In greenhouse shrimp farming, the highest per-mu yield of a single pond can reach 10,000 jin.
The shrimp ponds are built with cement, and steel-frame greenhouses are erected above them. The entire reinforced-concrete shrimp pond looks like a "rough swimming pool." This is the greenhouse farming of Ninghai County Binyuan Aquaculture Co., Ltd. in Zhejiang Province. The average per-mu yield of greenhouse-farmed shrimp is 7,000 jin to 8,000 jin, with the highest single-pond yield reaching 10,000 jin per mu, and the shrimp body size is 28 to 35 shrimp per jin.
Shrimp can also be farmed in greenhouses like vegetables and fruit. The shrimp ponds are built with cement, and steel-frame greenhouses are erected above them. The entire reinforced-concrete shrimp pond looks like a "rough swimming pool." This is the greenhouse farming of Ninghai County Binyuan Aquaculture Co., Ltd. in Zhejiang Province. It was among the first batch of high-standard greenhouse shrimp farming enterprises introduced in 2013 by the Ninghai Sanmen Bay Modern Fishery Park. In its first year of production this year, it delivered encouraging results: 30 ponds produced about 250,000 jin of whiteleg shrimp in total, with an average per-mu yield of 7,000 jin to 8,000 jin, the highest single-pond yield reaching 10,000 jin per mu, and the shrimp body size at 28 to 35 shrimp per jin. Recently, the author went to Shepantu in Ninghai County to explore the "password" behind the high per-mu yield of this "wealthy farming greenhouse."
Industrialized greenhouse farming
The author followed Lu Guihua, a technician at the company, along the walkway beside the shrimp ponds. Workers were hurriedly loading freshly caught whiteleg shrimp into baskets and placing them into the compartments of vehicles that had come to purchase them. The shrimp were jumping around lively, each about the length of a palm. Lu Guihua told the author that since the first batch of whiteleg shrimp was harvested in mid-May, buyers from all over the country have come every day to purchase stock, with sales amounting to about 10,000 jin.
"Such high yield is mainly due to the use of advanced technology and scientific management," Lu Guihua said. The company began building elevated ponds and purchasing advanced supporting equipment in March 2014. Through industrialized greenhouse farming, it controls the entire production process of the shrimp and improves the shrimp survival rate, thereby changing the traditional shrimp-farming model of "relying on the weather to eat shrimp." Last September, whiteleg shrimp began to be tried in greenhouses. After trial production with low-density fry numbers in the early stage, a large volume came onto the market in May this year.
The biggest difference between industrialized greenhouse farming and traditional open-air shrimp farms is that a comprehensive aeration system is installed inside. Through the greenhouse windows, one can see 4 machines placed at the four corners of the "swimming pool," with bubbles rising in the center of the pond. "These are all aerators, and they play different roles," Lu Guihua explained. The Roots blower in the center of the pond compresses air and pushes it into the aeration pipes, where it disperses to form very fine bubbles, and then dissolves oxygen into the water. With the stirring of the water, vertical convection is formed. The jet-type aerator can aerate the water body gently. Together with paddlewheel aerators distributed diagonally around the four sides, it can better help drive the water to form a circulation effect.
Water exchange and drainage is another key to successful farming. During high-density shrimp cultivation, leftover feed, metabolic waste, shed shells, and other debris settle at the bottom of the pond, making it very easy for pathogens to breed and harm the shrimp. Therefore, the shrimp pond needs daily water changes. In the middle stage, the water exchange volume is generally 10%. In the later stage, as the amount of feed increases, the water exchange volume correspondingly becomes 30%. "Adding new water not only drains away the dirt, but also restores some of the trace elements and minerals lost under high-density farming, thereby enhancing the hardness of the shrimp shell and improving the shrimp's resistance. This plays a fairly obvious role in later-stage farming," Lu Guihua said.
Shrimp greenhouses have "air conditioning" year-round
The shrimp greenhouses provide "air conditioning" year-round to maintain the temperature most suitable for shrimp growth. This is a kind of subversion of traditional farming ponds.
Near the window of the shrimp pond, the thermometer stayed above 25°C. "In traditional pond farming of whiteleg shrimp, almost only one crop can be raised each year, but the installation of a heating system makes temperature a controllable condition," Lu Guihua said. The most suitable temperature for whiteleg shrimp growth is 26°C to 29°C, and during the growth process it must not be lower than 14°C. To ensure normal shrimp growth, the water temperature in the greenhouse and shrimp pond must remain constant, and heating equipment plays an important role.
In addition, plastic film and the design of elevated ponds also help with heat preservation. Looking up at the top of the pond, one can see plastic film covering the steel-frame greenhouse, which improves the drawback of large temperature differences in open-air ponds. According to the introduction, shrimp farming in elevated ponds can raise water temperature to a certain extent.
High returns from fry rearing and transfer
At present, the company's entire farming ponds link the "eight major systems" (water intake, drainage, sewage collection, seepage prevention, aeration, heat preservation, heating, and electricity), so that each farming pond forms an independent, constant-temperature ecological circulation zone. At the same time, biological preparations such as photosynthetic bacteria are used to keep the pond water fertile, lively, tender, and refreshing.
Having all the installations and equipment does not constitute the entire "password" to high per-mu yield. Lu Guihua used the word "habit" as the final answer. "Small shrimp fry are air-freighted from the United States or Thailand and need to be first reared in ponds. From fertilized eggs forming larvae to postlarvae takes about 21 days. Under good conditions, transfer is not necessary, but habitually this step is carried out." Lu Guihua explained that fry rearing and transfer can improve resource utilization. For example, during the current harvest period, not all the shrimp have been sold, so several ponds are vacant. First, all the fry are concentrated in a few ponds for rearing. When they have been raised for 20 to 30 days, and after the shrimp in the other ponds have been sold and those ponds have been cleaned up and the water cultivated, the fry from the original few ponds are then transferred over. In this way, the pond bottom is relatively clean, which is beneficial for the second production cycle. It is worth noting that the transfer method carries high risk. When there are more fry in the same pond, management becomes more difficult. "The risk is high in the first month. Once the transfer is successful, the later stage will be more stable than traditional fry rearing." Lu Guihua said that although fry rearing and transfer carries the risk of high-density stocking, as long as scientific management gets through the risk period, it can achieve market listing by season and by batch, which not only improves resource utilization but also increases returns. The stocking density is generally 300,000 to 350,000 fry per mu. After about 65 days of farming, selective harvesting can begin. If 36 mu of whiteleg shrimp is calculated at 7,000 jin per mu and 27 yuan per jin, the returns for this season will exceed 6 million yuan, roughly achieving a 1:1.5 return on investment.