After the start of autumn, the weather gradually cools down, though the lingering heat remains. This period is known as the "autumn tiger," but the overall trend shows a more noticeable temperature difference between day and night—hot during the day and cooler at night. Autumn is a critical season for aquaculture management. Carelessness during this time can lead to significant losses or even undo all previous efforts. Here are some improved technologies and management strategies to ensure successful aquaculture operations:
**Water Quality Management**: As farmed species grow, the density in ponds increases, leading to the accumulation of leftover feed, excrement, and decaying aquatic plants. These materials consume oxygen and produce harmful gases like hydrogen sulfide, while also increasing ammonia levels and lowering pH. This can result in fish floating head or even mass die-offs. To prevent this, it's essential to change water frequently but in small amounts, drawing from the upper and middle layers to promote plankton diversity and reduce the risk of blue-green algae blooms ("blue lake water"). Additionally, applying beneficial microbial agents such as Bacillus, photosynthetic bacteria, nitrifying bacteria, and EM bacteria can help manage nitrite, ammonia, hydrogen sulfide, and high pH levels. For crab ponds, gradually increase water exchange with small amounts, avoiding sudden rises that could cause floatation and death. Every 10 days, apply lime at a rate of 5 kg per mu to maintain a pH between 7.8 and 8.5, with a transparency of 30–40 cm, which supports strong shell development and healthy growth.
**Feeding Strategies**: Improve feed quality for conventional fish, ensuring daily feeding is around 5–6% of their body weight, with 60% animal-based feed. For shrimp, feed should be 7–8% of their body weight. Crabs require a higher proportion of animal feed, around 65%, with daily feeding at 10% of their total weight. From early October onward, as water temperatures drop, feeding rates should decrease to 3–4% for fish, 3–4% for shrimp, and 4–5% for crabs. Early and mid-autumn is the peak feeding period for river crabs, when they feed on plants and snails. Ensure sufficient food sources by replenishing pond vegetation and snails if needed. In soft-shell turtle farming, focus on maintaining good water quality to enhance appetite. Use water purifiers to quickly reduce ammonia nitrogen and nitrous acid, then add biological agents like photosynthetic bacteria after two days to boost beneficial microorganisms. Feed should be rich in protein and fat, and adding up to 20% fresh or high-quality chilled fish slurry can improve feeding intensity and growth. To prevent enteritis, include herbs like Andrographis paniculata or garlic in the diet for a few days.
**Disease Prevention and Control**: Historically, fish diseases tend to peak after the start of autumn. Implementing proactive measures such as “prevention before disease†and “early treatment upon detection†can significantly improve outcomes. Regularly disinfect the entire pond using chlorine dioxide every 20 days, and add detoxifiers, calcium, and oxytetracycline to feed monthly. For ponds with poor water quality or low aquatic plant coverage, use the “kill and sterilize†method: net the fimbriae, treat with trichlorfon for fish, and apply appropriate treatments for shrimps and crabs. After three to five days, apply quicklime (5–10 kg per acre) and perform a thorough water change. In late autumn, as cold air arrives, tropical species like white shrimp and Macrobrachium rosenbergii may be affected. Prepare for cold weather by providing insulation and proper care.
**Pond Monitoring**: Maintain regular morning and evening patrols to check the activity of fish, shrimp, and crabs, observe their feeding behavior, and monitor water color, clarity, and pH. Remove any decayed plants or leftover feed promptly, and keep the feeding area clean. For species like river crabs and soft-shell turtles that are prone to escaping, inspect the anti-escape structures and inlet/outlet facilities regularly. Strengthen security checks at night to prevent theft and ensure a safe environment for aquaculture.
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