This winter is tough for fish. The reason is not the abrupt growth in the number of fishermen, but the enclosed water bodies under the thick layer of ice, where fish suffer from oxygen deficiency.
On an average, every fourth water body in the Nordic and Baltic countires has the shortage of oxygen. The water bodies are supplied with oxygen by aquatic plants which release oxygen into the surrounding water as a result of photosynthesis. Due to the unusually thick and long stayed ice and snow layer the light needed for photosynthesis has no access to them and therefore the water bodies have the risk to remain congested.
What to do to avoid this? The most simple way is to wipe the snow off the ice to enable the light to get through. Unfortunately the wiping is not sufficient and in this case oxygen should be added to the water body. This method is used, for example, by many open fish farms during summer period with the aim to secure welfare and speed up the growth of the fish.
Oxygen is a gas which dissolves relatively bad in water. To support the dissolving of oxygen into water it is important to generate small oxygen bubbles, thus to increase the contact surface between water and oxygen.
In order to increase the contact surface, oxygen is introduced to water with the help of diffuser hoses. These are rubber hoses with tiny holes. The addition of oxygen to water is further improved with the help of the “lattice“, i.e. oxygen mat made of the diffuser hoses.
Oxygen solubility depends on water temperature and pressure, the higher the pressure and the lower the temperature, the better the oxygen dissolves. The oxygen solubility effectiveness increases by about 10% per each meter of water depth. Thus the oxygen mat should be installed as deep as possible. The Linde Gas / AGA perforated hose is called SOLVOX® B.
Air can also be added to the water instead of pure oxygen, but this is not as efficient. As air contains only 21% of oxygen, about five times more air should be added to water. The higher the content of oxygen is in a gas mixture, the larger the quantity of soluble oxygen. It should also be kept in mind that the cleaner and colder the water, the better oxygen dissolves in it.
Although the enrichment of the natural water bodies with oxygen has not widely been tried out in the Nordic and Baltic countires, it has been already quite much used worldwide. Even River Thames in London has been(, for example,) enriched with oxygen – true, not to fight against ice, but pollution.