THE STEINHART AQUARIUM - Gulf of Guinea Science ...

96 A Docent Field Guide to the Species of the Steinhart Aquarium
Ocellated Freshwater Stingray
Potamotrygon motoro (Potamotrygonidae)
River stingrays
Distribution: South America: Uruguay, Paraná-
Paraguay, Orinoco, and Amazon Basins.
Habitat: Freshwater, able to tolerate only a
narrow range of salinities.
Appearance: Length to 1 m, weight to 15 kg.
Body greatly flattened and circular, composed
principally of expanded pectoral fins. Tail is
slender and longer than body with venomous
spine. Ventral color muddy brown inset with
darker brown circular markings.
Diet: Mostly benthic hard-shelled invertebrates,
such as clams, mussels, and crustaceans.
Also worms, insect larvae, and small fishes.
Like most rays, flat teeth are used to grip
and crush prey that is sucked into the ventral
mouth. Like all river stingrays, it has exceptionally
good eyesight and its jelly-filled sensory
pores (Ampullae of Lorenzini) detect prey buried
in the substrate or hidden in murky water.
Reproduction and Development: Sexes separate.
Fertilization internal. Livebearers.
Conservation Status: IUCN Data deficient. This
brackish water ray is poorly known and life history
and population data are lacking. Further
studies and a new assessment in the near future
have been highly recommended, due to the
limited geographic range and the major impacts
affecting river habitat of this species.
Remarks: River Stingrays (Family Potamotrygonidae)
spend much of the time buried in
sand or mud with only their relatively large
eyes protruding.
This family is the only group of rays adapted
exclusively to freshwater and is found only in
Neotropical river basins.
Potent venomous spine, used defensively,
makes this a dangerous species. Like all
stingrays, sheds spine periodically as the
individual grows.
White-blotched River Stingray
River Stingrays
Potamotrygon leopoldi (Potamotrygonidae)
Distribution: South America: Tocantins River
basin.
Habitat: Freshwater, able to tolerate only a
narrow range of salinities.
Appearance: Width to 45 cm. Body greatly
flattened and circular, composed principally
of expanded pectoral fins. Tail is slender and
longer than body, has venomous spine. Color
black, white polka dots.
Diet: See Ocellated Freshwater Ray above.
Reproduction and Development: Ovoviviparous.
Like all in the family, fetuses developing in
the mother’s uterus first feed on their yolk sacs,
after which filaments develop from the uterine
wall and carry nutrients and remove wastes from
the fetuses until they are fully developed.
Conservation Status: A rare, poorly known
river ray, possibly endemic to river drainages in
Brazil where freshwater habitat degradation is
occurring. Although this attractive freshwater
ray enters the ornamental fish trade, life history
and population data are lacking. Further study
and a new assessment in the near future is
highly recommended for this species.
Smooth Back River Stingray
Potamotrygon orbignyi (Potamotrygonidae)
River Stingrays
Distribution: Amazon and Orinoco basins;
rivers of Guyana.
Habitat: Riverine sandy substrate into which
they burrow.
Appearance: Mottled, grayish-brown, smooth
skinned; rough, flat teeth; At maturity, this
species can reach one meter in overall length.
Diet: Crustaceans, isopods, insects and their
larvae.
Reproduction and Development: Ovoviviparous;
as in all elasmobranchs, sperm transferred
by clasper to female for egg fertilization.
Copulate in rainy season; young are born in
next rainy season.
Remarks: Shed and regenerate stings regularly.
CLASS ACTINOPTERYGII
(RAY-FINNED OR BONY FISHES)
ORDER ACIPENSERIFORMES
(STURGEONS)
Pallid Sturgeon
Scaphirhynchus albus (Acipenseridae)
Sturgeons
Distribution: Missouri and Mississippi