I think FedEx does ship tropical fish. A very popular internet vendor told me they ship using FedEx and it's their preferred method.
FedEx will indeed accept live tropical fish as a general company rule. However, the manager (and sometimes just the counter jockey) will make their own decision and refuse to take the package.
The same situation happens at the U.S. POST OFFICE. Their regulations state that they do accept live animals for shipping (with specific strict requirements) but each individual location's Post Master General (aka the boss) can just make their own decision and refuse (even if you show them the written Postal regulations that allow it).
You are basically at the individual location's mercy whether they will accept your shipment.
I've been shipping live fish for probably going on more than 20 years now and my first choice is always air cargo through one of the airlines. In fact, I've even agreed on a regular basis to handle shipping through the airport for other hobbyists that do not have an airlines account. However, I have my own personal standards/requirements that have to be agreed on.
Since September 11th, 2001 ALL airlines require you to be what is called a "Known Shipper" which basically is they verify who you are and that you have to set up a shipping account with them.
There are certain specific circumstances when I will use UPS for a smaller shipment but I set a strict set of details I stick to.
p.s.
I gave up long ago using either the Post Office or FedEx
