Few people today are aware that there was a time when Karachi was considered to produce the best oysters in India. In the late 19th century, the British set up a commission to study the commercial potential of various districts in the subcontinent. I found a 1906 edition of its report on the footpath among Karachi’s Burns Road book vendors, and, according to the authors, Karachi’s oysters were of a very high quality. Oyster Rock, a small island off Clifton, is a mute reminder of those glory days.

Since then, pollution and a lack of demand have virtually killed off the production of this delicacy. In fact, I would be very suspicious if anybody offered me a local oyster. Ditto crabs. Crabbing in the Karachi harbour was once a favourite evening pastime. We would dangle our lines into the water, and the dim-witted crustaceans would obligingly cling to the bait, waiting to be cooked. The boatmen are adept at cleaning crabs and turning them into a wonderful curry to be eaten with fresh bread.

Now, of course, the harbour is so filthy that anything emerging from its murky depths is positively toxic. I haven’t been crabbing in years, but I’m told the boats carry crabs caught elsewhere and then cooked onboard.

For years, I had a rented house at Karachi’s French Beach where I would spend virtually every weekend. I would usually be alone on Saturday night, but visitors would occasionally come for Sunday lunch. The villagers often brought me fresh fish that I would barbecue, and once in a while, an old guy would bring me live crabs that he swore were from Gwadar. He’d boil them, and they would be served with a potato salad. Often, I’d stir fry them in a wok with garlic and black bean sauce, with a garnish of chopped green onions.

Crustaceans, while delicious, need to be handled with care. Hester Blumenthal, the chef behind the Fat Duck in Bray, outside London, had to face the ignominy of having to shut his restaurant for weeks because several customers suffered from food poisoning after eating there. Considering that his establishment had twice been voted the best restaurant in the world, this meant not just public humiliation, but thousands of pounds in lost revenues. It turned out that some of the oysters he bought regularly from a trusted supplier had ingested waste from a leaky sewage line.

Another problem with all crustaceans is that they are high in cholesterol. A decade or so ago, we had rented a house in France’s Carcassonne region on the coast for a couple of weeks. The area produces some of the country’s finest oysters, and they are sold very cheaply at local outlets run by families who own small oyster beds. Every evening, I would lead a small procession on a walk, and then stop at one of the shacks which sold six oysters for 2.5 euros. When I got to Pakistan, my cardiologist was horrified at my cholesterol level.

Oualidia, a small town on Morocco’s Atlantic coast, is another spot where I have over-indulged in reasonably priced oysters. The French established the beds in the mid-1950s, and trained locals in their upkeep. Now, restaurants across the country serve oysters from Oualidia, and locally, they are available for a fraction of the price one would pay in London or Paris.

Here in Sri Lanka, we have found oysters clinging to the rocks close to our holiday home on the beach. Unfortunately, they are hard to prise off, and there really aren’t that many to bother with. However, the island is blessed with some seriously large crabs, with most of them being exported to Singapore. The Ministry of Crab, a new Colombo restaurant owned in partnership by the cricket stars Sangakara and Dilshand, has begun serving them to a large, appreciative clientele.

We were taken there for dinner recently by Carlo, the restaurant’s architect, and really stuffed ourselves with prawns and crabs. The latter appeared cooked in a garlic-chilli sauce, as well as in a black pepper sauce. The pepper sauce had a hefty depth of flavour, while the chilli sauce was subtler.

Vikrom, an Indian friend who has a house near ours, had a wonderful crab curry made for some guests recently, and Deepaka, his cook, outdid herself. I took down the recipe, and plan to try it as soon as I can get some crabs from Negombo, north of Colombo, and a long way from us.