It's called oxidation. It's a pretty clear cut thing. If you want to prove that fish oil doesn't oxidize then go for it. I'm all ears. I've never heard anybody say that fish oil is non-perishable. That's a new one on me. Taste is just one way you can sometimes tell. It's not fool-proof. Oil goes bad. Some oils go bad faster than others.
Saturated lasts a long time. Monounsaturated (like olive oil) is second. And polyunsaturated (like fish oils) are very perishable. Cold is a way of slowing down the process of oxidation. There is nothing a manufacturer can do to take a polyunsaturated oil and stop that from eventually happening. Not without making the oil worthless.
But again, show proof it doesn't spool. Because asking someone to prove that it DOES is like asking them to prove that eggs spoil. Or that a can of green beans spoils once you open them. OF COURSE THEY DO. Even twinkies spoil
.
BTW, the risk of oxidation is even worse with the encapsulation process. You look at a big batch of fish oil there is going to be some oxidation. It can be measured by the end-products. You look at an actual bottle of fish oil caps and that oxidation will be worse. So lot number is more important than batch number. There is the IFOS program and there will be a web-site soon where manufactures will be able to post this stuff if I have my info right.
Some capsule products DO, btw, recommend refridgeration after opening on the label. Some just say store in a cool, dry, place. Some say store between approx. 60 to 70 degrees in a dry place. It probably shouldn't come as a surprise that manufactures do not agree on this. The trade off is moisture that collects on the caps when you open the container of cold capsules. There is most likely an absorbent in the bottle. Which is the best? I'd go for refridgeration until I find some real good info othewise. On the not encapsulated liquid oils, DEFINITELY refridgerate.