Veternarians have performed necropsies on the stingrays and say they have only found evidence of  irritation of the gills. This leads the vets to believe the problem is with the water environment. According to the zoo, the ongoing testing of the water show it to be in the normal range of sustaining the animals, so their attention is set to turn to toxins.

Those toxins, the officials at the zoo say, could have been added to the water intentionally. Once their own water environment tests are double checked, the zoo will send off samples of the water and dead animals to test for toxins. Also infectious diseases and cultures of the food will be tested, but given the sudden nature of the deaths, the most possible culprit is the likelihood of an introduced toxin.

To hear the zoo's reaction, click on the link.