In recent years, the farming of California bass has become popular due to its high economic benefits, but the liver disease problems that come along with it have been a headache for many farmers. This liver disease characterized by "fulminant hemorrhagic disease" spreads rapidly and has a high mortality rate. In severe cases, the mortality rate can reach over 90%, causing significant economic losses to farmers.
So, why are California bass farmed at high densities prone to liver diseases? Then, how can it be effectively prevented and controlled? This article will provide you with a detailed answer.
I. Causes of Liver Lesions in High-density Farmed California Bass
Excessive stocking density leads to deterioration of water quality and bottom quality
Most of the ponds affected by the disease are high-yield ones, with large amounts of feed and excretion. Long-term high-density farming of California bass has seriously deteriorated the water quality and bottom sediment of the ponds, inducing infection.
2. The feed is monotonous and the nutrition is unbalanced
Long-term and excessive feeding of frozen Marine fish can lead to vitamin deficiency in the fish and cause fatal damage to their livers.
3. Frequent use of chemical drugs
When fish farmers prevent and treat fish diseases, the long-term and frequent use of chemical drugs can also cause damage to the fish's liver and lead to liver diseases. Blind medication will increase the burden on the liver and create a vicious cycle.
4. Sudden changes in Water Environment and Stress responses
When the immune function of fish declines and their disease resistance decreases, once they are exposed to adverse external stimuli such as net pulling, sudden changes in water temperature or water quality, they are very likely to develop hemorrhagic syndrome, leading to the death of a large number of fish.
Ii. Common Symptoms of Liver Lesions in California Bass
Early identification of liver lesions is the key to timely intervention. Sick California bass will show the following symptoms:
When the disease is mild, the fish body only shows a slight redness at the base of the fin rays or the base of the caudal fin.
After the disease worsens, the diseased fish show symptoms such as being scattered along the edge of the pool, swimming slowly, floating on the water surface, turning black in color, or having congestion and bleeding on both sides of the body surface, or congestion and bleeding at the base of the fins and the fin membrane, or anemia in the gills, swollen and bulging eyeballs, and redness and swelling of the anus.
When dissecting diseased fish, it is found that the liver is swollen, with mottled spots, whitening, yellowing, and even necrosis. Some liver tissues have white granules, while others are in the shape of tofu residue. The gallbladder enlarges, and the bile turns black or becomes very light.
Iii. Comprehensive Prevention and Control Measures
1. Clean and disinfect the ponds to improve the breeding environment
For ponds that have been in aquaculture for a long time and have deep silt, they should be dredged, fully exposed to the sun, and thoroughly cleaned and disinfected with quicklime. Maintaining a good breeding environment is the foundation for preventing liver diseases.
2. Manage water scientifically to ensure fresh water quality
Strengthen water quality management, frequently change water, add fresh water, operate aerators, and regularly apply bottom sediment improvers or photosynthetic bacteria to improve water quality. The transparency of the pool water should be maintained at 30 to 40 centimeters. The water should be changed once every 10 to 15 days, with each change accounting for approximately one-third of the pool water. If micro-water flow or oxygenation measures can be adopted for breeding, the effect will be even better.
3. Feed reasonably and pay attention to balanced nutrition
Establish a reasonable stocking density; Feed the fish at regular intervals and in fixed quantities based on the weather, water quality and the growth and activity of the fish. Avoid using a single feed for a long time and pay attention to adding vitamins and minerals to the feed. Regularly adding vitamin C, vitamin E and choline chloride to the feed can effectively prevent the occurrence of liver diseases in California bass.
4. Use medication in a standardized manner and prevent diseases scientifically
Avoid long-term and frequent use of chemical drugs to reduce the damage of drugs to the liver. Regular disinfection and sterilization of the pool water with bactericidal drugs such as chlorine dioxide or trichloroisocyanuric acid can effectively prevent secondary infection of hemorrhagic disease in California bass.
5. Strengthen daily management
Establish a pond patrol inspection system to observe whether fish show signs of surfacing or other phenomena. Once the situation changes, timely measures should be taken to deal with it. Timely grading and thinning should be carried out, approximately once every two months. Fish of the same size should be released into the same pond to prevent large fish from eating small ones. Strictly prevent pesticides and other substances from flowing into the pool. Young fish are extremely sensitive to pesticides, and a very small dose can cause the death of all the fish fry in the pond.