Comprehensive prevention and control measures are needed for fish hepatobiliary syndrome

In recent years, with the continuous increase in the intensification of aquaculture, the incidence of fish hepatobiliary syndrome has been rising. Hepatobiliary syndrome can occur in various cultured fish, most notably in common carp and grass carp, and generally the incidence is high in adult fish.

There are many causes of fish hepatobiliary syndrome, which can be summarized mainly in the following aspects. (1) Pathogenic microorganism infection. Infections by pathogenic microorganisms such as Aeromonas hydrophila, Edwardsiella, and rhabdovirus and reovirus can directly or indirectly cause hepatitis in fish. Pathogenic microorganisms multiply in large numbers in the fish liver, producing toxins, causing metabolic disorders in liver cells, and leading to degeneration and necrosis of liver cells. (2) Nutritional factors. A feed nutrient level that is too high can easily trigger liver disease in fish. High-protein feed readily induces fat accumulation in the liver, damages liver function, and interferes with the normal physiological metabolism of fish; too high a carbohydrate content in feed can cause disorders of carbohydrate metabolism in fish, resulting in accumulation of visceral fat, hindering normal function, and triggering fatty liver; feeding feed containing too much fat can directly cause liver disease. In addition, feed nutritional indicators that do not match the cultured species, such as feeding common carp feed to blunt snout bream or grass carp, or feeding fry and fingerling feed to adult fish, can all cause liver disease. Overfeeding, with intensive feeding multiple times a day without interruption, can cause excessively rapid growth of the fish, resulting in obesity and fatty liver. Aldehydes produced by oxidized and rancid fats in fish feed are highly toxic, cause great damage to the fish liver, and affect the normal function of the liver. (3) Pharmaceutical factors. For example, heavy metal poisoning, and poisoning by pesticides, ammonia nitrogen, nitrite, and hydrogen sulfide, can cause degeneration and necrosis of fish liver tissue. Long-term addition of drugs harmful to the fish liver in feed and improper medication are the main causes of drug-induced hepatitis. Long-term addition of high doses of growth-promoting drugs such as olaquindox and flavomycin in feed can cause liver damage in fish. The use of insecticides at high doses also readily accumulates in the fish body and directly damages the fish liver.

Because there are many causes of fish hepatobiliary syndrome, comprehensive measures should be taken to prevent and control it. (1) Select high-quality feed and feed scientifically. Strictly in accordance with scientific @#@233@#@ requirements, select feed that is rich and comprehensive in nutrients, and by no means overfeed; prevent protein deterioration and fat oxidation, and prevent feed from becoming damp, moldy, and deteriorated. (2) Use drugs correctly. Do not add drugs harmful to the fish liver, such as oxytetracycline, sulfonamides, and tetracycline drugs, to feed at low doses over the long term; do not use fishery drugs with large side effects and high residues, such as trichlorfon and copper sulfate, and even less may nationally prohibited fishery drugs be used or pesticides be substituted for fishery drugs and applied to the water body. When treating fish liver disease, the pathogen should be identified as far as possible and both the root cause and symptoms treated. (3) Stock reasonably densely and do a good job in water quality regulation. The stocking density of fish must be reasonably controlled, and must be determined according to the pond water depth, bottom sediment conditions, water source and feed supply, and the level of aquaculture. If the stocking density exceeds the tolerance of the fish, it will increase the stress response of the fish and cause damage to the liver. When the ammonia nitrogen concentration in the water is too high, the ammonia metabolic products in the fish body are difficult to excrete normally and accumulate in the blood, which also readily causes the occurrence of fish hepatobiliary disease.