If the 'blaze' color leans more toward orange than yellow and the fish is simply labeled 'a large fish,' the item is not an event item but rather produced by the same bug that allowed creation of orange ingots. Legal to own, illegal to create. (Referring the the EA ToS, not the law, certainly.) As to value, I believe I saw one up for 1m. I have no idea if that is fair or a con. But I have not seen too many yet, so it may in fact be worth it.
That said, there are some event items that are similar, but distinguishable from these.