During the artificial breeding process of crabs, the quality of water quality determines the yield and quality of seedlings to a large extent. Water quality is directly affected by a variety of physical, chemical and biological factors, and is often subject to major changes. Due to the limitations of its detection methods, the blind use of large quantities of antibiotics and a large number of water changes have become the process of artificial breeding of most crabs by most technicians. Two major magic weapons for water quality control. However, the large use of antibiotics will lead to bacterial resistance and drug resistance of the seed, which may result in higher seed yield and lower seed quality. Low quality seed will inevitably bring the risk to the next farming link. In addition to increasing the aquaculture production cost, a lot of water changes are more difficult to form a stable ecological environment in the nursery water body, which is not conducive to the normal growth of the seedlings. If the water change is not timely, the water quality will deteriorate quickly, causing devastating losses.
I. Hazards and Causes of Water Quality Deterioration
1. Hazards Accumulation of heavy metal ions, ammonia nitrogen, hydrogen sulfide, and other harmful substances in the water of the crab breeding water and pH value may exceed the tolerance of the seed due to the introduction of exogenous sources and the accumulation of internal residues or excretions. The range resulted in poor growth (malformation, metamorphosis), decreased physical fitness (vigor), and even large-scale death. Furthermore, due to the accumulation of organic matter, a large number of pathogens and pathogenic protozoa are breeding, causing the occurrence of a variety of diseases, and reducing the survival rate and constitution of seedlings, leaving hidden dangers for the development of crabs.
2. The causes of water quality deterioration include natural sea area pollution, limited self-purification of water bodies, abuse of drugs, poor water quality regulation and treatment measures in daily management, and so on.
Second, on-site monitoring of water quality
Due to the unstable water quality in nursery ponds, the rate of change is rapid. Even if there are related instruments and equipment, it is difficult to respond quickly. However, the traditional method of observing water color is too rough and prone to errors and mistakes. Therefore, it is necessary to seek simplicity and effectiveness. The method to monitor the water quality of the nursery pool. According to the author's practical experience, it is believed that the pH value and biological indicators can be used as a practical indicator to effectively monitor the water quality of nursery ponds.
1. The pH value is a comprehensive physical and chemical index reflecting the change of water quality. There is a close correlation between pH and water quality. The pH of natural seawater is between 8.3 and 8.5. The pH of the aquaculture water increases with the increase of photosynthesis of phytoplankton (8.6 to 9.2). With the floating of water, plants The respiration, especially the consumption of oxygen by organic matter (decomposition of residual baits, feces, and dead bodies by microorganisms) is reduced (7.5 to 8.2), and is closely related to the production, volatilization, and toxicity of ammonia nitrogen and hydrogen sulfide. More importantly, the pH value directly affects the crustacean's physiological activity, especially the molting metamorphosis. By using a pH tester, you can instantly understand the values ​​and changes, provide reliable data for water quality testing in the nursery, and respond to changes in water quality in a timely manner.
2. Water quality indicator organisms are wind vanes that reflect the ecological changes in water quality. In addition to the daily observations of water crabs nursery farms with imperfect water quality detection methods, it is necessary for the technicians to select several organisms that can indicate the water quality conditions, monitor their species and quantity changes, and thus increase the sensitivity to water quality changes. Common indicator organisms include: gold algae (>1x10 cubics/mL), dinoflagellates (>1x10 cubics/mL), cryptophytes (>1x10 6/mL), native Animals (>1x10 6th power/mL) etc. When the above-mentioned organisms in the water body approach or exceed the density, the water quality deteriorates.
Third, the method of water quality control
1. To reduce the introduction of water pollution sources, select the timing of water supply from the open sea, avoid red tides or sewage peaks, and should select water during the tide; adopt a reasonable feeding plan, select feeding timing, palatability feed, Control the amount of feed to reduce the residual bait.
2. Perform proper water treatment. When water for storage is contaminated with biological and non-biological factors, it is necessary to carry out water treatment to eliminate the influence of pollutants. Commonly used treatments include EDTA complexing heavy metals, bleaching powders, and ozone to kill microalgae and microorganisms. In preventing the deterioration of pool water in nursery ponds, measures need to be taken in a timely manner. In addition to regular water changes, a certain amount of chemical drugs need to be put in place to regulate water quality. For example, antibiotics are used to inhibit bacterial growth, and potassium permanganate is antibacterial and reduces. Organic solution, chlorine dioxide kills unicellular pathogens and so on.
3. Water quality improvement measures
(1) Change the water properly. According to the water quality, the water exchange volume is determined to promote the sound development and balance of the micro-ecosystem, and to maintain and improve the self-purification capacity of the water body.
(2) Rationally use antibiotics to reduce the resistance of pathogens, and use drugs with short half-life as much as possible to reduce their residues in water and animals.
(3) Apply adsorbent to reduce the content of organic particles, soluble organic matter and ammonia nitrogen in the pool water.
(4) The use of chemical (acid and alkaline substances or buffering agents), physical (adjusting aeration, light, etc.) and biological (adding or removing monocellular algae) techniques to adjust the pH of the water, so that the pH value is maintained at 8.0 ~ 8.6 between.
(5) Putting a micro ecological preparation. Specific microorganisms can accelerate the decomposition of organic matter in the water. Photosynthetic bacteria, marine yeast, or artificially cultivated microalgae can absorb their decomposition products and thus play a role in water purification.
(6) Remove sediment in time to prevent deterioration of water quality due to sediment spoilage.
(7) Incorporate good water quality into nursery ponds to promote the ecological balance of the aquaculture and improve its water purification capacity.
Fourth, the summary
As a relatively independent semi-enclosed water body, the aquaculture water body has a certain ability of self-purification. The essence of water quality control is to effectively use and control the aquaculture water body so as to maintain its self-purification capability, so that it can maintain a good water quality condition with the least manual intervention conditions. For maximum economic benefits. The control of water quality cannot rely solely on water changes, or even arbitrary application of drugs, but on the situation of water bodies in different sea areas and in different breeding periods, analyze their ecological composition and change laws, cultivate beneficial organisms to enhance water purification capacity, and adopt water quality Water quality treatment, water exchange, and application of microorganisms that can decompose and absorb soluble organic substances to maintain and enhance their self-purification capability are the right ways to obtain good water quality.
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