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Julesgemstones is going to love this one. She’s a sucker for my scientific factoids.

There’s that really good joke about two goldfish in a bowl, swimming round it in opposite directions. They meet, and each one thinks ‘Oh look. There’s a goldfish.’ They carry on swimming, meet each other again, and go ‘Oh look. There’s a goldfish.’

The basis of this joke is the common belief that goldfish have very short memories. I’m afraid I’m going to blow that particular urban myth clean out of the water, so to speak. You can train goldfish. I know this, because I have. I don’t mean you can teach them to leap through blazing hoops, or attach limpet mines to enemy shipping, or spot misshapen objects coming off a mass production line. You need a pigeon to do that last one. I’m not kidding. Pigeons are very good at pattern recognition. They’ve been used for quality control in several industries.

You can train a goldfish to differentiate between simple geometric shapes. There’s an added advantage in that you don’t have to stick your head in its mouth. I saw a photograph once of an animal trainer called Hans Brick doing just that with a polar bear. No, I’m not fibbing.

So, what do you need to begin your career as Great Marvo the Animal Tamer? A goldfish, obviously. And a tank to keep it in. Bowls are bad news since the surface area is too small for adequate oxygenation of the water. If your goldfish in a bowl popped his clogs prematurely, he may well have drowned. Just to ensure this fate does not befall your experimental subject, invest in an aeration device.

You also need two pipettes or eyedroppers, and a load of tubifex worms. You can buy these threadlike worms at a pet shop. They look remarkably like goldfish turds, which may confuse you, but not the goldfish. If you ever do become uncertain, goldfish turds don’t wriggle. If it moves, it’s a worm. Keep that thought.

Lastly, two target shapes. I painted these on sheets of thin Perspex, but you can extemporise I’m sure. I chose a square and a triangle.

Now the naughty bit. You have to starve your fish. A bit. Not to death. Just so it gets peckish, and I use that term advisedly. You put the targets at opposite ends of the tank. Suck some tubifex worms into each of the pipettes/eyedroppers, and position one in front of each target. Eventually the fish will spot the worms and take a mosey over. It will peck at the pipette. The clever bit is that if it pecks at the one you want, say the one by the square, it gets rewarded with some worms. If it pecks at the wrong one, you do a Mr Bumble the Beadle on its sorry arse, and it goes hungry.

Believe it or not, it only takes four or five ‘training’ sessions for the fish to twig that the square means food (a square meal, perhaps) and the triangle doesn’t. It will always swim to the square. It’s a memory based behaviour.

Now you’re going to do something that will have animal rights activists firebombing your house. You have to get the fish to unlearn, and change its behaviour. You do this by simply not feeding the fish when it pecks at the square pipette, but at the triangle pipette instead. For the first few tries, the fish will just shake its head in a mixture of frustration and bafflement at the random nature of the world, and swim off looking even more mournful than goldfish normally do.

But then a small piscine light bulb flickers into life. The fish thinks, ‘Hang on, I’ll have a go at the pointy three sided thingy. It didn’t used to work, but it’s worth a try. I’ll be no worse off, will I? I didn’t get fed this end either.’ Lo! The fish gets fed! Strangely it learns this new trick faster than it learned the other one, so not only has it learned, it learns faster with experience.

So lay off with the goldfish jokes in future. While you’re at it, when you’ve finished messing with your fish’s head, buy it a companion. Goldfish are shoal creatures, and like to have their mates round them. In a tank, they live longer in pairs or groups than in solitary confinement.

Lastly, here’s Herr Brick with his head in a polar bear’s mouth. My mate Victoria likes this. She can’t get enough of polar bears.

polar bear trainer