Posts Tagged ‘goldfish’


These are blackmoor goldfish.


Of the goldfish I kept as a child, these were my favorite.

I think it’s because they reminded me of hammerhead sharks.

Read Full Post »


In case you didn’t know, black moors are actually goldfish.

The male black moor has his mating tubercles, which means he can go after the gravid females.

These fish actually produced fry, but many of them were deformed for some reason:


Goldfish are amazingly diverse in their phenotypes– almost as much as dogs are.

Read Full Post »

I’ve always been fascinated with the strange “fancy” gold fish that were always offered for sale at pet stores.

When I had a goldfish aquarium, I would always buy the strangest variety and then release it into a tank that included comets and “normal” goldfish.  As a ten-year-old, I didn’t know any better.  I didn’t know that the “wild-type” fish could swim faster than any of these fancy fish. I didn’t know that their speed made it easier for the wild-type fish to feed. I didn’t know that the wild-type fish would use this advantage to eat all the food before the fancy fish ever got turned around.

Most of my fancy fish didn’t last long.

But none had such a short lifespan as my bubble eye.

The bubble-eye, for those who don’t know, is a type of fancy goldfish. It has no dorsal fin and it is double-tailed. That means that its ability to move is already somewhat compromised, but it is even more compromised by its most obvious feature. These goldfish have fluid-filled sacks under their eyes.


These sacks slow the fish down quite a bit, and they also make it hard for the fish to turn around.

Now, I’m not saying they can’t swim well enough, and I’m not saying they aren’t maneuverable.

I’m saying that compared to the wild-type and the comets, they are very much at a disadvantage.

I saw one at a pet store, and I had to have it.  I brought it home, and I acclimated it to my tank, and he was able to surve about three days before he floated to the top. He was just a small one– mabye three inches long, and his sacks weren’t very large. (Nothing like ones on this fish).

If I were going to get another one, I’d just keep bubble eyes  separate from the other breeds of goldfish.

But I don’t think I could own something that bizarrely removed from the functional needs of its species. It is a freak that has been bred for our enjoyment. It has not been bred to be a normal goldfish.

And after seeing what has happened to so many purebred dogs, I don’t think I want to have any part in the goldfish fancy.

Read Full Post »

This is a feral goldfish caught in the US. It strongly resembles its ancestor, the Prussian carp.

This is a feral goldfish caught in the US. It strongly resembles its ancestor, the Prussian carp.

It is often pointed out how much domestication and selective breeding have changed the domestic dog.  But they are far from the only species in which our selective breeding has changed dramatically. Dogs have been with us for a very long time, and because of tandem repeats, they can evolve into various different forms rather quickly.

However, if you would like to see another species that has dramatically changed because of domestication, look no further than the goldfish. Goldfish are species of carp, and believe it or not, there are two wild subspecies of this carp that still exist in the wild. These are the Prussian carp (Carassius auratus gibelio) and the Crucian carp (Carassius auratus carassius). These fish can all produce fertile offspring with the goldfish, and the Crucian carp is known to come in a yellow mutation. It was thought that the goldfish descended from the Crucian subspecies, when now it is generally accepted that it descends from the Prussian subspecies.

Prussian carp

Prussian carp


Over a thousand years ago, the Chinese were breeding carp in ponds. Some of these fish were yellow in color, a common mutation in carp.


A yellow Crucian carp.

In 1162, an Empress of the Song Dynasty had a pond constructed solely for yellow and reddish fish. Yellow fish were the sole domain of the imperial family, so the gold colored were bred more often. As a result, the main color of the domesticated goldfish would become gold, not yellow.

Within a 150 years, the Chinese began to breed veil-tailed varieties of the fish, and soon, goldfish began to change dramatically.

This fancy breeding happened in East Asia first, but it soon spread to Japan, where the fancy breeding really took off.

My favorite type of Japanese goldfish is the ranchu. The ranchu has a large head with an arched back that dips down before it reaches its tail. And, like many fancy goldfish, it has two tails. On its head, it has lots of growths that are considered absolutely necessary for its breed standard. It also has no dorsal fin.


The ranchu, like most double-tailed “fancy” goldfish, cannot really live in a pond as its less exaggerated relatives can. The double tail and unstreamlined body prevent these fancy goldfish from swimming fast. They need to swim fast if they are to be pond fish, because they will be unable to compete with faster swimming goldfish in their school. Also, these fish have lost their ancestors’ tolerance for very cold water.

However, I would not count the ranchu as the most bizarrely exaggerated goldfish. That title goes to the bubble-eye.


The bubble eye also has no dorsal fin. It has a double-tail, which does slow the fish down. But its most striking feature are the fluid filled sacks that come off the bottom of its eyes. It cannot ever be pond fish or ever kept with fast moving goldfish. Those sacks and the double tail make it really slow in the water. It is very hard to keep in a fish tank, because the chances are very high that it might damage its eye sacks. I once purchased one of these and it lasted about a week in my goldfish tank. I had a common feeder-type goldfish in that same tank that lasted several years, so that should tell you which races of goldfish are the hardiest.

So our selective breeding has not changed only dogs. We like to really mess around with selective breeding, and if we can find novelty in our stock, we’ll breed for it. It is because of this almost inherited tendency in our species that we must draw the line at some point. Interest in novelty of all sorts may have been a great advantage for our species, allowing us to develop all sorts of new technology and art, but like everything else, our tendency to select for novelty can be excessive.

Read Full Post »

%d bloggers like this: