Common Diseases and Prevention in Eel Farming - Part 2
**Ichthyophthirius Multifiliis (White Spot Disease):**
Caused by parasitic Ichthyophthirius multifiliis.
- **Symptoms:** Visible to the naked eye, the infected eels have white spot-like cysts on their skin, fins, and gills.
- **Prevention and Treatment:** For eels with Ichthyophthirius, soak them in a potassium permanganate solution of 10-20 grams per cubic meter of water for 15-20 minutes. If the disease occurs in the eel pond, first sprinkle the entire pond with a potassium permanganate solution at a concentration of 5-7 grams per cubic meter of water; on the second day, sprinkle the pond with formalin solution at a concentration of 20-30 milliliters per cubic meter of water; on the third day, replace about half of the water with clean water or sprinkle the pond with sodium thiosulfate at a concentration of 1.5 grams per cubic meter of water; on the fourth day, sprinkle the pond with polyvinylpyrrolidone iodine (containing 1.0% effective iodine) at a concentration of 1-2 grams per cubic meter of water.
**Tetrahymena pyriformis Disease:**
Caused by parasitic Tetrahymena pyriformis from the class Ciliophora. The parasite resembles a stemmed wine glass when extended, with a circular oral disc surrounded by cilia at the front end; it has an oval-shaped macronucleus in the middle and is approximately 50 micrometers long.
- **Symptoms:** The parasites live on the skin or gills of the eels, usually consuming nutrients from the surrounding water without significantly affecting the eels. However, if a large number of parasites infect the fry, it can cause breathing difficulties and even lead to fish death. This disease can occur throughout the year but is more common between May and August.
- **Preventive Measures:** Thoroughly disinfect the pond with quicklime before stocking. Soak the fingerlings in a copper sulfate solution (8 grams per cubic meter) for 15-20 minutes before stocking.
- **Treatment Method:** After the fish are infected, sprinkle the entire pond with a mixture of copper sulfate and ferrous sulfate (at a ratio of 5:2) at a concentration of 0.7 grams per cubic meter of water.
**Parasitic Diseases:**
Infected eels become weak, often floating on the surface, restless, or swimming in circles. They also produce excessive mucus on their bodies. These diseases are commonly caused by parasitic infestations such as Trichodina, Tetrahymena, and Gyrodactylus. A treatment method is to sprinkle the entire pond with a mixture of copper sulfate and ferrous sulfate (at a ratio of 5:2) at a concentration of 0.7 grams per cubic meter of water, which can prevent and treat Trichodina and Tetrahymena diseases.
**Curved Backbone Disease:**
This condition occurs due to abnormal water temperature during hatching and a subsequent lack of vitamins during rearing.
- **Symptoms:** The spine of the eel becomes bent and delicate.
- **Prevention and Treatment:** Maintain an appropriate hatching water temperature and supplement the diet with various vitamins.
**Red Ring Disease:**
The body of the diseased eel turns grayish-white with red ring patterns. This disease is caused by prolonged storage after catching mud eels.
- **Prevention and Treatment:** Transfer the diseased eels to a still-water pool for temporary rearing.
**Gas Bubble Disease:**
Caused by changes in water quality and excessive nitrogen or other gases in the water. Therefore, during the cultivation of eel fry, avoid overfeeding or using too much fertilizer.
- **Symptoms:** The intestines of the eels swell, causing loss of balance. The eels float uncontrollably on the surface and may die if left untreated for a long time.
- **Prevention and Treatment:** Regularly add fresh water to the pond. If this disease occurs, quickly change the water, replacing more than one-third of the water volume.
**Water Quality Deterioration:**
Other Harmful Organisms:
Ponds used for raising eels should be thoroughly disinfected with quicklime. Screens should be installed at the inflow and outflow points to prevent harmful fish, aquatic insects, snakes, frogs, and other predators from entering the pond and harming the eel fry or adult eels. If water striders are found in the pond, they can be eradicated by sprinkling the entire pond with a 90% crystalline dichlorvos solution at a concentration of 5 grams per cubic meter of water.