مچھلی اور دمِ مسفوح
@AhmadShoaib the answer seems to be subjective (as I understood from the 2-parts answer by Ghamidi shb). Smaller fish have much much less amount of blood. That much amount of blood just remains left in almost all cases of tazkiya, even for chickens, goats, and others. However, if the fish is large enough then yes, you’d need to perform tazkiya on it, a proper slaughtering.