Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 173
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 173, with English translation by Maimonides (Rambam).
שלא לאכול דג טמא, שנאמר "ושקץ, יהיו לכם; מבשרם לא תאכלו" (ויקרא יא,יא).
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."