Among the many chemical properties of aquaculture water, the most closely related to fish are dissolved gases and inorganic salts and organic substances dissolved in water.
1. Dissolved gas
There are many kinds of gas dissolved in water, their main sources are two aspects, one is directly dissolved into the water body from the air, and the other is produced in the water body by the life activities of the aquatic organisms and the chemical changes in the substrate or water substances. The dissolution of gas is different due to the water environment, and the differences are as follows.
Inversely proportional to the temperature of the water, the temperature of the water increases and the dissolution of the gas decreases. It is proportional to the atmospheric pressure. As the pressure increases, the gas solubility increases accordingly. Inversely proportional to the concentration of impurities in water, water with more impurities will reduce the solubility of the gas.
1. Dissolved oxygen
The dissolved oxygen content in water is small and variable. The saturation of dissolved oxygen in fresh water is only 8-10mg / L, less than 1/20 of the oxygen content in the air, and the dissolved oxygen content in seawater is even less. This indicates that the fish in the water have poor breathing conditions and from time to time face the threat of hypoxia and suffocation. This shows that it is important for aquaculture to grasp the dynamic law of dissolved oxygen in water.
There are two sources of dissolved oxygen in water; one is that the oxygen in the atmosphere is in contact with the water surface and dissolved into the water, and the other is the oxygen released by the aquatic plant during photosynthesis. 1/10 of the amount.
2. Hydrogen sulfide
Hydrogen sulfide is formed by the decomposition of sulfur-containing organic matter under anoxic conditions, or in sulfate-rich water, reduced from sulfate to sulfide, and then generated hydrogen sulfide.Sulfide and hydrogen sulfide are both toxic to fish, and hydrogen sulfide is the most toxic. Generally, under acidic conditions, most sulfides exist in the form of hydrogen sulfide. When the dissolved oxygen in the water increases, the hydrogen sulfide is oxidized and disappears. The toxic effect of hydrogen sulfide on fish is to combine with the iron in hemoglobin, so that hemoglobin loses its ability to carry oxygen, resulting in hypoxia in fish tissues. Therefore, special attention should be paid to the presence of hydrogen sulfide in farming.
3. Ammonia nitrogen
Ammonia nitrogen is produced when organic oxygen decomposes when oxygen is insufficient, or because oxygen compounds are reduced by anti-digestive bacteria. The final products of aquatic animal metabolism are discharged in the state of ammonia. Ammonia nitrogen is toxic to fish and other aquatic organisms, and even low concentrations will inhibit the growth of fish, and must be closely monitored.
Test items in aquaculture
1. Temperature; 18-35 ℃ is the normal temperature, and 25-32 ℃ is the most suitable growth temperature.
2. PH value: 6.5-8.5, below 6.5, the fertilizer effect cannot normally exert its advantages, the toxicity of ammonia nitrogen and hydrogen sulfide increases, and it is prone to hypoxia floating head.
3. Salinity; 0-1%, too high salinity will affect the normal growth and reproduction of organisms in fresh water.
4. Ammonia nitrogen; 0-0.02mg / L, too high will damage the gills of fish and mussels, above 0.5 will cause inability to eat and breathe until death.
5. Hydrogen sulfide; 0-0.1mg / L, too high will damage the central nerves of fish and mussels, above 0.5 will cause illness or death.
6. Nitrite; 0-0.02mg / L, too high will cause hemorrhagic disease, is an important factor inducing fulminant disease, above 0.5 will cause illness or death.
7. Available phosphorus; 0.2-1mg / L, the growth of high-quality algae in the water body below 0.2 is affected, and even the occurrence of blooms is not conducive to the growth of bighead, silver carp and mussels.
8. Transparency; 20-30cm, too high fertility is not enough, too low affects photosynthesis.
9. Dissolved oxygen; ≥3mg / L, less than 3mg / L will affect the feeding of fish, when less than 2mg / L will appear floating head, less than 1mg / L will appear
It is now Pantang until a large number of deaths.