Negative commandment · Lo Ta’aseh #173 of 613
Not to eat non-kosher fish
שלא לאכול דג טמא
The verse · Vayikra 11:11
וְשֶׁקֶץ יִהְיוּ לָכֶם מִבְּשָׂרָם לֹא תֹאכֵלוּ וְאֶת־נִבְלָתָם תְּשַׁקֵּצוּ
“and they shall be abominable to you; you shall not eat of their flesh, but their carcasses you shall abominate.”
The Rambam’s words
Not to eat non-kosher fish, as [Leviticus 11:11] states: "They shall be [regarded as] a detestable thing for you. Do not eat of their flesh."
שלא לאכול דג טמא, שנאמר "ושקץ, יהיו לכם; מבשרם לא תאכלו" (ויקרא יא,יא).
Why · Sefer HaChinuch #156
To not eat impure fish
“It is from the roots of this commandment [that it is] because the body is an instrument of the soul — with it, it carries out its activity; without it, it can never complete its work.”
Who & when
“And [it] is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Forbidden Foods הלכות מאכלות אסורות