Is the whale the world’s largest fish? No. It looks like a fish, but it is really a mammal. （哺乳动物）Then what’s the world’s largest fish? It’s the whale shark.

Although the whale shark is our biggest fish and lives in many oceans around the world, few people have ever heard of it. Scientists have not been studying whale sharks for very long. Much more needs to be learned about them.

A whale shark is sometimes called a “gentle giant”. It likes to be alone and doesn’t care a bit about divers or humans. The biggest whale shark weighed 24,250 pounds and was nearly 40 feet long. This makes it heavier and longer than a school bus.

Inside its huge mouth are great numbers of very small teeth. To count all of them, you’ll need to do some maths. The whale shark’s teeth are arranged in rows. There are between eleven and thirteen rows on each jaw (颚) and around three hundred teeth in each row.

However, the whale sharkrarelyuses its teeth. It does not chew or bite its food. Large amounts of water are pulled into its mouth and then pushed out through its gills (鳃).

For a few months every year, a group of whale sharks comes to Ningaloo Reef, off Western Australia. This gives scientists a wonderful chance to study the large fish. Whale sharks do live in other oceans of the world, but no one knows their population. It is possible that our biggest fish may need protecting. It is one of the reasons why scientists continue to learn all they can about these gentle giants.

In recent weeks, a herd（群）of 15 wild Asian elephants, left their habitat（栖息地） in Xishuangbanna in Southwest China’s Yunnan province, has traveled for around 500 kilometers in China’sYunnan in the past year. According to the provincial Forestry Department, the herd has changed its direction（方向）since Friday, as experts tried to attract them to go farther from the downtown areas with delicious foods, such as pineapples.

The reason for their migration（迁徙）is not known, but experts think that either a food shortage or the “guide elephant” misleading the herd.

The herd’s march has triggered（引发）widespread public interest, and many videos recorded by local people have received thousands of “likes” on social media. The most popular of these are two videos recorded on Friday in Jinning. In one, an elephant turns on a water tap with its trunk （象鼻） and gives the herd members water. In another, two baby elephants almost fall into a small ditch（沟）but are saved by the adults.

“Asian elephants have a strong sense of society and value the family highly. If any member—especially the young family members—needs help, others will try their best to provide it.” Chen Mingyong, a science professor at Yunnan University, said on Sunday.

Yunnan is the sole wild Asian elephant habitat in China. Before the 1970s, the species（物种）was endangered by a number of reasons, including a rise in the human population, reduced forestry areas and illegal hunting（非法猎杀）. Their numbers dropped heavily. However, through protection efforts in recent years, China’s Asian elephant population has risen from 170 to 300 in the 1970s.

“Its growing population needs a larger habitat and more food. The well-protected forest resulted in the decrease of some small plants—the favorite food of wild elephants,” said Giuo Xianming director of the research institute at Xishuangbanna National Nature Reserve.