Can a fish be depressed? This question has been on my head ever since I spent a night in a hotel across from a sad-looking fish. His name was Bruce Lee.

The pleasant woman at the front desk assured me that he was well taken care of. Was I incorrectly assuming his laziness was a sign of being upset?

When I sought answers from scientists, I assumed that they would find the question ridiculous. But they did not. New research has been totally shifting the way that scientists think about fish cognition (认知)，building a case that pet and owner are not nearly as different as many assume. The neurochemistry (神经化学）is so similar that it’s scary, said Julian Pittman，a professor. We tend to think of them as simple living things, but there is a lot we don't give fish credit for.

Dr. Pittman likes working with fish, in part, because they are so obvious about their depression. A zebrafish gets dropped in a new tank. If after five minutes it is hanging out in the lower half, it’s depressed. If it’s swimming up top, then it’s not.

Is depression the right word? There's the obvious issue that we cannot ask animals how they feel, says Dr. Diego A. Pizzagali . Neither fish nor rats can catch the entire range of depression as we know it.

There is a heated debate about whether anxious or depressed is a more appropriate term. But what has convinced Dr. Pittman, and others, over the past ten years is watching the way the zebrafish lose interest in just about everything: food, toys, exploration, just like clinically depressed people who are withdrawn. The same is true of fish.

One of the things we're finding is that fish are naturally curious and seek novel things out, said Dr. Braithwaite. In other words, your goldfish is probably bored. To help get rid of depression, she urges introducing new objects to the tank or switching up the location of items.

A team of Australian scientists has discovered a curious “chocolate frog”, a tree frog, in the lowland rainforests of New Guinea. Tree frogs are known for their green skin — but due to its brown coloring, researchers named it “chocolate frog”.

“The closest known relative of ‘chocolate frog’ is the Australian green tree frog. The two species look similar except one is usually green, while the new species usually has a lovely chocolate coloring,”said Paul Oliver, the author who described the discovery in a paper in the journal Australian Journal of Zoology.

Australia and New Guinea were linked by land 2. 6 million years ago, which may account for(解释) the reason why they have similar species. But now, New Guinea is covered by rainforest, while northern Australia is mainly savannah(稀树草原). Green tree frogs can be found across northern and eastern Australia and New Guinea. Australian scientists discovered one of the new creatures in 2016, according to the paper, and they think the animal could be widespread across New Guinea.

“The ‘chocolate frog’ lives in very hot and wet areas with lots of crocodiles, which discourages exploration,” co-author Steve Richards said. Although the creatures may look like the magical snacks found in the Harry Potter series, the similarities stop there.

“We later named this new frog species Mira, which means ‘surprised’ or ‘strange’ in Latin, because it was a surprising discovery. It was Australia’s well-known and common tree frogs’ over-looked relative living in the lowland rain-forests of New Guinea,” Oliver said. “Researching into the biotic(生物的) interchange between these two regions is critical to understanding how the rainforest and savannah habitat types have expanded and narrowed over time,” Oliver said. “Our study on divergence(分化) of the new species shows that 5. 3 to 2. 6 million years ago, there was still connectivity between the two species across lowland tropical habitats of northern Australia and New Guinea.”

Some scientists believe that one of the most intelligent beings on Earth is in fact the octopus (章鱼).

Octopuses usually live at the bottom of river mouths and seas-areas which are not attractive to researchers. They are not social animals so it can be hard to study their interaction with others. And the octopus’ intelligence is not easy for humans to understand. When we observe some animals such as rats or dogs, we can often understand their behavior. Octopuses，however can seem like aliens (外星人). Scientists need to have a lot of imagination to understand what an octopus is thinking!

In the 1950s, the US Air Force sponsored scientists to study the way octopuses use their brains. They hoped that they could use this knowledge to help them build better computers. However, their brains were so complex that the scientists felt it of no significance to continue with it. Octopuses have a very complex nervous system and recent research suggests that they have some of their intelligence inside each arm, which means that each arm can “think” for itself. It also appears that they have a good memory, perhaps similar to a cat’s.

Perhaps the most striking thing about octopuses is their ability to change their color and body pattern. They do this to camouflage themselves to avoid their enemies and also to communicate with others. They can completely change their appearance in less than a second. It can change its skin to look like rocks, sand or planktron (浮游生物).

Some scientists have even suggested that these different patterns and colors are in fact a very hard language-and that each design is a different verb，adjective or noun. But nobody has been able to work out what they might be saying. There’s a long way to go to get to know the octopus completely.