IMO the only obsticle in keeping retics is getting a young speices home with the least amount of stress. once they are comfortable with their new environment they can be just as hardy as other rays
just picky eaters and usually low quality before they are purchased..
I think they are hardy though I have put mine through hell and back.. but it seemed like the first 2 weeks were the most important as they were very stressed, discolored, burrowing, and only ate blackworms..