Forget the plain old tank. Today's fish has to be seen in an arch, a lamp, or coffee table at least. The prices may draw gasps, says Ann Treneman, but the sight can be perfectly extraordinary
Melissa Perkins had every intention of buying a sofa when she left her small terrace house in Brighton one day just after Christmas. She had pounds 500 from her grandmother and was tired of sitting on the floor.

Then she made the mistake of stopping by the new aquarium shop.

"I went in and then I thought, well, you can sit on a sofa anywhere. You can go to a pub and sit on a sofa. Or you can go over to a friend's house and sit on a sofa," the 20-year-old Sussex University student says, with the impeccable logic of an impulse buyer. "Also, you cannot watch a sofa."

At this moment we are watching a lamp. More precisely we are watching the flashes of fish among the coral and plants in a 24-gallon bowl that is the base of the lamp. The whole thing - including large white shade - cost all of Melissa's pounds 500 and a bit more. Her boyfriend is "vaguely disapproving", but then having to sit on the floor cannot have improved his mood.

Melissa has succumbed to fish fever, and she is by no means alone. Fish hang from mobiles, swim across picture frames, dart around shower curtains. It used to be that people with fish symbols around the home had some sort of Christian connection, but now that need only mean a connection of the Dior variety: this summer's Christian Dior make-up range contains such fish-friendly products as Seashore eyeshadow, and Coral and Deep Sea nail enamel.

The real thing is more common, too, and we are not talking a tiny goldfish squashed in with a plastic mermaid and a bit of floating weed. The young lovers in Baz Luhrmann's film Romeo + Juliet meet across a crowded tank and Chris Evans is also in a tropical swim (though his is a computerised one) on his show on Channel 4. Some 3.5 million of us visit a sea life centre every year, and on Good Friday the new London Aquarium opened inside County Hall. It is expected to draw 2 million visitors a year; they will see 350 types of fish from at least three oceans (Pacific, Atlantic and Indian). Some of the fish come courtesy of the public: there is rumoured to be a gourami called Gary that is keen on chocolate biscuits.

At home, the tide is also in, with a boom in salt-water "living reef" tanks and in aquatic furniture. "It is quite an expanding hobby at the moment. People are buying a piece of furniture rather than just a glass fish box on a stand," says John Cook, of Shirley Aquatics in Solihull in the West Midlands.

Fish are supposed to be lucky, and are used a lot in feng shui, the popular Chinese art of arranging your home. Nine goldfish swimming around in your home's "wealth corner" are supposed to bring prosperity. The Bank of Scotland seems to have noticed the link - one of the more exotic fantails has managed to wiggle on to its credit card called, yes, the Goldfish.

That could come in handy when aqua shopping, because fish furniture is not cheap. "Our living reef tanks start at pounds 300 and pounds 400, but you can probably go up to pounds 20,000 if you want all the bells and whistles," says Trevor Wild of Oasis Aquariums in Manchester. "However, I would say that your average family would spend pounds 800 to pounds 1,200."

At Aqua-Tech in Brighton, the shop that snared Melissa, aquarium coffee- tables start at pounds 799 and go up to pounds 1,150. So far the 9ft-high archway with about 100 fish has attracted many squeals but no sales at pounds 3,000. Six-foot columns filled with dozens of fish cost from pounds 700. Some buy them as stress-busters - Sussex County Hospital is having one such column put into its emergency room to calm things down - but most customers are ordinary people who at some point succumb to fish fever.

Like Gary Marshall. Five years ago he and his partner Jan Millis had five plastic bags of possessions between them. Now he has a successful musical equipment retail business and they have two small children, a nice house in a Brighton suburb, shoals of fish and one very happy cat. "You are looking at a couple of thousand quids' worth of fish," Gary says, feet propped on a coffee-table swimming with the fancy, bug-eyed kind. Across the sitting-room is a luminous semi-circular salt-water tank inhabited by yellow tangs and electric blue damsel fish. "In fact I may have overdone it recently."

Jan disagrees. "I am a Pisces. I am a fish-woman," she declares. That is just as well because between their three tanks, she will soon be looking after 250 of the things. By far the biggest are the seven in the coffee- table: they are positively globular, with names like Hat on Head, Beautiful and Apricot Head. Big Ears is recently deceased.

Gary is not so sure about the coffee-table which, at 58in by 37in, is hardly discreet. "Some people have come in and been a bit uneasy about it," he says. "They look at it and go, `Oh God, why have they got that?'"

Jan does not care. "When I am vacuuming around the house, it just makes it a whole lot more exciting. I get real joy from washing that table twice a day. Real pleasure."

In a piscine sitting-room, television really is secondary entertainment. Why watch a soap opera when you've got a tankful of drama, murder and action right in front of you? "Marine fish have real personalities," says Melissa Perkins, pointing to her black-and-white humbug damsels. "They remind me of Reservoir Dogs, where the men had the black suits and white shirts. Then you get some fish that are real tarts, the ones that seem to have lipstick on."

She admits that she can "get a little obsessive" and it is surprising how people who really should know better lavish care and attention on cold-blooded creatures with one-second memories. "I've got one lady who has a 6ft column with big, fancy goldfish in it and she loves them to death," says Steve Prior, of Aqua Tech. "She spoils them; feeds them prawns. When she lost one, she was nearly in tears."

Steve Norris, the owner of a guest-house, has the kind of front room that famous names are drawn to, or so I gather as he introduces me to cold-blooded versions of Arnold Schwarzenegger (aggressive), Linford (speedy) and Nelson (one-eyed). I also meet Ginger the cat, whose purr is at industrial levels. Of course, it is not every cat that has a column with 34 fish to watch. Steve says he is thinking about having a few more columns, and using them as in a four-poster bed. The only thing that has got him down so far has been the death rate (though it seems fairly tame for the likes of Arnie). "About five have died, and that was a bit off-putting, but now I haven't had a death since 14 February," he says proudly.

Melissa, too, has had her share of fish fatalities - "I'm a really unlucky person" - but still thinks that she has made the right decision. She finally found a sofa that suited her a few weeks ago, for pounds 30, but she was absolutely right about one thing: no one wants to watch it. Instead, all eyes are glued to the lamp. "It's better than furniture because it's always moving. It's hypnotic. I think the secret is to get fish which move differently and at different speeds. It's like orchestrating a ballet, a ballet of fish."

And then we sit back, and watch the shown