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Wen 丨 Yujie History Museum
Editor丨Yujie History Museum
Chinese river crab, also known as river crab, hairy crab, hairy crab, etc., belongs to the crustacean in the phylum Arthropoda, belonging to the genus of river crabs in the square crab family. It is loved for its delicious taste, high nutritional value and medicinal potential.
In the natural environment, Chinese river crabs are mainly distributed in mainland Yangtze River, Yellow River, Ou River and Liao River and other rivers entering the sea.
However, since breaking through the bottleneck of artificial seedling technology in the 80s of the 20th century, the large-scale artificial breeding of Chinese river crabs has been realized, and after more than 30 years of rapid development, Chinese river crabs have become an important economic freshwater crab culture species in mainland China.
However, due to the influence of different water environments, the suitable aquaculture mode often has great differences, so it is necessary to conduct in-depth research on the key influencing factors in the aquaculture process.
So next, Yu Jie will tell you how the breeding density affects the growth performance of Chinese river crabs in the process of artificial breeding of Chinese river crabs.
Chinese river crab farming
Chinese river crab is an important freshwater cultured crab in mainland China and has significant economic value.
Since the 80s of the 20th century, the artificial seedling technology of Chinese river crab has made significant progress, solving the problem of seedlings, so that pond culture can be promoted on a large scale, and the aquaculture industry has gradually emerged.
By the middle and late 90s, the Chinese river crab breeding technology has matured, the industrial chain has gradually formed, including crab seedlings, crab species and adult crab complete production chain, after 2000, the artificial breeding of Chinese river crab has developed rapidly, the breeding range has been expanding, and the aquaculture output has increased significantly.
At present, under the active publicity and promotion of relevant government departments, the mainland Chinese river crab aquaculture has entered a new stage of development, that is, healthy, ecological and efficient breeding stage, aiming to maintain the ecological balance of the aquaculture water body while ensuring economic benefits, so as to promote the sustainable development of Chinese river crab culture and related industries.
According to statistics, in 1990, the national output of Chinese river crab aquaculture was only 04,800 tons, and by 2000 it had reached 200,000 tons. By 2016, the national production of Chinese river crab farming soared to 812,000 tons.
Aquaculture production decreased slightly in 2017 to 750,900 tonnes. The artificial breeding of Chinese river crab in mainland China covers 28 provinces and municipalities directly under the central government, among which the main production areas include Jiangsu Province, Hubei Province, Anhui Province, Liaoning Province and Jiangxi Province, accounting for 46.06%, 22.46%, 13.30%, 6.73% and 2.49% of the total national output respectively.
So, what are the effects of changes in key factors in the breeding process?
The impact of key factors on Chinese river crab culture
In the culture of Chinese river crabs, it is generally believed that several key factors directly affect the success of the culture, including the size, quality, water quality, feed nutrition and culture density of the buckle crab.
Although a large number of relevant studies have been carried out at home and abroad, there are significant differences in the appropriate breeding mode due to the different breeding conditions in different regions.
In the growth process of Chinese river crab, molting is a key link, and its growth mainly depends on molting.
A Chinese river crab needs to molt about 18 to 21 times in its lifetime, so the frequency of molting and the weight gain after each molt are key factors affecting its growth rate.
In adult crab culture, different button crab sizes can significantly affect the growth and molting of Chinese river crabs, for example, Yu Ningning's study found that smaller Chinese river crab individuals gain more weight after molting.
Ji Lianyuan pointed out that the stocking size was proportional to the weight of Chinese river crab, but in the later stage of breeding, the stocking size did not significantly affect the survival rate, breeding size and mu yield.
In addition, some studies suggest that for adult crab pond culture, the size of button crabs should be between 5 and 12 g/piece.
For high-quality large-size river crab culture, it should be between 5 and 10 g/pc, because too large size may cause difficulty in the first molting, and too small may affect the final market size, suitable button crab stocking size is about 5 g/pcs, suitable density is about 16875 per hectare.
Stocking large-sized button crabs can obtain better breeding results, including higher survival rate, breeding size and average yield, and the size of button crabs has an important impact on the adult crab culture of Chinese river crabs, but it is necessary to determine the appropriate size according to different regions and breeding patterns.
So, what is the impact of farming density on river crab farming?
Effect of culture density on river crab
In fish and shrimp and crab culture, the management of culture density is crucial, increasing the culture density can trigger internal struggles between aquaculture objects, including competition for food and space, which will negatively affect their survival, growth, physiology, behavior and accumulation of nutrients, in addition, the increase in culture density will also exacerbate the deterioration of water quality.
In shrimp and crab culture, the culture density also affects their survival rate, growth, breeding size and quality, and also affects the aquaculture environment.
Some studies have found that the survival, wet weight-specific growth rate, body length and weight gain of Penus vannabine decreases with increasing culture density.
The survival rate and weight gain of Chinese shrimp, Penaeus monodon and Protocrayfish cruzi were also significantly affected by the culture density.
The feeding intake, behavior, physiological and biochemical indexes and immune-related enzyme activities of shrimp and crabs at culture density also had a significant impact, thereby affecting their breeding specifications and nutrient accumulation.
With the increase of breeding density, oxygen consumption, metabolic waste discharge and residual food in the water body will also increase, resulting in an increase in the concentration of organic matter and harmful substances (such as nitrite, ammonia nitrogen, etc.) in the water body, posing a threat to the health and growth of aquatic animals.
One study found that when Penaeus vannabine was cultured indoors, the dissolved oxygen (DO) content and pH of the culture water decreased significantly as the density increased, and the total nitrogen (TN) and chemical oxygen demand (CODMn) increased significantly.
For the culture of Chinese river crab, different breeding densities will affect its breeding specifications, edible part content, biochemical parameters in serum, and various components in muscles and organs.
Therefore, culture density is regarded as a key factor in shrimp and crab culture, and inappropriate density may adversely affect the growth, nutrient accumulation, physiological immunity and aquaculture environment of shrimp and crab.
The range of suitable culture densities may vary depending on the region and culture conditions, so further research is needed to determine the appropriate density range.
The increase in culture density may adversely affect the breeding size, individual growth rate and nutrient accumulation of Chinese river crabs.
The group of 800 crabs per mu showed relatively high growth multiple and average growth rate. The group of 1200 crabs per mu showed relatively large average breeding size, the highest mean FC, and the minimum mean CV value among the growth indexes.
The crab groups of 1400 and 1600 per mu showed small breeding size, relatively low growth multiple and average growth rate, and there was a significant or very significant negative correlation between breeding density and crab body weight (BW), overall muscle weight (GMBW), overall shell weight (GMCL) and overall shell weight (GMCW).
This suggests that high culture densities may adversely affect the growth of Chinese river crabs.
Therefore, it is recommended not to set the breeding density more than 1200 crabs per mu when the size of button crabs is 160~220 / kg.
So what will happen to the water environment of cultivating Chinese river crabs in the change of breeding density?
The aquatic environment of Chinese river crab culture is affected by the density of pond culture
Good water quality conditions are the basic prerequisite to ensure the success of aquaculture, Jiangxi Province is located in the south of China, with the country's largest freshwater lake - Poyang Lake, which makes Jiangxi Province have high-quality water resources, providing great potential for the development of Chinese river crab culture.
In the aquaculture process, culture density is a key influencing factor, in general, high farming density may lead to the problem of deterioration of water quality, deterioration of water quality will adversely affect the feeding, growth and survival of shrimp and crabs, which in turn leads to a series of problems such as small size, poor quality, and low yield per unit of river crab.
As the culture density increases, the dissolved oxygen (DO) and pH in the water decrease, while the content of ammonia nitrogen, nitrous nitrogen, nitrate nitrogen, total nitrogen, total phosphorus and permanganate index increases.
Under different pH, salinity and water temperature conditions, the physiological and biochemical indicators of shrimp and crabs will also change significantly, which may trigger immune stress in severe cases.
Maintaining suitable farming density and water quality conditions is crucial to the success of the Chinese river crab aquaculture industry, and Jiangxi Province is well equipped to support the healthy development of this industry due to its geographical location and abundant water resources.
In the analysis of the nutritional composition of Chinese river crab, the water, fat and protein contents of muscle tissue and liver and pancreatic tissue showed some significant characteristics.
For the muscle tissue of Chinese river crab, the mean moisture content ranged from 77.68% to 79.63%, crude fat content between 2.86% and 4.09%, and crude protein content between 13.43% and 14.56%.
For hepatopancreatic tissues, the mean water content ranged from 39.27% to 51.67%, crude fat content between 38.97% and 51.55%, and crude protein content between 5.67% and 6.59%.
Under different breeding densities, the crude protein and crude fat contents of muscle tissue and liver and pancreatic tissue of Chinese river crab showed obvious changes.
Specifically, crude protein and crude fat content were highest in group crabs with 1,000 and 1,200 individuals cultured per mu, while those with 1,400 and 1,600 per mu were lower.
At the same time, the coefficient of variation showed that the variability was the smallest among group crabs with 1200 crabs cultured per mu, while the variability was greater in group crabs with 1400 and 1600 crabs cultured per mu.
In addition, in terms of amino acid composition, 17 amino acids were detected in muscle tissue and liver and pancreatic tissue, of which the content of Glu and Asp was relatively high, and in muscle tissue, the total amino acid content (TAA), essential amino acids (EAA) and non-essential amino acids (DAA) reached the highest value in group crabs with 1200 farmed per mu, and decreased in group crabs with 1400 and 1600 farmed per mu
The EAA/TAA ratio was highest in group crabs with 1000 reared per acre and lowest in group crabs with 1600 reared per acre.
The DAA/TAA ratio was highest in the group crab group with 800 animals cultured per mu and lowest in the group crab group with 1400 animals cultured per mu.
Correlation analysis showed that there was a significant negative correlation between breeding density and TAA, EAA and DAA content in muscle tissue, that is, these contents decreased as the density increased.
The EAA/TAA and DAA/TAA ratios in hepatopancreatic tissues also decrease with increasing density.
These data provide important information about the nutrient composition and amino acid composition of different tissues of Chinese river crabs, as well as the trends of these components under different breeding densities.
Chinese river crab is an important freshwater farmed crab that is loved for its high nutritional value.
Aquaculture technology has developed rapidly in China, but suitable culture patterns vary from region to region and conditions, and the size and density of button crabs are key factors, and the increase in culture density may have a negative impact on crab growth and water quality.
The analysis of nutrient composition and amino acid composition revealed the characteristics of different tissues of crabs, providing important information for healthy farming, and Jiangxi Province has become an important production area for Chinese river crabs, but more systematic research is still needed to support the sustainable development of the industry.