Why do Jews eat filtered fish? I've noticed that they mainly eat it on Friday night, with a small piece of carrot on top.
One of my personal "ponders" is why manufacturers catch tuna that was already in the water, take it out of the water, then they shape it round and finally, they put in back in a can with water all over again.
But, being that's what it is, there are toxins all over the place, in this process. The ocean has sewage spilling into it. The tuna eats the toxins from this sewage, and tuna tends to have high levels of mercury. Then, the tap water they use to can the fish. Well, that had *better** be filtered, because then you're eating intoxicated fish.
So, in general, Jews look specifically for filtered fish, esp. when buying canned tuna and salmon or any canned fish. I would assume that jarred fish is the same. I can't say for what happens with fresh fish, but, I gather that in a kosher fish store, when they "kasher" the fish (No, it's not soaked and salted or slaughtered, but the mashgiach makes it a kosher fish, somehow) they probably filter it, too.
That's what makes eating it safe and healthy. If you've been eating non-filtered fish, I suggest that you see a good GI specialist immediately, and have a colonoscopy done.