Fishing Lines: Beware troubled water if you're sitting on the dock of the bay

There's nothing interesting about fish, according to Jonathan Ross on his Saturday- morning Radio 2 show. Well, what about a fish that can change sex? Or swim 6,000 miles when a baby? Or kill you when it's dead? Could a glorified disc jockey, even one with an OBE earning £6 million a year, do that?

Several species of fish can kill you, for example. I'm not even bothering to include the electric eel here. Sure, it could give you a blast of around 600 volts (more than double the power of a wall socket), but that would probably just knock you over.

On the other hand, you'd be heading for hospital if you trod on a lionfish, a scorpion fish or especially a stonefish. Unless you get immediate treatment for the last-named's poison, you'll be playing "Tell Laura I Love Her" for the last time.

Fish are a lot more humanoid than we give them credit for (and after all, wasn't the water where we all started millions of years ago?) There are walking catfish, flying fish and climbing perch. Lungfish can live out of water.

Scientists have just discovered a fish that would rather crawl into crevices than swim, and may be able to see in the same way that humans do. Found this year in Indonesian waters, it is a type of angler fish with eyes that appear to be directed forward, providing binocular vision. Some common members of the species have a piece of dorsal spine protruding over their mouths, mimicking a baited fishing rod, to attract their prey. ("Caught In A Moment", by the Sugababes?)

Ever tried puffer fish? Don't. Its liver, ovaries and skin contain the poison tetrodotoxin, which paralyses your muscles. You stay fully conscious until you die from asphyxiation. There is no known antidote.

But you can eat it in certain Japanese restaurants, though only licensed chefs are permitted to prepare it. They must undergo a two-year apprenticeship, then have to take an official test. Dining to music by The Killers, maybe?

My scariest fish isn't the great white shark (though I bet you never knew they don't like rough weather). It's the candiru, an Amazon fish scarier than any anaconda. Never swim naked in the river and take a pee: this fish is attracted by the urine, and swims up and into the source.

A book I read said: "The pain is said to be excruciating. The only cure is to get to a hospital before your bladder bursts, and ask the surgeon to cut your penis off."

Fishing in an Amazon tributary, the Tiputini, I decided to have a pee into the river for research purposes. Sure enough, these tiny catfish were milling on the surface within seconds. Made me take a quick step back in case, like salmon, they could ascend the falls. Suitable tune: "Gimme That Thing."

While we're on the subject of sex, how about various species of wrasse, which can change sex if there's a shortage of males or females? It's not just wrasse either. On Washington's Potomac River, nearly four out of five male smallmouth bass show sexual abnormalities, having both testicular and ovarian tissue, probablycaused by chemicals leaching into the water.

Perhaps a spin of "Both Sides Now", Wossy?