I used to work in a warehouse, shipping packages through UPS and Fedex. I think it was best that you weren't able to get the package in that state. Like jlnguyen said, it just releases all of the liability on you; you wouldn't be able to do squat about the fish that didn't make it. If it was released to you, UPS or the shipper wouldn't be able to prove what did or did not make it. Unless it's an irreplaceable or super rare fish, it was definitely the right thing to do to get it sent back.
Anyways, UPS covers up to $100 for their packages (if your fish was worth more than $100, you should double check to see if the shipper had the package insured for its proper value).
