The level of dissolved oxygen in water determines the quality of water quality
The dissolved oxygen level in the water of fish ponds is the main indicator of water quality. All terrestrial animals and marine aquatic animals on Earth must survive and reproduce under aerobic conditions, and if they lack oxygen, they will die. In pond fish farming, oxygen deficiency in the water can cause fish and shrimp to float their heads, and in severe cases, suffocate and die from flooding, causing significant economic losses.
1, Standard for dissolved oxygen requirements in fish and shrimp farming water bodies
According to the long-term aquaculture practice of aquaculture industry practitioners, the dissolved oxygen in general pond water should be maintained at 5 milligrams/liter to 8 milligrams/liter, with a minimum of 3 milligrams/liter. Below this value, fish and shrimp may die from flooding in the pond.
In aquaculture, although mild hypoxia of water does not cause fish and shrimp to die, it also seriously affects their growth rate, increases the feed coefficient, increases production costs, and reduces aquaculture benefits.
Someone has determined that grass carp, for example, requires a dissolved oxygen level of 5 milligrams per liter or above or a saturation level greater than 70% in water during its main growth period as the normal range, with a minimum of 2 milligrams per liter and a lethal point of 0.4 milligrams per liter. At 2 milligrams per liter, grass carp begin to float.
Grass carp showed a 98% decrease in growth rate and a 4-fold increase in feed efficiency at a dissolved oxygen level of 2.72 milligrams per liter compared to 5.56 milligrams per liter. Other fish and shrimp are roughly the same.
Reasons for insufficient dissolved oxygen in aquaculture water quality
1. High temperature
The solubility of oxygen in water decreases with increasing temperature. For example, at one atmospheric pressure, when the water temperature rises from 10 ℃ to 35 ℃, the solubility of oxygen in pure water can increase from 11.27 milligrams per liter to 6.93 milligrams per liter. High temperature can cause a decrease in dissolved oxygen.
In addition, fish and other organisms consume more oxygen due to increased feeding and exercise during high temperatures, which is also an important reason.
2. Excessive breeding density
Fish farming blindly pursues high yields, and the amount of seedlings released per acre is too large, exceeding the normal amount. In this way, the respiration of fish and aquatic organisms increases, and the oxygen consumption also increases.
3. Decomposition of organic matter
The decomposition of a large amount of organic matter causes bacterial activity, consuming a large amount of oxygen in the water, which can easily lead to hypoxia.
4. The oxidation of inorganic substances causes hypoxia
Hydrogen sulfide, nitrite, and other substances present in the water and sediment of aquaculture ponds can undergo oxidation, leading to the consumption of a large amount of dissolved oxygen.
5. The pond silt is too deep and fertilized
In fact, excessive depth and fertilization of pond sludge are also a major factor in consuming dissolved oxygen in water bodies. According to some tests, the main consumption factor of dissolved oxygen in water is not fish and aquatic organisms, but the consumption of organic matter oxidation in water and sediment. Generally, fish consume 12% to 15%, while sludge accounts for more than 40% of oxygen consumption. Therefore, dredging and disinfection work is very important and cannot be ignored.
3, Status of hypoxia response in fish
When there is mild hypoxia, fish and shrimp become restless, and the waves of fish and shrimp swimming can be clearly seen from the water surface. Some fish and shrimp have their heads floating out of the water, and their breathing accelerates; When there is severe hypoxia, a large number of fish and shrimp will float their heads and even die.
Someone has determined that silver carp begin to die in large numbers when dissolved oxygen reaches 0.6 milligrams per liter.
When fish are exposed to dissolved oxygen of 1 milligram/liter to 3 milligrams/liter for a long time, they basically stop feeding, their growth rate slows down, their disease resistance decreases, and fish diseases and deaths occur. This is the reason why the feed coefficient of ponds with frequent floating heads increases.
