How is white spot disease treated in grouper farming?

Symptoms: White spot disease is one of the serious diseases of grouper, especially common in high-density holding tanks and cage farming. This disease spreads quickly; in severe cases, 3—4 days can kill all the fish in a pond. In cages, it forms a concurrent infection with monogeneans, with an infection rate of 90% and a mortality rate of over 50%. The disease is prevalent in Fujian, Guangdong and Zhejiang, China, and mostly occurs in summer. Pathogen: The pathogen is the ciliate grouper scuticociliate, Cryptocaryon sp. (grouper petal-body ciliate). The parasite is tiny and slightly transparent, similar to the freshwater carp Chilodonella, oval or egg-shaped, measuring 45—80×29—53 microns. The ventral surface of the parasite has 32—36 ciliary rows, while the rest is bare. There is a round cytostome in the middle of the anterior part, and an oval macronucleus in the middle of the body, with a flower-shaped petal-like structure behind the macronucleus. Symptoms: The parasite lives on the body surface, gills and fins of grouper. Irregular white spots appear on the body surface of diseased fish, and in severe cases the white spots merge into one patch. The fins of dead fish extend forward and press tightly against the operculum. The body surface and gills of the fish produce increased mucus, which flows slowly, and the fish have difficulty breathing and often float at the water surface. Diagnosis: A preliminary diagnosis can be made based on body surface symptoms. Confirmation requires scraping mucus from the body surface and gills for microscopic examination, which can reveal large numbers of the parasite.

Treatment methods: White spot disease of grouper is a common disease in grouper cage farming, and its harm is also serious, so the treatment methods for grouper white spot disease should be mastered. Specific methods include: (1) Copper sulfate seawater bath: place the diseased fish in a 2 mg/L copper sulfate seawater solution and soak for 2 hours, then rinse with seawater, repeating every other day. (2) Freshwater bath: place the diseased fish in freshwater and soak for 4-5 minutes, once a day, for 3 consecutive days. (3) Bleaching powder or potassium permanganate solution bath: place the diseased fish in a 5-8 mg/L bleaching powder or potassium permanganate freshwater solution and soak for 2-3 minutes, repeating every other day.