Technical communication

Feasibility of factory shrimp farming

The optimum pH value of Penaeus vannamei is 7.8 -- 8.5. Low pH value can make the pH value in the blood of shrimp breeding decreased, weaken the oxygen carrying capacity of the blood, although the dissolved oxygen in the water is higher, or to cause fish, shrimp physiological hypoxia, often floating head, and growth blocked or sick. A high pH can increase the toxicity of ammonia nitrogen. A drop in pH is a sign that water quality is deteriorating and that dissolved oxygen is decreasing, and that toxic hydrogen sulfide is increasing. The increase of ammonia nitrogen and hydrogen sulfide content can inhibit the growth of prawn. If the pH value is too high, it may corrode the gill tissue of fish and shrimps and solidify the mucus. In serious cases, the mucus becomes filamentous, and shrimps and other shrimps lose the ability to breathe and die in large numbers. Blue-green algae blooms and insoluble tricalcium phosphate are easily formed in water with high pH, which leads to the slow down of nutrient and energy circulation in water. In addition, the pH value of the water is too high or too low, will cause the microbial activity in the water to be inhibited, organic matter is not easy to decompose.

The pH value is a comprehensive index of aquaculture water, which is mainly closely related to the CO32--HCO3--CO2 buffer system and the Ca2+-CaCO3 solid buffer system in the water, and has a certain correlation with the organic acid and humus buffer system. Therefore, the pH value in the water will change with the hardness of the water and the increase and decrease of CO2. The pH value in the pond usually rises gradually with sunrise, reaching a maximum between 16:30 and 17:30 PM (or around 13:00), and then continues to decline until it reaches a minimum just before sunrise the following day, and so on. The normal daily variation range of pH value in ponds is 1-2. When the pH value in water is too high, too low or the variation range is too large, it will affect the growth of aquatic organisms.

Changes of pH value in culture
1. The change rule of pH value in the whole process of prawn culture: from the perspective of the whole process of prawn culture, the pH value in the fertilizer and water stage before releasing seedlings is the highest, sometimes exceeding 9.6, and then it will continue to decline to the middle and late stage and even below 7.0. If the water quality is not adjusted, the pH value will continue to change.

2. Changes in pH during the day: photosynthesis, respiration and various chemical changes of aquatic organisms can cause changes in pH. So the more photosynthesis you have during the day, the longer you're exposed to light, the higher your pH is going to be; When photosynthesis stops at night and acidic carbon dioxide increases in the respiration of prawns and other organisms (mostly microorganisms), pH levels gradually drop, reaching a minimum before dawn. If it's cloudy and rainy, pH changes the least throughout the day.

3. The influence of weather change on pH value: the pH value varies in sunny days, cloudy days and rainy days. In sunny days, photosynthesis consumes a large amount of acidic carbon dioxide in the water, so the pH value will rise, while in cloudy days, the situation is just the opposite. Continuous cloudy and rainy days will make the pH value of the pool water drop very low, which must be adjusted timely.

Regulation of pH
1. Pre-release control: the survival rate of shrimp seedlings will be greatly affected if the pH value is higher than 9.0 (measured at about 10 am) at the time of releasing seedlings, so the control of pH value before releasing seedlings is an important part of breeding work. Acidic chemical substances can be applied, such as adding acetic acid, citric acid, oxalic acid, etc., water can also be changed or new water can be injected (underground deep well water is better), and the pH value can be reduced to below 9.0 (above 8.5) as far as possible, so as to ensure that the survival rate of shrimp seedlings after release can meet the production requirements.

2. In the first two thirds of the whole process of aquaculture, the water quality indicators are generally normal, such as NH3, H2S and other concentrations are very low, the adverse impact on prawns is very small, at this time can be assured and bold to control the pH value in the most suitable range for the growth of prawns. Subsequently, the pH value gradually decreases, and if the pH value measured at 10 am is below 8.0, it should be adjusted higher in time. 20ppm of quicklime can increase the pH value by 0.5.

3. Medium-late regulation: Prawn breeding entered the later period, the water quality indicators have is very poor, especially in the case of high density cultivation, NH3, H2S concentration is inevitable rise even exceeds bid, and pH decline particularly fast again, this time if you don't adjust pH value, even if the aerator capacity kept running, and there will still be physiological hypoxia prawns in danger of floating head, It causes unnecessary losses to the farmers, so the pH value regulation technology in the middle and late period requires relatively high requirements, and it is also the key link to determine the quality of the breeding effect. Since the toxicity of NH3 and H2S is closely related to the level of pH value, the adjustment of pH value in the middle and late period must be considered comprehensively. If the concentration of NH3 is very high and the concentration of H2S is very low, the pH value can be adjusted to a lower normal level at this time, which can reduce the toxicity of NH3 and ensure that it will not cause physiological hypoxia of pshrimp. If the opposite is true, the pH can be adjusted to the higher normal level. The general principle is to keep the pH level normal while minimizing the toxicity of NH3 and H2S in the water, which will increase the yield of farming.

Treatment measures for low or high pH values
Treatment measures for low pH value:
(1) the old water can be drained out of the pool, inject new water, 2-3 times repeatedly, in order to adjust the pH value in the water;
② Splashing quicklime water every half a month (if the pH value of the prawn pond is lower than 7.8 and the dosage is 5-15kg per mu) can not only adjust the pH of water body, but also prevent and control diseases;
(3) For water whose pH value drops too fast or too low, NaOH or baking soda can also be used for adjustment. 1% NaOH solution must be diluted (such as diluted 1000 times), a small amount of evenly splashing repeatedly, and the pH value of water can be determined in time to determine the effect.
(4) accelerate the cultivation of phytoplankton, the formation of new algal phase, for the formation of blue-green algae to control in time, when necessary, topical application of inorganic fertilizer, to promote the growth of fine algae;
(5) Fully increase oxygen and control the generation of reducing substances.

Treatment measures for high pH value:
① Pour in fresh water.
(2) adjust with talcum powder (main component magnesium silicate), the dosage is 1-2kg per mu. Generally, the pH of water can be reduced by 0.5-1 if talcum powder is sprinkled in the whole pool at 1.5-2.5g/m3.
(3) Use 0.5-1kg alum per mu, sprinkle the whole pool
(4) on the pH is too high or rise too fast water can also use dilute hydrochloric acid or acetic acid sprinkling, a small number of sprinkling, and timely determination of the pH value of water; Adjust with hydrochloric acid, generally use 300 milliliters to 500 milliliters per acre, fully diluted after the whole pool sprinkle.
⑤ Apply more organic fertilizer to regulate alkali by fertilizer.

Fourth, dissolved oxygen
Dissolved oxygen is the most important physical and chemical index in water. The amount of dissolved oxygen in aquaculture ponds is usually required to be between 5-8mg/L or at least not less than 4mg/L. When dissolved oxygen is lower than 3mg/L, shrimp will be irritable and uncomfortable, mild hypoxia, accelerated respiration, reduced food intake, thus affecting the growth. Lower levels of dissolved oxygen can cause death to aquatic animals. The amount of dissolved oxygen in water depends on the fluctuation of oxygen increasing and oxygen consuming factors. The dissolved oxygen in the pond mainly comes from the photosynthesis of phytoplankton (which is greatly affected by light and temperature). Air dissolution (related to wind waves, horizontal and vertical movement of water); The use of aerators or oxygenators; Fresh water carries oxygen and other aspects. The consumption of dissolved oxygen in water includes the oxygen consumption in respiration and metabolism of aquatic organisms and microorganisms, and the decomposition of reductive substances such as organic matter in pool water and bottom material.

The main emergency measures that can be taken when there is insufficient dissolved oxygen in the pond:
(1) Reasonable use of aerator; ② reasonable water change; (3) reduce the amount of good oxygen such as organic matter and microorganisms in the pond; (4) reasonable use of oxygenating agent; (5) The suitable new algal phase was cultivated gradually.
At present, the main oxygenating agents are briefly described:
A Sodium Perborate, a small white crystalline powder, is a mild oxidant, which can release oxygen slowly. When the water temperature is higher than 40℃, oxygen escape is accelerated, and dissolved oxygen in water can be increased. The use of sodium perborate can increase the alkalinity of the water and raise the pH of the pond water. When used, after dissolving with water, sprinkle the whole pool with the final concentration of 1g/m3 of water, but pay attention not to mix with acid substances.

B calcium peroxide, white crystalline powder, after reaction with water to produce large amounts of oxygen, can increase the dissolved oxygen in water, improve water, alkaline, improve the pH value, flocculation and colloidal particles, organic matter and may reduce the ammonia nitrogen in the water, removing carbon dioxide and hydrogen sulphide, prevent the breeding of anaerobic bacteria, and kill pathogenic bacteria, have the effect of clear water, improve water quality. When used, after the water is dissolved, the whole pool is splashed with the final concentration of 1g/m3 of water. For anoxic ponds, please refer to the usage in the following table.

C sodium percarbonate [Na2CO3.3H2O2] white, free flowing granular crystalline powder. The aqueous solution is alkaline with 14% reactive oxygen content and is oxidizing. The reactive oxygen content of dry sodium percarbonate powder is equivalent to 30% hydrogen peroxide. After the use of sodium percarbonate, the pH value of the pond solution is alkaline, generating reactive oxygen species, thus playing its sterilization, bleaching and decontamination functions. Prevent hypoxia with the final concentration of 0.075-0.15g/m3 of the whole pool sprinkling; In the case of hypoxia first aid, the amount can be doubled by splashing 0.15-0.22g/m3 of water. In addition, the 0.02% sodium percarbonate solution can also be used to transport live fish, dosing every 5-6h.

Five, the ammonia nitrogen
Ammonia nitrogen is produced by the decomposition of organic matter such as bait residues, feces and plankton carcasses in the pool. When the accumulation of ammonia nitrogen in the water reaches a certain concentration, fish can be poisoned. Over-standard ammonia nitrogen usually occurs in the middle and late stage of cultivation. At this time, due to the increase of residual baits and feces, harmful substances at the bottom of the pond continue to deposit, resulting in overstandard ammonia nitrogen and nitrite. It is advisable that the ammonia nitrogen in normal aquaculture water should not exceed 0.2㎎/L. In the breeding process, the content of ammonia nitrogen should be reduced as far as possible, and the ammonia nitrogen should be controlled below 0.5mg/L. The toxicity of ammonia nitrogen is closely related to the pH value and water temperature of the pool water. In general, the higher the temperature and pH value, the stronger the toxicity.

The toxic mechanism of ammonia nitrogen
Ammonia nitrogen is found in water in two forms. One is ammonia (NH3), also known as nonionic ammonia, which is fat-soluble and toxic to aquatic life. The other is ammonium (NH4+), also known as ionic ammonia, which is non-toxic to aquatic life. When ammonia (NH3) through gills to aquatic organisms, will directly increase the burden of ammonia nitrogen excretion of aquatic creatures, higher concentration of ammonia nitrogen in the blood, the blood pH with the corresponding rise, a variety of enzyme activity in aquatic organisms is restrained, and can reduce blood oxygen ability, destroy the gills epidermis tissue, reduce blood carry oxygen ability, Resulting in poor exchange of oxygen and waste and suffocation. In addition, the high concentration of ammonia in water also affects the permeability of water to aquatic organisms and reduces the concentration of internal ions.

Hazard of ammonia nitrogen to aquatic animals
The harm of ammonia nitrogen to aquatic animals can be divided into acute and chronic. The harm of chronic ammonia nitrogen poisoning is: reduced ingestion and slow growth; Tissue damage, reduce oxygen transport between tissues; Both fish and shrimp need to carry out ion exchange (sodium, calcium, etc.) with water. High ammonia nitrogen will increase the permeability of gills and damage the ion exchange function of gills. Make aquatic organisms in a long-term stress state, increase the susceptibility of animals to diseases, reduce the growth rate; Reduce reproductive capacity, reduce the number of pregnant eggs, reduce the viability of eggs, delay oviposition and reproduction. The harm of acute ammonia nitrogen poisoning is: aquatic organisms show hyperactivity, loss of balance in water, convulsions, and even death in severe cases.

Main measures to prevent and control high ammonia nitrogen in the breeding process:
(1) In the early stage of cultivation, the pond should be strictly cleared and silted to reduce the nitrogen storage capacity in the pond;
(2) pay attention to the use of organic fertilizer in the early stage of cultivation;
(3) Establish reasonable stocking density according to the actual bearing capacity of water body;
(4) select the bait with high digestibility and feed it scientifically;
(5) often start the aerator;
⑥ The use of zeolite powder (15-20g/m3) or activated carbon (2-3g/m3) in the middle and late stage of culture to improve the substrate, adsorption of ammonia nitrogen, degradation of organic matter;
Regularly detect the index of ammonia in water, if the ammonia nitrogen exceeds the standard, early prevention, early treatment;
Timely clean up the dirt at the bottom of the aquaculture waters and aquaculture animals excreted feces and other measures.
⑨ Proper and rational use of live bacteria such as photosynthetic bacteria and EM bacteria can effectively reduce ammonia nitrogen in water bodies, remove hydrogen sulfide and nitrite in water bodies, improve sediment and sediment in ponds, stabilize pH value in water bodies, and accelerate energy and material circulation in water bodies. However, in the use of live agents, attention should be paid to the adaptive conditions and use methods of different bacteria, otherwise the expected effect will not be achieved. If sprinkle live bacteria preparation before and after 3-7 days avoid disinfectant, also can't with disinfectant, antibiotic and so on use at the same time. When photosynthetic bacteria are used at sunrise, the effect is remarkable. When using nitrifying bacteria, they cannot be activated by brown sugar and pool water like Bacillus; Nitrifying bacteria reproduction rate is slow, it is best to use with other live bacteria preparation staggered use, after use zeolite powder, the effect will be more significant; After using nitrifying bacteria, try not to drain water for 3-4 days.

Six, nitrite
Aquatic animal excretion by the ammoniation of organic waste ammonia, shrimp secrete ammonia to produce ammonia, artificially produced using inorganic nitrogen ammonia, ammonia in the gradually oxidized under the action of nitrifying bacteria in water by the nitrite is converted to nitrate, this process is called nitrification, once the nitrification is blocked, the result will cause the middle substance of nitrification the accumulation of nitrite in water body.
In the middle and late stage of culture, it is very common to have high nitrite in the pond, which is related to the increase of feeding amount and the increase of biological and nitrogen storage, while the nitrifying bacteria own reproduction is relatively slow and the growth is easily inhibited by other bacteria.

Toxicity mechanism of nitrite
When the concentration of nitrite in the aquaculture water is too high, it can enter the blood through the infiltration and absorption of the shrimp body surface, and make the hemoglobin in the blood oxidized into methemoglobin. Because the methemoglobin can not combine with oxygen, the blood loses its oxygen-carrying capacity.

Effects of high and low nitrite concentration on shrimp
Under normal conditions, the content of nitrite in normal aquaculture water is less than 0.1mg/L. Under such conditions, shrimp and aquatic animals can live normally on their own without any health effects. Reduced when the aquaculture water dissolved oxygen, ammonia and nitrate level is high, often leads to water nitrite level increases, when the content of nitrite is 0.1 to 0.5 mg/L, and long-term to maintain the usual monohydrate, shrimp gradually reduce the number of the number of red blood cells and hemoglobin, blood loss of the ability of carrying oxygen gradually, causing shrimp chronic nitrate poisoning, characterized by food intake down, Difficulty breathing, slow swimming, restlessness. When the level of nitrite in aquaculture water continues to increase, and the content is higher than 0.5mg/L, the symptoms of shrimp poisoning continue to worsen, including physical decline, inability to swim, and function failure of some metabolic organs. Serious cases will lead to death. Long-term exposure to a high concentration of nitrite in the water causes prawns to lose their gills and turn black, leading to death in severe cases. The toxicity of nitrite varies among shrimp species and individuals, so the safe concentration for different shrimp species varies greatly. In order to ensure the safety of shrimp (especially in the seedling stage), the content of nitrite is controlled below 0.2mg/L by backlight.

Influencing factors of nitrite level in aquaculture water
The higher the ammonia content, the lower the dissolved oxygen level, the lower the pH value and the lower the water temperature, the higher the nitrite level.

Prevention and control measures of excessive nitrite:
(1) Start the aerator or sprinkle the whole pool with chemical aerating agent to promote the conversion of NO2- to NO3-;
(2) the use of ammonia ion chelating agent, activated carbon, adsorbent, humic acid polymer with water quality adsorbent such as nitrite desorption agent, through ion exchange, adsorption or degradation of nitrite;
(3) The use of Bacillus, nitrifying bacteria, photosynthetic bacteria, actinomycetes and other microbial agents, the use of live bacteria to accelerate the decomposition and transformation of NO2-;
(4) Apply more phosphorus to lean water bodies

PREVIOUS：Fish in the south and fish in the north. Cali NEXT：Why is your fish pond starved of oxygen?