Its a real pain in the ass to get them eating. As miles said, they have a really small mouth and can hardly eat anything. Even tiger rays are easy compared to antennas. Another problem is their tail. Its usually like 4-5 times as long as its disc, but usually gets broken during shipping, this is the other factor why they're so hard to keep. Not sure about brackish water though. I kept mine for about a month before i got tired of the constant need of blackworms.