Here’s the actual source:
Yoreh deah 13. Taz #1 quotes the passuk Numbers 11:22 in Bahalosecha, which shows that fish just need to be gathered- the passuk uses “gathering” for fish and “slaughtered” for animals. You can eat them dead or do eiver min hachai as well. But u can’t eat them alive and wriggling. Sorry Gollum. Same with Mr. Crunchy Smiles the grasshopper.