The growth rate of fish and the health status of the constitution mainly depend on the nutritional value of feed and the balance of nutrition. The quality of fish feed has a decisive position in healthy farming. However, cases of damaged fish health caused by feed quality are more common, especially fish nutritional liver disease.
At present, China's more prominent fish liver and gallbladder syndrome mainly occurs in the common main fish such as carp, carp, grass carp, and head lice. Factors such as nutritional factors, toxic substances, and drug-derived factors are the causes of such diseases. Therefore, there are many causes of fish liver disease. The specific causes of the disease are summarized as follows:
1. The culture density is too high and the water environment deteriorates. When the concentration of ammonia nitrogen in the water is too high, the ammonia metabolites in the fish are difficult to discharge normally and accumulate in the blood, causing liver and gallbladder disease due to imbalance of fish metabolism.
2. Feed nutrition is not suitable for fish nutrition needs. For example, if the protein content is too high, the carbohydrate content is high, or long-term use of animal fats and highly saturated fatty acids, the feed energy-protein ratio is too high. High-protein diets can easily induce liver fat accumulation, destroy liver function, and interfere with normal physiological and biochemical metabolism of fish. Excessive amounts of carbohydrates can cause fish sugar metabolism and cause the accumulation of visceral fat. Severe fatty liver can also cause liver lesions, causing the liver to lose normal function.
3. Feed oxidation, spoilage, mildew, deterioration. Fat is a substance that is easily oxidized. The aldehydes, ketones and acids produced by the oxidation of fat are toxic to fish and will directly damage the liver. One month after carnivorous feeding, carp suffers from thin back disease, muscle fiber atrophy and necrosis; after fish such as grass carp and group head carp eat, it can easily cause liver and gallbladder syndrome in fish.
4. Drug abuse. Long-term addition of high-dose olaquindox, flavomycin, and other growth-promoting drugs to feed will cause liver damage in fish. Insecticide-sterilized drugs also tend to accumulate in fish and directly damage the fish liver.
5. Vitamin deficiency. Such as choline, VE, biotin, inositol, VB, etc. are involved in fat metabolism in fish, the lack of the above vitamins can cause fat metabolism disorders in fish, resulting in fat accumulation in the liver, induced liver disease.
6. Feed contains toxic and hazardous substances. For example, gossypol in cottonseed meal, sulphur gluconate in vegetable mash, nitrite in inferior fishmeal, and other toxic and harmful substances can all cause hepatobiliary diseases in fish.
Some nutritional diseases can lead to the death of farmed fish. While some nutritional diseases do not directly lead to the death of farmed fish, they are vulnerable to attack by pathogens or affect the value of goods because of the decline of fish disease resistance. The increase in the incidence of fish nutritional diseases warns that we should pay attention to the quality of aquatic feed.