Common goldfish can top 30cm/12" in length and ideally need a spacious pond. The fancy varieties can also grow fairly large and need a big tank to match along with a good filter. Moving a large tank backwards and forwards every year would be hard work and would only cause unnecessary stress for the fish, and you most certainly can't move a pond.

Shipping fish in between countries often entails certain legal complications and livestock import/export licences may be required, shipping will also have to arranged as you can't just stuff the fish into hold baggage (that is if you are travelling by air). If you intend to move the fish into and out of the UK then I would have a word with Defra.

In any case fish that have otherwise been well cared for can go for a considerable period of time without food.

Be warned that fishkeeping isn't as easy as it looks, and quite a bit of spare cash for extra equipment will be needed. Tropical fish are 'generally' easier to care for and there is a greater choice of fish available for smaller aquariums, however research into each individual species is needed, as not all fish are suitable for beginners.