Levamisole is safe with rays, but only when dosed correctly. Otherwise, all bets are off. I posted the following years ago, and again just yesterday in another discussion here on MFK. The correct manner to treat is treat using dosage stated below (2 ppm) for 24 hrs, wait 2 weeks, and treat again.
http://edis.ifas.ufl.edu/fa091
One effective bath treatment dose is 2 ppm (mg/liter) levamisole for 24 hours, with a repeat treatment in two to three weeks.
The scientific community considers 2ppm of Levasimole HCl to be an adequate dosage, which works out to 1gr per 100 gallons, not 5gr per 100 gallons as constantly reported on the internet.
The 5gr dosage rate originates from Charles Harrison, who is a chemist/ fish hobbyist, that sells (or used to sell?) Levasimole HCl, not a VMD that specializes in treating tropical fish. (such as Dr. Roy Yanong)
Dr. Yanong also suggests that the treatment duration be 24 hrs, not 3 days as currently suggested by Charles Harrison. It appears that Charles got his info from a killi hobbyist (Ken Laidlaw), that as far as I can tell has no real qualifications for treating fish for disease etc beyond the hobbyist level.
Dr. Roy Yanong's bio ......
http://sfrc.ufl.edu/people/faculty/yanong/
HTH