Q. Is there a prohibition to eat parts cut from a fish while it was still alive. I have seen that done in various fish stores. Is that not Eiver Min Hachai? (eating a piece of a live animal).
A. Tosafos (Shabbos 90b) rules that it is permitted since the prohibition of eating Eiver Min Hachai applies only to animals that can undergo Shechita and not to fish.
However, there is a prohibition of Baal Teshaksu (or doing something disgusting) involved, when one bites into a living fish. (See Shulchan Aruch Y.D. 13).
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a