We know that hairtail and yellow croaker are marine fish and live in the sea; Crucian carp and carp are both freshwater fish, living in ponds, lakes and other fresh water. Seawater and fresh water are quite different in salinity and pressure.
The researchers found that the pressure in seawater is much greater than that in fresh water. Hairtail and yellow croaker live in seawater at an altitude of 15~40 meters, and they are under great pressure from seawater every day. After a long time, they form internal and external structures that adapt to the huge pressure of seawater, such as thin bones and elastic muscles.
Fish that live in seawater all the year round are suddenly arrested. After leaving the seawater, the external pressure suddenly drops. As a result, the air in the swim bladder expands due to the decrease of external pressure, even exceeding its capacity, and then bursts. In addition, the change of air pressure may also lead to the rupture of some small blood vessels in the body, gastrointestinal discomfort and exophthalmos. All these may cause hairtail and yellow croaker to die soon after leaving seawater.
If we carefully select a few live hairtail and yellow croaker, and immediately put them into a container filled with seawater to maintain the quality of seawater and make the container have a certain depth and appropriate water pressure, we can still transport them to the vegetable market alive. But in order for them to continue to survive in the vegetable market, in addition to seawater, they also need certain technology and equipment, which is too expensive and completely unnecessary, so the hairtail and yellow croaker seen in the vegetable market are all dead.
Some people may wonder why marine fish can't be raised with fresh water. This is because the salinity of fresh water is much lower than that of seawater. When marine fish are put into fresh water, the osmotic pressure of fresh water is smaller than that of fish, so external water will flood into fish tissues, the cells of marine fish will be filled with water, the blood tissues will be destroyed, the circulation will be disordered, and marine fish will die.
Hairtail lives in seawater with a depth of about 60 meters and is a migratory fish.
Have the habit of moving vertically day and night. The water depth is different at different times of day and night.
Generally speaking, this group lives in the middle and lower ocean during the day and moves on the sea at night. Stay at home during the day and go out at night.
So it does not belong to deep-sea fish.
Low-and middle-level fish with a water depth of more than 200 meters are often called deep-sea fish.
People call the water depth of 200-3000m as semi-deep, the water depth of 300-6000m as deep, and the trench below 6000m as ultra-deep. Deep-sea light is dim, food is poor and pressure is high, so deep-sea fish have various shapes, and their colors are generally silver, black and purple-black.