As for TJ's fish oil, as a general practice, I avoid all store brand fish oils. Years ago, I used to buy a local health store brand (similar to Whole Foods), and one day broke open the gel. It was completely disgusting. Not just fishy, but rotten fish head fishy.
If your oil is fishy, but not sewer-quality, then I'd say it probably isn't rancid, but there certainly could be some oxidation going on. One option is to simply return it to Trader Joe's, tell them it's rotten, and get your money back.
And one weird thing I've noticed about Nordic naturals is, it too has a somewhat fish taste (masked by lemon). It's not bad or anything, but compared to low concentrate Carlson or Barlean's, it's certainly fishier. Now, that doesn't mean it's oxidized, as it could simply have to do with its processing. But if you are really fish adverse, there are some brands out there that have little to no fish flavor at all.
I would say the TJ brand is on the edge between fishy and rotten fish head - it was surprisingly strong, which prompted me to make the post in the first place to see if anyone with the same product could see how their TJ pills smelled/tasted.
I agree that the Nordic Naturals is also somewhat fishy, but it not nearly as much as the TJ. But as I said before its not really 1:1 because of the lemon. I do respect that this brand has undergone much more scrutiny than the TJ "generic" as to its quality etc, and I am just going to stick with it (or Carlson, e.g.), and trust the test results. (And I think I will return the TJ pills, I had thought about that but wasn't sure, but now I will just tell them its rotten as you recommended.)
It's always debated whether or not the fish burps are a sign of oxidation or just the body getting used to the fish oil. I think we can figure it out based on 245's experience, though.
Did you get the same fish burps from Nordic Naturals that you had with the trader joe's brand?
I don't know that I we can draw any general conclusions from my single experience. That said, the Nordic Naturals do not seem to give me fish burps (again: could be lemon-related). As above, basically I thought I could save some money going with the cheaper TJ brand, but my experience was not good, so I will pay a bit more and stick with something I believe I can trust a bit more.