1. The primary causative agent of hemorrhagic disease is *Vibrio* bacteria. There are numerous species within the *Vibrio* genus, and several have been confirmed to be highly pathogenic. These include *Vibrio anguillarum*, *Vibrio parahaemolyticus*, *Vibrio harveyi*, *Vibrio vulnificus*, and *Vibrio alginolyticus*. These pathogens can cause severe infections in aquatic organisms, especially in marine fish. 2. Disease Outbreaks: Hemorrhagic disease can affect a wide range of marine fish species, making it a significant threat to aquaculture. It can occur throughout the year, particularly in warm water conditions where *Vibrio* bacteria thrive. This makes early detection and prevention crucial for fish farmers. 3. Symptoms and Diagnosis: The clinical signs of the disease may vary depending on the fish species, environmental conditions, and the mode of infection. Common symptoms include: - Skin erosion with visible hemorrhages on the body, especially around the trunk area. Internal organs such as the liver and kidneys may become enlarged and discolored, showing yellow spots or lesions. In some cases, the intestines may be congested, and the anus may swell or bleed. - In red snappers, the body color may darken, and there may be blood in the feces. Eye swelling, hemorrhaging, and bleeding from the gills and fins are also common. The internal organs, including the liver, gonads, and intestines, often show signs of diffuse bleeding and spotting. - In some cases, the ovaries may appear swollen, and the skin may develop ulcers or patches of discoloration. Fish may exhibit erratic swimming behavior. Fin bases and the trunk area might show signs of ulceration, bleeding, and swelling around the anus. - General symptoms include reddening of the body surface, redness at the anal opening, prominent eyes, and bleeding from the eye or other parts of the body. Internal organs and muscle tissues may show whitening or spot-like lesions. A definitive diagnosis usually requires bacterial isolation, culture, and identification. 4. Control Measures: Several strategies can be employed to manage and prevent vibriosis in fish populations: - Vaccination has proven effective in preventing certain types of *Vibrio* infections. For example, in the U.S., vaccines for rainbow trout and *Bdellovibrio* have been commercialized. Similarly, Japan has developed vaccines for ayu fish. These can be administered through intraperitoneal injection, immersion, or oral feeding. - The Pearl River Fisheries Research Institute in China has developed a marine fish *Vibrio* vaccine available in both injection and oral forms. It is easy to use and has been successfully applied in small fry and larger fingerlings. Field trials have shown its effectiveness in preventing *Vibrio* infections in over a dozen cultured species, including groupers, red snappers, yellow snappers, and large yellow croakers. - Medication is another key approach. For example, sulfadimethoxine can be fed at a dose of 100–200 mg per kilogram of fish daily for 4–6 days. Doxycycline can be added to feed at 20–50 mg per kilogram of fish per day for 6 days. Florfenicol is another option, given at 50–80 mg per kilogram of fish daily for 5–6 days. - In cage culture systems, diseased fish can be treated by soaking them in a solution of quaternary ammonium salt iodine at a concentration of 2–3 mg/L for 5–10 minutes. In pond or cement tank environments, bleaching powder (with 30% available chlorine) at 1 mg/L or quaternary ammonium salt iodine at 0.5 mg/L can be used. These treatments should be repeated every other day as needed. It is essential to observe the withdrawal period for antibiotics, ensuring that no drugs are used for at least 20 days before fish are marketed. Additionally, pre-market testing for drug residues is strongly recommended 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