A group of fish lined up and crawled ashore after the heavy rain! Why don't they die when out of the water? Where are they headed?

Have you ever seen fish walk? Not the kind that thrashes and struggles in shallow puddles, but the real deal—marching in an orderly line, like an expeditionary force, climbing onto the shore in a massive, unstoppable crawl.

They wriggle their bodies and inch forward—organized and disciplined. They don’t move fast, but they’re extraordinarily persistent. The sight is both ridiculous and downright magical.

Fish live in water—that’s the unchanging common knowledge for thousands of years. What kind of fish can purposefully crawl on land? Did these fish become something more than fish?

This fish has a tough-sounding name: guò shān jì. Some people also call it pān lú, walking fish, or tree-climbing fish. Just hearing the names tells you it’s not something ordinary.

Other fish can’t handle it once they leave the water for ten minutes; this one, though—getting onto land is like strolling around town. So the question is: a fish—why is it so amazing? Let’s start with the most fundamental question: why do fish die when they leave the water?

Fish breathe through their gills in water. Gills are like lots of tiny combs; when they’re in water, these “comb teeth” are spread out so they can fully come into contact with oxygen in the water.

But once they leave the water, those delicate gill filaments become stuck together, just like hair after getting wet—one by one they cling to each other. When the gill filaments stick together, their surface area drops drastically, and they simply can’t absorb enough oxygen. That’s why common crucian carp, carp, and silver carp suffocate and die after leaving the water.

But the guò shān jì is different. This creature hides a secret weapon inside its gill cavity—an “above-gill organ.”

So what exactly is this above-gill organ? You can think of it as a “backup lung” for fish. It sits next to the gills, like a little flower, and it’s packed with capillaries. With it, the guò shān jì can absorb oxygen directly from the air. When other fish are gasping on the shore and can’t catch their breath, the guò shān jì is already breathing freely.

Research shows that after leaving the water, as long as it keeps its body moist, it can survive for more than six days. What does six days mean? If it crawled fast enough, it could probably make its way from Guangdong to Guangxi—of course it isn’t that fast, but its endurance is genuinely unbelievable.

But the most interesting part is right here: the guò shān jì can breathe on land, yet in water it feels a bit stifled.

Why? Because its swim bladder has “changed careers.” In ordinary fish, the swim bladder is a buoyancy “balloon” that helps regulate buoyancy. But in the guò shān jì, the swim bladder becomes a breathing “mini-lung.” Without buoyancy regulation, if it doesn’t swim in water, it sinks to the bottom.

Plus, its gills in water are already not great at oxygen absorption, so it has to frequently poke its head out to breathe. That’s why staying in the water for long periods is uncomfortable. Breathing on land, on the other hand, is easier.

Think about it: a fish that might drown if it stays in water too long, but lives just fine once it’s on land. What is that called? It’s against common sense!

So here comes another question: if breathing on land is easier, where are they going in the first place? On the way there are rocks, slopes, and pits—you might even run into water birds or humans. How dangerous could it be? If they don’t stay in the water properly, why put in all that effort to crawl onto shore?

The answer is actually pretty simple: the original home just can’t support them anymore.

But first, let’s make one thing clear: guò shān jì can come ashore only under certain conditions. It’s not like they can crawl out whenever they feel like it. They need to move when it’s after a rain, when the ground is damp and soaked through. If it’s a bright, hot day with dry ground, they wouldn’t dare come out.

Then why do they usually come ashore? The first reason is lack of oxygen. Around the time of heavy rain, oxygen in the water drops. The guò shān jì feels stifled in the water and crawls onto shore first to get some air. Once the oxygen in the water recovers, it goes back. But more common—and more important—is the reason of relocation.

The guò shān jì is unusually strong in both survival and reproduction. A single female can lay over two thousand eggs in one go. Once it reproduces that much, the original body of water quickly can’t fit them all—there isn’t enough food, and the living space gets too small. That’s when some fish stand up and say, “Let’s go find a new home.”

But how can fish relocate? Swim along the water flow? What if the connected body of water is crowded too? The guò shān jì’s solution is: we’re not swimming—we’re taking the dry route.

It uses its gill cover like a “climbing pole,” its pectoral fins like “oars,” and when it pushes with its tail and twists its body, it moves forward with that “three-piece setup” working together. Don’t judge by the posture—it’s awkward, but the speed really isn’t bad. There are records saying the guò shān jì can crawl more than a hundred meters in half an hour. If it hits a gentle slope, it can even go faster.

Their goal is very clear: climb over this obstacle and find another place where they can live, then start anew. Sometimes you’ll see a group of guò shān jì crawling in a line toward the same direction on the road—that isn’t coincidence; it’s their collective migration.

Speaking of this, there’s still one long-standing legend: guò shān jì can climb trees.

The earliest version of this claim dates back to 1791. A Danish naturalist, while investigating in India, found a living guò shān jì on a tree.

Local people told him this fish can climb up and feed on tree sap. Later, this was written into reports and caused a sensation. Fish on trees, and feeding on tree sap—when you think about it now, it sounds pretty wild. But back then, nobody had seen a fish like that.

Afterwards, later scientists, through repeated observations and experiments, reached another conclusion: guò shān jì doesn’t climb trees on purpose. So how did the fish on the tree get there? Most likely, they were carried up by birds.

A bird caught a guò shān jì, intending to enjoy a meal. But it found the thing was covered in spines; its scales were as hard as armor and couldn’t be swallowed at all. So it had no choice but to loosen its grip and drop it.

What’s more, it happened to get stuck on a tree branch. So next time you hear someone say, “Fish can climb trees,” you can tell them: it’s not that the fish has the ability—it’s that the bird’s eyes were bad.

After talking about the guò shān jì’s legendary abilities, I want to say something that isn’t so lighthearted.

These fish were once especially common in the Two Provinces region—Guangdong and Guangxi. After heavy rains, you could see their crawling footprints everywhere—by the roadside, in the grass. But in recent years, can you still see them?

It’s not because they were eaten out completely. Although guò shān jì can be eaten, the armor-like scales are too troublesome to process, and there isn’t much meat anyway—so there really aren’t many people who go out of their way to eat them.

The real reason, when you say it, is a bit heartbreaking.

Sometimes guò shān jì comes onto land because the original water has been polluted and can’t support them anymore. Fertilizers and pesticides from farmland run into canals and ditches; factory wastewater is discharged into streams; and domestic sewage turns patches of water dark and foul-smelling. They risk being baked to death, being dehydrated to death, being captured by humans, or being eaten by birds—just to find a cleaner body of water.

But the question is: can they find it?

They crawl out of one puddle, into another puddle, and find that the second one isn’t any better. They scramble and search desperately, but there’s less and less clean water. Coming ashore isn’t a hobby for them—it’s their helplessness.

Yet the places they can go are shrinking. Sometimes I feel like the guò shān jì is just like us.

Who isn’t crawling forward while feeling stifled? Who hasn’t been forced to leave a place where they can’t stay anymore, clenching their teeth and starting over somewhere else? Who isn’t covered in spines and utterly miserable while on the road, but knows in their heart—only by moving forward is there a way to live?

After the next rain, when you see a guò shān jì twisting its body as it walks, please make way for it. It’s desperately looking for a new home. It has already traveled a long way—don’t go disturb it.