The regulation and management of freshwater fish aquaculture water quality is the key to successful breeding.
In order to increase the yield and benefit per unit area, people often carry out high-density farming. However, high-density aquaculture can cause a series of problems: increased chemical oxygen demand, increased oxygen consumption, decreased dissolved oxygen, and increased acidity of sediments. Some toxic substances accumulate in large amounts in water bodies, and water quality deteriorates. Continuation of this causes water ecosystems. The destruction. Therefore, water quality control technology has more important significance in this situation.
To do a good job in water quality regulation and management, on the one hand, we must understand the biological, chemical, and physical processes that take place in aquaculture water bodies, fully understand the laws governing the production, migration, and conversion of substances in water bodies and the routine detection methods for water quality indicators; on the other hand, water quality regulation And management is very practical. Water quality control is the key to ensure the normal development and growth of all kinds of fish. Therefore, the pond must maintain good water quality. In the proverb, “to raise a pool of fish, we must first manage a pool of water.†This is the truth.
In order to manage water quality, we must first understand the concept of water quality. The so-called water quality is simply the quality of the water body. It has different requirements depending on the species of aquatic animals raised, and mainly includes: dissolved oxygen, pH, pH, Ammonia nitrogen content and nitrite content, transparency and organic matter oxygen consumption (COD value).
1. Dissolved oxygen. The amount of dissolved oxygen in the water directly determines the breathing conditions of aquatic animals. If breathing is difficult, why not talk about strong food intake and healthy growth? Therefore, dissolved oxygen is the most closely related to the survival and growth of aquatic animals. At the same time, the high water-soluble oxygen in the pool can suppress and reduce the toxic effects of ammonia nitrogen, nitrite, and hydrogen sulfide on farmed animals. In China, the dissolved oxygen requirement of common domestic fish such as Qingcaoqi is higher than 2-3 mg/l, and the individual fish is required to reach 4-5 mg/l, otherwise the respiratory frequency will increase, the energy consumption will increase, and the life function will increase. Weakness, sluggishness, poor feeding, decreased feed efficiency, and inhibited growth.
2. pH value. The pH value can affect the effect of applying inorganic fertilizer in the pond, and can also affect the balance of ammonia and ammonium ions in the water. The decrease or increase of pH value has direct damage to fish. Especially in acidic environment, the pH value of fish in the blood drops, so that the oxygen partial pressure in the blood is small, which reduces the oxygen carrying capacity and destroys the tissue. Cells and epidermis reduce the hemoglobin oxygen-carrying capacity, resulting in decreased physical fitness, reduced resistance to disease, and prone to disease. China's freshwater aquaculture ponds require neutral alkalinity. Generally, suitable pH values ​​for fish are 7.5-8.5, and individual fish requirements are 7.0-8.0.
3. Ammonia nitrogen and nitrite. Ammonia mainly refers to non-ionic ammonia. High water temperature, high pH, ​​high non-ionic ammonia content. High concentrations of non-ionic ammonia will prevent the outward excretion of ammonia in the fish, reduce or stop the intake of fish, reduce the growth rate, and even lead to death. The concentration of non-ionic ammonia in freshwater aquaculture should generally be less than 0.02 mg/l.
Nitrite is an intermediate product of organic matter decomposition. When it reaches a certain content in water, it can quickly destroy the cerumen tissue and cause the cerumen to enlarge and proliferate. After the nitrite ion is absorbed into the blood circulation system by the fish, it makes Hemoglobin is converted to methemoglobin, which reduces the amount of oxygen that can be carried by the blood, which can force the fish to reduce their intake of food, reduce oxygen in the body, weaken the body, and cause fish disease. The concentration of nitrite in freshwater aquaculture should be less than 0.2 mg/l.
4. Transparency and COD values. Transparency is mainly determined by plankton in water. Phytoplankton contributes dissolved oxygen to the ponds, and zooplankton consumes dissolved oxygen, but they all provide biofeeds for filter-feeding fish, and they are also responsible for regulating water quality. Therefore, the transparency of the water should be appropriate, generally controlled at 30 cm or more. COD values ​​are related to fish robbing oxygen. On the surface, the smaller the better, but the oxidation of organic matter in the water provides nutrients for plankton. Therefore, the COD value should be controlled within a certain range. The ponds, which are generally dominated by cockroaches, are used to control 10-20 mg/L. In general, freshwater aquaculture is ideal if it is to achieve a water-rich, live, tender, and cool state. The so-called fat refers to a large number of plankton and the number of fish digestible species, transparency is about 30 centimeters; live means that the water color and transparency often change, do not die, is the performance of phytoplankton in a prosperous period; tender refers to The water is fresh and not easy to digest, and the phytoplankton are easily digested (the cyanobacteria and other indigestible species reproduce in large quantities, and the gray-blue or blue-green color of the water, or the senescence of the phytoplankton cells will reduce the freshness of the water and become “old waterâ€); The water quality is refreshing, not polluted, the water surface has no floating membrane, the turbidity is small, the transparency is generally 20-25 cm, and the dissolved oxygen is higher in water. When water is thin, it is necessary to fertilize properly to promote the growth of phytoplankton; the color of water does not change or the color is old, dirty, and the transparency is small. Maintaining the water quality of fertilizer, live, tender and cool is the guarantee for the cultivation of high-yield and culture-free aquatic products.
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