If you gut your dogfish straight away you sould not get any ammonia smell at all. Fillet and bag your dogfish, or any fish for that matter, without washing it. I repeat don’t wash the fillets in saltwater or freshwater. Just bag it as is. If the shark has not been cleaned straight away after capture, soaking the flesh in fresh water will only remore a little of the ammonia smell. It will not work if there is a strong smell of ammonia. I would also add that you should remove the red muscle from the fillets as this will be stronger flavoured.
According to the late David H. Graham, in [i:dpywlgo3]A Treasury of New Zealand Fishes[/i:dpywlgo3] Canada and the United States carried on large scale fisheries and canneries for utilising dogfish where it was sold as greyfish. So it is perfectly OK to eat.