Prevention and treatment of liver disease of farmed grass carp

I. the main functions of the liver

The liver of grass carp, located in the abdominal cavity, is the largest digestive gland, roughly divided into the left and right lobes, the right lobe is larger, extends to the first bend of the intestine, and occupies all the space of the first bend. The liver is mainly composed of hepatic lobules, and pancreas is scattered in the liver tissue. The main functional unit of hepatic lobules is hepatocytes, and the main functions of liver are:

1. Secrete bile: can emulsify fat and promote the digestion and absorption of fat. The gallbladder is the place where bile is stored.

2. Metabolic function: various nutrients absorbed from the digestive tract enter the liver through the portal vein and are processed and processed in the hepatocytes to synthesize important substances needed by the body, such as albumin, fibrin and some globulins. Hepatocytes can also synthesize and decompose glycogen and participate in the metabolism of vitamins and hormones.

3. Detoxification: some toxic substances absorbed by the intestinal tract and toxic substances metabolized by the body are transformed or combined by hepatocytes to eliminate or reduce toxicity.

4. Defense function: liver macrophages have active phagocytosis ability, which can eliminate bacteria, harmful substances and aging white blood cells.

Second, how liver disease is caused

From the perspective of pathology, the causes of grass carp liver disease can be divided into two categories, one is primary liver disease, which is mainly caused by bacteria and viruses, and the other is secondary liver disease. mainly caused by other pathological changes, malnutrition and drugs. From what we have learned so far, the occurrence of primary liver disease is rare, and there are no reports of successful isolation of pathogenic bacteria or viruses of grass carp liver disease, such as human hepatitis A virus, hepatitis B virus, etc.), that is to say, at present, the liver disease is mainly secondary liver disease, from our investigation in the areas with high incidence of liver disease, we believe that there is no epidemic of liver disease. The main factors leading to the high incidence of grass carp liver disease are as follows:

1. Drug-induced: one of the main functions of the liver is detoxification. At present, farmed grass carp are basically mixed culture, and most of them stay at a low level of culture, the management technology of the pond is relatively backward, in disinfection treatment and prevention of parasites, basically are the use of some toxic and side effects of drugs (for example, disinfection is mostly chlorine-containing agents, after the use of water will produce carcinogenic amines Pyrethroids and organophosphorus are used to kill insects, which are highly toxic to fish). After the use of these drugs, if the frequency or dose is higher, it will increase the burden of the liver and cause damage or even necrosis of liver cells. resulting in liver lesions.

2. Environmental causes: in some aquaculture areas, due to the extreme deterioration of the water environment and the unreasonable design of the pond water system, toxic and harmful substances in the water environment are often inadvertently added to the pond (such as adding water), resulting in the deterioration of the water quality in the pond. increase the burden of detoxification on the liver. At the same time, due to the backward management level of the pond, especially the extensive use of organic fertilizer and the unreasonable use of inorganic fertilizer, as well as the non-cleaning or timely cleaning of the residues in the pond, the water body of the pond can worsen, make the toxic and harmful substances in the pond water rise, make the fish in a bad environment for a long time, and make the detoxification function of the liver in a state of high load for a long time. Cause damage or even necrosis of hepatocytes, resulting in liver lesions.

3. Feed causes: grass carp basically feed on aquatic grasses in natural water bodies, and can swallow some water fleas at the same time, but under the condition of artificial culture, it is basically impossible to feed aquatic plants, but with terrestrial Gramineae plants or artificial bait instead. In some areas, it is basically artificial bait. Because the economic value of grass carp itself is not high, the artificial bait used is also some low-priced varieties, and the variety of feed used is relatively single, especially in some areas, agricultural and sideline products are used, especially rapeseed meal and cotton meal are widely used, and in the process of use without detoxification, a large number of toxic and harmful substances are eaten by grass carp, thus increasing the burden of grass carp liver and causing liver pathological changes.

How to prevent the occurrence of liver disease in grass carp

To prevent the occurrence of liver disease in grass carp, we should mainly start from the following aspects:

1. Improve the culture environment: pay attention to the change of water source and pond water body, add new water and use microecological agents to regulate water quality at any time.

2. Rational use of drugs: use some less toxic drugs for the prevention and treatment of fish diseases, use drugs with definite efficacy, and reduce the frequency of use, especially in prevention, we should not only consider the cost of drugs.

3. Rational feeding: with the combination of grass feeding and artificial bait, properly change the variety of feed, especially when feeding agricultural by-products, we must pay attention to the performance of the product, and those containing toxic and harmful substances should be detoxified.