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The reason why fish living in the sea is as salty as sea water

The answer is no. In fact, the sea fish we eat such as mackerel and tuna are not as salty as seawater. If we eat these sea fish and find that they are salty, we process them with salt to keep them for longer.

Fish that live in seawater can be divided into two main groups: bony fish and cartilaginous fish.

In the gills of scleractinians, there is a special type of cells called salt-secreting cells. Salt-secreting cells can secrete salt. They can absorb salt from the blood, concentrate it and then secrete it out of the body together with a sticky liquid. These salt-secreting cells are always working efficiently, so the fish always remain low in salt.


It is possible for cartilaginous fish in seawater to maintain a low salt content in their bodies. Usually in these fish, the blood concentration is higher than that of seawater, thus minimizing salt penetration, so their flesh is never salty.

Why do some fish have fish scales and some do not?

Most fish have a hard coating on their bodies. Scales are a derivative of fish skin and serve to protect the fish’s body, but there are some species that do not have scales on their bodies because their scales have degenerated. Eels, for example, have their entire body covered by a very sticky mucus. The endocrine glands in their skin secrete large amounts of mucus. This mucus layer cannot resist the impact of hard objects, but it prevents the invasion of toxic bacteria. Also, because the mucus is very slippery, it is difficult to catch them. The scales on the eel’s body are degraded into a thin layer of skin with many small blood vessels to support breathing. The presence or absence of scales is due to the natural environment in which they have adapted to form during development.

Why glowing fish scales?

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In the real skin layer, there are many pigment cells and light cells distributed above and below the scales. But if there were only pigment cells, it would not be possible for the fish to appear so brightly colored.

In the fish’s skin, there are also photocells, and these cells contain guano, turtle droppings that are colorless or white crystals that accumulate in the cells.

When the light reaches the body of the fish, through the reflection and interference of the crystals in the cells, the light that appears before our eyes immediately turns into a shining silvery glow. So the fish scales shine, mainly thanks to the action of the light cells.


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