima 2009). Prey varies by age and environment, with juveniles eating small molluscs and crustaceans while adults add small fish and larger crustaceans to their diet (Almeida et al. 2010).

References

Almeida MP, Lins PMO, Charvet-Almeida P, Barthem RB (2010) Diet of the freshwater stingray Potamotrygon motoro (Chondrichthyes: Potamotrygonidae) on Marajo Island (Para, Brazil). Braz J Biol 70.

Froese R, Capuli E, Garilao C, Pauly D (no date)Potamotrygon motoro. https://www.fishbase.us/summary/SpeciesSummary.php?ID=6382&genusname=Potamotrygon&speciesname=motoro&AT=Potamotrygon+motoro&lang=English (accessed April 25, 2024)

Garrone-Neto D, Sazima I (2009) Stirring, charging, and picking: hunting tactics of potamotrygonid rays in the upper Parana River. Neotrop Ichthyol 7.

Motoro Ray (no date)https://www.georgiaaquarium.org/animal/motoro-ray-2/ (accessed April 25, 2024)

Ng HH, Tan HH, Yeo DCJ, Ng PKL (2010) Stingers in a strange land: South American freshwater stingrays (Potamotrygonidae) in Singapore. Biol Invasions 12.

Oliveira AT, Araujo MLG, Lemos JRG, Santos MQC, Pantoja-Lima J, Aride PHR, Tavares-Dias M, Marcon JL (2017) Ecophysiological interactions and water-related physiochemical parameters among freshwater stingrays. Braz J Biol 77.

Spiegel J (2013) Potamotrygon motoro Black river stingray (Also: Ocellate river stingray; South American freshwater stin). https://animaldiversity.org/accounts/Potamotrygon_motoro/ (accessed April 25, 2024)

Tresberg JR, Speers-Roesch B, Piermarini PM, Ip YK, Ballantyne JS, Driedzic WR (2006) The accumulation of methylamine counteracting solutes in elasmobranchs with differing levels of urea: a comparison of marine and freshwater species. J Exp Biol 209:860–870.