Autumn is a critical time for the outbreak of "black spot" and "red spot disease" in farmed green shrimp. These diseases can affect both juvenile and adult shrimp, significantly impacting the productivity of aquaculture operations. It is essential to implement effective prevention and control measures to minimize losses.
First, let's discuss black spot disease. This condition typically occurs in high-density shrimp ponds, primarily due to poor water and sediment quality. The accumulation of organic matter promotes the growth of bacteria that break down chitin, leading to rapid infection. Symptoms begin with small gray or brown spots on the shrimp’s body, which gradually spread to the abdomen, appendages, and even the carapace. In severe cases, the spots become sunken and ulcerated, causing damage to internal tissues. Affected shrimp show reduced activity, lose their appetite, and often float near the surface or gather in shaded areas before dying.
To prevent black spot, farmers should take the following steps during summer and early autumn:
1. Regularly add fresh water to maintain good water quality. In areas with limited water exchange, apply quicklime (25 mg/m³) or a water quality enhancer once or twice a month.
2. Ensure feed is clean and fresh, and follow a regular feeding schedule—feeding at fixed times, locations, and quantities to avoid leftover food polluting the water.
3. Reduce stocking density, especially in high-density ponds. Keep shrimp numbers below 80,000 per mu to reduce stress and disease risk.
4. If an outbreak occurs, treat the entire pond with nitrofurazone (1 mg/L) or formalin (25 μg/L). After 12 hours, completely change the water daily for 2–3 days, depending on the severity.
5. For large-scale outbreaks, mix 0.3% sulfonamides like sulfadiazine or iodothiazole into the feed and administer it for 5–7 days.
Next, red spot disease. Although not as sudden or widespread as black spot, this disease causes persistent and recurring mortality. Early symptoms include one or two red spots on the shrimp’s appendages, carapace, or tail. Over time, the number of spots increases, and in severe cases, one side of the shrimp turns black. If left untreated, infected shrimp may crawl out of the water within 2–4 days and die in shallow areas. Shrimp that survive the disease often have poor meat quality, making them unsellable at good prices.
Prevention strategies for red spot disease include:
1. Maintain clear water with a transparency of at least 40 cm and ensure half of the pond area has sufficient water coverage.
2. Apply quicklime (25 mg/m³) or a water quality improver monthly, and manage stocking density appropriately.
3. Feed shrimp with 1 kg of norfloxacin per kilogram of bait for 7 consecutive days, without any other feed.
4. After using norfloxacin, combine it with 0.8 mg/L of "Strong Chloride." It is best to apply this treatment on a sunny day to maximize its effectiveness.
By implementing these preventive and treatment measures, shrimp farmers can significantly reduce the impact of these diseases and improve overall production efficiency.
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