1. The main pathogen: Hemorrhagic disease in fish is primarily caused by bacteria belonging to the genus *Vibrio*. Several species of *Vibrio* are known to be highly virulent, including *Vibrio anguillarum*, *Vibrio parahaemolyticus*, *Vibrio harveyi*, *Vibrio vulnificus*, and *Vibrio alginolyticus*. These pathogens are commonly associated with severe infections in aquatic animals, especially in marine environments. 2. Epidemic situation: This disease can affect a wide range of marine fish species, making it a significant threat in aquaculture. It occurs throughout the year, particularly in warm water conditions, and can lead to high mortality rates if not managed properly. 3. Main symptoms and diagnosis: The clinical signs of hemorrhagic disease vary depending on the species of fish, their health status, and the mode of infection. Common symptoms include: - Skin lesions such as pinpoint hemorrhages and severe erosion on the body surface; enlarged liver and kidneys, with the liver appearing yellow and spotted; sometimes intestinal congestion or swollen anus, along with ulcers or bleeding in different areas of the body. - In red snapper, symptoms may include darkened body color, blood in the anal area, internal blood stasis, eye swelling, and redness in the gills and eyes. There may also be diffuse bleeding in the intestines, liver, and gonads, with mucus containing blood in the gut. - In some cases, the ovaries may become inflamed, leading to surface ulcers and fading of body color. Fish might show erratic behavior, with bleeding and ulcers on the fins and trunk, along with swollen anus. - General signs include reddening of the skin, redness around the anus, bulging eyes, and bleeding from the eyes. Internal organs and muscle tissues may appear pale or have spots. Diagnosis typically requires bacterial isolation, culture, and identification to confirm the presence of *Vibrio* species. 4. Control methods: Preventive and treatment measures are crucial in managing vibriosis in aquaculture: - Vaccination is one of the most effective strategies. For example, the U.S. has developed vaccines for rainbow trout and *Bdellovibrio* strains, while Japan uses vaccines for Ayu fish. These can be administered through injection, immersion, or oral feeding. - The Zhujiang Fisheries Research Institute in China has developed both injectable and bath-formulated vaccines against *Vibrio* infections. These vaccines are easy to use and have been tested in field trials for various species like groupers, red snappers, yellowtail, and large yellow croakers. - Medication is often used alongside vaccination. For example, sulfadimethoxine can be given at 100–200 mg per kg of fish body weight daily for 4–6 days. Doxycycline is another option, at 20–50 mg per kg of feed for 6 days. Florfenicol can be mixed into feed at 50–80 mg per kg of fish for 5–6 days. - For cage cultures, diseased fish can be soaked in a solution of quaternary ammonium iodide at 2–3 mg/L for 5–10 minutes. In ponds or concrete tanks, bleaching powder (containing 30% available chlorine) at 1 mg/L or quaternary ammonium iodide at 0.5 mg/L can be applied. Treatments should be repeated every other day as needed. It is essential to follow the withdrawal periods for antibiotics and ensure that no drugs are used within 20 days before fish are marketed. Residue testing is also required prior to sale to ensure food safety and compliance with regulations. organic hibiscus tea,red rose tea,best hibiscus tea,organic chrysanthemum tea,flowering tea gift set ZHONGSHAN G.H.L. TRADING CO., LTD. , https://www.ghltrade.com