A study published in the most recent issue of the journal Neotropical Ichthyology has reported the feeding behaviour of freshwater stingrays in the wild.
Domingos Garrone-Neto and Ivan Sazima observed and recorded the hunting tactics of two species of potamotrygonid rays (Potamotrygon falkneri and P. motoro) in upper Paran River.
After a total of 132 observations (62 P. falkneri and 70 P. motoro) made snorkeling and scuba diving both day and night, the authors recorded three forms of foraging behaviour:
The first was for the ray to hover close to the bottom or settle on it, and undulate its disc margins. This stirred the substrate and uncovered hidden small invertebrates (mostly larval insects, snails, and crabs), apparently trapped under the ray s disc.
The second was for the ray to slowly approach the shallows and charge at prey concentrated there, stunning or trapping them under its disc. This hunting behaviour was observed only at night and targeted freshwater shrimps and small tetras.
The third was for the ray to approach vertical or inclined surfaces such as tree stumps, boulders, and concrete slabs and walls. The ray exposed the anterior part of the disc above the water surface and picked out prey (mostly snails) adhering to the substrate.
For more information, see the paper: Garrone-Neto, D and I Sazima (2009) Stirring, charging, and picking: hunting tactics of potamotrygonid rays in the upper Paran River. Neotropical Ichthyology 7, pp. 113"116.