Dissolved oxygen is one of aquaculture’s most important and problematic water quality factors. Most of this is related to the fact that the dissolved oxygen cannot meet the demand. Today I will talk to you about the dissolved oxygen in aquaculture.
In most high-yield ponds, photosynthesis and mechanical aeration of phytoplankton become the main source of dissolved oxygen in the pond. The rest mainly comes from air dissolution, while water respiration and the consumption of farmed animals are the main consumption sources of dissolved oxygen.
For pond culture, dissolved oxygen is one of the water quality factors that limit the density of the culture. In the ponds where fish are raised in China, the dissolved oxygen in the water body can only grow normally when the dissolved oxygen in the water is kept at four to five milligrams per liter. Although most farmed fish have a strong ability to tolerate low oxygen, generally the dissolved oxygen is as low as two milligrams per liter to obey, but the fish and shrimp living in low dissolved oxygen water for a long time are not only inhibited in growth but also in various physiological activities. The impact will eventually lead to an increase in the feed coefficient and affect the economic benefits of farming.
Dissolved oxygen is an essential substance to ensure the normal physiological function and healthy growth of fish, but also an essential substance to improve water quality and the bottom layer. Sufficient dissolved oxygen in water can not only improve the immunity of farmed animals, but also inhibit the chemical reactions that generate toxic substances, and transform and reduce the content of toxic substances such as ammonia nitrogen, and nitrate. However, the supersaturation of dissolved oxygen will also cause embolism after the fry eats air bubbles by mistake, resulting in death. Such water will cause anaerobic decomposition of organic matter and ammonia nitrogen in the water, as well as some toxic substances such as nitrite, and it is easy to breed bacteria, resulting in a large number of deaths of cultured organisms. It can even cause severe anemia and slow growth. Respiration is obstructed in the resting state, fish and shrimp only eat and stop growing, consuming their own energy, when the dissolved oxygen is lower than its minimum limit, it will cause suffocation and death.
The dissolved oxygen content in water is mainly affected by the atmospheric oxygen partial pressure, water temperature, salinity, and other factors. As the water temperature increases, the saturated dissolved oxygen decreases, and the salinity of the water increases, and the dissolved oxygen in the water also decreases significantly. Secondly, the dissolved oxygen in the water will also change regularly with the daily season and the vertical depth. For example, under the photosynthesis of algae in the water body during the day, the dissolved oxygen concentration gradually rises and reaches the maximum value before sunset, and continues to decrease at night due to the cessation of photosynthesis, until it reaches the minimum value before sunrise in the morning, it is very prone to hypoxia and fondant.
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