Dissolved oxygen and causes of insufficient dissolved oxygen
First, fish raise water, good water raise good fish
As the saying goes: "fish raise water first, good water raise good fish". Water is the living environment of fish, shrimp, crab, turtle, frog and other aquaculture animals. The quality of water directly affects the growth and development of aquaculture organisms, thus affecting the yield and economic benefits. Each aquatic animal needs to have suitable water quality conditions for its survival, if the water quality can meet the requirements, breeding animals can grow and develop smoothly. If some basic indicators of water quality exceed the range of adaptation and tolerance of organisms, the growth rate of light breeding animals will be slow, the survival rate will be reduced, the feed coefficient will be improved, and the economic benefit will be decreased. Severe cases may cause a large number of deaths of farmed animals, causing serious economic losses.
The deteriorating water quality is not only harmful to the health of animals, but also endangers their lives. As we all know water is a good solvent and suspending agent, it can dissolve all kinds of gas, such as oxygen, carbon dioxide, ammonia and hydrogen sulfide, also can dissolve various salts, such as nitrite, phosphate, carbonate, sulfate and so on, can also be suspended dust, organic detritus, small protozoa, bacteria, algae, and all kinds of eggs, etc. Dissolved in water and suspended substance of tangible or intangible and composition, part of is necessary for the growth and development of aquatic animals, some of them are not good, and another is harmful, or there are most harmful in content, also, they to other creatures in the water, also has the favorable and unfavorable aspects, especially some health and growth of farmed animals, And for some pathogens (such as pathogenic bacteria, paRASitic protozoa) reproduction, breeding and production of virulence is necessary, it is easy to lead to the occurrence of diseases.
Water quality plays a crucial role in the breeding of aquatic animals. Normal aquaculture water (not polluted by industry), the main indicators affecting the water quality are pH value (pH), dissolved oxygen, ammonia nitrogen, nitrite, hydrogen sulfide and other 5 indicators. Heavy metals, pesticides, chemical sewage and other polluted water sources, if they exceed the "Fishery Water Quality Standards", cannot be used for aquaculture production. To aquaculture water, must carry on regular comprehensive scientific test. If one-sided detection or subjective judgment only based on experience, it may lead to disastrous consequences.
Scientific tests can produce correct data. These data can tell the farmers the state of the water quality, so as to determine whether the water quality meets the requirements of aquatic animal growth, and whether it will cause disease. Another function of water quality testing is to provide a basis for improving water quality and drug use for fish diseases, and to reduce the loss of fish death caused by daily management such as fertilization, baiting and drug use. Therefore, water quality testing is necessary to ensure the health of water quality, but also the basis of healthy aquaculture.
Dissolved oxygen - life element of aquatic animals
Like humans, aquatic animals must also live on oxygen. The difference is that humans breathe oxygen in the air, while aquatic animals breathe dissolved oxygen in the water. Water hypoxia can make it floating head, serious flood pond death.
1. Dissolved oxygen requirements in water for aquaculture (seedling)
Generally speaking, the dissolved oxygen in the water should be maintained at 5~8mg/ L (PPM), or at least above 3mg/ L. Dissolved oxygen requirements of various fish and shrimp are shown in the table below.
Table: range of dissolved oxygen required for various fish and shrimp (mg/ L)
varieties
Suitable range
Start floating head
Asphyxia death
mandarin fish
Although mild hypoxia is not fatal, the growth of fish and shrimp will slow down, the feed coefficient will increase, and the production cost will rise. Excessive dissolved oxygen in water can cause fish bubble disease.
(Good Water Quality)
2. Causes of insufficient dissolved oxygen
(1) High temperature. The solubility of oxygen in water decreases with the increase of water temperature. For example, when the water temperature rises from 10℃ to 35℃ under one atmospheric pressure, the solubility of oxygen in air in pure water can drop from 11.27mg/ L to 6.93mg/ L, and high temperature will cause the decrease of dissolved oxygen in water. In addition, increased oxygen consumption by aquatic animals and other organisms at high temperatures is also an important factor.
(2) The breeding density is too high. The respiration of many organisms in the water increases, so does the oxygen consumption of organisms.
(3) decomposition of organic matter. The more organic matter there is, the more active the bacteria are, and this process usually requires a lot of oxygen to carry out, so it is prone to hypoxia.
(4) oxidation of inorganic substances. In the presence of inorganic substances such as hydrogen sulfide and nitrite in water, oxidation will occur and consume a large amount of dissolved oxygen.
3. Causes of fish and shrimp floating head
(1) The temperature difference between the upper and lower water layers of the pond or reservoir produces sharp convection. In the summer and autumn high temperature season, the water quality of the intensive cultivation pond is rich, and the oxygen difference between the upper and lower water layers is great during the day. In the afternoon, the upper water is saturated with dissolved oxygen, while the lower water is severely anoxic. Due to the thermal resistance of the water and the calm wind, the upper and lower water layers are not easy to convection. Later in the evening, if suddenly the thunder shower or windy, make the surface temperature fell sharply, causing a sharp convection, upper and lower layer of the upper high oxygen water convection rapidly to the lower level, was quickly lower the organic material consumptions in the water net, repay "anaerobic", so that the entire pond oxygen quickly dropped, hypoxia caused by hypoxia.
(2) the water is too rich or corrupt. Summer, autumn high temperature season, pond or reservoir temperature is higher, try to cast a lot of bait, make pool water is very fat. If there is no rain for a long time, and no new water is added for a long time, it is easy to make the water too fat (water color turns black) or corrupt (due to excessive phytoplankton reproduction and lead to a large number of deaths, water color turns muddy and smolky), causing fish floating head.
(3) It is caused by weak photosynthesis. Due to rain or fog, resulting in poor lighting conditions, phytoplankton photosynthesis is weakened, the amount of dissolved oxygen in water is less, and a variety of biological respiration and organic decomposition in the pool water and constantly consume oxygen, so that the supply of dissolved oxygen in water exceeds the demand, causing fish hypoxia floating head.
(4) caused by the massive reproduction of zooplankton. Due to the excessive reproduction of water flea, rotifers and other zooplankton, a large number of filter feed phytoplankton, so that the water in the pool is clear, the dissolved oxygen in the water is mainly supplemented by air, far from meeting the oxygen consumption demand, causing fish floating head.
4. The reaction of fish and shrimp when they are deprived of oxygen
When there is mild hypoxia, the fish and shrimp are agitated. The waves of swimming fish and shrimp can be seen obviously on the water surface. The head of individual fish and shrimp floats on the water surface, and the fish and shrimp breathe faster. Severe hypoxia, a large number of fish and shrimp will float, or even die. For example, Wuchang fish and silver carp began to die in large numbers when dissolved oxygen was 0.6mg/ L. Long-term exposure to 1.0-3.0mg/ L of dissolved oxygen would basically stop the feeding of fish and shrimps, slow the growth rate and decrease the resistance. This is why the high yield pond of often floating head, feed coefficient is high, the reason that often comes on.
5. The relationship between dissolved oxygen and other toxic substances
Maintaining sufficient dissolved oxygen in the water inhibits the chemical reactions that produce toxic substances, converts and reduces the levels of toxic substances (e.g., ammonia, nitrite and hydrogen sulfide), such as: Ammonia and hydrogen sulfide are produced after the decay of organic matter in water. In the presence of sufficient oxygen, ammonia will be converted into nitrite and then into nitrate through the oxygen-consuming decomposition of microorganisms, while hydrogen sulfide will be converted into sulfate, which will become non-toxic final products and be absorbed by plankton photosynthesis. So it's important to have enough dissolved oxygen in the water for aquaculture. If deprived of oxygen, these toxic substances can quickly reach harmful levels. It was determined that when the dissolved oxygen in water increased from 1.54mg/ L to 2.2mg/ L, the content of NH3 decreased from 0.4mg/ L to 0.2mg/ L, and the nitrite decreased from 0.04mg/ L to 0.01mg/ L.
6. Methods of oxygenation
The best way is to often inject new water, sunny noon or after midnight often use aerator, maintain water quality "fertilizer", "live", "tender", "cool". In order to keep water quality fresh, sprinkling microbial water quality modifier is also an effective method to increase oxygen. In anoxic floating head, sprinkling reactive oxygen modifier is an emergency measure for water anoxia, but chemical oxygenating agent can not fundamentally solve the problem of water anoxia. Regardless of the aerator solid content should not exceed 13%, liquid content should not exceed 18%. Such as 1 mu pond (average depth of 1 meter), sprinkled 1 kg of oxygenating agent, its dissolved oxygen but also increased 0.25mg/ L, and the fish start floating head death to the normal dissolved oxygen gap of more than 2mg/ L.
Therefore, measures such as appropriately reducing stocking density, injecting more water or turning on aerator or using microbial agents (such as photosynthetic bacteria, etc.) are the most fundamental solutions to aquaculture floating head or pool.
