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Wen 丨 Yujie History Museum
Editor丨Yujie History Museum
Chinese river crab, also known as river crab, belongs to the phylum Arthropoda, Decapodae, Bow Crab family, and river crab.
In the late 80s and early 90s of the 20th century, scientists broke through the bottleneck of river crab breeding, the river crab aquaculture industry rose rapidly, river crab has become an important object of mainland aquaculture, and river crab has begun to enter the table of more families.
At present, the development of river crab industry is mainly based on pond culture, but there are many problems in the high-density river crab culture mode, and due to the lack of effective management, the water quality problem is serious, which is also one of the main reasons for the frequent occurrence of river crab diseases.
Secondly, because farmers unilaterally pursue output, ignoring the specifications and quality of river crab finished products, resulting in a large number of river crabs on the market, so the price of river crabs has also depreciated, and large-size, high-quality parent crabs are "one in a hundred".
Therefore, by stocking high-quality and large-sized button crabs, the ecological breeding mode of large-sized river crabs is explored, and large-size and high-quality river crabs are cultivated, which can provide consumers with more high-quality hairy crabs, and it is also more convenient for river crab nursery institutions to choose high-quality parent crabs.
In this breeding mode, different water purification methods were used to develop the water quality control technology of the most suitable large-sized river crab ecological breeding mode, and analyze whether the use of purified water could affect the growth and development, nutritional flavor quality of river crab, so as to help the healthy development of large-sized river crab culture.
Next, let's take a look with Yujie: in the large-scale ecological breeding of river crabs, how the use of water purification agents increases the growth rate of river crabs.
Chinese river crab industry
The first stage, natural fishing: In the 50s of the last century, river crabs were all naturally caught, and the catch was only more than 10,000 tons. Then, due to the construction of water conservancy projects, the river crab production fell sharply.
The second stage, artificial release period: In order to solve the dilemma of the previous period, scientists developed and used crab seed resources to artificially release in rivers and lakes, and the production of river crabs increased.
The third stage, the artificial breeding period: in the late 80s and early 90s of the 20th century, scientists broke through the bottleneck of river crab breeding, and the river crab breeding industry developed rapidly.
At present, it has formed an industrial chain composed of a series of links such as seedlings, feed, breeding, medicine, catering, tourism, etc., with an output value of more than 50 billion yuan, driven by its huge market, the mainland river crab aquaculture industry has developed rapidly, and by 2018, the output of mainland farmed river crab reached 757,000 tons.
River crab aquaculture is one of the important economic sources of mainland aquaculture, which is widely distributed in the river crab culture areas in the Liaohe, Yellow River and Yangtze River basins, of which river crabs in the Yangtze River and Liaohe River systems are the main cultured species.
According to statistics, the average output per mu of river crab aquaculture is about 75 kg, and the output per mu in areas with relatively high breeding technology can reach 200 kg, and the benefit per mu is about 1200 yuan, which has become an important source of income for farmers.
River crab farming has also become a beautiful landscape in some areas, such as the annual Yangcheng Lake Crab Festival, which attracts tourists from the surrounding area and even all over the country.
However, with the continuous increase of the intensification of river crab aquaculture, farmers' blind pursuit of economic benefits has caused a series of problems such as deterioration of aquaculture water quality, drug abuse, and disease outbreaks, which have seriously hindered the healthy development of river crab aquaculture.
On the other hand, due to the construction and expansion of cities, the construction of scenic and tourist areas, and the improvement of people's awareness of environmental protection, the available resources for river crab farming have gradually decreased.
Coupled with the improvement of labor costs, bait, drugs and other inputs, transportation, the cost of river crab farming is increasing year by year, because river crabs still come more from pond culture, so it is planned to develop a green and sustainable aquaculture model for river crabs.
So, what is the ecological breeding technology of river crabs?
Ecological breeding technology of river crabs
The crab pond has sufficient lighting, is suitable for rectangular shape, ranging from several acres to dozens of acres, the depth of the pool is 1.2 to 1.8 meters, and there is about 10 cm of silt, the water quality is fresh and pollution-free, and there are anti-escape and aeration facilities.
Before the Spring Festival, drain the pond water, remove the silt and expose it to the sun for half to a month, keep about 20 cm of water in the pond, and then use quicklime to clear the pond, the amount per mu is 150 to 200 kg, quicklime can kill pests, but also increase calcium, keep the pond ecological environment good, so that crabs grow and shell.
Mainly planted with Eleuce, yellow silk grass and black algae, aquatic weed planting has many advantages, firstly, aquatic weed can be used as a direct food source for crabs and release a lot of oxygen through photosynthesis;
Secondly, aquatic plants provide shade, shelter and shelling places for crabs; Finally, aquatic plants can also absorb nutrients in the silt, which can not only ensure their own growth, but also purify water quality.
First choose a high-quality button crab with a robust physique, the size is 100 to 200 per kilogram, the crab seed is filled with new water a week before stocking, the water level is controlled at about 50 cm, with organic fertilizer fertilizer water, 500 to 1000 per mu, in order to achieve super-large size river crab culture, you can further select large-size button crabs to reduce the density of mu stocking.
(In the early stage, river crab compound feed, middle and late stage are mainly chilled fish, and some grains such as corn and soybeans can also be added, and the feed intake depends on the weather and the daily feeding of river crabs.)
From March to May, the water depth is maintained to increase the water temperature by 50-60 cm and promote the molting of river crabs; From June to September, due to the hot weather, in order to reduce the water temperature, the water depth should be maintained 1-1.5 meters.
Water quality testing is carried out every few days to maintain a good environment of aquaculture water, and microecological preparations can be used to restore the water environment.
When aquatic plants grow too densely, part of the aquatic plants should be removed, covering 60%-70% of the pond and maintaining the distribution of aquatic weeds in blocks.
Under the above well-managed conditions, vitamins, minerals and other trace elements are supplemented during molting to ensure the nutritional balance of river crabs.
So, what are the effects of the addition of water purification agents on river crab farming?
Effect of water purifier on Chinese river crab
The nutritional quality analysis of Chinese river crab is mainly achieved by analyzing conventional biochemical composition, fatty acids, amino acids, nucleotides, etc.
Through research, it is not difficult to find that the nutritional and flavor quality comparison of Chinese river crab is the main research object due to factors such as different bait feeding, different breeding methods, different genders, different seasons, and different watersheds.
Under the background of intensive breeding of Chinese river crabs, the water environment has become the only variable factor under the condition that the feed feeding and breeding methods are consistent, and whether the different water environments can affect the quality of Chinese river crabs needs to be studied.
Microecological preparation is a kind of live bacterial preparation, which is widely used in aquaculture because of its green, environmental protection, safety, high efficiency and no side effects, which can effectively improve the ecological environment of aquaculture water, enhance the metabolism of intestinal nutrients of farmed animals, promote growth, improve the immunity of aquatic animals, prevent diseases and survive rate.
EM bacteria is a representative microecological preparation, which is a microbial active agent composed of photosynthetic bacteria, lactic acid bacteria, yeast, actinomycetes and other microorganisms.
EM improves the water environment, inhibits the reproduction of intestinal harmful bacteria in aquatic animals, improves the immunity of aquatic animals, and promotes the healthy growth of aquatic animals, and has been widely used in the aquaculture industry, and there are few studies on the nutrition and flavor of aquatic products whether it is used as a feed additive or directly splashed.
EM fungus can promote the growth and development of river crabs, so the effect of adding EM fungi to the aquaculture water on the nutritional flavor quality of mature river crabs was explored, aiming to provide a theoretical basis for the practical application of EM fungi in the ecological breeding of river crabs.
The effects of EM bacteria in cultured water on the nutritional quality of Chinese river crab were mainly evaluated from three aspects: conventional biochemical indexes, fatty acids in edible parts and muscle hydrolyzed amino acids.
From the perspective of conventional biochemical indicators, the crude fat and crude protein content of the edible parts of the experimental river crab were higher than those of the predecessors, which may be related to the replacement of compound feed to small trash fish at the end of March in this experiment.
Previous studies have found that the nutritional composition of crustaceans is mainly affected by the type of food and growth environment. Lipids play a very important role in the reproductive development of river crabs and are also important nutrients.
Feeding large pan with yeast can significantly increase its crude fat content, yeast is a dormant yeast, EM bacteria in water purification agents have this fungus, and EM bacteria can enrich the species and content of phytoplankton.
Therefore, more natural food may be ingested during the breeding process of button crab in the EM fungus group, which can inhibit the reproduction of intestinal harmful bacteria and help the digestion of aquatic animal bait, which may be the reason for the increase in crude fat in the edible part of the Chinese river crab in the EM group.
Fatty acids are rich in nutrients and are also important indicators for evaluating crab nutrition, and the highest content of fatty acids is oleic acid C18:1 and palmitic acid C16:0.
The unsaturated fatty acids C20:2, C20:3 and C20:4 (ARA) of female crabs in the EM group were significantly higher than those in the control group (P<0.05).
The study found that the higher the ARA content, the better the maintenance of normal physiological function, and for female crabs, the addition of EM bacteria to the cultivated water had a certain improvement on the nutritional quality of fatty acids in the edible parts of Chinese river crabs.
For male crabs, there was no significant difference in fatty acid content between the two groups, and the fatty acid composition of the feed easily affected the fatty acid composition of Chinese river crabs, while the feed used in different groups in this experiment was always consistent.
In Chinese river crab, amino acids are also one of the important indicators to evaluate its nutritional value, among which the ratio of essential amino acids to total amino acids (E/T) is an important reference value for evaluating amino acid nutritional indicators.
The study found that the ideal ratio of essential amino acids to total amino acids (E/T) was about 0.4, and the ratio of essential amino acids to total amino acids (E/T) in both groups was about 0.33, indicating that all groups had good muscle amino acid nutrition.
The ratio of amino acids to total amino acids (E/T) and essential amino acids to non-essential amino acids (E/N) in the EM group was significantly higher than that of the control group, while the ratio of non-essential amino acids to total amino acids (N/T) was lower than that of the control group (P < 0.05).
This shows that the addition of EM bacteria to the farmed water can improve the nutritional quality of female crabs muscle amino acids to a certain extent, but has little effect on male crabs.
The effects of EM bacteria in cultured water on the flavor quality of Chinese river crab were evaluated from two aspects: free amino acids in muscle and flavored nucleotides in edible parts.
Arginine (Arg), glycine (Gly), alanine (Ala), and plastine (Pro) are the highest free amino acids in the muscles of this experimental crab, which is consistent with the results of previous studies.
Among female crabs, serine (Ser) in the control group was lower than that in EM group, while alanine (Ala) was higher than in EM group (P < 0.05), and only these two were sweet amino acids, and the difference between the two groups of total sweet amino acids was not significant (P > 0.05), so the flavor of the two groups showed little difference in the flavor of muscle free amino acids.
In male crabs, only the sweet amino acid alanine (Ala) was different between the two groups, and the control group was greater than that of EM bacteria group (P < 0.05), so for male crabs, the addition of EM bacteria in cultured water had no effect on the flavor quality of free amino acids in muscles.
Through the review of the history of river crab farming, we understand that the river crab farming industry in China is developing rapidly, but it also faces many problems, such as water quality and quality management.
The results showed that the addition of EM bacteria to the aquaculture water had a certain effect on the nutritional quality of Chinese river crabs, especially for female crabs, the amino acid ratio in the muscles and the content of some fatty acids increased significantly, which helped to improve the nutritional value of river crabs and had a relatively small impact on male crabs.
The study also found that the addition of EM bacteria had a limited effect on the flavor quality of Chinese river crabs, mainly in the content and taste of free amino acids, although there were some differences in female crabs, but overall, the flavor of the two groups of crabs was not much different.
This also provides new ideas and methods for the ecological breeding of large-sized river crabs, and also provides a theoretical basis for the application of EM fungi in river crab culture.
It is expected to further promote the healthy development of China's river crab aquaculture industry, provide more high-quality river crab products, and also help protect the water ecological environment.