yeah, thats the only problem with the bag. the spikes on the tail might tear it. you can guide the stingray into the tote and take out as much water as possible. leaving about 1/2 inch of water. then you just fill it back up. just make sure to tell the sting ray to hold its breath. 
I don't need a trip to the hospital trying to explain I had a 24" south american stingray prick me.. 