At present, the prominent fish and liver biliary syndrome in Huai'an District of Huai'an City, Jiangsu Province mainly occurs in conventional main fish such as carp, carp, grass carp, and scorpionfish. Typical symptoms: hepatomegaly, discoloration, and fragile texture. The mortality rate is as high as 40%-50%.
Nutritional factors, toxic substances and drug-induced 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 breeding density is too large, the feed quality is poor or excessive feeding, and the water environment is deteriorated. When the concentration of ammonia nitrogen in the water is too high, the metabolites of ammonia in the fish are difficult to be discharged normally and accumulate in the blood, causing imbalance of fish metabolism and causing hepatobiliary diseases.
2. Feed nutrition is not suitable for fish nutrition needs. If the protein content is too high, the carbohydrate content is high or long-term use of animal fats and highly saturated fatty acids, etc., the feed energy protein ratio is too high. High protein feed is easy to induce liver fat accumulation, destroy liver function, and interfere with normal physiological and biochemical metabolism of fish. Excessive carbohydrate content can cause fish sugar metabolism disorder, resulting in accumulation of visceral fat. Severe fatty liver can also cause liver damage, causing the liver to lose its normal function.
3. The feed is oxidized, rancid, moldy, and deteriorated. Fat is a substance that is easily oxidized. The aldehydes, ketones and acids produced by oxidation of fat are poisonous to fish and will directly cause damage to the liver.
4. Drug abuse. Long-term addition of high-dose olaquindox and other growth-promoting drugs to the feed will cause fish liver damage. Insecticides also accumulate in fish and directly damage the liver.
5. Vitamin deficiency. Such as choline, VE, biotin, inositol, VB, etc. are involved in fat metabolism in fish, the lack of these vitamins will cause fat metabolism disorder in fish, leading to accumulation of fat in the liver, induced liver disease
6. The feed contains toxic and hazardous substances. For example, gossypol in cotton aphid, glucosinolate in rapeseed meal, nitrite in inferior fish meal and other toxic and harmful substances can cause liver and gallbladder diseases in fish.
7. Overfeed. Overnutrition, long-term increase in fish liver burden, causing liver and gallbladder disease. The sign of overfeeding is uncertain, and it is necessary to make judgments based on the current farming situation, continuous observation and record of fish feeding activity, satiety time, and residual bait.
Hepatobiliary syndrome is not easy to find in the early stage, and even if it does not cause the death of farmed fish in the later stage, it is vulnerable to pathogen invasion or inability to pull net transportation or affect the value of the commodity due to the decline of fish disease resistance. The increase in the incidence of fish nutrition diseases warns us that we should pay attention to the quality of aquatic feed and feeding technology. (Huaiyin District Aquatic Station Wang Weibo)
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