Lol no. Trick question right? Betadine is a human topical medication, a Barramundi is a fish. You can not use human treatments on fish. Your fish most likely has what is called 'white spot', or Ich. It is caused usually by new fish added into the tank, or new plants, otherwise if these aren't possible, it's usually due to worsened water parameter conditions. This happens from time to time. Sudden water changes can stress your fish which lowers it's immune system making it more susceptible to diseases and infections. A lot of these are already laying dormant in your tank, so most likely the Ich was already there and the changes in the water caused the fish to stress and get it. Water parameter changes are things such as ph level changes, temperature, an increase in ammonia or nitrite or nitrate (or a combination of these) and water hardness, which could be caused by your normal water changes or neglect of not changing the water as often as it needs to. Ich is caused by a external parasite called Ichthyophthirius mulifiliis, it has a life cycle that usually lasts about 28 days, and can be shortened if you raise your tank temperature to about 27 degrees. Because you have a Barra, you will have to do this very slowly, so it doesnt cause your fish more stress. You will also need to add in a Ich treatment (avail. from any fish or pet shop), which has the active ingrediant of malachite green. This will cause the bacteria to drop off into your gravel, so if you have other fish in there, you should try and remove them because rubbing on the gravel will cause them to get Ich if they aren't in good health. You will need to add in extra aeration, as Ich infects the gills and causes respiratory problems. Don't worry too much about it, it's a very common fish disease, and lucky, its easy to cure.
