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.
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.
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 degree to 35 degree , 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.
2. Excessive breeding density
3. Decomposition of organic matter
4. The oxidation of inorganic substances causes hypoxia
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
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.
