Parasitic Diseases Occur in Fish Farms
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In recent years, outbreaks of fish diseases in surface waters have become increasingly common. Among these, parasitic infections are the most prevalent, often leading to hemorrhagic symptoms. These parasites attach themselves to the fish, causing severe damage. Fish parasitism typically peaks between July and October, affecting reservoirs and lakes ranging from 500,000 to 5 million cubic meters. The widespread nature of the infestation and its long duration cause significant economic and ecological losses. One of the major challenges in treating these diseases is the large water surface area and the high cost involved. Therefore, it's essential to discuss effective prevention and treatment strategies for serious waterborne parasites.
**I. Symptoms and Epidemiology**
1. **Chinese Fish Carp Disease**: Infected fish show signs such as difficulty breathing, restlessness, increased mucus production, and white tips on their gills. Female *Cuculus* (Chinese scorpion) hook into the fish’s gills with large hooks. When heavily infested, white nodules appear along the gill edges, also known as rickets. This parasite mainly affects grass carp, silver carp, and red-eared turtles. Affected fish may swim erratically or float near the surface, a condition called "tail disease." Weight loss, stunted growth, and even death can occur. This disease is widespread across China, with peak prevalence from April to October, especially between June and September.
2. **Cysticercosis**: Fish infected with this disease exhibit increased mucus, pale coloration, and difficulty breathing. Under a microscope, cysts can be seen in the gills. This disease is common nationwide and usually occurs in late spring and early summer, primarily affecting carp and grass carp.
3. **Anchor Worm Disease**: The anchor worm attaches to the entire body of the fish, with part of its body embedded in the host and the rest visible outside. Severe infestations make the fish look as if they are wearing a coat, hence the name. The infection causes skin inflammation and pomegranate-like swellings. Grass carp and carp often lose scales due to the worms. Infected fish become restless and lose their appetite. This disease is found throughout the country.
**II. Prevention Methods**
1. **Improve the Environment**: After winter harvesting or before the spring rainy season, disinfect the water using lime at a rate of 25–40 grams per cubic meter. This method reduces costs and ensures better results.
2. **Insecticide Use**: After disinfection, apply standard insecticides like 90% trichlorfon at 0.7 grams per cubic meter, following manufacturer instructions.
3. **Fish Bathing Before Stocking**: Soak fish in a 20-gram-per-cubic-meter potassium permanganate solution for 15–20 minutes, or use 500 grams per cubic meter of trichlorfon for the same duration.
4. **Reasonable Stocking Density**: Overcrowding or improper mixing increases stress, leading to higher disease susceptibility. Maintain optimal stocking levels.
5. **Enhanced Management**: Minimize stress by avoiding sudden changes and promoting natural behavior. This improves the fish’s immune response.
**III. Treatment Methods**
1. **Spray Trichlorfon**: Apply 0.7 grams per cubic meter of 90% trichlorfon across the entire water body.
2. **Feed Medication**: Mix 100 grams of trichlorfon with 30 kilograms of bran or compound feed and feed for four days.
**IV. Prevention and Treatment Experience**
1. **Prevention Awareness**: Large-scale aquaculture requires proactive measures. Prevention is more effective than treatment, as many fish die before showing symptoms.
2. **Etiological Analysis**: Ensure proper quarantine of imported fish to prevent new pathogens. Avoid overstocking and maintain good water quality by regularly removing sediment and properly managing organic waste.
3. **Disinfection After Insecticide Use**: Immediately after applying insecticides, use 35 grams per cubic meter of lime water or other disinfectants to eliminate remaining parasites.
4. **Drug History Consideration**: If certain pesticides were used in the previous year, consider switching drugs to avoid resistance.
5. **Accurate Dosage**: Adjust the dosage by 20% to account for environmental factors and drug degradation, ensuring maximum effectiveness.
6. **Bait Attraction Technique**: For large water bodies, use bait laced with spices like sautéed bran and cinnamon to concentrate fish in specific areas. This allows targeted treatment and is effective for mild cases.
By combining these strategies, aquaculturists can significantly reduce the impact of parasitic diseases and ensure healthier, more productive fish populations.