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1. Salt content and salinity
1 Salt content: The number of grams or milligrams of dissolved salts contained in 1 liters of water is called salt content mg/L (mg L -1 )
ppm
2 Salinity salinity: The number of grams of dissolved salts contained in 1000g water is called salinity (ppt)
• The weight of 1 L of fresh water is about 1000 g, so the salt content of fresh water is basically equal to the salinity, while the salinity of brackish water is slightly lower than the salt content.
• The salt content or salinity is usually calculated based on the total amount of anions and cations contained in 1 liter of water.
Usually, Na + , K + , Ca 2+ , Mg 2+ , HCO 3－ , CO 3 2－ , SO 4 2－ , Cl － , etc. 8 main ion contents can represent the total salt or salinity of fresh water
3 Salinity of fresh water and seawater: • The upper limit of salinity of fresh water is 0.5• Salinity of seawater: 16-47‰
• Shrimp Farmings Fade
Effect of salinity on freshwater fish
• Salt content is too low: The alkalinity and hardness of water do not meet the basic requirements, and fish growth is affected
• The salt content is too high, which is not good for freshwater fish growth and even endanger the survival of fish
• The salt tolerance limit of various fish: the silver carp species period is 5~6, adult fish 8~10; grass carp species are 6~8, adult fish 10~12. Most freshwater fish and bait organisms can live normally in water bodies with salinity of less than 5.
2. Carbonates, alkalinity, hardness and calcium, magnesium
◆Alkalinity: 20℃, the amount of substances that require hydrogen ions when all alkaline substances in 1L of natural water are neutralized.
◆Including strong alkali (NaOH), weak alkali (NH 4 OH), strong alkali weak acid salt (carbonate, etc.)
◆Hardness: Ca +, Mg + and other metal ions above divalent. The main composition of freshwater salts is calcium and magnesium carbonates, so the values of total alkalinity and total hardness of freshwater are generally not much different.
Fish farming water requires a certain alkalinity and hardness
➢Calcium and magnesium are indispensable nutrient elements in biological.
➢Calcium is an important component of animal bones and plant cell walls, and it has a great impact on the metabolism of proteins and carbohydrates, the absorption and transformation of nitrogen and phosphorus.
➢Magnesium is the main component of chlorophyll. Magnesium deficiency causes nitrogen metabolism to be disordered and affects the absorption of calcium
➢Calcium can reduce the toxicity of heavy metal ions and monovalent metal ions.
➢Ca + and Mg + are the modification agents for the water quality and base of aquaculture water.
• Adjust the pH value of the pool water to maintain the balance of CO 2 in the water, and the carbonate and bicarbonate in the water are in the CO 2 equilibrium system.
Day photosynthesis is strong CO 2 is exhausted, HCO 3 - Explanation releases CO 2 for algae utilization, the pH will not rise too high;
Night respiration, free CO 2 accumulates in water, and carbonate in water absorbs CO 2 and turns into bicarbonate, and the pH will not drop too low.
Effect of alkalinity and hardness on fish
• Excessive alkalinity is poisonous to fish, a large amount of mucus is secreted on the surface of the fish, and gills are bleeding and die quickly.
• At a certain total alkalinity, the higher the pH value, the greater the toxicity.
• Water with low alkalinity and hardness means that it has weak buffering capacity and unstable pH, which cannot provide sufficient carbon source.
• Improvement: Adding quicklime increases the concentration of bicarbonate in water, and the alkalinity and hardness also increase.
3. Nitrogen compound
1 The form of nitrogen compound present
• Inorganic nitrogen: NH 3, NH 4 + , NO 3 - , NO 2 -
• Organic nitrogen: nitrogen contained in amino acids, proteins, nucleic acids, humic acids, etc.
2 The role of nitrogen in fish farming ponds
• NH 4 + , NO 2 － , NO 3 － can be directly used by phytoplankton, first using NH 4 + , second using NO 3 － , and finally NO 2 － , these three are called effective nitrogen.
• The effective nitrogen in water mainly comes from dead organisms and fish excrement, etc.
• Some algae and microorganisms can directly use organic nitrogen
• The molecular nitrogen dissolved in water is transformed into nitrogen by nitrogen-fixing bacteria and nitrogen-fixing cyanobacteria and is used by phytoplankton;
• It is generally believed that the appropriate nitrogen content required for phytoplankton reproduction is about 0.3 mg/L. The effective nitrogen in Wuxi refined fish pond in summer and autumn is 0.2~4 mg/L. The effective nitrogen in summer and autumn is 0.89~1.8 mg/L.
tetrakistan, phosphate
1 The form present in the pond water
• Dissolved inorganic phosphorus: mainly in H 2 PO 4 － and HPO 4 2 － The form of
• Dissolved organic phosphorus: It can be converted into inorganic phosphorus after hydrolysis
• Dissolved organic phosphorus: It can be converted into inorganic phosphorus after hydrolysis
• Dissolved organic phosphorus: It can be converted into inorganic phosphorus after hydrolysis
• Granular phosphorus: The sum of the three parts above three parts of various phosphate lipids suspended in water in granular form, such as polyphosphate, hydroxy calcium phosphate, etc.
is called total phosphorus.
2 Source and function of phosphorus
• Mainly derived from dead organisms and excrement from fish, etc.
• Constituting the raw material for the cytoplasm and can accelerate gonadal development.
• Promote the large-scale reproduction of algae (N:P = 8~10:1)
• Phosphorus is usually a restrictive element in pond water. A small amount of phosphorus fertilizer can be used to proliferate phytoplankton and quickly fertilizer water.
5. Iron compound
Function: Iron is the main nutrient element of algae, and iron deficiency cannot form chlorophyll, affecting the photosynthesis of algae.
• Iron is an important part of heme, cytochrome, oxidase, peroxidase, and nitrogenase, and plays an important role in the process of biological redoxification.
6. Sulfate
1 Function
• It is an indispensable component that constitutes proteins and enzymes.
• Participates in the redox process in organisms.
2 Existing form
• Existing with SO 4 2—, the content is generally 20~30mg/L, and is often the first place of anion.
• Water flowing through sulfur-containing substances, water affected by seawater and hot spring water, has a high sulfate content.
3 Effect on fish
SO 4 2— It is non-toxic and has a safe concentration of 5.6g/L for silver carp.
• The bottom of the pond is full of organic matter, and the water in the lower layer is often dehydrated, and it is easy to be reduced by sulfate reduction bacteria to reduce SO 4 2- to toxic H 2 S. Therefore, water containing a large amount of sulfate should be avoided injecting water into the pond.
7. Chloride
• 1 The salt content in fresh water is low, the chloride content is not high, generally 20mg/L, but the chloride content in near-salt ore and ponds by the sea is relatively high;
• 2 All algae photosynthesis requires chlorine, and chloride ions are non-toxic;
• 3 For the pond water of farmed carp, chloride ions can be adapted below 4g/L.
• Bleaching powder, chlorine, and chloride
Bleaching powder: the main ingredient is calcium hypochlorite [Ca(ClO)₂], which also contains calcium hydroxide and calcium chloride.
• Bleach is easily exposed to air and fails:
• Tap water cannot be used directly to raise fish (Cl 2).
