As a sleep Pisces and why the city's lighting system can kill you?

Now imagine how looks fish — have you ever noticed that their eyes are constantly bulging and they never blink? The fact is that due to the aquatic mode of life, their eyes never dry out and they don't need eyelids to moisten them. It may seem that because of the inability to close the eyes, fish never sleep, but it's not. Just unlike humans, fish don't sleep in the truest sense of the word, and are just stationary. Their body rests, but they are always on the alert — in the event of danger, the fish are always thrown in all directions. And the poses and the places where they sleep, depend on their class, because fish are divided into bone and cartilage. But what is the difference between them and why scientists think that urban lighting able to kill those, and others?

What are fish?

The Main distinguishing feature between conventional fish and sharks, it is the presence and the absence of swim bladder. This is an inside fish bag with air and he is the only bony fish. When the fish is gaining in it the oxygen, it rises to the top and may just "freeze" at the same depth. And when the sack opusteet air — fish becomes heavier and sinks to the bottom. Due to this on most fish can still be in the water and relax, but with open eyes, because they can always in danger and they need to be alert. During sleep, the fishes actively move their gills and suck in water to extract from it the particles of oxygen and thereby "breathe".

here is the structure of the bony fish, the swim bladder is right in the middle

The position of the body during sleep, all fish are different. According to biologists, cod during sleep releases its swim bladder and is lying on his side, dropping to the bottom. Herring is able to sleep belly up, and flounder all burrows in the sand — apparently they hope so they will not notice predators. It is noteworthy that almost all fish prefer to sleep among vegetation, because there the probability of being detected by predators is very small.

Flounder — a very strange fish with a tapered body. No wonder she's comfortable sleeping in the sand — it is almost impossible to notice.

Sharks and rays, which belong to the cartilaginous fish, sleep in a completely different way. Due to the lack of swim bladder, they can't just stop and "freeze" at the same depth — so they'll just sink to the bottom and suffocate. But they can suffocate due to the fact that they have no moving gills, through which they can absorb water and extract the oxygen. They have only fixed Gill slits, in which the water enters only during the movement of the shark. So, it turns out that during sleep, the sharks need to stay in motion?

look at these exhausted eyes, the guy is clearly lack of sleep

Not always, but there are dormant during sleep sharks. For example, the shark-Katran during sleep, leaving only the spinal cord, which makes moving swimming muscles. While the brain of a shark is resting, so we can assume that she sleeps. Do tiger sharks have a decent replacement gills in the form of small holes behind the eyes, through which they suck the oxygen-enriched air. The species of sharks and rays, which are not able to sleep on the go and does not have the analogue of the gills, just go to the bottom where there is over — water alone penetrates into their body, though not in such large numbers than with suction. In General, they air is enough.

What harm does the city light?

As you can see, a lot of fish quite difficult to relax — they always need to be alert and look for secluded places to sleep. According to German Professor Werner Kloas, because people have to fish even harder. The fact that urban lighting increases the brightness of the water and the fish were not able to relax. Moreover, exposed to bright light they produced little melatonin hormone that is responsible for immune function and proper growth and development of the body. This was recently reported .

This Professor found out, having conducted a little experiment. He placed four groups of fish in different aquariums. For ten days the first group of fish was kept in complete darkness, and others subjected to light with a brightness of 0.01, 0.1 and 1 Suite. To understand what brightness was exposed to fishes, imagine a night with a full moon — according to calculations of scientists, in such circumstances, there is brightness at the level of 0.3 Lux. But the city is able to emit a brightness level of 150 Lux, that is almost blind fish.

So looks greatcities from space — they literally Shine

After 10 days, all groups of fish tested the melatonin levels. It turned out that intense light greatly slowed the production of melatonin, and in the dark a hormone produced in the optimal mode. According to researchers, disturbances in the development of this hormone can lead to the fact that fish will no longer grow and multiply. If the city will generate even more light than before it can lead to the extinction of fish.

Generally, researchers have long worried that cities emit too much light. This problem even has an official name — light pollution. As the lights of the cities so bright that you can see from space, they interfere with scientists to explore distant planets and galaxies. In one of the articles my colleague Love Sokovikova even speculate on whether a strong glow of cities . Turned out pretty interesting, so I strongly recommend reading!

If you have trouble sleeping at night, imagine what fish — they literally can't close my eyes