Catch of the day Where's the chef? Gone fishing.

Rory Ross took Mark Hix out of The Ivy's kitchen to the shores of Costa Rica, where sealife is big and anglers' tales are even bigger.

Hooked on Costa Rica

Zzzzzzzzzz... a reel smoked. I grabbed an arching rod, rammed it in the holster of the fighting chair and began reeling and lifting. It felt like there was a whale on the end of the line. About 100 yards off, a great neon-blue-and-yellow fish leapt out of the cobalt ocean, flexed wildly, then dived back in. I reeled frantically, fingers blistering, forearms screaming. Eventually, a large-billed shape loomed up. I'd landed my first sailfish. It only took 20 minutes, but I felt shattered. As she was lowered back into the ocean, my exhaustion turned into a rush of adrenalin and somersaulting endorphins. A profound thrill surged around my body. I had hooked not just a fish, but a deep throwback hunter-gatherer chord.

I was fishing in Costa Rica with Mark Hix, the Chef Director of glamorous celebrity haunts The Ivy and Le Caprice, creator of recipes for The Independent's Saturday Magazine, and a keen angler. Sandwiched between Panama and Nicaragua, Costa Rica is the catch-and-release El Dorado. Would-be Hemingways pay four-figure sums per day to take on the ocean's heavyweights: marlin, sailfish and tuna. From December to June, when the fish move north, you can get up to 30 shots at sailfish in one day. The tennis player Pat Rafter and the former US president Jimmy Carter are big fans. Fishing fanatics in Britain are catching on, too.

We were staying at Crocodile Bay, a tiny fishing resort in manicured 44-acre gardens in the Corcovado National Park in the jungly south-west, prowled by jaguars and tapirs.

Todd Staley is the Director of Fishing. A wily sea-dog from Florida, Staley has tackled every species of sporting fish, and most types of sporting fisherman. "If the fish bite, everything's fine," he says. "If they don't, suddenly the ceiling fans are squeaky and the loos don't flush fast enough."

To induct me, we spent an afternoon in-shore fishing in the Golfo Dulce on the Osa Peninsula, "the most ecologically intense place on Earth", drools National Geographic. Snapper, Jack Crevalle, Spanish mackerel, snook, turvli, barracuda and corvine queue up to be hooked. We were going for roosterfish. Staley bared a thick bicep tattooed with a fish with radio antennae coming out of its head. "The biggest here is 160lbs; 20 to 30 pounders are common." Marine engines growled and we powered off. "If this was Florida," said Staley, prodding a cigarette at the panorama of mountain, jungle, sea and foraging pelicans, "it would all be condominiums."

In his flip-flops and fish-emblazoned shirt over powerful shoulders, Staley was a dead ringer for Robert Shaw's portrayal of Quint, the grizzled captain in Jaws. He even knew Gregorio Fuentes, Hemingway's captain in Cuba who died in January at 104. Staley's finest hour was landing a 12-foot shark in a 13-foot boat. "Came up like a VW. I had to kill it to prove I'd caught it. Took four and a half hours. It was a macho thing." Staley's ocean-blue eyes misted. "To grow so large, he must've swum many miles. Today, I'd have let him go." A bite on my line cut short Staley's reverie. It was a humungous... piece of rock. "I couldn't catch my own arse with both hands," said Staley as we trudged home. The next day, Staley took us off-shore, into the lair of marlin, sailfish, dorado and wahoo. "Last week we caught a 190lb tuna," he said, brandishing great reels like something British Telecom wired up telephone exchanges with. "That's a couple of hours at the end of a string."

Seven miles out, a heavy swell tossed our 33-foot white plastic boat. Schools of feeding bonito (small tuna) leapt; turtles lazily rolled in the swell; a whale arched its back; birds strafed the waves. We cast baited lines and teasers. Teasers are iridescent plastic "fish" that look like piscophile sex-aides. "When the fish chases the teasers," said Staley, "we put the boat into neutral, reel in the teasers and Mark will cast his fly."

While we churned the Pacific, Staley explained the skills and thrills of ocean-fishing. Fast, powerful, acrobatic, the marlin is the trophy. It leaps, dances, turns neon purple and dives. "You don't catch marlin," said Staley. "You hunt them. You read the waves, birds, bait and currents. The marlin will take several hundred yards of line off your reel. You hold on and watch him go. Then you work him back. It's like tug-of-war. It can take 30 hours. You need strength and skill." The elusive "'blue-water" grand slam is to land the three marlins – black, Pacific blue and striped – all in one day.

Several hours later, we were still waiting in our glorified bathroom appliance, when our captain gave out a loud cry. A bill thrashed the foam. We scrambled to reel in the lures while Hix cast his fly. The rod went horseshoe-shaped. Fly-fishing in the ocean is like trying to catch a train with a piece of dental floss. It's an all-skill game; muscle doesn't come into it. After a 40-minute duel between man and fish, an 80lb sailfish was posing for pictures on Hix's lap.

That evening in the bar, I caught the fishing prattle... He caught a sail with a fly? Dynamite! That's the coolest... The yellowfin action here is unbelievable... like catching a refrigerator with a mind of its own... Tuna have two spines... It probably lost 20lbs just fighting me. I know I did... Tuna dig deep, but no acrobatics...

Fishing might be big and getting bigger in Costa Rica, but it's the jungle that first springs to mind. And if the fish aren't biting, you can check out the interior, which teems like the steamy bits of London Zoo crossed with the hothouse at Kew. Although only slightly larger than Denmark, Costa Rica hosts 5 per cent of all the species on the planet. Everywhere you look, extraordinary creatures crawl, slither, flutter, leap or hop past. Those are the visible ones. I'd never have imagined that that brown blob in my path was a coiled fer-de-lance snake – until my jungle guide pointed it out to me. "We have 117 species of snake," he said. "Thirty-two are venomous. Fer-de-lance grows up to three metres. If it bites, blood comes out of your eyes, ears and mouth." I stepped gently and uninsured over Costa Rica's deadliest serpent.

The Spaniards never really bothered with Costa Rica. The gold reserves paled beside Peru's and Mexico's, and the jungle was too full of creepy-crawlies. Today, however, that jungle is Costa Rica's bounty and Costa Ricans have come up with numerous imaginative ways of introducing visitors to its raw beauty. There are "canopy tours" (invented in Costa Rica as an ornithological aide), crocodile safaris, kayak tours, bungee-jumping, white-water rafting and snorkelling. What you don't get is culture and shopping. That lack is itself part of Costa Rica's cultural heritage.

Parched from exploring barren Caribbean islands, Columbus named it Veragua ("See water") in 1502. Isolated, forbidding and poor in "human resources", it became the "Siberia" of the Spanish empire, haunted by rogues, dissidents and refugees. Pirates, such as Captain Morgan and Juanito "Bloody Sword" Bonito, terrorised the coastline. The swashbuckling tradition lives on, albeit less bloodily.

"Biodiversity" is the buzz word among pharmaceutical executives alighting here to research new drugs, emboldened by Costa Rica's shining record of political and economic stability. The reason for this biodiversity is the rich volcanic soil. Costa Rica used to be ocean, until volcanic activity threw up islands, which evolved into today's seismically pulsating isthmus. There are nine active volcanoes; the most spectacular is Poás, near San José, with its mile-wide steaming sulphurous crater.

And then (I was here with a chef) there's the food. At El Pelicano in Playa Herradura the owner gave us a canapé tour of Costa Rica's greatest kitchen hits: marlin ceviche with green plantain and cassava; pejibaye (miniature coconut) cream soup; grilled sea bass with tropical fruit sauce; tenderloin with tamarind; green papaya hash with onion garlic and ground beef served in a banana leaf; then passion fruit mousses, all washed down with guaro, a local rum. Even Hix was impressed.

Travellers' guide

Getting there: There are no direct flights from London to Costa Rica. Specialist agencies such as Journey Latin America (020-8747 3108) and South American Experience (020-7976 5511) offer cheap flights to San Jose for around £500.

Staying there: The writer stayed at Crocodile Bay Lodge, Puerto Jimenez, (00 506 735 5631, www.crocodilebay.com). It offers three-day fishing trips for $2,195 (£1,463) per person, based on two sharing, including two nights in San Jose, transfers to the lodge, full-board accommodation and fishing. Exsus (020-7292 5050, www.exsus.com) offers an eight-night trip to Costa Rica, which includes a three-night fishing trip at Crocodile Bay Lodge for £2,720 per person. The cost includes return flights, transfers and accommodation.