Detailed Explanation of Key Points in Black Tiger Shrimp (Penaeus monodon) Aquaculture Technology
Essentials of Black Tiger Shrimp (Penaeus monodon) Aquaculture Technology
Although the domestic market price of black tiger shrimp fluctuates greatly, the farming profit remains considerable, with an annual profit of up to 12,000 yuan/mu, making it one of the excellent alternative species to whiteleg shrimp (Litopenaeus vannamei) farming
□Text by Xu Anmin, Wang Ping, Li Yijun, Hainan Changjiang Nanjiang Biotechnology Co., Ltd.
The black tiger shrimp (Penaeus monodon Fabricius), commonly known as grass shrimp or tiger shrimp, is classified under Arthropoda, Crustacea, Malacostraca, Eumalacostraca, Decapoda, Dendrobranchiata, Penaeoidea, Penaeidae, Penaeus. In China, it is mainly distributed along the coasts of Taiwan, China, Hainan and Guangdong, becoming fewer the further north one goes. It has a large body, tender and fresh meat, rich nutrition, strong tolerance to high temperature and dryness, and is suitable for sale as live shrimp at a relatively high price, having become an important aquaculture species in many countries and regions.
This article focuses on the author's exploration of black tiger shrimp aquaculture technology in high-level ponds in recent years, for the reference of black tiger shrimp farmers.
I. Shrimp Fry Stocking
1.1 Pre-stocking Preparation
From stocking to harvest, the entire grow-out phase lasts only a few short months, while the preparation work includes draining the shrimp pond, reservoir and ditches, clearing and leveling the pond bottom, repairing embankments, clearing ditches, removing silt and pests, filtering intake water, culturing basic feed organisms, as well as purchasing fry and transportation. The above work is highly time-sensitive and heavy in workload, requiring each step to be closely linked and done conscientiously and steadily.
Silt removal and pond drying are key steps in healthy aquaculture, and the pond must be thoroughly cleared. After harvesting shrimp at the end of each year, drain the pond water, close the sluice gates and dry the pond until the bottom cracks, then move residual feed, debris and silt to outside the embankment. Apply 70-100 kg of quicklime per 667 sq m, distribute it evenly over the pond bottom, then plow and harrow the bottom for tilling and sun exposure.
1.2 Aquaculture Water Preparation
The aquaculture water is filtered seawater from sand filter wells. About 15 days before stocking, add water to about 100-120 cm, then disinfect the water body with a chlorine preparation at an effective chlorine concentration of 5-10 g/m3. Two days later, choose a sunny morning for fertilization to culture basic feed organisms; for fertilizing the water, organic fertilizer combined with 15 kg of dolomite powder per 667 sq m can be used. Thereafter, apply supplementary fertilizer every 3-5 days depending on the pond water color and plankton biomass to ensure abundant basic feed organisms. Use less inorganic quick-acting fertilizer, because inorganic fertilizer quickly colors the water but is difficult to maintain. Whether the basic feed organism culture is proper directly affects the growth rate and survival rate of the stocked shrimp fry. The best pond water color is light brown.
1.3 Shrimp Fry Selection
Shrimp fry are required to be uniform in size, robust, strong in vitality, good at swimming against the current, with a clean body surface free of attachments, and a body length of more than 1.2 cm. The two small flagella at the front end of the first antennae, which fork in a V shape, should often be held together, and the body segments should be sparse and long. Preferably P12-P18 dark-shell fry, with 4-6 spines already grown on the rostrum. Shrimp fry should also be tested for viruses and Vibrio, must not carry specific pathogens such as WSSV, TSV, IHHNV and IMNV, and the Vibrio count should be controlled within a safe range.
1.4 Stocking Shrimp Fry
The first crop can be stocked from late March to early April, choosing clear weather with water temperature stable above 25°C. Two hours before stocking, turn on the aerators to agitate the water body, and simultaneously apply stress-reducing products such as VC and glucose. When stocking, try to avoid stirring up the pond water; first place the fry bags in the pond to soak for 20 minutes so that the water temperature inside the bags approaches that of the pond water (temperature difference not exceeding 3°C), then release the fry downwind at a deeper spot on the windward side. The salinity difference between the fry bag water and the pond water should not exceed 5‰. The second crop can be stocked in mid-July.
Stocking density should be determined according to the pond conditions, water environment and management level.
II. Feeding Management
The number of feedings depends on stocking density. The author mostly chooses four feedings a day at 60,000/mu. Due to daily water quality changes, it is preferable to feed more during the two daytime meals and less during the morning and evening meals. This can both meet growth needs and stabilize water quality.
2.1 Feed Selection
Generally, high-quality compound feed is selected for feeding. High-quality compound feed not only provides sufficient protein and amino acids to ensure normal shrimp growth, but also facilitates shrimp digestion and absorption. However, feed selection should not be based solely on protein content as the standard, but rather on stable quality. In actual operation, the author broke with convention and used white shrimp feed to raise grass shrimp for three consecutive years, with no negative effects observed.
2.2 Feeding Frequency
In the early 7 days, feed No. 0 feed, two meals a day, once in the morning and once in the afternoon, 0.5 kg per 100,000 shrimp, supplemented with Artemia once a day; from 8-15 days, feed No. 1 feed, three meals a day, with 30% of the feed amount at 6:30, 40% at 12:00, and 30% at 19:00; after 16 days, switch to 4 meals at 6:30, 11:30, 17:00 and 22:00 (feed amount proportions of 20%, 30%, 30% and 20% respectively).
2.3 Feeding Techniques
The daily feeding amount should be flexibly controlled according to weather, water quality, shrimp health and activity. In the first 40 days, it is difficult to measure feed by observation net, so the principle is generally that no residual feed remains on the feeding tray at the next meal, and it is best if the feed is consumed within 2.5-3 hours after feeding; in the middle and late stages, feed measurement can be kept within 1-1.5 hours. In muggy weather or during thunderstorms, feed less or not at all, which can reduce the feed conversion ratio and lessen pollution of the water body.
Improve shrimp immune capacity and stress resistance. Add 3‰ immune polysaccharides, 2‰ bioactive enzyme additives, 5‰ vitamin C, and 3‰ vitamin E to the feed, feeding continuously for 5 days, 2 meals a day; in high-temperature seasons, add 2-4‰ allicin, and at the same time splash 300 g vitamin C and 500 g glucose per 667 sq m.
III. Water Quality Regulation
Maintaining good aquaculture water conditions can ensure the normal appetite of black tiger shrimp, reduce the feed conversion ratio, and increase growth rate. The main means of water quality management is to regularly monitor various physical and chemical factors and biological factors of the aquaculture pond water and bottom sediment, with rapidly changing indicators monitored daily.
3.1 Basic Water Quality Requirements
pH value can serve as an indicator of pond water quality, and in the middle and late stages of aquaculture it should be 8.0-8.8, with daily fluctuation less than 0.5. The dissolved oxygen content measured before 6:00 a.m. should not be lower than 4 mg/L. The most suitable salinity for shrimp ponds is controlled between 15-25‰. If salinity is too low, shrimp shells are thin, blue individuals are more numerous, and parasites are more likely; if salinity is too high, shells are thick, molting frequency is lower and growth is slow. Total alkalinity should be above 100 mg/L, nitrite content below 0.02 mg/L, and ammonia nitrogen content below 0.3 mg/L.
3.2 Timely Regulation of Water Color Changes
Water color is a comprehensive reflection of the quality and quantity of plankton in the pond water. How to maintain a good water phase is directly related to the success or failure of aquaculture.
In ponds for black tiger shrimp aquaculture, the ideal water color should be yellow-green or tea-brown formed by green algae or diatoms. During black tiger shrimp aquaculture, sudden water color changes and excessive reproduction of filamentous algae should be avoided. Especially in the early stage, the water level should be consciously raised and water added in small amounts multiple times, which has positive significance for stabilizing the water phase and preventing massive reproduction of filamentous algae; in the middle and late stages of aquaculture, the pond water should be at a high level, with an average water level preferably above 160 cm, and water intake should preferably be drainage-linked water supplementation, keeping pond water transparency at 30-40 cm; in the late stage of aquaculture, appropriate water exchange can be carried out according to the following conditions, keeping pond water transparency at 35-45 cm. ① Daily pH fluctuation range greater than 0.5, pH < 7 or pH > 9; ② Pond water transparency greater than 50 cm or too turbid and less than 20 cm; ③ Pond water color significantly darkens and the amount of inorganic suspended solids increases; ④ Stable foam appears on the pond surface, with much organic matter and increased oxygen consumption; ⑤ Shrimp gasp at the surface and the pond bottom turns black. There is another situation, which is that in the late stage blue-green algae water often appears, algal blooms prevail, and the more water is exchanged, the denser it becomes. During this period, drugs that can inhibit or kill blue-green algae should be selectively used, and combining this with water exchange will produce better results.
3.3 Improving the Pond Bottom and Rational Use of Beneficial Microorganisms
For black tiger shrimp, shrimp farming is bottom cultivation. Black tiger shrimp have a relatively obvious bottom-dwelling habit, so the quality of the bottom sediment directly determines the success or failure of aquaculture, making bottom sediment treatment crucial. Using beneficial microbial preparations for shrimp farming is a major breakthrough in shrimp aquaculture technology, and it plays an important role in improving bottom sediment. Regarding the use of beneficial microorganisms, the following points should be noted: ① Persist in regular use, adding beneficial microbial preparations once every 7-10 days starting before stocking; only continuous use can reduce the accumulation of organic matter in the pond and bring convenience to later management. ② Persist in selecting high-quality biological preparation products; for example, using compound microbial preparations such as Novibac water purifying agent, oxidants, and ammonia-nitrite removal preparations can effectively improve the pond bottom and reduce H2S, ammonia nitrogen and nitrite, with a dosage of 15-20 g per 667 sq m. ③ The growth and reproduction of microbial preparations require certain conditions, such as dissolved oxygen, light, and a certain carrier; their effectiveness varies under different conditions, so grasping the conditions of use is crucial.
3.4 Ensuring Sufficient Dissolved Oxygen
Dissolved oxygen in water is the primary condition for shrimp survival, and it not only affects shrimp feeding rate, feed utilization rate and weight gain rate. When dissolved oxygen is insufficient, the physical and chemical conditions of the water environment are poor, shrimp constitution declines, which can cause outbreaks of some epidemic diseases, and severe oxygen deficiency can also cause death from hypoxia, resulting in major losses in shrimp aquaculture. Therefore, creating a three-dimensional aeration mode and irregularly using liquid and solid oxygen enhancers to maintain sufficient aeration is very beneficial to the healthy growth of shrimp. The dissolved oxygen content in black tiger shrimp pond water should be higher than 3 mg/L. To ensure sufficient dissolved oxygen during aquaculture, aerators should be reasonably turned on and oxygen enhancers such as hydrogen peroxide and calcium peroxide should be used according to weather, water quality, bottom sediment and water chemistry conditions, keeping dissolved oxygen in the shrimp pond (especially at the pond bottom) sufficient.
IV. Disease Prevention and Control
Because black tiger shrimp have many diseases during growth, the key to successful shrimp aquaculture lies in the prevention and control of shrimp diseases, and the principle of "prevention first, comprehensive control" must be adhered to. Due to aquaculture water pollution, climate change, decline in fry quality and other reasons, black tiger shrimp have many types of diseases, and the common ones are as follows:
1. Ciliatosis
Diseased shrimp have large numbers of ciliates (Vorticella, Epistylis, Zoothamnium, etc.) parasitic on the body surface. This disease occurs very easily in water with much organic matter. When a small number of sessile ciliates attach to the shrimp body, symptoms are not obvious and the shrimp show no pathological changes, but when large numbers of ciliates attach, the gills, body surface and appendages of the shrimp appear black, and the body surface appears gray-black and fluffy. Diseased shrimp float on the water surface in the morning, respond slowly, do not feed, do not molt, growth is hindered, and other complications are easily caused. The main harm of ciliatosis is affecting shrimp respiration, and under low dissolved oxygen conditions, mass mortality is more likely. The main cause is that the water is too fertile, with massive reproduction of Vorticella, Epistylis, Zoothamnium, etc.
Treatment methods: 1. Drain 20-30 cm of water, use 0.75-1 g zinc sulfate powder per cubic meter of water once a day, and use it twice consecutively in severe cases; after 36 hours, add fresh seawater to restore the water level, and after 4 days regulate and fertilize the water. 2. Tea seed cake 10-15 g/m3, plus lime 5-10 g/m3 at the same time; combining with water exchange will produce better results. 3. Pay attention to salinity regulation, as low-salinity water more easily breeds ciliates.
2. White Spot Syndrome
Diseased shrimp float on the water surface, swim slowly, and have a slightly reddish body color, with slightly pinkish white spots on the carapace of the body surface. The size and shape of the white spots are irregular, most likely to appear on the shrimp's cephalothorax, and in severe cases the entire cephalothorax turns white. Next is the dorsal and lateral sides of the abdomen; the carapace surface at the white spots shows no obvious change, only loss of transparency.
Prevention method: Oral administration: florfenicol 3‰, vitamin C 5‰, vitamin E 5‰, yeast 5‰, brown sugar 10‰, for 5-7 consecutive days.
Precautions: Strictly prohibit water exchange and irrigation, and strictly prohibit disinfection that stimulates shrimp stress. Halve the daily feed. If it is in the late stage, harvest shrimp promptly to reduce losses, and at the same time pay attention to isolation to avoid infecting surrounding shrimp ponds.
3. Baculovirus Disease
Caused by MBV baculovirus infection, it damages the shrimp hepatopancreas, causing it to turn white, atrophy, or swell and rot. Diseased shrimp are anorexic, do not molt, have shells that are easily peeled off and opaque, and grow slowly, with no special appearance symptoms. Juvenile shrimp about one month old are susceptible to infection, with a mortality rate as high as 100%.
Prevention and treatment methods: Same as white spot syndrome.
4. Red Gill and Black Gill Disease
During long-term hypoxia or when the body is weak and resistance is poor, if gill tissue is damaged, it is easily subject to secondary bacterial infection, causing the gills to turn red and black. Under a microscope, tree-branch-like red pigment can be seen in the gills, with local diffuse necrotic decay of gill filaments. The more severe the disease, the darker the color. Diseased shrimp have poor vitality but can still feed normally.
Prevention and treatment methods: Mix 3‰ florfenicol into feed for oral administration, and at the same time use chlorine dioxide for continuous disinfection 3 times, once a day. Before disinfection, drain 20% of the water level; 2-3 days after disinfection, replenish water to the original level, and use microbial preparations to regulate water quality.
5. Soft Shell Disease
Diseased shrimp have obviously softened shells, emaciated bodies, weakened activity, and slow growth, and in severe cases death can occur. This disease may be caused by excessive organic matter in the water, low pH, and long-term nutritional deficiency.
Prevention and treatment methods: Add fresh water, improve water quality, splash lime at 5 kg/667 sq m mixed with water to raise the pH of the water, and feed high-quality compound feed. Orally administer active calcium and vitamin C to strengthen calcium supplementation, promote molting, and enhance constitution.
6. Blue Body
The shrimp body is blue and the shell is thin. At harvest, individuals with this appearance are particularly intolerant of live handling, thereby reducing economic benefits. The specific cause is unknown, but the cause is mostly inclined to be nutritional imbalance.
Treatment method: External use: regularly splash 2-3 g/m3 calcium monohydrogen phosphate over the whole pond.
Oral administration: vitamin E + vitamin C + yeast + brown sugar, once a day, for 7 consecutive days.
7. Muscular Necrosis Disease
Diseased shrimp are emaciated, with muscle atrophy separated from the shell. In the early stage of the disease, white spots appear on the dorsal side of the abdomen, after which the entire abdomen turns white, the gills and muscles necrose, and finally death occurs. The incidence rate is 2-3%. The mortality rate during live shrimp transportation is extremely high, even as high as 90%, greatly affecting the selling price. The cause is unknown, and this disease is not caused by biological pathogens.
Treatment methods: 1. In aquaculture ponds during high-temperature seasons, prevent excessively high water temperature or sudden changes; exchange water frequently and maintain a certain water level and sufficient dissolved oxygen. 2. Oral administration: florfenicol 3‰, vitamin C 5‰, vitamin E 5‰, yeast 5‰, brown sugar 10‰, for 5-7 consecutive days.
V. Harvest
Black tiger shrimp have relatively poor low-temperature tolerance and are not suitable for overwintering along the coast of the South China Sea. Especially in the season when temperature fluctuations are large during the autumn-winter transition, diseases are mostly highly prevalent. Therefore, harvest time should be strictly controlled, mainly determined by factors such as the health of the pond shrimp themselves, molting condition, bottom sediment, water quality, and production arrangements.
Once abnormal shrimp activity is found, harvest should be carried out promptly. Usually, marketing around New Year's Day is ideal. Shrimp harvest is mostly carried out at night, using electric trawl nets or push nets for capture.
From the late crop of 2006 to the present, the author has achieved success for five consecutive crops, with average yield per mu rising steadily from 300 kg to 500 kg now, and the highest yield per mu reaching 612 kg. The size is mostly 80-100 shrimp/kg. Although the market price of grass shrimp fluctuates greatly, the farming profit is still considerable, with the average profit per mu over several years basically maintained at around 12,000 yuan, and the highest profit per mu reaching 21,000 yuan.
□Text by Xu Anmin, Wang Ping, Li Yijun, Hainan Changjiang Nanjiang Biotechnology Co., Ltd.
The black tiger shrimp (Penaeus monodon Fabricius), commonly known as grass shrimp or tiger shrimp, is classified under Arthropoda, Crustacea, Malacostraca, Eumalacostraca, Decapoda, Dendrobranchiata, Penaeoidea, Penaeidae, Penaeus. In China, it is mainly distributed along the coasts of Taiwan, China, Hainan and Guangdong, becoming fewer the further north one goes. It has a large body, tender and fresh meat, rich nutrition, strong tolerance to high temperature and dryness, and is suitable for sale as live shrimp at a relatively high price, having become an important aquaculture species in many countries and regions.
This article focuses on the author's exploration of black tiger shrimp aquaculture technology in high-level ponds in recent years, for the reference of black tiger shrimp farmers.
I. Shrimp Fry Stocking
1.1 Pre-stocking Preparation
From stocking to harvest, the entire grow-out phase lasts only a few short months, while the preparation work includes draining the shrimp pond, reservoir and ditches, clearing and leveling the pond bottom, repairing embankments, clearing ditches, removing silt and pests, filtering intake water, culturing basic feed organisms, as well as purchasing fry and transportation. The above work is highly time-sensitive and heavy in workload, requiring each step to be closely linked and done conscientiously and steadily.
Silt removal and pond drying are key steps in healthy aquaculture, and the pond must be thoroughly cleared. After harvesting shrimp at the end of each year, drain the pond water, close the sluice gates and dry the pond until the bottom cracks, then move residual feed, debris and silt to outside the embankment. Apply 70-100 kg of quicklime per 667 sq m, distribute it evenly over the pond bottom, then plow and harrow the bottom for tilling and sun exposure.
1.2 Aquaculture Water Preparation
The aquaculture water is filtered seawater from sand filter wells. About 15 days before stocking, add water to about 100-120 cm, then disinfect the water body with a chlorine preparation at an effective chlorine concentration of 5-10 g/m3. Two days later, choose a sunny morning for fertilization to culture basic feed organisms; for fertilizing the water, organic fertilizer combined with 15 kg of dolomite powder per 667 sq m can be used. Thereafter, apply supplementary fertilizer every 3-5 days depending on the pond water color and plankton biomass to ensure abundant basic feed organisms. Use less inorganic quick-acting fertilizer, because inorganic fertilizer quickly colors the water but is difficult to maintain. Whether the basic feed organism culture is proper directly affects the growth rate and survival rate of the stocked shrimp fry. The best pond water color is light brown.
1.3 Shrimp Fry Selection
Shrimp fry are required to be uniform in size, robust, strong in vitality, good at swimming against the current, with a clean body surface free of attachments, and a body length of more than 1.2 cm. The two small flagella at the front end of the first antennae, which fork in a V shape, should often be held together, and the body segments should be sparse and long. Preferably P12-P18 dark-shell fry, with 4-6 spines already grown on the rostrum. Shrimp fry should also be tested for viruses and Vibrio, must not carry specific pathogens such as WSSV, TSV, IHHNV and IMNV, and the Vibrio count should be controlled within a safe range.
1.4 Stocking Shrimp Fry
The first crop can be stocked from late March to early April, choosing clear weather with water temperature stable above 25°C. Two hours before stocking, turn on the aerators to agitate the water body, and simultaneously apply stress-reducing products such as VC and glucose. When stocking, try to avoid stirring up the pond water; first place the fry bags in the pond to soak for 20 minutes so that the water temperature inside the bags approaches that of the pond water (temperature difference not exceeding 3°C), then release the fry downwind at a deeper spot on the windward side. The salinity difference between the fry bag water and the pond water should not exceed 5‰. The second crop can be stocked in mid-July.
Stocking density should be determined according to the pond conditions, water environment and management level.
II. Feeding Management
The number of feedings depends on stocking density. The author mostly chooses four feedings a day at 60,000/mu. Due to daily water quality changes, it is preferable to feed more during the two daytime meals and less during the morning and evening meals. This can both meet growth needs and stabilize water quality.
2.1 Feed Selection
Generally, high-quality compound feed is selected for feeding. High-quality compound feed not only provides sufficient protein and amino acids to ensure normal shrimp growth, but also facilitates shrimp digestion and absorption. However, feed selection should not be based solely on protein content as the standard, but rather on stable quality. In actual operation, the author broke with convention and used white shrimp feed to raise grass shrimp for three consecutive years, with no negative effects observed.
2.2 Feeding Frequency
In the early 7 days, feed No. 0 feed, two meals a day, once in the morning and once in the afternoon, 0.5 kg per 100,000 shrimp, supplemented with Artemia once a day; from 8-15 days, feed No. 1 feed, three meals a day, with 30% of the feed amount at 6:30, 40% at 12:00, and 30% at 19:00; after 16 days, switch to 4 meals at 6:30, 11:30, 17:00 and 22:00 (feed amount proportions of 20%, 30%, 30% and 20% respectively).
2.3 Feeding Techniques
The daily feeding amount should be flexibly controlled according to weather, water quality, shrimp health and activity. In the first 40 days, it is difficult to measure feed by observation net, so the principle is generally that no residual feed remains on the feeding tray at the next meal, and it is best if the feed is consumed within 2.5-3 hours after feeding; in the middle and late stages, feed measurement can be kept within 1-1.5 hours. In muggy weather or during thunderstorms, feed less or not at all, which can reduce the feed conversion ratio and lessen pollution of the water body.
Improve shrimp immune capacity and stress resistance. Add 3‰ immune polysaccharides, 2‰ bioactive enzyme additives, 5‰ vitamin C, and 3‰ vitamin E to the feed, feeding continuously for 5 days, 2 meals a day; in high-temperature seasons, add 2-4‰ allicin, and at the same time splash 300 g vitamin C and 500 g glucose per 667 sq m.
III. Water Quality Regulation
Maintaining good aquaculture water conditions can ensure the normal appetite of black tiger shrimp, reduce the feed conversion ratio, and increase growth rate. The main means of water quality management is to regularly monitor various physical and chemical factors and biological factors of the aquaculture pond water and bottom sediment, with rapidly changing indicators monitored daily.
3.1 Basic Water Quality Requirements
pH value can serve as an indicator of pond water quality, and in the middle and late stages of aquaculture it should be 8.0-8.8, with daily fluctuation less than 0.5. The dissolved oxygen content measured before 6:00 a.m. should not be lower than 4 mg/L. The most suitable salinity for shrimp ponds is controlled between 15-25‰. If salinity is too low, shrimp shells are thin, blue individuals are more numerous, and parasites are more likely; if salinity is too high, shells are thick, molting frequency is lower and growth is slow. Total alkalinity should be above 100 mg/L, nitrite content below 0.02 mg/L, and ammonia nitrogen content below 0.3 mg/L.
3.2 Timely Regulation of Water Color Changes
Water color is a comprehensive reflection of the quality and quantity of plankton in the pond water. How to maintain a good water phase is directly related to the success or failure of aquaculture.
In ponds for black tiger shrimp aquaculture, the ideal water color should be yellow-green or tea-brown formed by green algae or diatoms. During black tiger shrimp aquaculture, sudden water color changes and excessive reproduction of filamentous algae should be avoided. Especially in the early stage, the water level should be consciously raised and water added in small amounts multiple times, which has positive significance for stabilizing the water phase and preventing massive reproduction of filamentous algae; in the middle and late stages of aquaculture, the pond water should be at a high level, with an average water level preferably above 160 cm, and water intake should preferably be drainage-linked water supplementation, keeping pond water transparency at 30-40 cm; in the late stage of aquaculture, appropriate water exchange can be carried out according to the following conditions, keeping pond water transparency at 35-45 cm. ① Daily pH fluctuation range greater than 0.5, pH < 7 or pH > 9; ② Pond water transparency greater than 50 cm or too turbid and less than 20 cm; ③ Pond water color significantly darkens and the amount of inorganic suspended solids increases; ④ Stable foam appears on the pond surface, with much organic matter and increased oxygen consumption; ⑤ Shrimp gasp at the surface and the pond bottom turns black. There is another situation, which is that in the late stage blue-green algae water often appears, algal blooms prevail, and the more water is exchanged, the denser it becomes. During this period, drugs that can inhibit or kill blue-green algae should be selectively used, and combining this with water exchange will produce better results.
3.3 Improving the Pond Bottom and Rational Use of Beneficial Microorganisms
For black tiger shrimp, shrimp farming is bottom cultivation. Black tiger shrimp have a relatively obvious bottom-dwelling habit, so the quality of the bottom sediment directly determines the success or failure of aquaculture, making bottom sediment treatment crucial. Using beneficial microbial preparations for shrimp farming is a major breakthrough in shrimp aquaculture technology, and it plays an important role in improving bottom sediment. Regarding the use of beneficial microorganisms, the following points should be noted: ① Persist in regular use, adding beneficial microbial preparations once every 7-10 days starting before stocking; only continuous use can reduce the accumulation of organic matter in the pond and bring convenience to later management. ② Persist in selecting high-quality biological preparation products; for example, using compound microbial preparations such as Novibac water purifying agent, oxidants, and ammonia-nitrite removal preparations can effectively improve the pond bottom and reduce H2S, ammonia nitrogen and nitrite, with a dosage of 15-20 g per 667 sq m. ③ The growth and reproduction of microbial preparations require certain conditions, such as dissolved oxygen, light, and a certain carrier; their effectiveness varies under different conditions, so grasping the conditions of use is crucial.
3.4 Ensuring Sufficient Dissolved Oxygen
Dissolved oxygen in water is the primary condition for shrimp survival, and it not only affects shrimp feeding rate, feed utilization rate and weight gain rate. When dissolved oxygen is insufficient, the physical and chemical conditions of the water environment are poor, shrimp constitution declines, which can cause outbreaks of some epidemic diseases, and severe oxygen deficiency can also cause death from hypoxia, resulting in major losses in shrimp aquaculture. Therefore, creating a three-dimensional aeration mode and irregularly using liquid and solid oxygen enhancers to maintain sufficient aeration is very beneficial to the healthy growth of shrimp. The dissolved oxygen content in black tiger shrimp pond water should be higher than 3 mg/L. To ensure sufficient dissolved oxygen during aquaculture, aerators should be reasonably turned on and oxygen enhancers such as hydrogen peroxide and calcium peroxide should be used according to weather, water quality, bottom sediment and water chemistry conditions, keeping dissolved oxygen in the shrimp pond (especially at the pond bottom) sufficient.
IV. Disease Prevention and Control
Because black tiger shrimp have many diseases during growth, the key to successful shrimp aquaculture lies in the prevention and control of shrimp diseases, and the principle of "prevention first, comprehensive control" must be adhered to. Due to aquaculture water pollution, climate change, decline in fry quality and other reasons, black tiger shrimp have many types of diseases, and the common ones are as follows:
1. Ciliatosis
Diseased shrimp have large numbers of ciliates (Vorticella, Epistylis, Zoothamnium, etc.) parasitic on the body surface. This disease occurs very easily in water with much organic matter. When a small number of sessile ciliates attach to the shrimp body, symptoms are not obvious and the shrimp show no pathological changes, but when large numbers of ciliates attach, the gills, body surface and appendages of the shrimp appear black, and the body surface appears gray-black and fluffy. Diseased shrimp float on the water surface in the morning, respond slowly, do not feed, do not molt, growth is hindered, and other complications are easily caused. The main harm of ciliatosis is affecting shrimp respiration, and under low dissolved oxygen conditions, mass mortality is more likely. The main cause is that the water is too fertile, with massive reproduction of Vorticella, Epistylis, Zoothamnium, etc.
Treatment methods: 1. Drain 20-30 cm of water, use 0.75-1 g zinc sulfate powder per cubic meter of water once a day, and use it twice consecutively in severe cases; after 36 hours, add fresh seawater to restore the water level, and after 4 days regulate and fertilize the water. 2. Tea seed cake 10-15 g/m3, plus lime 5-10 g/m3 at the same time; combining with water exchange will produce better results. 3. Pay attention to salinity regulation, as low-salinity water more easily breeds ciliates.
2. White Spot Syndrome
Diseased shrimp float on the water surface, swim slowly, and have a slightly reddish body color, with slightly pinkish white spots on the carapace of the body surface. The size and shape of the white spots are irregular, most likely to appear on the shrimp's cephalothorax, and in severe cases the entire cephalothorax turns white. Next is the dorsal and lateral sides of the abdomen; the carapace surface at the white spots shows no obvious change, only loss of transparency.
Prevention method: Oral administration: florfenicol 3‰, vitamin C 5‰, vitamin E 5‰, yeast 5‰, brown sugar 10‰, for 5-7 consecutive days.
Precautions: Strictly prohibit water exchange and irrigation, and strictly prohibit disinfection that stimulates shrimp stress. Halve the daily feed. If it is in the late stage, harvest shrimp promptly to reduce losses, and at the same time pay attention to isolation to avoid infecting surrounding shrimp ponds.
3. Baculovirus Disease
Caused by MBV baculovirus infection, it damages the shrimp hepatopancreas, causing it to turn white, atrophy, or swell and rot. Diseased shrimp are anorexic, do not molt, have shells that are easily peeled off and opaque, and grow slowly, with no special appearance symptoms. Juvenile shrimp about one month old are susceptible to infection, with a mortality rate as high as 100%.
Prevention and treatment methods: Same as white spot syndrome.
4. Red Gill and Black Gill Disease
During long-term hypoxia or when the body is weak and resistance is poor, if gill tissue is damaged, it is easily subject to secondary bacterial infection, causing the gills to turn red and black. Under a microscope, tree-branch-like red pigment can be seen in the gills, with local diffuse necrotic decay of gill filaments. The more severe the disease, the darker the color. Diseased shrimp have poor vitality but can still feed normally.
Prevention and treatment methods: Mix 3‰ florfenicol into feed for oral administration, and at the same time use chlorine dioxide for continuous disinfection 3 times, once a day. Before disinfection, drain 20% of the water level; 2-3 days after disinfection, replenish water to the original level, and use microbial preparations to regulate water quality.
5. Soft Shell Disease
Diseased shrimp have obviously softened shells, emaciated bodies, weakened activity, and slow growth, and in severe cases death can occur. This disease may be caused by excessive organic matter in the water, low pH, and long-term nutritional deficiency.
Prevention and treatment methods: Add fresh water, improve water quality, splash lime at 5 kg/667 sq m mixed with water to raise the pH of the water, and feed high-quality compound feed. Orally administer active calcium and vitamin C to strengthen calcium supplementation, promote molting, and enhance constitution.
6. Blue Body
The shrimp body is blue and the shell is thin. At harvest, individuals with this appearance are particularly intolerant of live handling, thereby reducing economic benefits. The specific cause is unknown, but the cause is mostly inclined to be nutritional imbalance.
Treatment method: External use: regularly splash 2-3 g/m3 calcium monohydrogen phosphate over the whole pond.
Oral administration: vitamin E + vitamin C + yeast + brown sugar, once a day, for 7 consecutive days.
7. Muscular Necrosis Disease
Diseased shrimp are emaciated, with muscle atrophy separated from the shell. In the early stage of the disease, white spots appear on the dorsal side of the abdomen, after which the entire abdomen turns white, the gills and muscles necrose, and finally death occurs. The incidence rate is 2-3%. The mortality rate during live shrimp transportation is extremely high, even as high as 90%, greatly affecting the selling price. The cause is unknown, and this disease is not caused by biological pathogens.
Treatment methods: 1. In aquaculture ponds during high-temperature seasons, prevent excessively high water temperature or sudden changes; exchange water frequently and maintain a certain water level and sufficient dissolved oxygen. 2. Oral administration: florfenicol 3‰, vitamin C 5‰, vitamin E 5‰, yeast 5‰, brown sugar 10‰, for 5-7 consecutive days.
V. Harvest
Black tiger shrimp have relatively poor low-temperature tolerance and are not suitable for overwintering along the coast of the South China Sea. Especially in the season when temperature fluctuations are large during the autumn-winter transition, diseases are mostly highly prevalent. Therefore, harvest time should be strictly controlled, mainly determined by factors such as the health of the pond shrimp themselves, molting condition, bottom sediment, water quality, and production arrangements.
Once abnormal shrimp activity is found, harvest should be carried out promptly. Usually, marketing around New Year's Day is ideal. Shrimp harvest is mostly carried out at night, using electric trawl nets or push nets for capture.
From the late crop of 2006 to the present, the author has achieved success for five consecutive crops, with average yield per mu rising steadily from 300 kg to 500 kg now, and the highest yield per mu reaching 612 kg. The size is mostly 80-100 shrimp/kg. Although the market price of grass shrimp fluctuates greatly, the farming profit is still considerable, with the average profit per mu over several years basically maintained at around 12,000 yuan, and the highest profit per mu reaching 21,000 yuan.