This year's Mid-Autumn Festival and National Day "combined", next week coincides with two festivals, crabs will usher in the annual hot season. Sales of not only crabs, but also seafood such as fish and shellfish are increasing.
When it comes to eating seafood, many people think of coastal cities, and it seems that the freshest seafood can only be eaten by the sea. Surprisingly, the "seafood" they ordered online may have come from inland areas such as Xinjiang, Gansu and Ningxia.
In September this year, Xinjiang, "China's farthest place from the sea", ushered in a bumper harvest of "seafood". In this regard, many netizens are very confused, there is no sea in the interior, how to raise "seafood"?
The answer points to a key word - the "seafood terrestrial" model. The "terrestrial seafood culture" model refers to the creation of an ecological environment similar to the sea on land, and the artificial cultivation of fish, shrimp and crabs, shellfish and other seafood.
So, how are these "seafood" raised? What is the yield and taste of the "seafood" raised in this way? In this regard, the reporter of Science and Technology Daily interviewed relevant experts.
Penaeus vannamei "swims" into the Hexi corridor
"The water here is rich in strontium, and the shrimp raised are highly transparent and sweet to eat. The recently harvested stubble of shrimp, which is enough for 8000,200 catties, has been sold out. It's the Mid-Autumn Festival soon, and we've caught another shrimp that is currently on sale. Li Zhigang, head of Fengsen Agriculture, Fishery and Breeding Cooperative in Zhangye City, Gansu Province, said in an interview with a reporter from Science and Technology Daily. The shrimp farmed by the aquaculture cooperative is mainly sold to Zhangye, Jiayuguan, Jiuquan and other places, radiating the market within 3 kilometers, and a shrimp can be served to the consumer's table as soon as about <> hours after shipment.
Li Zhigang introduced that Zhangye City is located in the middle of the Hexi corridor, and the arid climate makes it difficult to achieve live shrimp transportation, and the price of live shrimp flown in is very high, for example, Japanese shrimp are sold for up to 200 yuan per catty. In order to allow local consumers to eat affordable and fresh seafood, technicians from Fengsen Agriculture, Fishery and Aquaculture Cooperative in Zhangye City, Gansu Province, introduced South American white shrimp and shrimp fry, and built a "nest" suitable for breeding and growth here.
Aquaculture tailwater is generated during the cultivation of "seafood". According to the requirements, these aquaculture tailwater needs to be treated by precipitation, filtration, purification and other treatments to meet the tailwater discharge standards before it can be discharged to the outside.
"However, we do not have the conditions to discharge aquaculture tailwater here. In order not to pollute the environment and achieve green aquaculture, Fengsen Agriculture, Fishery and Aquaculture Cooperative in Zhangye City, Gansu Province, Lanzhou Jiaotong University and other universities independently developed a set of water circulation system equipment to simulate the marine aquaculture environment and installed graded purification equipment. After the water enters the equipment of this circulation system, it can be replaced for 5 years without being replaced if the water quality has always reached the standard. Li Zhigang added that Zhangye City has a high altitude and low winter temperature, and under the low temperature conditions of minus 2023 degrees Celsius in January 1, they successfully farmed vannamei shrimp for one month in an intelligent constant temperature greenhouse independently developed, and the technology has also obtained national invention patent certification.
The reporter learned that when the first phase of the construction project of the aquaculture cooperative farm was running, the technicians found that the higher the salinity of the aquaculture water, the stronger the resistance and faster the growth rate of the shrimp; However, as the salinity of water bodies increases, the corrosion resistance of equipment such as water circulation systems decreases. At present, the second phase of the farm construction project is underway, and the aquaculture cooperative has established cooperation with Shanghai Jiao Tong University. In addition to improving the corrosion resistance of farm equipment, researchers at Shanghai Jiao Tong University have also developed relevant software to install "smart brains" on farms, so that farmers can remotely monitor and control water temperature, oxygen content, salt content and other water data without going to the farm.
"In the second phase of the farm's construction project, we have gradually increased the salt content of aquaculture water. After the completion of the first phase of the farm, the annual output of vannamei shrimp is 3,4 to 30,<> jin, and after the completion of the second phase of the construction project, the annual output of vannamei shrimp is expected to reach <>,<> jin. In addition, we have recently introduced a new species, black tiger shrimp, to give consumers more choices. Li Zhigang said.
Large green crabs "grow" in the saline soil
Data show that Ningxia has been using the Yellow River water to raise fish for decades, and in recent years, it has developed the use of saline water to simulate marine aquaculture of shrimp and crabs. Ningxia Yiyu saline water and soil distribution is extensive, soil salinization in the yellow irrigation area is mostly a saline soil distribution type, salinity is between 2 and 18, pH value is between 7.7 and 9.3, the development of seafood aquaculture has obvious advantages.
In 2010, Ningxia began to use saline-alkali land resources to promote the cultivation model of vannamei shrimp in solar energy-saving greenhouses. By the end of 2022, Ningxia's aquaculture production of South American vannamei shrimp and other seafood reached 217 tons. The cultivation of seafood such as green crab has also started in Ningxia.
"The green crabs we raise are relatively large, the big one is only more than six taels, mainly for the local market, and some are sold to neighboring provinces and cities." Gao Changcheng, head of Ningxia Helan County Jingcheng Aquaculture Co., Ltd. (hereinafter referred to as Jingcheng Company), said in an interview with a reporter from Science and Technology Daily that after this year's National Day, the green crabs produced by his company will be listed in large quantities to meet the needs of consumers in the northwest region.
Green crab is widely distributed in the South China Sea and East China Sea, and is loved by consumers because of its delicious taste and rich nutrition. Can let the green crabs living in the sea "camp" in Ningxia, but the technicians of Jingcheng Company have made a lot of effort.
In 2021, Jingcheng, which only farmed vannamei shrimp at the time, bought a batch of crab seedlings from Ningbo City, Zhejiang Province for trial cultivation, and the final survival rate was less than 1%. Later, Jingcheng Company cooperated with Ningbo University to carry out technical research in transportation, desalination and cultivation (usually using sea salt to adjust the aquaculture water body into seawater and gradually desalination it to help shrimp and sea crabs adapt to the freshwater aquaculture environment), which greatly improved the survival rate of green crabs.
"Previously, in the process of transporting green crab and crab seedlings, a foam box was about thirty or forty pounds, and the environment was narrow and caused by extrusion, and many crab seedlings died before they reached the place. Now we divide the foam box into several layers, just like building a building, each layer only holds a few pounds, so that the survival rate of green crab and crab seedlings exceeds 90%. Gao Changcheng further said that they have also improved the desalination and cultivation method of green crabs, shortening the previous desalination cultivation time from 7 days to 5 days, and extending the time for green crabs to adapt in low-salinity water. In addition, they also reared desalinated blue crabs and vannamei shrimp in ponds.
"Such adjustments can improve the utilization of water space in the pond, and green crabs like to feed on some organic debris, carcasses of fish and shrimp and other animals, as well as certain intermediate hosts that carry shrimp pathogens, which indirectly inhibits the reproduction of various microorganisms, reduces the occurrence of shrimp diseases, and achieves a win-win situation." Gao Changcheng said, "At present, the survival rate of our company's green crabs has reached 60%. ”
Is it safe to "migrate" inland shrimp and crabs?
Can "seafood" raised with saline water be eaten with confidence? This is a question that many consumers will have when they first encounter such products.
"Marine fish farming in saline-alkali lands has long been practiced." Li Jian, a researcher at the Yellow Sea Fisheries Research Institute of the Chinese Academy of Fishery Sciences, said in an interview with a reporter from Science and Technology Daily. For example, China's Ningxia began to develop fishery production in the mid-50s of last century, and in recent years began to dig ponds on saline-alkali land to raise fish, develop integrated rice and fishery breeding, facility fisheries, etc., and has now used saline-alkali land to carry out 15,9 mu of precision aquaculture of pond bulk freshwater fish, and a total of 100 million mu of comprehensive rice and fishery cultivation. In addition, Australia, India, the United States and other countries have also carried out some small-scale saline aquaculture, such as rainbow trout culture in Australia, and Roche marsh shrimp and Vannabin shrimp culture in India.
"Ningxia, Gansu and other inland areas of China, industrial development is relatively insufficient, sparsely populated, and environmental pollution is light, so the quality of 'seafood' produced in these places is guaranteed." In addition, in terms of nutrition, taste, etc., relevant experts have also carried out research, and the saline-alkali aquaculture method is not much different from the traditional aquaculture method. Due to the higher ion concentration of saline water than fresh water, some cultured species have a higher content of flavored amino acids and better muscle color. Li Jian said. (Science and Technology Daily reporter He Peician)