I agree, never ordered fish before (but will be!) but have used priority mail a lot. About half the time nothing is updated until after the package is received. FedEx and UPS are much better about that if it is important to you, but I like priority mail.
Ps: I try to stay away from FedEx ground, they only handle the shipment for part of the trip, then hand off to the post office or DHL. The double handling always seems to cause delays.