Why does it say "v'Sheketz Yihyu"?
Rashi: To forbid a mixture containing them if they add taste.
Seforno (Pasuk 2): The Torah refers to the species that contaminate the soul but not the body 1 as Sheketz.
Targum Yonasan: To include the juice and the brine of Tamei fish in the Isur.
Seforno: This incorporates Tamei species of fish (Pasuk 11, 12), birds (Pasuk 13, 20), locusts (Pasuk 23) and rodents (Pasuk 41), since all of these are not subject to Tum'ah.
Why does the Torah write specifically "mi'Besaram"?
Rashi: To preclude the fins and the bones from the prohibition.
What is the extra word "Teshakeitzu" coming to teach us?
Rashi: It teaches us that Yavchushin (gnats 1 ) that have been sifted are included in the prohibition.
Targum Yonasan: It comes to place an Isur Hana'ah on Sheratzim. 2
QUESTIONS ON RASHI
Rashi writes that "v'Sheketz Yihyu" forbid a mixture containing them if they add taste. We have other sources to forbid a mixture with taste of Isur!
Moshav Zekenim: One might have thought that brine is a mere secretion. Even though another verse forbids it, if not for this verse, one might have thought that their mixture is permitted.
Rashi writes that "v'Sheketz Yihyu" forbid a mixture containing them if they add taste. Toras Kohanim gives different Shi'urim of Bitul, and one of them is one part in 192!
Mizrachi: Perhaps Toras Kohanim discusses Min b'Mino, and Rashi discusses Min b'Eino Mino.
Gur Aryeh: The Tana'im in Toras Kohanim argue about how much gives taste. R. Yehudah holds that it is very potent, therefore the Shi'ur is one part in 192.