It sounds strange, after all, fish live in the water, just as human sitinals live in the air so natural, that drowning a fish in the water is not the same as suffocating people in the air? But it is possible to drown a fish.
The theoretical basis of drowned fish: the way the fish breathes
To know how to drown a fish, you must first know how the fish breathe.
We all know that most fish are breathed with gills, and each of them is supported by a bow. In general, the gills are located on both sides of the pharynx and communicate with the outside world through fissures. The protein wire structure in the gills is called the small piece of the gills and can increase the area of contact between the gills and the oxygen in the water.
The bow and herring of the white-spotted dogfish Picture: Wikipedia
When a fish breathes, it regularly inhales water from its mouth and forces it to flow through the gills, and small patches absorb oxygen through contact with the water flow, so the large oxygen-intake area of the protein wire is very important for fish ventilation. With gradual adaptation, most fish can no longer survive from the water, the density of the water can ensure that their gills do not stick to each other and lose their ability to breathe.
Of course, not all fish are breathing with gills, such as African lung fish is directly breathing air, eel fish can breathe through the skin, these are a few, the vast majority of fish are used in the gills, so here we only discuss the fish breathing with the gills.
For fish, breathing is not as simple as you might think, because oxygen is quite less soluble in water. At 20 degrees C, a standard atmospheric pressure, a liter of water can dissolve only about 9 milligrams of oxygen, which is only about 1/35 of the oxygen content in the air. This also means that as long as the environment of the water changes, the amount of dissolved oxygen in the water may not be enough for the fish to breathe normally.
Therefore, fish living in water can only breathe properly if it gets as much water as possible through its gills to get enough oxygen. So how do you get enough water?
Because the hard-bone fish has a cap, the cap can adjust the water pressure of the throat to ensure that there is a suitable amount of water through the gills, so most of the practice of hard-bone fish is to continue to swallow water with the mouth, do not need to constantly swim to replace the gas, but there is no hard cap of cartilage fish, such as sharks, can only be constantly swimming to let more water into their mouths.
The shark’s respiratory system Picture: bio.classes.
Whale shark’s slug picture: Wikipedia
How to drown a fish?
So we know that trying to drown a fish is essentially to keep the fish out of breath. So let the fish do not breathe oxygen, first of all, can make the amount of dissolved oxygen in the water less, and second, let the fish respiratory system problems.
The amount of ambient dissolved oxygen at the time of the fish’s asphyxiation death, known as the point of suffocation, is different in the type of fish, and asphyxincy is not the same. For example, the suffocation point of herring in summer (27 to 28 degrees C) is 0.72 to 0.34 mg/L, while the herring is 0.68 to 0.34 mg/L.
If you want to make the amount of dissolved oxygen in the water smaller, the easiest way is to change the temperature of the water environment, because the amount of dissolved oxygen in the water has a lot to do with the temperature. As the temperature rises, the ability to dissolve oxygen in the water decreases rapidly.
Changes in dissolved oxygen in water with temperature Picture: Fondriest Environmental
At a standard atmospheric pressure, a litre of water at 0 C can dissolve 14.6 milligrams of oxygen, while at 35 degrees C, only 6.9 milligrams can be dissolved. For a fish with a strong metabolism, the oxygen consumption will also increase, and the water temperature is slightly higher and may suffocate.
Different fish requirements for water body temperature (Fahrenheit temperature) Picture: IMAGES LOBSTER AND FISH 2018
Sometimes in the sweltering summer, you can see some suffocating fish swimming on the water, poking their heads out of the blue and opening their mouths in order to breathe more air.
Goldfish breathing out of the water Picture: The best fish 2018
So the first way to drown a fish is to let the water temperature rise. If you have goldfish in your house, you can throw it in heated water and drown in a short time. This is also why you can not use boiled water to raise fish, boiled water at high temperature to extract a large amount of dissolved oxygen, and with the change of time in room temperature is difficult to restore to the normal oxygen content, resulting in it is not suitable for fish farming.
If you don’t want to change the temperature of the water, you can also change the salinity of the water, salt the water is fine, because the salinity in the water also affects the water’s dissolved oxygen. Increased salinity in the water body is accompanied by a decrease in the dissolved oxygen saturation of the water body, which is one of the reasons why freshwater fish cannot run into the sea, as it is possible to suffocate.
Theoretically, the amount of dissolved oxygen in the water body can be reduced by changing the air pressure, the lower the air pressure, the lower the dissolved oxygen content in the water. But it’s too hard to actually live in, so it’s not recommended to drown a fish by lowering the air pressure. In the natural environment, the air pressure will be lower, so the fish will also probe out blue blue to breathe.
Drowned fish IMAGES LOBSTER AND FISH 2018
How to drown a shark
It has been said that cartilage fish can only swim around to get enough oxygen, so if you want to drown a shark, in addition to changing the amount of dissolved oxygen, there is another way, is not to let the shark swim.
This happens in the sea, because sharks are sometimes trapped by fishnets in the sea, and sharks that can’t move can’t get enough water into their mouths and end up drowning.
National Wildlife Photography Competition
And because there is a demand for shark fins on the market, shark meat is really hard to eat (why shark meat is so hard to eat can be answered by another question i’ve had before), so it’s often the shark’s fins cut off and thrown back into the sea. Sharks that can’t swim will eventually drown because they lose their fins.
Sharks that drowned with their fins Picture: fishkeeping world
That’s why when catching sharks, they have to be pumped into their mouths and pumped directly to allow water to flow through their gills to avoid shark suffocation.