I don't know, whether it is an intended food spoiling mechanic, or just a plain bug. Someone reported is a year ago, but I couldn't find any answer to that, so I decided to repeat it:
About a week or two ago I was fishing, and decided to put the really big ones (2.5kg+) on the drying frame to try out, how great gluttony value they will have. If I remember correctly, the largest, 3.08kg fish got about 80 as the maximum value (the minimum was 1, as it's stated on the wiki). The max value quickly drops as the weight decreases, so I just kept the two best fishes (two Angel-Winged Seabasses) for my next gluttony session and put them into containers.
Now the problem comes here, as I was reorganizing some storage (still days until full and fed up wears out) I checked the fishes. Both of them have gluttony values reset to 0.0-1.0, technically they were rendered worthless. No change to the item name or any of the other values, just the gluttony.
I'm not sure, wether this is a bug or a mechanic. I intend to catch more fishes and try out whether the decline is procedural, or happens instantly after a certain time. If it turns out to be a mechanic, I will post about it in the wiki thread, though I'd like to repeat what the guy in the previous complaining post said, that dried fish is practically useless even without loosing gluttony values, and with it, it's just a waste of time and drying rack place.