If you are wondering why no "Fish" the answer is very simple. If you are looking for information on the Internet about the Brewis family by just inserting the word "Brewis" into the search engine you will get many pages referring to Fish and Brewis, which has nothing to do with the Brewis family.
One explanation of 'Brewis' in this context is:
REMINISCENCES OF SHEFFIELD IN THE EIGHTEENTH CENTURY.
By R.E. Leader
SMITHIES, APPRENTICES, DAMES, DRESS, AND CUSTOMS
…Oatcake and porridge formed the staple fare of apprentices,
but the one was too often mouldy or sour, and the latter too
often made with water. A cutler in Allen Street named
Barber, who had sixteen apprentices, was noted, even among
the penurious, for his especial meanness. It was the custom
in his household to make the oat cakes in large batches, so
that they might be stale enough, when placed before the
apprentices, to discourage inordinate appetite. The lads, when
opportunity offered, would snatch an oat cake hot from the…
bakestone, to enjoy it fresh, and to this end they would hide
the stolen morsel anywhere, under their shirts, or thrust in
the coal hole. As a rare treat, there was sometimes for dinner
brewis, or brewes (oat cakes, mixed with dripping and hot
water, and seasoned with salt and pepper), still the traditional
dish when the members of the Cutlers' Company lunch
together at the annual swearing in of the Master Cutler.
It has become one of the classic Newfoundland dishes, "Fish 'n Brewis" (pronounced broos). Brewis is bread soaked in water, then boiled. Traditionally, it is made with hardbread or hardtack - -a cracker-like, nugget-shaped dried ship's biscuit. There is no single recipe for fish and brewis. Every Newfoundland cook has his or her own way of preparing it, every area its style. Usually it's served for breakfast, but it could be eaten any time. (Made with Fresh or Salt Fish)