China Aquatic Products Channel reported that hepatobiliary syndrome is one of the more frequent fish diseases that have occurred in the process of grass carp farming in recent years, and the impact on grass carp farming production is becoming more and more serious. The symptoms of hepatobiliary syndrome are similar in appearance to rotten cheek disease, enteritis, and red skin disease, and are easily misdiagnosed by fishermen as the traditional grass carp disease, resulting in incorrect medication, which not only increases the production cost but also delays the treatment of fish disease, and brings great economic losses to fishermen.
After grass carp suffers from hepatobiliary syndrome, its liver, gallbladder, gills, intestines and other organs, body shape and activity will be abnormal, which is manifested in the following seven aspects:
1, rotten gills, but different from the general bacterial gill disease. Mild grass carp gill filament dark red, congestion and edema; severe grass carp gill filament end rot and split, some fish gill filament has green mud moss, there is no obvious "open skylight" phenomenon. The incubation period is longer than that of bacterial gill rot.
2. Intestinal inflammation. Grass carp in the late stage of the disease is more similar to the general symptoms of bacterial enteritis disease, there is a small amount of blood in the intestinal wall, there is no food in the intestine and is full of yellow mucus, the anus is red and swollen, and the fish in the early stage of the disease may have a small amount of food in the intestine, and the disease is mild.
3. The liver of the diseased grass carp is hematomatous, yellow, whitish or locally green, becoming a flower liver, with high fat content, brittle and fragile texture, and loose tissue.
4. The gallbladder of diseased grass carp is enlarged and full, the bile is rich, green or dark green, and a small number of severe grass carp will have a small amount of bile spillage before death, spreading to adjacent internal organs or muscle surfaces.
5. The body color of the diseased grass carp is dull, the local scales on the back and abdomen are loose and obscure, a few back muscles are rotten, and some of the diseased grass carp are hyperemic on the chest and abdomen, orbit, gill cover, and fin base; especially the base of the tail fin is hyperemic, the eyeball is prominent and accompanied by blood capillaries; some of the fins are decayed and forked at the ends, with the tail fin being the most serious.
6. The body shape is not normal, it is shorter and thicker than normal fish, the abdomen is expanded, and the early and late diseased fish have different degrees of ascites phenomenon, and the fat (oil) in the body can be seen after dissection.
7. Abnormal activity, the diseased fish in the pool drifted to the edge of the pool at the beginning of the disease, the reaction was slow, the amount of food was reduced, there was no obvious change in the surface of the sick fish, and there was channeling or spasm after feeding, while the severe grass carp almost did not eat, swam alone at the edge of the pool, and died in the early morning.
This disease mostly occurs in the intensive ponds of grass carp that are mainly fed with compound feed, mainly endangering first- and second-instar grass carp fingerlings. The epidemic season mainly occurs from May to October, and has become widespread throughout the country.
During the cultivation of first-instar grass carp fingerlings, the onset of the disease is mostly in late August or early September, and the disease can last for 30-40 days, and the mortality rate is 20-40%.
Second-instar grass carp species develop diseases one after another for 20-30 days after eating inferior compound feed, and the disease can last for 1-2 months.
Mortality is related to the extent of morbidity, the pond environment and the treatment measures taken, mainly affecting grass carp weighing 100-250 g, with mortality rates of up to 30% or higher in severe cases.
There are many direct causes that can cause grass carp to suffer from hepatobiliary syndrome, and there are mainly the following five points from the feed:
1. Add forbidden growth promotion additives such as quinoethanol to the feed, and the content is high, resulting in the growth of fish fingerlings too fast, the fat content of the liver is high, the formation of fatty liver, and the weakening of the function of the liver.
The liver is the largest gland, which, in addition to secreting bile, helps digestion and absorption, also synthesizes the absorbed substances into glycogen, fat and protein. In addition, it plays an important role in intermediate metabolism, detoxification, storage of vitamins and the production of immune substances.
However, once the fish species form a fatty liver, the biliary ducts in the liver are blocked or compressed, the secretion, transportation of bile and the discharge of bile from the gallbladder to the intestine will have different degrees of obstacles, and the digestion and absorption of food in the intestine of the seedlings will be seriously affected, which will eventually lead to the metabolism and supply of various nutritional elements, especially fat, fat-soluble vitamins and B vitamins, etc. Lesions will occur in the seedling fins, gills, muscles, etc., the liver function will gradually be lost, and its physique and disease resistance will decline rapidly.
2. Indiscriminate use of drugs, such as low doses, long-term addition of furazolidone, chloramphenicol, sulfonamides, etc. to the feed, or the use of fish drugs with large side effects and high residues, such as dimethoates, copper sulfate and other drugs, resulting in liver damage.
3. The imbalance of various nutrients in the feed, such as high protein content, high carbohydrate content or long-term use of animal fats and highly saturated fatty acids, resulting in too high feed energy protein ratio.
High protein feed is easy to induce liver fat accumulation, destroy liver function, interfere with the normal physiological biochemical metabolism of fish; carbohydrate content is too high, will cause fish sugar metabolism disorders, causing visceral fat accumulation, hindering normal function, its main lesion site is the liver, a large number of liver sugar accumulation and fat infiltration, resulting in hepatomegaly, fading color, dull appearance, serious fatty liver can also cause liver lesions, so that the liver loses normal function; fat content is too high, exceeding the needs of grass carp, resulting in fat deposition in the fish body too fast, Especially in the liver, it is enriched and a fatty liver is formed, which leads to a weakening of the function of the liver and a decrease in the body's resistance to diseases.
4. The choline content in the feed is insufficient, which cannot meet the needs of fish species, resulting in slow growth of fish, disordered fat metabolism, and the formation of fatty liver.
5. Feed mildew or fat oxidation produce toxic and harmful substances, such as aflatoxin, which will damage the liver and other internal organs of the fish to varying degrees. In addition, the excessive density of aquaculture, the deterioration of the water environment, the excessive concentration of ammonia nitrogen and nitrite in the pond water, and the large number of pathogenic bacteria can also accelerate the spread of this disease and the deterioration of the disease.
When choosing feed, farmers should choose manufacturers with good reputation and certain technical strength, pay attention to brand and quality, and avoid making it up and coveting cheap.
High-quality feed is not only of good raw material quality but also comprehensive and reasonable nutrition, which is more suitable for the needs of grass carp at all stages of growth. In actual production, it is best for farmers to choose feeds with different protein content at different stages according to the growth status of grass carp in their ponds, such as:
Second-instar fingerlings and commercial fish are cultured using compound feeds with a protein content of 26-28%.
Of course, if the feed amino acid ratio is balanced, in order to increase the yield, high-protein feed can be fed.
The proportion and stocking density of filter-feeding fish (such as silver carp, silver carp) and grass carp and other feeding fish should be scientific and reasonable, and farmers should summarize the breeding experience and lessons year by year, and gradually optimize the breeding mode.
Scientific feeding, do not force feeding, excessive feeding. In particular, the early stage of the first-instar fish fingerling culture stage should be fed in an appropriate and even manner, and the feeding rate should be about 4% to avoid individual size differentiation.
Pay attention to the combination of refined feed and green feed, grass carp fingerlings about two inches, start feeding a certain amount of duckweed; second-instar grass carp fingerlings in late March to early May in the appropriate amount of rye grass feeding. Timely flushing or sprinkling quicklime and other regulation of water quality, reduce the content of ammonia nitrogen and nitrite, improve the water environment for the survival and growth of fish, the transparency of the water body is maintained at 25-30cm, and the aquaculture water body should be "fat and tender".
4. Regular use of quicklime, bromochlorohydantoin or chlorine dioxide and other drugs to kill harmful bacteria in the aquaculture water body, the drug prevention dosage is the same as the therapeutic dose, should not be halved, so as to avoid bacteria drug resistance.
Do not add drugs that damage the liver of fish to the feed in low doses for a long time, such as furazolidone, chloramphenicol, sulfonamides, quinoethanol, tetracycline antibiotics, etc. It is necessary to achieve rational use of drugs, do not use fish drugs with large side effects and high residues, such as bromethrin, dichlorvos, dichlorvos, dimetha, copper sulfate, enemy killing, lindane, etc., and can not use national prohibited fishing drugs or pesticides instead of fishery drugs to apply in water bodies.
During the breeding period, feed and early and late patrols of the pond to observe the feeding and activity of fish, pay attention to whether there are abnormalities; in addition, every half a month to the pond grass carp a sampling examination, observe their body shape, body surface and liver and gallbladder and other internal organs are abnormal, so as to achieve early detection and early treatment.
Because many farming factors are uncontrollable, sometimes even if the best preventive measures are achieved, hepatobiliary diseases will occur. As long as the cause of the disease is scientifically diagnosed, combined with effective treatment measures, it can also be cured in time.
When it is found that such diseases occur in farmed grass carp, it is first necessary to comprehensively analyze the water quality conditions, feed quality, dosage forms and frequencies of drug application, nutritional balance and other factors of the culture pond; the author found that almost all hepatobiliary diseases are caused by the combination of the above factors, and the specific treatment methods are as follows:
1, found that this disease is recommended to first stop eating for two days, liver and gallbladder disease is mainly lipolysis, metabolic function is blocked, appropriate reduction of nutrient intake, can effectively stabilize and alleviate this disease.
2. Ponds with excessive chemicals and mixed varieties are first sprinkled with water quality regulators or detoxification drugs to precipitate, floccinate and complex some residual chemical agents.
3. It is recommended to sprinkle spores or em bacteria in the breeding pond in an appropriate amount to effectively adjust the osmotic pressure of the fish body and decompose and excrete excess fat.
4, take the above steps 1 - 2 days later, basically can stabilize the fish condition, careful observation to stabilize the condition after the choice of high-quality feed feeding, the beginning can be fed 50% of the normal feeding amount, and in the feed to add immune polysaccharides, strong coat vc, liver protection or liver protection drugs, into a solution evenly sprinkled on the feed, continuous feeding for 4-5 days, the cure probability is generally more than 95%. If you can't find a suitable feed, you can mix rice bran or wheat bran with liver and gall medicine.
5. After the condition is basically cured, the amount of bait can be appropriately increased (using the daily increment method, generally increasing the amount of feeding daily by 3-5%). If some diseased fish have scales falling off the epidermis, resulting in inflammation and bleeding symptoms, because the fish body has just recovered at this time, the physique is relatively weak, it is recommended to use mild disinfectants such as thiosefloxacin or povidone iodine for external sprinkling disinfection to treat inflammation. Do not use strong stimulants such as bleach or strong chlorine to avoid causing a rebound in the condition.