If I am not mistaken, Potamotrygon sp. C is what people commonly refer to as hystrix.
Here is an excerpt from this very insightful pdf.
http://journal.nafo.int/35/charvet-almeida/22-charvet-almeida.pdf
"The species Plesiotrygon iwamae, Paratrygon
aiereba, Potamotrygon motoro, P. orbignyi, P. schroederi,
Potamotrygon sp. C certainly have their reproductive
cycles closely related to the hydrologic cycle of the river
basins that they inhabit. For these species the hydrologic
cycle triggers the beginning or directly influences all
reproductive cycle stages of these potamotrygonid rays."
If you look at table 1 in the paper, you will see that Potamotrygon sp. C specifically copulates during the rainy season. Attempting to replicate the environmental cues that would trigger reproductive behavior in rays in the wild might be your best chance at success. As mentioned before, large, cold water changes might do the trick. Perhaps several during the course of a week or more, two or three changes a day might work. I was told about a program that featured a guy that breeds rays who took a hose and sprayed cold water directly over a female ray and within minutes a male was after her.
