Recently, with the increase in summer temperatures and feeding amounts, the problem of fatty liver in California bass has once again swept through major aquaculture areas. This metabolic disease may seem mild, but it can easily become a hidden killer that causes large-scale deaths, and many ponds have suffered heavy losses as a result.
Why is the California bass called a "born fatty liver patient"?
Due to its unique physiological characteristics, the California bass has a naturally weak ability to metabolize carbohydrates and fats.
Defect in sugar metabolism: The activity of glucokinase in the liver is low, and the ingested sugar cannot be efficiently converted into energy. Instead, it is synthesized into fat through circuitous pathways, leading to fat accumulation in the liver.
Fat digestion bottleneck: When the fat content in the feed exceeds 12%, the digestive system of California bass cannot handle it, and the unabsorbed fat directly deposits in the liver, forming "oil dripping liver".
High-feeding trap: During the peak summer farming period, in pursuit of rapid growth, excessive feeding of high-protein (>35%) and high-fat (>15%) feed leads to a sharp increase in liver load, with the incidence of fatty liver soaring to over 80%!
Second, the masterminds behind fatty liver
1. Imbalance in feed formula: Sugar and fat bomb
High sugar trap: When the starch content in the feed exceeds 10%, the activity of glycogen synthase in the liver of California bass decreases, and the sugar metabolic product pyruvate is converted into acetyl-CoA, which directly promotes fat synthesis.
Fat overload: When the crude fat content in the feed is ≥15%, the rate of lipid deposition in the liver increases by three times, and the area covered by lipid droplets expands by 50%.
Nutritional deficiency: Lack of liver-protecting components such as choline and vitamin E leads to blocked fat transport and aggravates liver damage.
2. Deterioration of water quality: Chronic poison
Excessive ammonia nitrogen: When the ammonia nitrogen concentration in water bodies exceeds 0.2mg/L, the activity of antioxidant enzymes in the liver of California bass decreases by 40%, and the content of lipid peroxides (MDA) surges by two times, accelerating the oxidation and accumulation of fat.
Nitrite toxicity: When the nitrite concentration is greater than 0.1mg/L, the blood's oxygen-carrying capacity decreases, the liver is in a state of hypoxia, and the inhibition rate of fat-decomposing enzyme activity reaches 65%.
Algal toxin invasion: The microcystin released by the outbreak of cyanobacteria directly damages the structure of the liver cell membrane, leading to disorders in fat metabolism.
3. Drug abuse: Making things worse
Antibiotic residues: Long-term use of antibiotics such as florfenicol and enrofloxacin interferes with liver mitochondrial function, reducing energy metabolism efficiency by 30%.
Insecticide irritation: Insecticides such as dichlorvos and copper sulfate inhibit the activity of liver detoxification enzymes, increasing the accumulation of toxins in the liver by five times.
Disinfectant impact: Strong oxidizing disinfectants such as strong chlorine can damage the liver cell membrane, causing fat extravasation and exacerbating liver swelling.
Iii. Prevention and control measures
1. Nutritional regulation
Select balanced and high-quality compound feed specifically for sea bass, and regularly and appropriately add functional additives such as Chinese herbal medicine, liver-protecting and gallbladde-promoting substances, liver and gallbladder relaxants, and bile acids to promote the digestion and absorption of the feed and enhance the ability of sugar and lipid metabolism, thereby protecting liver health.
2. Scientific feeding
During the juvenile stage, the daily feeding amount should account for 3% to 5% of the fish's body weight, and during the adult stage, it should account for 1% to 3% of the fish's body weight. Especially when the water temperature is too high, appropriately reduce the frequency or amount of feeding as the water temperature rises. Feed once in the morning or stop feeding. For ponds with good aquaculture water environment, feeding can be done once in the morning and once in the evening, but a small amount should be given at night to prevent oxygen deficiency at night.
3. Water quality management
Maintain dissolved oxygen above 5mg/L and extend the operation time of the aerator at night to prevent hypoxia stress. Regularly sprinkle bacillus (1g/m³) + photosynthetic bacteria (0.5g/m³) to decompose organic matter and reduce the concentrations of ammonia nitrogen and nitrite.
4. Other matters needing attention
During the period of illness, try to minimize the use of insecticides, antibiotics, etc. The use of these disinfectants will further aggravate the condition of "fatty liver".