The ship's bridge, the sea and the sky reflected a flame-coloured spot in the distance that spread out along the horizon to the left and right. Ohishi and the other 22 crew members of the Daigo Fukuryu Maru watched the glow with growing unease for about three minutes, until it disappeared.
"We were just fishermen," says Ohishi. "We knew nothing of nuclear weapons tests or their effects. When we saw the explosion, some of us thought it had to be some sort of natural disaster, like an undersea eruption."
What they had actually witnessed was the detonation of the Bravo nuclear device, a 15-megaton bomb that was the biggest ever tested at Bikini Atoll, in the Marshall Islands, and equivalent to 1000 times that dropped on Hiroshima.
Of the 23 men who were aboard the Daigo Fukuryu Maru on 1 March 1954, 12 have since died, mostly of kidney or lung cancers, while the survivors have all suffered illnesses of varying degrees that they attribute to the bomb.
Ohishi, now 70, says he's the luckiest of them all; the treatment he underwent for kidney cancer appears to have been successful, although his first child was still-born and deformed.
Speaking at the museum that has been built in Tokyo's waterfront district to house the ship and tell the tale of its crew, it is clear that Ohishi still bears the scars of that voyage.
He is angry at the deaths of his friends, more angry at the failure of the United States government to take responsibility for the results of the blast - and determined to do all that he can to rid the world of nuclear weapons.
A campaign was launched to
expose the impact of N-tests
"As my colleagues died, one by one, my mind has been occupied with thoughts regarding nuclear weapons and life," he says.
"For more than half a century, peace movements have argued that humans cannot coexist with nuclear weapons and have called for their abolition. But the number of nuclear weapons has not diminished. Today, there are even more."
"I believe ordinary people cannot allow the existence of nuclear weapons," he adds.
"Is there anything we can do? Yes, we must work for the abolition of atomic weapons." This year - the 50th anniversary of the Bravo test - he is spearheading a campaign to raise awareness of the continuing legacy of nuclear tests and weapons. As a victim, he feels he has a unique perspective.
Ohishi first went to sea at the age of 14. His father had just died and he was the oldest son and had to leave school to earn money for the family.
Five years later, he joined the Daigo Fukuryu Maru, a 140-tonne tuna fishing boat whose name means Lucky Dragon No Five. But the 25-metre-long vessel was anything but lucky, he says.
The misfortune began even before the ship sailed to sea from Shizuoka, southern Japan, on 22 January 1954, with five of the regular crew quitting after getting into an argument with the captain.
Ohishi with the Daigo Fukuryu
Maru in the background
The vessel briefly ran aground. Then they hit a patch of bad weather that battered the boat with waves 20 metres high. Then, in waters of the Midway Island, they lost 170 of their fishing lines and their holds were still virtually empty of tuna.
In search of better fishing grounds, the Fukuryu Maru took a south-westerly course for home and, after six weeks at sea, was about 160 km east of Bikini Atoll when the bomb was detonated.
"After we saw the light, we were all uneasy and thought we had better get away," says Ohishi.
"We hauled in the lines and were preparing to get under way when, about seven or eight minutes after the flash, we felt this noise approaching us. It was as if it came from beneath the boat and was coming up. It was like a roaring noise and the men on the deck threw themselves down flat."
About 15 minutes later, the sun rose and in the distance they could see a towering mushroom cloud. As they watched, the upper levels of the cloud - about 34km high - began to decay as winds began to catch it.
The winds brought the cloud directly towards the Fukuryu Maru until it covered the entire sky above them, he recalls. A thick white ash began to fall on them, finer than snow but it stuck to their skin. It got into their mouths and hair but it had no smell or flavour and none of them was particularly worried.
That evening, however, most of the crew were vomiting and had headaches, while patches of skin that had been exposed to the falling ash turned black.
It took the boat two weeks to return to its home port, with Ohishi and the rest of the crew only able to speculate as to what they had seen.
Remarkably, few of them knew much about the nuclear bombs that had been dropped on Hiroshima and Nagasaki nine years earlier as the Japanese government enforced a news blackout on the attacks to try to win favour with Washington.
He believes, however, that the ship's radio operator, Aikichi Kuboyama, might have known what had happened because he told the crew to keep a lookout for other ships or aircraft.
Ohishi believes that Kuboyama feared the US might sink the ship if they thought it had witnessed the secret test. Kuboyama died seven months later of kidney failure caused by exposure to radiation.
Ohishi suffered from kidney
cancer after the explosion
Once ashore - with a catch of just 159 fish, which would not even cover the costs of the trip - they learned from media reports that the US Atomic Energy Committee had announced the test that they had experienced.
Some 800 Japanese fishing boats were affected by the fallout from the blast, but none was as close as the Fukuryu Maru.
"At first everyone had sympathy for us, but that quickly changed when it was realised that the entire catch was also radioactive and we couldn't sell it," says Ohishi.
"What was worse was that everyone believed that all tuna caught at that time in the Pacific was contaminated and no one could sell anything. Fishing was the whole basis of life in that part of Japan so the attention soon focussed on the hardship of the industry and the communities there rather than on us."
Only one of the ship's crew ever sailed to sea aboard a fishing boat again.
For the next 12 months, as her crew received the rudimentary treatment that was all that was available at the time for exposure to radiation, the Fukuryu Maru was examined by researchers for the effects of a hydrogen bomb.
"The crew were victims of a nuclear test but the compensation we received was all down to political considerations"
When the radioactivity level had fallen to permissible levels, she was used as a fisheries training ship for 10 years before being left to rot in Tokyo Bay. In 1968, a campaign was begun to salvage the vessel and the Daigo Fukuryu Maru Exhibition Hall opened in 1976.
"The crew were victims of a nuclear test but the compensation we received was all down to political considerations," Ohishi says.
"The 'hibakusha' from the Hiroshima and Nagasaki bombs have received care throughout their lifetimes, but we haven't been recognised. The US gave us some money in 1955, but it was described as condolence money, not judicial compensation."
Much of the money went to support the fishing industry and each of the Daigo Fukuryu's crew received Y2 million (US$19,000 at today's rates).
"The Bikini tragedy isn't finished yet," he says. "It is still making people ill and there is no comprehensive ban on nuclear tests. It's important that people like me don't let people forget what happened 50 years ago still affects all of us today."