Garum, a fish sauce which was even more ubiquitous to the romans than soy sauce or Worcestershire sauce (which supposedly happens to taste somewhat similar) is to us, was made by basically leaving heaps of anchovies out in the sun to rot and then collecting the drippings, or when made industrially you'd instead have biiiiig clay vats full of fish getting the same treatment. that's a kind of goop! and they made lots of it too
I can't attach an image of it being made because I can't add a CW to this post and,, it's gross,, so take my word for it haha
instead, here's a very gorgeous shot of the not-goop that you end up with after the years of fermentation
