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Myliobatiformes Potamotrygonidae (the River Stingrays )

Myliobatiformes Potamotrygonidae (the River Stingrays ). Jeff Guertin 11/27/07. Roughly 3-4 genera, 20 spp. Most literature still lists under Rajiformes, not Myliobatiformes 4 genera Potamotrygon - most of the species Paratrygon Plesiotrygon

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Myliobatiformes Potamotrygonidae (the River Stingrays )

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  1. Myliobatiformes Potamotrygonidae (the River Stingrays) Jeff Guertin 11/27/07

  2. Roughly 3-4 genera, 20 spp. • Most literature still lists under Rajiformes, not Myliobatiformes • 4 genera • Potamotrygon - most of the species • Paratrygon • Plesiotrygon • amphi-American Himantura signifer (Family Dasyatidae?)

  3. 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 * Freshwater rays in asia and africa?

  4. 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

  5. Potamotrygon motoro - Ocellate river stingray Plesiotrygon iwamae - Long-Tailed River Stingray Paratrygon aiereba - Discus Ray Potamotrygon henlei - Polka-dot stingray

  6. 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

  7. Food Habits • Carnivorous bottom feeders • Worms • Crustaceans • Mollusks • Insects • Catfish

  8. 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.

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

  10. 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

  11. 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. <http://www.flmnh.ufl.edu/fish/>. Downloaded on 25 November 2007. • IUCN 2006. 2006 IUCN Red List of Threatened Species. <http://www.iucnredlist.org>. 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.

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