Exploring the unknown

It may seem glamorous, going to exotic destinations, but there is often some element of danger involved, not least the risk of the bends, or decompression sickness, as well as attacks from aggressive marine animals.

"I have encountered many dangerous moments underwater, including being hit by a sperm whale, experiencing a volcanic eruption and the use of dynamite by fishing boats," Zhang says.

However, he knows that marine animals are much more tolerant to humans than humans are to them.

He has experienced the surprise of meeting a fish at the same diving spot days or months apart. "Some fish have a fixed reef as their home," he explains.