If things like this happen, you want the airline to completely lose your package and not ever find it. That way they will re-imburse you for the content amount that you declared.
If they "mis-place" your package and later found it, then they won't do anything but refund the shipping cost as their guarantee. NO shipping company will cover dead fish...when you put your declare content, you're only giving them a value in case they completely lose the package.