Rashi explains that the word udshu originates from the word ds (fish). Thus, the blessing was that Efraim and Menashe should multiply and grow just as fish multiply and grow without the evil eye affecting them. This part of the blessing was so basic that the fish symbol served as the emblem on the banner of the tribe of Efraim. Even today the fish emblem serves as a talisman against the effect of the evil eye. This effect stems from the occult power of the jealousy, hatred, and envy of others. The Sefas Emes states that if Yosef and his offspring were to be shielded from the effects of the evil eye, it was in the merit of Yosef closing his eyes to the seductress, Potiphar’s wife. Yosef deserved the title of “tzaddik” because of the “sanctification of his vision” which he had achieved.
We may suggest that Yaakov may have had a different reason for invoking the symbol of fish. We have seen that throughout Yaakov’s life journey, he tended to lead a solitary life: He always kept distant from the native population, forever seeking to raise his children in a homogeneous milieu, sheltered from foreign culture. Accordingly, when he blessed his children he saw before him the image of the aquatic world. Fish live their own lives in an element apart, in calm, and in depths unseen. And humanity, inhabitants of a completely foreign element to their own, hardly suspect this joyous, carefree, and serene existence of theirs which endures from generation to generation. This is how the Patriarch wanted his descendants to live, but in the midst of the land. they were to flourish in security and happiness in an element which was their very own. They were to be unencumbered by the outside world, which can not appreciate the significance of their lives. This is truly the greatest blessing – to live among the people in a world all our own.