Glad you were able to get the fish lice off but I would still treat the tank because if you can see the adults then there is eggs for sure and they will continue to come back. I don't know if the medications others have mentioned will be safe to use with a ray. Rays can be very touchy when it comes to using medications and after some searching I found an archived post from MFK and they recommend using the medication that I mentioned called Dimilin. Here is a post from that thread:
Stingrays in captivity are usually not susceptible to the common diseases of other tropical fishes. Occasionally, newly imported specimens may carry fish lice (Argulus spp.). These ectoparasites appear as small brown circular spots, about 2-3 mm in diameter, and are more readily seen on light-color stingrays. Fish lice are usually only observed in small numbers (i.e., 2-3) and if gently touched the parasite will skitter across the skin of the stingray. When on the dorsal surface, fish lice can be removed readily with forceps. When on the ventral surface, removal is more difficult as it is difficult to invert stingrays. In these circumstances, it is easier to pinch the parasite through a net, from underneath, in order to remove it. Sudden heavy outbreaks of fish lice may occur within an exhibit, without the addition of new stingray specimens. These outbreaks are probably caused by a few unobserved parasites successfully reproducing. Dimilin or diflubenzuron (e.g., Anchors Away®, Jungle Laboratories Corp., USA), a chitin inhibitor non-toxic to fishes, is effective at treating fish lice outbreaks at a dosage 2,650 mg l-1. This treatment should be repeated once after a two week period.
Edit: I have found some conflicting info out there about Prazi being used with rays. A few people have said they used it with their rays and they were fine but I also found a post that said on the bottle of Prazi pro in the fine print it says a lot of anti parasitic meds are not good for catfish and rays, so I would suggest looking at the bottle of Prazi and see what it says but use at your own risk.
All matter is merely energy condensed to a slow vibration, we are all one consciousness experiencing itself subjectively, there is no such thing as death life is only a dream which is an imagination of ourselves. Bill Hicks
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Last edited by ua hua; 07-28-2013 at 04:17 AM.
Reason: added info