Myliobatiformes Potamotrygonidae (the River Stingrays)

Jeff Guertin

11/27/07

Roughly 3-4 genera, 20 spp.

  • 4 genera
  • Potamotrygon - most of the species
  • Paratrygon
  • Plesiotrygon
  • Amphi-American Himantura signifer (Family Dasyatidae?)

General Characteristics

  • Only family of batoids restricted to freshwater habitats
  • Generally medium to large sized batoids
  • Dorsal surface of the disc and tail usually covered with many denticles, thorns and tubercles
  • Up to four stings may be present in one individual
  • Oral teeth are small with short cusps in usually less than 50 rows in either jaw
  • Colorful dorsal arrangements
  • Max salinity they can withstand is 15ppm (pure seawater is around 35ppm)
  • Stings are continuously worn, shed and replaced

Distinctive Features

  • Potamotrygon
  • Sting is well developed and more posterior
  • Finfolds posterior to caudal stings
  • Eyes moderately large
  • Paratrygon (one spp.)
  • Slender whiplike tails, sting is reduced and located near tail base
  • No finfolds
  • Small eyes
  • Plesiotrygon (one spp.)
  • Slender whiplike tails, sting is well developed and more posterior
  • Only ventral finfold
  • Small eyes

Habitat

  • Tropical - only occur in South American rivers that drain into the Atlantic Ocean or Caribbean Sea
  • Shallow areas
  • Most species have distributions restricted to a single basin or river system, with only a few species present in more than one basin

Food Habits

  • Carnivorous bottom feeders

Size, Age, & Growth

  • Population doubling time ~14yrs
  • Six are dwarfspecies with maximum sizes between 23 and 29 cm disk width
  • P. humerosa, P. magdalenae, P. orbigvi, P. schuemacheri, P. vepezi, P. signata
  • Others larger (80-90cm DW)
  • Paratrygon aiereba, Potamotrygon brachvura
  • Females usually larger than males
  • Size at maturity for male Potamotrygonids 20-25 cm DW and females 24-32 cm DW
  • Gestation thought to be a little over 3 months.

Reproduction

  • Ovoviviparous (aplacentally viviparous)
  • Seveloping embryos are nourished by uterine milk secreted by trophonemata
  • Both uteri are functional
  • Usually between 2-7 pups/litter

Conservation

  • Only 5 listed on IUCN
  • 4 DD, 1 LC
  • Generally considered harmless, not used in aquarium trade
  • Thought to be threatened due to endemic nature
  • Considered by most south americans to be dangerous due to their venomous sting, but not really hunted

Bibliography

  • Barbaro K.C. et al. 2007. Comparative study on extracts from the tissue covering the stingers of freshwater (Potamotrygon falkneri) and marine (Dasyatis guttata) stingrays. Toxicon 50: 5.
  • Carrier, J,, Musick, J., and Heithaus, M. 2004. Biology of Sharks and Their Relatives. CRC Press, Boca Raton.
  • Florida Museum of National History. < Downloaded on 25 November 2007.
  • IUCN 2006. 2006 IUCN Red List of Threatened Species. < Downloaded on 25 November 2007.
  • Oldfield, R.G. 2005. Biology, husbandry, and reproduction of freshwater stingrays II. Tropical Fish Hobbyist. 54(1): 110-112.
  • Silva, TB. 2007. Preliminary data on the feeding habits of the freshwater stingrays Potamotrygon falkneri and Potamotrygon motoro (Potamotrygonidae)from the Upper Parana River basin, Brazil. Biota Neotropica v7.