Since goldfish are creatures of the water, a lot of the aspects that make a goldfish show different than, say, a cat show revolve around water. There has to be good water available at the show site, of suitable quality for goldfish. The water that the fish are in has to be monitored for quality and changes performed if the parameters deviate too far from ideal. There also has to be aeration available, aquariums or other show vessels of suitable size and complete cleanliness, and a venue that has a uniform, appropriate temperature, and space for the aquariums that is out of direct sunlight.
Let us say you have all these things. Are you ready to hold a goldfish show? Oh we wish! The best goldfish shows in the United States begin preparation for their big annual events the previous year with a "lessons learned" meeting right at the end of that year's show. Usually the first question is "do we really want to do this again?". Most answer "Yes!" and then it is off to find a location, line up sponsors, sign up vendors, lock in judges, put in place an advertising campaign, hire caterers, ... you get the idea.
Okay, okay you say ... but how does a show work? Usually there is a show committee and a show chairman who oversee the various activities and the budget to make sure everything comes together. Entries are accepted for the show, and right before the start of the show aquariums are set up, filled with properly treated water and with the aeration system put in place. Hours are established to bring the fish in and put them in the show.
When the fish are brought in by the exhibitors, they are "benched". This involves logging the fish in and associating its entry number with its aquarium number. The fish is then placed in the aquarium and a benching committee member (often the show chairman) verifies the health of the fish and the variety and class entry. A fish with any visible external sign of ill health will be disqualified and the owner asked to remove it from the show. Because of the variability of goldfish, verifying that the fish is in the correct class is not always that easy.
In the "old days", goldfish and Koi were often judged in the traditional Asian manner, where fish in the same class might all be combined in the same container, usually a tub or small pool. And then class winners would be combined in another container to judge the overall show winners. This is very good for the judges and worked well when everyone was from the same club in the local area, with no unknown fish from other areas.
But the modern-day shows have fish from all over the world in them. In this scenario, often even the owners may not realize what latent diseases their fish are carrying. So for safety, most goldfish shows are "English style" shows where the fish remain in their aquariums and the judges move around to view all the fish in the class and select a winner. Much harder for the judges, but far safer for the fish.
Usually there is a team of judges, most often a head judge and one or two assistants. There will be a period of time reserved for judging, when the public is excluded from the show floor and the judges make their decisions. It is not at all unusual to have judging require 5 or 6 hours, particularly if there are a large number of high quality fish.
Usually a winner is selected in each class, and then these fish are judged against each other to select a grand champion and reserve grand champion. There are often a number of special awards that are given based on other criteria. Examples are the "chairman's award" which lets the show chairman pick his or her favorite fish and commemorative awards that honor the favorite varieties of cherished past members.
There is always an awards ceremony to honor the owners of the best fish and entertain the rest. There will be a specific period of time for the exhibitors to remove their fish. And then clean up of the tanks and the show site. And the start of preparations for next year!