John Calvin on Isaiah 19:8

8. And the fishers shall mourn. Isaiah still keeps in his eye the condition of Egypt. We have formerly mentioned {Bogus footnote} that the prophets made use of those figures of speech by which, when any country is mentioned, they chiefly name those things which abound in that country, and for which it is celebrated. Thus, when a vinebearing country is spoken of, they mention vines; if it abound in gold, they speak of gold; and if it abound in silver, they speak of silver. Accordingly, when he speaks of Egypt, which was well watered, and contained abundance of streams, he mentions fishing.

They who spread a net on the face of the waters shall languish. Some translate the word אמללו, (ămlālū,) “they shall be cut off,” but the more correct rendering is, “they shall be weakened;” for this corresponds to the mourning and lamentation which was formerly mentioned. Now, we know that in that country there was a great number of fishers, and that these formed a great part of the wealth of Egypt. When fishers were taken away, of whom there were vast numbers among the Egyptians, and of whom their wealth chiefly consisted, they must have been weakened. Now, if the nation be deprived of that which is its ordinary food, great poverty will follow. He therefore describes an astonishing change that shall pass on the whole country.