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Cyanobacteria, everyone knows and hates but is also helpless. In fact, the occurrence of cyanobacteria depends largely on temperature. Cyanobacteria are sensitive to temperature when they reproduce, and when the water temperature is below 17 ° C, they do not occur in large quantities or do not pose a hazard to fish. When the water temperature rises to 28 °C, cyanobacteria are prone to form dominant populations and erupt in large numbers. When cyanobacteria are multiplied, the pH is mostly above 8.5. Cyanobacteria is an external manifestation of eutrophication in water. In recent years, cyanobacterial blooms have shown a high incidence, frequency and outbreak in aquaculture water bodies. Therefore, cyanobacteria upset us, but we can't avoid it, and it lingers!
Cyanobacteria mainly include microcystic algae, fishy algae, cromococcus, spirulina, collar-like algae, coloceroid algae, pointed algae, split-sided algae, colloidal algae, bundle of hairy algae and other more than ten genera, of which microcystic algae is the most widely distributed and most common cyanobacteria. Cyanobacteria prefer water bodies with high nitrogen and low phosphorus. Cyanobacterial blooms often spread in less than three to five days to cover the entire pond surface in the right season. Algae communities have the ability not to be matched and suppressed by other algae, and tend to be in a state of uncontrolled reproduction when the environment is suitable.
First, the main environmental conditions for cyanobacterial outbreaks
Cyanobacteria growth: cyanobacteria + light + temperature + suitable environment. The specific description is as follows:
First, the continuous sunny and hot high temperature weather, from the algal phase ecosystem to see the temperature is its main influencing factor, most of the algae can live in a large temperature range, but the most suitable growth temperature variation is narrow. Generally speaking, diatoms, golden algae, and xanthobacteria are at a lower temperature of 14 to 18 °C, green algae are higher at 20 to 23 °C, while cyanobacteria are higher and prefer to grow at a temperature of 20 to 32 °C. Among them, the most harmful microcystis can grow at 10 to 40 °C, and the optimal temperature is 28 ~32 °C.
The growth rate of cyanobacteria accelerates with the increase of water temperature. At room temperature, some beneficial single-celled algae do not grow slower than cyanobacteria, and only when the temperature reaches above 20 ° C and the water temperature is 25-35 ° C, the growth rate of cyanobacteria will be faster than other algae. Therefore, due to the growth of other algae species, cyanobacteria is unlikely to erupt on a large scale under normal temperature conditions, and only in the high temperature season will the growth rate advantage of cyanobacteria be reflected. So temperature is one of the main factors in cyanobacterial outbreaks.
Second, the water body is strongly alkaline (pH 8.8 ~ 10), in the summer is often high temperature for several days, the illumination is extremely strong, the water algae photosynthesis is extremely strong, the carbon dioxide consumption is the largest, and the pH value will rise sharply.
The third is the necessary energy conditions for the production of light phytoplankton, and the light-loving characteristics of cyanobacteria promote it to float on the surface of the water, but it is often scattered in the water body at night, because there is no light or weak light at night.
Fourth, the water body is rich in high nitrogen and low phosphorus organic matter. The main cause of eutrophication in aquaculture waters is the accumulation of nutrients, especially excessive amounts of dissolved nutrient salts.
Fifth, eutrophication, when the water body eutrophication, cyanobacteria will appear frequently. Or after entering the peak period of breeding, the eutrophication in the aquaculture water body, the excrement of the aquaculture organism itself is also a pollution to the aquaculture water body. Therefore, cyanobacteria are often more likely to erupt in ponds that do not change water frequently. If cyanobacteria are not adequately nourished, it is also difficult to grow.
Sixth, the stocking structure is unreasonable, and the excreta, carcasses and other humus of aquatic animals in the aquaculture water body can indirectly provide nutrition for the reproduction of algae after bacterial decomposition. However, if the stocking structure is unreasonable, the proportion of eating fish and filter-feeding fish (such as white carp) is out of balance, and the water quality in the high temperature season is old, it will provide convenience for the large number of plankton. Although these factors cannot directly cause eutrophication of aquaculture water bodies, they can make a fundamental change in the water quality of aquaculture water bodies and facilitate the formation of eutrophication.
When cyanobacteria reproduce normally, it does not cause harm, such as the initial "cyanobacterial bloom" silver carp can suck it, and it is also an excellent bait for silver carp. Any stocking of the water in the water in an appropriate number of silver carp generally does not erupt cyanobacteria. Or the absence or improper proportion of silver carp and filter-feeding fish in fish ponds can lead to cyanobacteria flooding.
(Cyanobacterial blooms)
Second, the characteristics of cyanobacterial outbreaks
Cyanobacteria are very fertile and adaptable, in some nutrient-rich water bodies, some cyanobacteria often multiply in large quantities in the summer, and form a layer of blue-green and fishy odorous foam on the surface of the water, called "water bloom". Cyanobacteria mostly occur in the summer from June to September, showing obvious seasonality, with a high pH value and suitable light intensity and light time, pseudo-empty cells (air sacs) in cyanobacteria will make them float on the surface of the water body for group reproduction to form blooms.
Cyanobacteria have the characteristics of the growth of general algae, and their life cycle is about 30 days. Cyanobacteria multiply quickly, the fastest can be 2-3 days to cover the entire pond, to the night in the water dissolved oxygen will be a large number of cyanobacteria consumption or encounter weather changes, algae will die due to lack of oxygen and a large number of deaths. When cyanobacteria die, a large number of toxic and harmful substances such as hydroxylamine and hydrogen sulfide will be produced, and these substances will accumulate more in the water and cause fish poisoning and death.
Cyanobacteria can change the expansion pressure, in the case of high temperature and strong light weather conditions, gather on the surface of the water body, absorb most of the sunlight, in their own large numbers while inhibiting the growth of other algae. The large number of cyanobacteria continues to secrete toxic metabolites to the water body, which affects the population succession and reproductive cycle of plankton, and can also cause a large number of deaths of some zooplankton. Therefore, the real harm of cyanobacteria is in the stage of cyanobacteria death rather than during the growth process of cyanobacteria.
Cyanobacteria have a high degree of resistance to adverse environments and a general nitrogen fixation ability, and only cyanobacteria can multiply in large quantities when other algae cannot reproduce in hypoxic environments.
Third, the harm of cyanobacterial outbreaks
1. Reduce dissolved oxygen in water
When the cyanobacteria outbreak in the aquaculture water body, on the one hand, it seriously inhibits the oxygen generated by the photosynthesis of phytoplankton, and on the other hand, it also blocks the gaseous substances in the air from entering the aquaculture water body, resulting in a serious shortage of dissolved oxygen in the aquaculture water body, and a long period of hypoxia or hypoxia, which makes the aquaculture water body continue to deteriorate, thereby directly or indirectly exacerbating the occurrence of adverse accidents.
2. Produce toxic and harmful substances
When a large number of cyanobacteria die, cyanobacterial toxins, a large number of hydroxylamine and hydrogen sulfide and other toxic and harmful substances will seriously corrupt the breeding water body, directly endangering the farmed animals; in addition, the dead cyanobacteria release a large amount of organic matter, emitting a fishy odor, which stimulates the breeding of chemical energy heterotrophic bacteria, most of which are not beneficial bacteria but pathogenic bacteria for aquaculture animals, which further leads to the occurrence of secondary infectious bacterial diseases.
When cyanobacteria grow in large quantities, these algae can release toxins that are toxic to fish. Although cyanobacteria grow rapidly, they can also die quickly because the nutrient salts in the water may be exhausted. After a large number of cyanobacteria die (inverted algae), in the process of decay and decomposition, it also consumes a large amount of dissolved oxygen in the water, and will rise to the surface of the water to form a layer of green sticky matter, making the water body seriously odorous.
Fourth, the precautions for cyanobacterial water bodies
Using the food chain, the initial goal of controlling cyanobacteria can be achieved by stocking filter-fed fish in water bodies. Reasonable combination of filter-feeding fish (such as silver carp) is the most effective prevention and control measures, many people think that silver carp is delicious and valuable, heavy bighead carp light silver, some people think that silver carp (bighead carp) is also filter feeding fish, only polyculture silver carp and not set silver carp or set few white carp. In fact, although the silver carp are filter feeding fish that regulate water quality, the silver carp is more focused on animal bait food, while cyanobacteria is a plant aquatic biomass, and it just so happens that the feeding habit of silver carp is based on plant bait, which is self-evident here. Therefore, stocking a certain number of filter-feeding fish (e.g., silver carp) is the preferred measure to eradicate cyanobacterial outbreaks.
It is said that silver carp with a tail weight of more than 200 grams have a significant inhibitory effect on cyanobacteria, and when the total amount per acre reaches 200 catties, there is basically no outbreak of cyanobacteria. Some people have also found in experiments that the stocking of 400 fish/mu white carp density can achieve a good control effect on cyanobacteria. During the period from 2000 to 2003, the Institute of Hydrobiology of the Chinese Academy of Sciences conducted an experiment in Dianchi Lake to cultivate silver carp and silver carp to control cyanobacteria, and the result was that a silver carp of about 2 kilograms could eat 4 kilograms of cyanobacteria in 1 month, and 1 silver carp of the same size could consume more than 7 kilograms of cyanobacteria in 1 month.
Conditional farms often fill new water without making the organic matter content of the pond water too high and not eutrophicating the water body, which is also a good method. In addition, most of the water bodies of cyanobacteria bursts have high PH values, note that the pH of the pool water is not high, it is appropriate to control the pH value below 8.5, when the pH value is above 8.5, organic acids and similar drugs such as "alkaliminic" can be used to reduce the pH value of the pool water. Therefore, quicklime cannot be used in cyanobacterial surplus water bodies because quicklime is alkaline.
If it is a fertilizer fish culture, special attention should be paid to the ratio of nitrogen and phosphorus, and the ratio of nitrogen and phosphorus required for the growth of cyanobacteria is 7.2:1, and the nitrogen is more and less phosphorus. Therefore, under general conditions, the ratio of urea and calcium superphosphate should be: 100 kg of urea with 200 kg of superphosphate is appropriate. In particular, there are more organic matter in ponds and bottom layers, and it is particularly necessary to increase the amount of phosphate fertilizer. Appropriate amounts of phosphorus fertilizer are added to cultivate beneficial algae, which can also prevent the occurrence of cyanobacteria.
Fifth, the prevention and control measures of cyanobacterial water bodies
In the actual breeding and production, in addition to increasing feeding filter fish, planting aquatic plants (aquaponics) and other methods, chemical disinfection method is the current main treatment of cyanobacteria, the use of algae can kill algae products, such as chlorine preparations, strong chlorine, copper sulfate, complex copper, bleaching powder, potassium persulfate compound salt powder or cyanobacteria decomposition products sold on the market to kill cyanobacteria, is not a way to kill cyanobacteria. Therefore, the use of algae control method will cause a large number of cyanobacteria concentrated death, will cause a large number of fish and shrimp to adapt or even die, so when forced to kill algae must be turned on to increase oxygenation or add water, in case of accidents. The following is only a brief introduction to the main antiseptic drugs:
1. Cyanobacterial decomposition drugs
At present, most of the cyanobacterial decomposition drugs sold on the market are named "cyanobacterium decomposition essence (vegetarian)", and most of the main ingredients on the instructions are not indicated, which have a certain effect after use, and must be used after a detailed understanding of the instructions for use.
2. Erythromycin thiocyanate
Erythromycin thiocyanate is a macrolide antibiotic and is the thiocyanate of erythromycin. This product is a legal veterinary drug, used for infection of gram-positive bacteria and mycoplasma; more as an initial raw material for the synthesis of erythromycin, roxithromycin, azithromycin, clarithromycin and other macrolide antibiotics.
The biggest difference between cyanobacteria and algae belonging to eukaryotes is that it has no chloroplasts, no eukaryotic, 70S ribosomes, and peptidoglycans in the cell wall, which is the principle that the use of erythromycin can kill cyanobacteria. The use of erythromycin thiocyanate (0.35-0.70 g/m3) alone is effective in spilling, if erythromycin thiocyanate + crude salt (table salt, 2-5 kg per acre) the effect will be better, because table salt has an inhibitory effect on cyanobacteria, and after use, oxygenation and detoxification. The use of erythromycin thiocyanate also has a bactericidal and disease-proof effect.
In addition, people with erythromycin enteric-coated tablets are also effective, the method of use is human erythromycin enteric-coated tablets + coarse salt (table salt, 2-5 pounds per acre), 1 bottle per acre, the tablets can be crushed after the powder can be water, people have been sold in pharmacies.
3. Polyaluminum chloride
Polyaluminum chloride (PAC) is a highly efficient water purifier, which is currently widely used in urban and rural tap water purification agent, polyaluminum chloride is a highly efficient inorganic polymer coagulant. It has a wide range of uses in purifying various water bodies, and the effect is very good. When using polyaluminum chloride for the treatment of aquaculture wastewater, the concentration of the aqueous solution is 3 g/m3, which can be referred to when killing cyanobacteria.
The use of polyaluminium chloride to kill cyanobacteria or green algae is fast-acting, but prone to repetition. In fact, many fishery drug manufacturers what is the "algae killer" itself has the component of polyaluminum chloride, the product is sold in fishing pharmacies or chemical reagent stores.
4. Copper sulfate
Copper sulfate is a traditional insecticidal algae drug, its principle of killing cyanobacteria is mainly copper ions and algae body protein binding, the generation of protein salts to make them denatured and inactive and die; followed by copper ions and the active genes of some enzymes of algae combined, hindering its normal physiological metabolism to achieve the purpose of controlling algal reproduction.
Since copper sulfate is a heavy metal salt, it inevitably produces toxic side effects after use. The sulfate ions produced after copper sulfate are dissolved in water are most likely to cause hypoxia in the water, and at the same time, they are reduced to sulfides and hydrogen sulfide toxins under hypoxic conditions, which has a strong toxic effect on fish, causing poisoning and hypoxia dead fish. Therefore, after the drug is poured with copper sulfate, the aerator must be started.
In general, the above prevention and control methods are only "treatment", from the current degree of social development and scientific and technological level, for the cyanobacteria "zhili" must start from the basis of biology, to understand and master the biological learning of cyanobacteria and the characteristics of aquatic ecosystems, the use of biological balance methods may be the current recipe, such as: polyculture filter feeding aquatic animals (such as silver carp, catfish. White crucian carp, etc.), often add water bodies, cultivate beneficial bacteria algae to become a dominant population, often regulate water quality, etc., only this may be a long-term strategy, otherwise, kill the algae today, maybe after ten and a half days cyanobacteria will come back, it will be trouble!
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