A Brief Introduction to Greenhouse Farming of Whiteleg Shrimp in Longhai
A Brief Introduction to Greenhouse Farming of Whiteleg Shrimp in Longhai
In recent years, various places have been experimenting with winter greenhouse farming one after another, and by combining local farming conditions, they have worked out successful farming models suited to their own areas. Thanks to its superior geographical advantages, Longhai has become one of the main areas for winter greenhouse shrimp farming in China, and its farming model is representative and can serve as a reference.
□Article by Yang Yongquan, Fuzhou Dafu Feed Co., Ltd.
Whiteleg shrimp (Litopenaeus vannamei) is a tropical shrimp species, with a suitable water temperature range of 15-32°C; it stops feeding when the water temperature drops to 18°C, and dies when the water temperature falls below 12°C. To cope with cold weather, coastal areas in the south generally use greenhouses for shrimp farming in winter. Since January and February each year coincide with the Lunar New Year, temperatures are low, the number of live shrimp is relatively small, and demand is high, so shrimp prices are often particularly high. Therefore, winter greenhouse shrimp farming has become the main model in Longhai. The heat-preserving greenhouse generally uses miscellaneous wood, steel wire and nylon film as the main materials, making it sturdy, light-transmitting and heat-preserving while also reducing costs. Greenhouse farming of whiteleg shrimp has characteristics such as weaker light, less air exchange, lower water temperature, a longer farming cycle (generally one month longer than summer shrimp), and fewer natural enemies. It is highly technical, and especially the control of water quality and the prevention and treatment of diseases in the middle and late stages are the key to determining the success of greenhouse shrimp farming. Based on the characteristics of greenhouse farming, an analysis of some problems currently encountered by farmers, and combined with production practice, the author summarizes the techniques for greenhouse farming of whiteleg shrimp in Longhai as follows for reference.
I. Pond Conditions and Greenhouse Construction
1. Pond Conditions
The pond for greenhouse farming of whiteleg shrimp should not be too large; if the pond is too large, it is relatively difficult to cover it with a greenhouse. A generally suitable farming area is 3-5 mu. The pond is mostly rectangular, with a length-to-width ratio of 5:3, a pond depth of about 2 m, and a water depth that can be maintained at about 1.1-1.5 m, with a complete water intake and drainage system. If conditions permit, it is best to install a central sewage discharge facility in the pond.
2. Greenhouse Construction
The greenhouse should not be built too high; if it is too high, its wind resistance is poor and materials are wasted. The base edges of the gable shape should be close to the pond edges. The greenhouse is built as a gable-shaped frame, like a house, with the length and width of the gable exactly matching the length and width of the pond. The greenhouse uses Chinese fir timber and steel wire ropes to build the pile frame and support grid, over which plastic film is laid, and then steel wire ropes are stretched perpendicular to the support grid to form a retaining network that keeps the plastic film flat and taut; the steel wire ropes are fastened to short wooden stakes set around the pond base, and the intersections of the two steel wire ropes of the support grid and the retaining network are then tied and fixed with iron wire, forming a closed heat-preservation system covering the entire pond.
The Chinese fir timber selected has an end diameter of more than 6 cm, and the spacing between wooden posts is 1.2 m; the selected steel wire rope has a diameter of 2.4 mm, a tensile strength of 1570 MPa, and a total breaking force of 5.52 KN. The arrangement spacing of the support grid steel wire ropes is 0.5 m, and the arrangement spacing of the retaining network steel wire ropes perpendicular to them is 1.0 m; the plastic film uses polyethylene film. Above and below the film, one piece each of polyethylene netting with a diameter of 2.4 mm and the same size as the pond is used, with a mesh size of 10×10 cm, to secure the film and prevent it from being blown off by the wind.
The construction of the greenhouse is mostly completed in October or early November. One 1-kilowatt aerator is installed per mu of shrimp pond to prevent oxygen deficiency in the later stage of farming.
II. Preparation Before Releasing Shrimp Fry
Before stocking whiteleg shrimp fry, the pond must be cleaned and the water quality adjusted.
1. Pond Clearing
(1) Rinse the pond bottom: wash away the organic humus sludge, salts, alkalis and metal deposits where pathogens breed;
(2) Dry the pond thoroughly: kill pathogens and mineralize organic matter.
(3) Remove weeds from the pond base.
(4) Apply quicklime: apply 100-150 kg of quicklime per 1 mu and splash it over the whole pond. If the pond is relatively alkaline, quicklime cannot be used. In addition, the amount of quicklime used can be adjusted according to the pH of the pond soil.
2. Water Intake
Most farmers in Longhai use groundwater, while some pump river water. Those pumping groundwater may not need a filter net, while those pumping river water must pass it through a filter net. The filter net is a double-layer silk screen, with the inner layer 80 mesh and the outer layer 200 mesh. It must be replaced frequently during pumping to avoid clogging. The filter net can filter out wild fish, insect eggs, and so on.
3. Water Disinfection
Disinfection generally uses bleaching powder (30% effective chlorine) at 30 ppm. The disinfection effect should reach the point where the water is clear to the bottom, with no plankton at all.
4. Water Quality Adjustment
The water quality before releasing fry must be properly adjusted to avoid affecting the survival rate of the shrimp fry. The pH value is 7.8-8.6, alkalinity 80-200 ppm, calcium ions >300 ppm, magnesium ions >300 ppm, no ammonia nitrogen and nitrite, dissolved oxygen > 4.0 ppm, transparency<50公分，盐度最低5℃，最好接近育苗场（差异小于2℃）。
In freshwater areas, since various indicators such as salinity cannot meet the standards, it is best to make a temporary holding pond, add seawater or brine, and adjust the water quality of the temporary holding pond to the required standard before releasing fry. After the fry are placed in the temporary holding pond for 7-10 days, they can be put into the large pond. Some farmers in freshwater areas of Longhai do not make a temporary holding pond, but instead lower the water level; the overall survival rate of this farming method is relatively low.
For fertilizing the water, rice bran, sea fish extract, brown sugar, Subaobei, etc. can be fermented and then splashed on. Most farmers in Longhai use some commercial water-fertilizing products from aquaculture drug stores, such as amino acids, Lishisu, etc. Using beneficial bacteria to fertilize the water before releasing fry can allow the beneficial bacteria in the water to become dominant and inhibit the growth of harmful bacteria. Algal growth is balanced, and the overall ecological environment of the water body is improved.
III. Releasing Fry
When releasing fry, the temperature difference must be within 2°C; it is best to release fry after the greenhouse has been covered. In Longhai, the fry release time for the first greenhouse season is mostly in the ninth lunar month, and by the time of stocking most greenhouses have been covered; some are covered with the greenhouse within 20 days after fry release. The stocking density of CP fry is 35,000-45,000 fry/mu. The fry release time for the second greenhouse season is on the 15th day of the first lunar month, and the stocking density of CP fry is 40,000-50,000 fry/mu. When the shrimp are raised to 50 shrimp per jin, according to the farming situation, part of the shrimp are harvested first, and the rest are raised to 30-35 shrimp per jin before being sold. The greenhouse farming period should not exceed the Dragon Boat Festival at the latest.
IV. Daily Management
1. Feeding
Within half a month after the shrimp fry enter the pond, they mainly feed on the basic bait in the pond water, supplemented with shrimp opening feed, 0# feed, etc. The feed amounts are 500 grams per 100,000 shrimp per day, divided into 3-4 times. Add 200 grams each day. Feed using the method of small amounts and multiple times. After 20 days, feed completely with high-quality compound shrimp feed. The specific feeding method is 2-4 times per day: for body length 1-3 cm, the feeding amount accounts for 10-7% of body weight; for body length 3-7 cm, the feeding amount accounts for 7-4.5% of body weight; for body length 7-10 cm, the feeding amount accounts for 4.5-3% of body weight; for body length greater than 10 cm, the feeding amount accounts for 3-2% of body weight. To accurately control the feeding amount, 2-3 feeding trays should be set in each pond, and the amount of feed placed on each tray is 2% of the amount fed for that meal. According to the size of the shrimp, check the amount of residual feed in the feeding trays 1.5-2.5 hours after each feeding, and appropriately adjust the feeding amount according to the residual feed situation combined with weather, water temperature and water quality.
2. Water Quality Management
Longhai mostly adopts a semi-closed farming method. When releasing fry, the water level is 60-100 cm. In the early stage, the method of adding water is used, adding 3-5 cm of water each day; after it is full, a small amount of water is exchanged according to water quality conditions. In the first month after stocking the shrimp fry, water is mainly added; afterward, no water is exchanged or only a small amount is exchanged, and the amount of water exchanged at one time should be controlled at about 1/5-1/6 of the total water body. Large-scale drainage and irrigation must not be carried out, to prevent stress reactions in the shrimp.
The salinity of the pond water is maintained above 3‰. In freshwater areas, seawater or brine is regularly added about once a month. During the shrimp farming process, dissolved oxygen, pH value, ammonia nitrogen, hydrogen sulfide, nitrite, salinity, transparency, water color and other physical and chemical factors are usually used to indicate the chemical indicators and physical properties of water quality. Changes in these indicators and properties directly affect the growth, yield, quality and economic benefits of shrimp.
(1) Dissolved oxygen: one 1-kilowatt aerator must be equipped per mu, and it should be turned on flexibly to increase oxygen, so as to ensure that the dissolved oxygen in the pond water is above 5 mg/L and the dissolved oxygen at the bottom layer of the pond is above 4 mg/L.
(2) pH value: because the temperature in greenhouse farming is relatively low, algae grow slowly, and the pH value is relatively low, so fertilizer must be applied frequently. It is better to apply fertilizer in small amounts and multiple times, and control the amount of water fertilization according to water color, pH value, transparency, etc. Excessive water fertilization will lead to an excessively high pH value. If the pH value is lower than 7.5, use quicklime to adjust it, with an amount of 5-10 kg per mu. If the pH value is higher than 9, use calcium carbonate to adjust it, with an amount of 40 kg per mu, or use biological preparations such as photosynthetic bacteria and EM bacteria, or exchange water. Within one month of releasing fry, the pH value must not be higher than 9.2, otherwise the survival rate will be affected.
(3) Ammonia nitrogen: most groundwater in Longhai contains ammonia nitrogen, so when adding or exchanging water, close attention must be paid to the ammonia nitrogen in the pond. During the farming process, the ammonia nitrogen content should be reduced as much as possible and controlled below 0.5 mg/L. The control methods are: first, applying zeolite powder to adsorb ammonia in the water; second, applying microbial preparations to degrade ammonia in the water body; third, cultivating a certain amount of algae.
(4) Nitrite: in greenhouse farming, due to the greenhouse, the dissolved oxygen in the water body is generally relatively low, the conversion of nitrite is slow, and nitrite will be relatively high in the middle and late stages of farming, which should be noted. Especially in freshwater areas, nitrite is more toxic. Control methods: first, apply beneficial microbial preparations and bottom quality improvers to improve the bottom environment; second, apply microbial preparations; third, cultivate a certain amount of algae. Fourth, increase the salinity of the water body.
(5) Transparency: if the transparency is less than 20 cm, water should be exchanged, water added, or zeolite powder applied in a timely manner; if the transparency is too high, nitrogen fertilizer and phosphate fertilizer can be applied.
(6) Water color: the ideal water color for farming whiteleg shrimp is the yellow-green and yellow-brown formed by green algae or diatoms; these algae play a purifying role in water quality. During the farming process, applying microecological preparations such as Bacillus and EM bacteria can promptly reduce organic matter in the water body and stabilize the pond water color. Close attention should be paid to the growth of zooplankton; when their number increases, Xianchongjing can be applied and 30 small-size bighead carp per mu can be polycultured for control. If floating toxic algae appear, copper-green Microcystis appears, or red-brown dinoflagellates appear, chelated copper can be applied, and draining and exchanging the pond water should also be considered.
(7) Total alkalinity and total hardness: regularly add calcium carbonate and supplement minerals before and after shrimp molting, to prevent soft shells and stealth death in shrimp.
(8) Dissolved oxygen: except during feeding time, turn on the aerators all the time. Increase or decrease the number of aerators according to weather, shrimp size and water quality conditions.
3. Disease Prevention and Treatment
Disease prevention and treatment should adhere to the policy of "prevention first", implement healthy farming technical measures in every farming link, maintain good water quality, and prevent sudden changes in the farming environment. Frequently inspect shrimp feeding, activity, growth and water quality changes. Take corresponding measures, patrol the pond frequently, and prevent biological enemies such as snakes, rats and frogs. Disinfect when entering and leaving shrimp ponds to prevent the spread of viruses. Regularly add vitamin C, vitamin E, immune polysaccharides, liver-protecting drugs, etc. to the feed.
□Article by Yang Yongquan, Fuzhou Dafu Feed Co., Ltd.
Whiteleg shrimp (Litopenaeus vannamei) is a tropical shrimp species, with a suitable water temperature range of 15-32°C; it stops feeding when the water temperature drops to 18°C, and dies when the water temperature falls below 12°C. To cope with cold weather, coastal areas in the south generally use greenhouses for shrimp farming in winter. Since January and February each year coincide with the Lunar New Year, temperatures are low, the number of live shrimp is relatively small, and demand is high, so shrimp prices are often particularly high. Therefore, winter greenhouse shrimp farming has become the main model in Longhai. The heat-preserving greenhouse generally uses miscellaneous wood, steel wire and nylon film as the main materials, making it sturdy, light-transmitting and heat-preserving while also reducing costs. Greenhouse farming of whiteleg shrimp has characteristics such as weaker light, less air exchange, lower water temperature, a longer farming cycle (generally one month longer than summer shrimp), and fewer natural enemies. It is highly technical, and especially the control of water quality and the prevention and treatment of diseases in the middle and late stages are the key to determining the success of greenhouse shrimp farming. Based on the characteristics of greenhouse farming, an analysis of some problems currently encountered by farmers, and combined with production practice, the author summarizes the techniques for greenhouse farming of whiteleg shrimp in Longhai as follows for reference.
I. Pond Conditions and Greenhouse Construction
1. Pond Conditions
The pond for greenhouse farming of whiteleg shrimp should not be too large; if the pond is too large, it is relatively difficult to cover it with a greenhouse. A generally suitable farming area is 3-5 mu. The pond is mostly rectangular, with a length-to-width ratio of 5:3, a pond depth of about 2 m, and a water depth that can be maintained at about 1.1-1.5 m, with a complete water intake and drainage system. If conditions permit, it is best to install a central sewage discharge facility in the pond.
2. Greenhouse Construction
The greenhouse should not be built too high; if it is too high, its wind resistance is poor and materials are wasted. The base edges of the gable shape should be close to the pond edges. The greenhouse is built as a gable-shaped frame, like a house, with the length and width of the gable exactly matching the length and width of the pond. The greenhouse uses Chinese fir timber and steel wire ropes to build the pile frame and support grid, over which plastic film is laid, and then steel wire ropes are stretched perpendicular to the support grid to form a retaining network that keeps the plastic film flat and taut; the steel wire ropes are fastened to short wooden stakes set around the pond base, and the intersections of the two steel wire ropes of the support grid and the retaining network are then tied and fixed with iron wire, forming a closed heat-preservation system covering the entire pond.
The Chinese fir timber selected has an end diameter of more than 6 cm, and the spacing between wooden posts is 1.2 m; the selected steel wire rope has a diameter of 2.4 mm, a tensile strength of 1570 MPa, and a total breaking force of 5.52 KN. The arrangement spacing of the support grid steel wire ropes is 0.5 m, and the arrangement spacing of the retaining network steel wire ropes perpendicular to them is 1.0 m; the plastic film uses polyethylene film. Above and below the film, one piece each of polyethylene netting with a diameter of 2.4 mm and the same size as the pond is used, with a mesh size of 10×10 cm, to secure the film and prevent it from being blown off by the wind.
The construction of the greenhouse is mostly completed in October or early November. One 1-kilowatt aerator is installed per mu of shrimp pond to prevent oxygen deficiency in the later stage of farming.
II. Preparation Before Releasing Shrimp Fry
Before stocking whiteleg shrimp fry, the pond must be cleaned and the water quality adjusted.
1. Pond Clearing
(1) Rinse the pond bottom: wash away the organic humus sludge, salts, alkalis and metal deposits where pathogens breed;
(2) Dry the pond thoroughly: kill pathogens and mineralize organic matter.
(3) Remove weeds from the pond base.
(4) Apply quicklime: apply 100-150 kg of quicklime per 1 mu and splash it over the whole pond. If the pond is relatively alkaline, quicklime cannot be used. In addition, the amount of quicklime used can be adjusted according to the pH of the pond soil.
2. Water Intake
Most farmers in Longhai use groundwater, while some pump river water. Those pumping groundwater may not need a filter net, while those pumping river water must pass it through a filter net. The filter net is a double-layer silk screen, with the inner layer 80 mesh and the outer layer 200 mesh. It must be replaced frequently during pumping to avoid clogging. The filter net can filter out wild fish, insect eggs, and so on.
3. Water Disinfection
Disinfection generally uses bleaching powder (30% effective chlorine) at 30 ppm. The disinfection effect should reach the point where the water is clear to the bottom, with no plankton at all.
4. Water Quality Adjustment
The water quality before releasing fry must be properly adjusted to avoid affecting the survival rate of the shrimp fry. The pH value is 7.8-8.6, alkalinity 80-200 ppm, calcium ions >300 ppm, magnesium ions >300 ppm, no ammonia nitrogen and nitrite, dissolved oxygen > 4.0 ppm, transparency<50公分，盐度最低5℃，最好接近育苗场（差异小于2℃）。
In freshwater areas, since various indicators such as salinity cannot meet the standards, it is best to make a temporary holding pond, add seawater or brine, and adjust the water quality of the temporary holding pond to the required standard before releasing fry. After the fry are placed in the temporary holding pond for 7-10 days, they can be put into the large pond. Some farmers in freshwater areas of Longhai do not make a temporary holding pond, but instead lower the water level; the overall survival rate of this farming method is relatively low.
For fertilizing the water, rice bran, sea fish extract, brown sugar, Subaobei, etc. can be fermented and then splashed on. Most farmers in Longhai use some commercial water-fertilizing products from aquaculture drug stores, such as amino acids, Lishisu, etc. Using beneficial bacteria to fertilize the water before releasing fry can allow the beneficial bacteria in the water to become dominant and inhibit the growth of harmful bacteria. Algal growth is balanced, and the overall ecological environment of the water body is improved.
III. Releasing Fry
When releasing fry, the temperature difference must be within 2°C; it is best to release fry after the greenhouse has been covered. In Longhai, the fry release time for the first greenhouse season is mostly in the ninth lunar month, and by the time of stocking most greenhouses have been covered; some are covered with the greenhouse within 20 days after fry release. The stocking density of CP fry is 35,000-45,000 fry/mu. The fry release time for the second greenhouse season is on the 15th day of the first lunar month, and the stocking density of CP fry is 40,000-50,000 fry/mu. When the shrimp are raised to 50 shrimp per jin, according to the farming situation, part of the shrimp are harvested first, and the rest are raised to 30-35 shrimp per jin before being sold. The greenhouse farming period should not exceed the Dragon Boat Festival at the latest.
IV. Daily Management
1. Feeding
Within half a month after the shrimp fry enter the pond, they mainly feed on the basic bait in the pond water, supplemented with shrimp opening feed, 0# feed, etc. The feed amounts are 500 grams per 100,000 shrimp per day, divided into 3-4 times. Add 200 grams each day. Feed using the method of small amounts and multiple times. After 20 days, feed completely with high-quality compound shrimp feed. The specific feeding method is 2-4 times per day: for body length 1-3 cm, the feeding amount accounts for 10-7% of body weight; for body length 3-7 cm, the feeding amount accounts for 7-4.5% of body weight; for body length 7-10 cm, the feeding amount accounts for 4.5-3% of body weight; for body length greater than 10 cm, the feeding amount accounts for 3-2% of body weight. To accurately control the feeding amount, 2-3 feeding trays should be set in each pond, and the amount of feed placed on each tray is 2% of the amount fed for that meal. According to the size of the shrimp, check the amount of residual feed in the feeding trays 1.5-2.5 hours after each feeding, and appropriately adjust the feeding amount according to the residual feed situation combined with weather, water temperature and water quality.
2. Water Quality Management
Longhai mostly adopts a semi-closed farming method. When releasing fry, the water level is 60-100 cm. In the early stage, the method of adding water is used, adding 3-5 cm of water each day; after it is full, a small amount of water is exchanged according to water quality conditions. In the first month after stocking the shrimp fry, water is mainly added; afterward, no water is exchanged or only a small amount is exchanged, and the amount of water exchanged at one time should be controlled at about 1/5-1/6 of the total water body. Large-scale drainage and irrigation must not be carried out, to prevent stress reactions in the shrimp.
The salinity of the pond water is maintained above 3‰. In freshwater areas, seawater or brine is regularly added about once a month. During the shrimp farming process, dissolved oxygen, pH value, ammonia nitrogen, hydrogen sulfide, nitrite, salinity, transparency, water color and other physical and chemical factors are usually used to indicate the chemical indicators and physical properties of water quality. Changes in these indicators and properties directly affect the growth, yield, quality and economic benefits of shrimp.
(1) Dissolved oxygen: one 1-kilowatt aerator must be equipped per mu, and it should be turned on flexibly to increase oxygen, so as to ensure that the dissolved oxygen in the pond water is above 5 mg/L and the dissolved oxygen at the bottom layer of the pond is above 4 mg/L.
(2) pH value: because the temperature in greenhouse farming is relatively low, algae grow slowly, and the pH value is relatively low, so fertilizer must be applied frequently. It is better to apply fertilizer in small amounts and multiple times, and control the amount of water fertilization according to water color, pH value, transparency, etc. Excessive water fertilization will lead to an excessively high pH value. If the pH value is lower than 7.5, use quicklime to adjust it, with an amount of 5-10 kg per mu. If the pH value is higher than 9, use calcium carbonate to adjust it, with an amount of 40 kg per mu, or use biological preparations such as photosynthetic bacteria and EM bacteria, or exchange water. Within one month of releasing fry, the pH value must not be higher than 9.2, otherwise the survival rate will be affected.
(3) Ammonia nitrogen: most groundwater in Longhai contains ammonia nitrogen, so when adding or exchanging water, close attention must be paid to the ammonia nitrogen in the pond. During the farming process, the ammonia nitrogen content should be reduced as much as possible and controlled below 0.5 mg/L. The control methods are: first, applying zeolite powder to adsorb ammonia in the water; second, applying microbial preparations to degrade ammonia in the water body; third, cultivating a certain amount of algae.
(4) Nitrite: in greenhouse farming, due to the greenhouse, the dissolved oxygen in the water body is generally relatively low, the conversion of nitrite is slow, and nitrite will be relatively high in the middle and late stages of farming, which should be noted. Especially in freshwater areas, nitrite is more toxic. Control methods: first, apply beneficial microbial preparations and bottom quality improvers to improve the bottom environment; second, apply microbial preparations; third, cultivate a certain amount of algae. Fourth, increase the salinity of the water body.
(5) Transparency: if the transparency is less than 20 cm, water should be exchanged, water added, or zeolite powder applied in a timely manner; if the transparency is too high, nitrogen fertilizer and phosphate fertilizer can be applied.
(6) Water color: the ideal water color for farming whiteleg shrimp is the yellow-green and yellow-brown formed by green algae or diatoms; these algae play a purifying role in water quality. During the farming process, applying microecological preparations such as Bacillus and EM bacteria can promptly reduce organic matter in the water body and stabilize the pond water color. Close attention should be paid to the growth of zooplankton; when their number increases, Xianchongjing can be applied and 30 small-size bighead carp per mu can be polycultured for control. If floating toxic algae appear, copper-green Microcystis appears, or red-brown dinoflagellates appear, chelated copper can be applied, and draining and exchanging the pond water should also be considered.
(7) Total alkalinity and total hardness: regularly add calcium carbonate and supplement minerals before and after shrimp molting, to prevent soft shells and stealth death in shrimp.
(8) Dissolved oxygen: except during feeding time, turn on the aerators all the time. Increase or decrease the number of aerators according to weather, shrimp size and water quality conditions.
3. Disease Prevention and Treatment
Disease prevention and treatment should adhere to the policy of "prevention first", implement healthy farming technical measures in every farming link, maintain good water quality, and prevent sudden changes in the farming environment. Frequently inspect shrimp feeding, activity, growth and water quality changes. Take corresponding measures, patrol the pond frequently, and prevent biological enemies such as snakes, rats and frogs. Disinfect when entering and leaving shrimp ponds to prevent the spread of viruses. Regularly add vitamin C, vitamin E, immune polysaccharides, liver-protecting drugs, etc. to the feed.