In the process of grass carp breeding in recent years, the incidence of grass carp "liver and gallbladder syndrome" is getting higher and higher, resulting in a decline in the bait coefficient in the breeding process, a slowdown in growth rate, a decline in the physique and immunity of fish, easy to appear secondary bacterial diseases, the use of irritating disinfectants and insecticides, prone to an increase in the amount of death, the decline in the anti-stress ability of fish, fishing and transportation, prone to death. These have caused significant losses to farmers.
"Hepatobiliary syndrome" this kind of mention is mainly in the grass-roots breeding process of everyone for the fish liver and gallbladder lesions of the popular name, in fact, in the process of breeding in the process of fish liver and gallbladder lesions, the biggest threat, the most important problem is fatty liver. The main symptoms include that the scales are easily shed, and anatomically shows that the liver is significantly enlarged compared to the normal liver of fish of the same size.
Fig. 1 Shows grass carp liver and gallbladder lesions, which are earthy yellow
Fig. 2 Shows the whitish tail fin of a grass carp
This paper mainly discusses the pathogenesis and prevention and control measures of grass carp fatty liver, and provides a reference for farmers to prevent and control the disease in the process of breeding.
Mechanism of development of fatty liver
Fatty liver, simply put, is. There are two main reasons for the continuous accumulation of fat in the liver: one is that there are too many sources of fat in the liver of a fish, and the other is that the liver's ability to transport fat out is not enough, resulting in the accumulation of fat in the liver.
The source of liver fat in fish is mainly the following aspects, one is that the oil in the feed is absorbed into the blood after the product digested by the digestive tract, transported to the liver through the circulatory system, and synthesized in the liver again. Secondly, the amino acids formed after digestion by excess sugars and proteins ingested into the body by fish are converted into fat in the liver.
It is generally believed that fat accumulated in the liver is transported to the bloodstream in the form of lipoproteins, which are then transported to other tissues for reuse or storage in adipose tissue. If the synthesis of lipoproteins in aquatic animals is insufficient, the fat in the liver cells cannot be transported out in time, which will cause fat to accumulate in the liver.
The imbalance of the energy-to-protein ratio in the feed, the incomplete ratio of nutrients and the excessive feeding during the breeding process are the most important causes of fatty liver in fish.
Bile is secreted by the liver, collects through the bile ducts in the liver to the gallbladder, and finally passes through the catheters into the digestive tract. In the process of the formation of fatty liver culture in grass carp, the cell tissue with the accumulation of fat, the volume continues to increase, once the nearby intrahepatic bile ducts are squeezed, it will cause the liver to secrete bile discharge obstruction, when the squeezed bile ducts reach a certain number, bile stasis in the liver tissue will be stained green, forming a green liver.
Figure 3 Shows the green liver of grass carp
Effects of hepatobiliary lesions on other parts of the body
1. The role of the liver in the metabolism of fish body substances
In the life activities of fish, the liver is the center of material metabolism and transformation, its main functions include protein synthesis and decomposition in the body and the formation of ammonia, but also one of the main places for the synthesis of fat in the body, bile is also secreted by the liver, the liver through biochemical reactions in the body of toxic substances into non-toxic substances.
At the same time, the liver is also an important blood storage organ in the body, when the fish body loses too much blood, the stored blood enters the body's circulatory system.
2. The impact of liver lesions on the health status of the whole body
It is precisely because the liver undertakes such an important function in the body's life activities, so its health status and the overall body's constitution and immunity are closely related, as soon as the liver has a problem, the fish's constitution and immunity inevitably decline, and the fish is prone to secondary gills, red skin and other diseases.
In the treatment process of fish disease, it is also necessary to pay attention to the fact that aquatic animals are an organic whole, and the functions of various organs have mutual influences, such as the common liver and gallbladder complicated by bacterial gills, and the treatment experience at the grass-roots level shows that repeated elimination, the results will often be counterproductive, because the elimination is essentially the control of pathogenic bacteria on the surface of the body and the water environment, and the control of the ulceration of the lesion site continues to develop, however, the existing ulcerated parts of the gills need to rely on their own body to repair themselves, the fish body has concurrent liver and gallbladder problems, and the physique declines. The healing time of the ulcerated lesion is prolonged.
When the liver and gallbladder problem is serious, the fish's adaptability to the external environment and anti-stress ability will decrease, and the use of irritating disinfectants will increase the amount of death.
Fig. 4 Shows that grass carp liver and gallbladder disease are complicated with gills
Prevention of fatty liver
(1) Feed selection
In the process of feed selection of farmers, there are the following misunderstandings
1. The higher the crude protein content of the feed, the better the quality of the feed?
The growth of the fish body is mainly achieved by continuously synthesizing body proteins, and the amino acids that synthesize the body's proteins mainly come from the proteins in the food they eat. The protein in the feed is digested in the fish digestive tract to absorb amino acids, which are absorbed into the fish body and used to synthesize their own proteins, which is affected by the overall proportion of amino acids, and the level of utilization depends on the lowest proportion of amino acids, which is what we often call the barrel principle.
If the crude protein content in fish feed is too high, but the proportion of protein used to synthesize its own body protein is low, then the protein in the feed is digested and absorbed, and more is converted into fat accumulated in the liver or mesentery, resulting in fatty liver of fish.
Figure 5 shows that grass carp has a serious accumulation of visceral fat
In the protein of grass carp feed, the proportion of plant protein used is larger, and what is easily lacking in plant feed is lysine. Its most important physiological function is to participate in the synthesis of body proteins and increase the deposition rate of proteins in the feed. The growth rate of fish is closely related to it.
Therefore, in the process of feed selection, we need to pay attention not only to the crude protein content, but also to the content of lysine on the feed label.
Generally, the content of lysine will be marked on the feed label
Figure 6 is the feed label
The appropriate levels of lysine in grass carp feed can be referred to the table below
2, the faster the growth rate, the better the quality of the feed used?
Growth rate is indeed an important parameter to measure the quality of feed, but we can not only pay attention to the growth rate of feed in the process of breeding, but also pay attention to the health of the fish intestine and liver and gallbladder during the feeding process.
Because the growth rate and the health of the fish itself is a contradiction, the faster the growth rate, the more it violates the natural growth law of the fish, and the long-term process of fattening and fattening will lead to the decline of the fish's own physique and immunity, and the risk of diseases such as hepatobiliary disease will become higher and higher.
Therefore, in the process of comparing feed quality, it is necessary not only to compare the growth rate, but also to compare the health status of the fish during feeding. Regular sampling dissection to observe the health of the liver, gallbladder and intestines of the fish.
3. The lower the feed price, the lower the cost of breeding?
In the process of actual breeding, there are many farmers who have such a concept that the lower the price of feed, the lower the cost of breeding, which is actually a misunderstanding, because feed is essentially the means of production in our breeding process, and the ultimate impact on the profit margin of breeding is the cost of feed per kilogram of fish rather than the price of feed itself.
In the actual breeding process, in most cases, the relatively low price of low-grade materials due to the cost of raw materials used by themselves, compared with the use of high-grade materials in the breeding pond mouth, more likely to appear the problem of hepatobiliary disease.
(2) Misunderstandings in the feeding process
When the fish price market is good, many farmers have the psychology of grasping feeding and letting their own farmed fish go to market in the morning, and many feed salesmen consider their own interests, and they all hope that farmers will use more materials, instill enough feeding to farmers, list fast, catch up with high prices, shorten the breeding cycle, and accelerate the return of funds. Not to mention whether the fish price market is difficult to predict, the breeding cycle is short, and the fish price must be high when it comes out of the pond, whether it is consistent with the real market situation in the market, but.
If the diseased dead fish eventually need to stop feeding or feeding bait and other physical adjustment, the final time to reach the same market specifications will not be earlier than the breeding pond that controls the feeding volume during the peak feeding period, but because of the cost of dead fish and medication, the final breeding cost will increase.
Therefore, in the peak period of feeding, in order to reduce the load of fish liver and gallbladder, it is necessary to properly control the amount of feeding, it is best to plant green feed such as elephant grass on the pond base, stop feeding for 1 day per week during the peak feeding period, and use green feed for feeding, which can not only supplement vitamins, but also reduce the pressure of fish liver and gallbladder metabolism.
(3) Regularly supplement the anti-fatty liver factor in the feed
In the process of farming, in order to reduce the incidence of fatty liver, it is possible.
B vitamins in the choline, biotin, inositol, vitamin B, etc. are involved in the fat metabolism in the fish, choline is involved in the synthesis of lecithin, promote the transport of fat in the liver, the lack of fat metabolism in the fish will cause fat metabolism disorders in the fish, resulting in the accumulation of fat in the liver.
Betaine hydrochloride has the function of supplying methyl, which can provide methyl for other substances involved in the process of fat metabolism, so it can accelerate the decomposition of fat and reduce the deposition of fat in the liver and body.