Vayechi – Hamalach Hagoeil V
“May the angel who redeems me from all evil bless the lads, and may my name be declared upon them, and the names of my forefathers Abraham and Isaac, and may they proliferate abundantly like fish within the land.” (Genesis 48:16)
Jacob’s considerations may have been similar to the blessings God bestowed on the fish in Genesis 1:22. I explained there that a special blessing for the fish was called for due to their habitat being less suited for successful and enduring procreation than the conditions prevailing on dry land. God therefore increased the fish’s natural reproductive prowess to counter the negative conditions prevailing in their habitat.
Jacob too accorded Joseph’s sons greater power of reproduction when he blessed them by comparing their fruitfulness to that of the fish. Inasmuch as Ephraim and Menashe did not reside in regions which are hostile to human reproduction, Jacob’s blessing was even stronger than God’s blessing for the fish. (Or Hachaim HaKadosh)
Perhaps Jacob intended to bless Israel with the ability to continue to reproduce no matter how hostile our environment. The women in Egypt continued to bear children even when their husband’s had given up all hope for the future.