I know that I would not eat, nor would I feed my family, food that has been thawed and then refrozen. So, I probably wouldn't do it with a fish either.
Ive done this before, and havent had problems, considering the kind of things fish eat in the wild i dont think this is too bad, unless of course its been defrosted for a rather long time
i just meant if its only been thawed for a couple hours that should be fine, but i expect it would start to go off after a day or so. Sorry i cant be precise, how long has yours been left for?