Hmmm.
We are probably talking about two different prawns then. The ones I have only go to brackish water to mate/breed. They then travel back upstream. Most growth and shedding occurs in freshwater. Which is why I add the iodine. I purchase them as post larval/juevies and grow out in fresh. There's no contact with mine with any brackish or marine. Now, the farm I get them from breeds them in brackish....but mine never see it. But since most of the growth/shedding occurs during the 4 month grow out, I have to add the iodine or risk trapped prawns. Its a production issue.