Before reading this article, please click "Follow" to facilitate your discussion and sharing, bring you a different sense of participation, thank you for your support
Wen 丨 Yujie History Museum
Editor丨Yujie History Museum
Grass carp is the main force of China's freshwater aquaculture industry, occupying an important position, widely distributed in the northern and southern waters of China, and has become one of the largest fish in the world in terms of production and consumption.
According to statistics, the annual output of grass carp has reached tens of thousands of tons, accounting for about part of the country's freshwater fish aquaculture production, and the market sales have exceeded 100 million yuan.
The amount of grass carp produced in China is about tens of thousands of tons every year, and grass carp is known as "cattle and sheep in the water" with its unique herbivorous habits, which efficiently converts plant protein into high-quality animal protein.
There are many types of microecological preparations, including nitrifying bacteria, photosynthetic bacteria, Bacillus subtilis, actinomycetes, lactic acid bacteria, yeasts, streptococcus, and microbial flora.
They have a number of important functions, such as improving water quality, reducing ammonia nitrogen content in aquaculture water, inhibiting the growth of pathogenic bacteria, improving the disease resistance and immunity of animals and plants, and promoting the growth of aquaculture objects.
The widespread application of microecological preparations in aquaculture has yielded remarkable results, especially in improving water quality and as feed additives.
This field shows great development value and broad application prospects, and is expected to provide strong support for the sustainable development of aquaculture.
Then, let's follow Yujie to see how the growth performance of grass carp is affected by microecological preparations during the feeding process.
Freshwater culture of grass carp
Grass carp, commonly known as squid, oil squid, grass squid, white squid, grass carp, grass root northeast, mixed seed, etc., belongs to the order Cyprinidae, cyprinidae, Yaroth subfamily, grass carp genus, and blue carp, toadfish, eel and called the four major freshwater fish in the mainland.
The body of the grass carp is slightly cylindrical, the head is slightly flattened, the tail is flattened, the mouth is curved, no need, the upper collar is slightly longer than the lower collar, the body is light tea yellow, the back is blue gray, the abdomen is gray, the thorax and ventral fins are slightly grayish-yellow, and the other fins are light gray.
Inhabiting rivers and lakes in plain areas, generally prefer to live in the middle and lower layers of water and nearshore aquatic grass areas, sexually active, fast swimming, often foraging in groups, typical herbivorous fish, wintering in the main stream or deep water of lakes, broodstock have retrospective swimming habits in the reproductive season.
Grass carp has delicate flesh, more bone spurs, rich in nutrition, and is very suitable for cutting knives to make chrysanthemum fish and other shapes, which are deeply loved by the public and are popular in the plains from Guangdong to Northeast China except Xinjiang and the Qinghai-Tibet Plateau.
Grass carp is rich in unsaturated fatty acids, which are beneficial to blood circulation and are good food for cardiovascular patients, grass carp is rich in selenium, and often eaten has anti-aging and beauty effects.
And also has a certain prevention and treatment effect on tumors, for people with thin bodies and loss of appetite, grass carp meat is tender but not greasy, can be appetizing and nourishing.
Because of its simple diet, wide range of food sources, rapid growth and high yield, grass carp is often used as the main stocking object for pond culture and lakes, reservoirs and rivers.
Since the success of artificial induction and fertilization hatching technology, the source of fry and fingerlings is easy and has become the main intensive culture object in the mainland, and grass carp has also been used by fishermen to stock it outside for one or two years because of its ability to remove grass in water bodies and along the coast, in order to clear land and weed.
Grass carp is often mixed with abalone and toad, and grass is put into grass to raise grass carp, and the feed left in the water and the waste excreted by grass carp are used to cultivate plankton as fodder for abalone and toad.
With the continuous expansion of aquaculture area and production scale, as well as the sharp increase of aquaculture output and the continuous improvement of the degree of aquaculture intensification, aquaculture production itself has produced a certain degree of pollution to the environment of aquaculture waters.
Aquaculture water bodies often decay and decomposition of bait, aquatic biological excrement and corpses in the pond, resulting in deterioration of water quality, abnormal changes in nutrients, etc. in the water and harmful substances.
For example, ammonia nitrogen, nitrite, etc., biological oxygen consumption, ammonia nitrogen, nitrite, sulfide and other water quality indicators are prone to exceed the standard, causing the disease and even death of fish, shrimp and other aquaculture objects, which seriously hinders the development of aquaculture in mainland China.
In the traditional freshwater aquaculture process, the classical theory believes that "fish farming first raises water", which is actually to achieve the balance of the ecosystem to ensure that the various indicators in the water are within the appropriate range for the survival of farmed animals.
Taking pond culture as an example, in a reasonable process, in addition to the feed, fertilizer and fishery drugs input outside the system are converted into aquaculture products or non-aquaculture products that can be exported to the export system, there are still a considerable amount of material and energy residues in the system.
The successful utilization and transformation of these substances and energies by the biological chains of the system mainly depends on the following two aspects: first, the stability and self-purification capacity of the water body, and second, whether the input residual substances and energy exceed the water load.
So, what role do probiotics play in water quality regulation?
Application of probiotics in aquaculture water quality regulation
A clear definition of microecological preparations, i.e. live bacterial preparations containing a large number of beneficial bacteria made according to the principles of microecology, sometimes containing their metabolites and the addition of beneficial growth promoting factors.
These microecological preparations have the function of maintaining the microecological balance of animal and plant bodies as well as human beings and their internal and external environments, or adjusting their microbiotic disorders, improving their health level and protecting the environment.
Its mechanism of action is mainly through the production of a variety of enzymes that can degrade organic matter, including proteases, amylase, lipase, etc., which can directly use nitrates and nitrites in water to fight the growth of pathogenic bacteria.
By adding two kinds of bacillus into the aquaculture water body, the concentration of ammonia nitrogen and nitrite nitrogen was successfully reduced, and the water quality of the aquaculture water body was significantly improved.
A strain was screened and named "Bacillus cereus", which was tested to have an ammonia nitrogen removal rate of up to as high as Shi under optimal conditions, and the removal rate was also achieved by using Bacillus subtilis to purify shrimp nursery wastewater.
After the application of Bacillus monodon strains in P. monodon culture ponds, it was found that the survival rate of P. monodon increased, the proportion of Vibrio luminescent in the sediment at the bottom of the pond decreased, and the number of other pathogenic bacteria in the water was also minimized.
Researchers believe that Bacillus subtilis can inhibit the growth of Vibrio hastello, the pathogen of Penaeus monodon blackgill disease, and long-term use can significantly reduce the lethality of shrimp.
It should be pointed out that Bacillus subtilis is an aerobic gram-positive bacterium, which is non-toxic and harmless to humans and animals. It is widely distributed in nature, and it is allowed to be used as a feed additive at home and abroad.
After the proliferation of Bacillus subtilis in water, the extracellular enzymes produced can decompose organic matter such as starch, protein and fat in the aquaculture water and sediment, thereby reducing the eutrophication degree of the aquaculture water and reducing the formation of sediment.
In this decomposition process, part of the organic matter is converted into bacterial somal matter, and most of it is used for bacterial life activities, including the release of metabolites such as ammonia, nitrogen and carbon dioxide from the water into the air, further reducing the concentration of ammonia nitrogen and nitrogen in the water.
So under the influence of microecological preparations, what about grass carp farming?
The water quality of grass carp culture is affected by Bacillus bacillus
Ammonia nitrogen in water mainly comes from the accumulation and decay of aquatic animal and plant corpses, excreta and remaining food, in which nitrogen-containing organic compounds will be decomposed into ammonia nitrogen small molecule inorganic matter by saprophytic bacteria.
The effect of ammonia nitrogen on aquatic animals is mainly reflected in the invasion of mucosa, especially the epidermis and intestinal mucosa of fish gills, and then affects the nervous system, resulting in damage to the liver and kidney system of aquatic animals, causing hyperemia of body surface and internal organs, muscle hyperplasia and tumors, which may eventually lead to hepatic coma and death.
Even at low concentrations of ammonia nitrogen, long-term exposure can cause damage to gill tissue, manifested as bending, sticking, or fusion of small pieces of gills.
Therefore, reducing the concentration of ammonia nitrogen in aquaculture water is of great significance for the survival and growth of aquatic animals.
Bacillus preparations added to water require a certain period of time to achieve the effect of reducing ammonia nitrogen, and when Bacillus preparations are added to water and feed at the same time, the effect of reducing ammonia nitrogen is more significant.
The strains of Bacillus halotolerum with high degradation ability for ammonia nitrogen were isolated and screened, and the initial concentrations of ammonia nitrogen were several sums under simulated freshwater and seawater conditions, and the degradation rates of ammonia nitrogen were respectively.
These test results show that the addition of Bacillus can effectively reduce the ammonia nitrogen content in the water body, proving that Bacillus participates in the nitrogen cycle in the aquaculture water body.
On the one hand, Bacillus may convert ammonia nitrogen into its own nutrients through assimilation, and on the other hand, it may reduce the ammonia nitrogen content in the aquaculture water by other means, such as nitrification.
At the same time, adding Bacillus preparations to water and feed can obtain better ammonia lowering effect, because Bacillus can produce a variety of digestive enzymes, such as amylase, protease, lipase, after entering the digestive tract, to assist the body to digest organic matter, improve the conversion efficiency of food, and reduce the excretion of organic matter.
It can also inhibit the decomposition of organic matter by intestinal bacteria into harmful substances such as ammonia nitrogen, reducing the ammonia nitrogen content in fish excreta.
Therefore, compared with adding microbial water purification agents to water alone, adding bacillus preparations to water and feed at the same time is more effective.
The addition of Bacillus braceus preparations in water had no significant effect on nitrous nitrogen content, and the addition of Bacillus preparations to water and feed significantly increased the nitrosagen content.
This result is inconsistent with previous studies, which isolated Bacillus subtilis in aquaculture water and sediment, and the results showed that Bacillus subtilis can quickly and effectively reduce nitrite content in water, and the removal rate is above
When the nitrogen removal characteristics of Bacillus aerobic denitrifying were strained, it was found that even if the initial nitrogen concentration was higher, the maximum degradation rate could be achieved.
The main reason for the inconsistency of the results may be that when the predecessors studied the role of Bacillus in purifying water quality, they provided the most suitable conditions for bacterial growth, so the degradation effect of nitrite was better.
However, this test was carried out in a water tank, and the water was not changed during the entire experiment, the temperature was low, and the Bacillus blossomus preparations added were also a single flora, so the effect of reducing nitrite nitrogen was not good.
As for the significant increase in nitrous nitrogen content caused by the addition of Bacillus preparations in water and feed, the main reason may be that the nitrification effect of Bacillus braceus in fish is significantly enhanced compared with that in water, and more ammonia nitrogen in feed is converted into nitrite nitrogen, resulting in an increase in nitrite nitrogen concentration.
Grass carp is one of the main forces of China's freshwater aquaculture industry, with an important position, with an annual output of tens of thousands of tons and market sales of more than 100 million yuan.
Grass carp is known as "cattle and sheep in water" for its efficient plant protein transformation ability, and its biological characteristics include extensive adaptation, preference for aquatic grass areas, and rapid growth, making it an ideal choice for freshwater fish farming.
With the expansion of aquaculture scale and the problem of water pollution, the application of microecological preparations such as probiotics and Bacillus in water quality regulation has become an important research field.
Studies have shown that Bacillus preparations can effectively reduce the ammonia nitrogen content in aquaculture water, especially when added to both water and feed.
In the case of nitrous nitrogen, results are inconsistent due to differences in conditions and may be related to strains, water environments, and experimental conditions.
Grass carp culture has great potential, but effective water quality management measures, including the application of microecological preparations, are needed to ensure sustainable development and meet the growing market demand, and these studies provide important references and directions for the future development of freshwater aquaculture.