I don't know why people are under that impression. Maybe hard to bring back to health during the first 6 months due to stress, starvation and parasites, but other than that, feed them worms and do water changes and they should be fine.
Most of the people that buy them have no experience with rays and have a huge 55 gallon aquarium! They rays don't feed and die. Most probably don't make it out of the fish store.
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