Diagnosis and control of freshwater fish tail disease

2. Symptoms: In the early stages of the disease, yellow or yellow-white mucus is typically observed on the outer edge of the fins and the caudal peduncle. As the condition progresses, redness, inflammation, and erosion appear at the caudal fin and tail base. In severe cases, the tail fin may rot completely, and the muscles around the tail may become ulcerated and bleed, leading to death. During colder seasons, this disease often occurs alongside fungal infections, such as those caused by aquatic molds.

3. Epidemic Situation: The disease usually begins after a fish has sustained a tail injury, allowing pathogens to enter through skin contact. It affects various freshwater species, including eels, grass carp, tilapia, and clams, and can lead to mass mortality. While adult fish can also be affected, their mortality rate is generally lower compared to younger fish.

4. Diagnosis: Initial diagnosis is based on clinical symptoms and the pattern of disease spread. However, for confirmation, it's essential to isolate and identify the specific pathogen through laboratory testing.

5. Control Methods: In the early stages, applying a disinfectant throughout the pond 1–3 times can effectively treat the infection. If the disease is advanced, internal antibiotics are required. For every 100 kg of fish, administer 15 grams of Yutai No. 8 drug twice daily (morning and afternoon) for 5–7 days. When broodstock is severely infected and loses appetite, additional treatment includes intramuscular injections of streptomycin sulfate—20 ml per kilogram of fish weight. This may be repeated if necessary.

If the pathogen is identified as *Columnaris* bacteria, the following treatment protocols should be followed:

External Treatment: Apply chlorine-based disinfectants to the entire pond to reduce environmental contamination.

Internal Treatments:

(1) Mix 2–3 grams of compound sulfamethoxazole per kilogram of feed and feed it twice daily (morning and afternoon) for 3–5 days.

(2) Add 3–4 grams of an intestinal anti-inflammatory agent per kilogram of feed. Administer this medication twice a day for 3–6 days.

(3) Incorporate 2–3 grams of sulfamethoxazole-6-dimethoxypyrimidine into the feed. On the first day, double the dose and feed once daily for 4–6 days.

This comprehensive approach ensures effective control and reduces the risk of further outbreaks in aquaculture systems. Always follow local guidelines and consult with a veterinarian before administering any treatments.

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