I still remember the day the goldfish died. Their names were Gretel and Black-eyed Susie and I was looking after them for a friend. I found them fins up in their bowl one morning. It was traumatic. I was only nine - they were even younger.
There seems little doubt that the pair swam off to eternity sooner than they should. Goldfish can live up to 25 years, and the Guinness Book of Records marks the life of a certain Tish, who made it to 43. (His owner, Mrs Hilda Hand of Doncaster, claimed her golden oldie's secrets were a life in the shade and not too much food. A lesson there for all of us.) Tish represents perhaps the zenith of a fish-keeping tradition that began 4,500 years ago in ancient Sumer. Later, the Romans, presumably after they had killed all the really exciting animals, kept fish for food and entertainment. And about the same time as William the Conqueror was domesticating the English, the Chinese of the Sung Dynasty were performing the same trick on goldfish.
Now there are more than 125 types, including the common pet-shop "comet". Owners fishing for compliments have selectivelybred for protruding eyes, spots, a three-lobed tail - and a gold colour.
If these "gold" fish escape into the wild, as has happened in eastern America, they are likely to revert over the generations to a less conspicuous pond brown. They also tend to grow from their bowl-sized 5-10cms in length up to 30cms.
Goldfish belong to the carp family, but lack those dangly mouth parts that make their relations so attractive. These "barbels" are covered in taste buds, presumably allowing carp to sample their food before swallowing. Goldfish are not fussy eaters and clearly do not need barbels - plants, small animals, crustaceans and chopped mosquito larvae will all do nicely.
For many years scientists thought that goldfish could not learn, and subjected them to "reversal" experiments where, for example, their food would appear in a tunnel on the right of their tank for three weeks, then on the left for three weeks, then on the right and so on. It never sunk in.
Recently the goldfish's intelligence has been talked up slightly, but, let's be blunt: they're still wet behind the ears.