This fisherman in China must have thought his luck was in when he pulled in his net on Friday to find a “giant fish” weighing two tonnes trapped inside.

Seemingly unaware that what he found was an endangered – and protected – whale shark, fishing captain Cai Chengzhu strapped the fish to the back of a truck and took it off to market.

The extraordinary images that followed have caused quite a stir on Sina Weibo, the closest Chinese equivalent to Twitter, with photographs showing the vehicle completely dwarfed by its magnificent cargo.

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Cai said that he and his colleagues had been lifting their net out of the water when they spotted a huge hole in the side.

In an interview with News 163 translated by the Shanghaiist, the captain said: “It's believed that the giant creature broke the net and got inside to eat the fish we caught.”

Cai said that the whale shark struggled to escape the net but died shortly afterwards, so the fishermen took it to shore with the rest of their haul.

They reportedly planned to sell the enormous fish for between 10,000 and 20,000 yuan (£960-£1920) at the wholesale market in Xiangzhi until officials from the Fujian fisheries department stepped in.

Whale sharks are a vulnerable species and classed as protected in China, making it illegal to either buy or sell them.

They are the largest of all fish species – an adult being roughly the size of a single-decker bus – and can live up to 100 years. Fully-grown they measure between 5.5 and 10m-long – suggesting that, at 4.5m, the specimen caught by Cai and his colleagues was a juvenile.