You should have seen the shark that got away...

Big? It's enormous. It's immense. It's the whopper of all whoppers, the largest fish ever caught on rod and line in the waters of the British Isles. And it was caught by a pensioner.

It took Joe Waldis 35 minutes of almighty struggle to bring the 12ft 9ins bluntnose six-gill shark to the side of his boat off the coast of County Clare in south-west Ireland, after it took his mackerel bait. When it was brought ashore it was found to weigh a staggering 1,056lbs (480kg) – or just under half a ton. This decisively smashes the record for the heaviest rod-caught fish in British or Irish waters, overtaking a 968lb bluefin tuna caught in 2001 (also off Ireland), and is more than double the weight of the heaviest rod-caught fish within the UK, a porbeagle shark of 507lbs taken off Orkney in 1993.

It is nearly three times the weight of the heaviest fish caught in freshwater in Britain, a sturgeon of 388lbs which was taken from the River Towy in South Wales in 1933. It is the angling tale to cap all angling tales, and it left Mr Waldis, 70, a visiting Swiss fisherman who lives near Zurich, as astonished as the rest of the angling world.

But alongside the astonishment, there is also controversy, as the question is now being widely asked: shouldn't he have put it back alive, rather than having it killed and brought ashore to be weighed? For these days, increasingly, "trophy" fish are returned to the water – and some anglers think this should apply no less to the biggest trophy of them all. The stirrings of unease can be found even in the columns of the fishermen's bible, Angling Times, which this week gives over all of its pages two and three to Mr Waldis's remarkable capture, complete with a series of dramatic pictures showing him dwarfed by his prize.

The newspaper quotes both Luke Aston, the skipper on the record-breaking trip, and the chairman of the Shark Trust, Richard Peirce, as expressing disappointment that Mr Waldis did not release his capture. "It is regrettable that such a magnificent fish had to be taken to shore to be weighed to verify a record, but in these situations it is the angler's decision," said Mr Aston. Another huge six-gill shark was caught from his boat last summer – but that one was put back.

"This shark was a mature specimen and likely to have been a female," said Mr Peirce. "It's wonderful news to hear of the existence of large breeding animals, but from a conservation point of view, it was a shame the shark was not released alive."

Mr Waldis caught the shark on an 80lb breaking-strain line. He would not have had to reel in half a ton, as the fish's weight was supported by the water, but even so, he said, the effort involved in bringing in the fish was considerable. "Every time I gained a metre of line, the fish took it straight back again," he said. "It was the fight of my life."

The biggest fish caught on a rod and line anywhere in the world is believed to have been a 3,427lbs great white shark, caught in 1986 off Montauk, New York, by Frank Mundus – the fisherman thought to have been the model for the shark hunter Quint in the novel and Stephen Spielberg movie Jaws.

Monsters of the deep: Six-gill sharks

* Six-gill sharks are a deep-water species, typically inhabiting depths of more than 300ft, and they have been recorded more than 6,000ft down.

* The sharks are found all over the world, from the Atlantic and the Mediterranean to Australia and Alaska, and have a diverse range of prey, from molluscs and crustaceans to salmon, hake and even seals.

* They are only rarely caught, and that is usually at night when they tend to come nearer the surface.

* The females grow bigger than males and can reach as much as 5.5m (18ft) long.