The wintering period in Brazil varies by region, with a shorter duration in the south and longer in the north. In eastern China, the overwintering season typically lasts from November to April of the following year, spanning about six months. Throughout this entire period, the survival and health of Brazilian fish during winter do not directly impact their reproductive performance in the next year. Instead, their success is largely dependent on the quality of daily management. If husbandry practices are neglected, it can lead to high mortality rates among overwintering fish. Therefore, it is essential to have dedicated personnel responsible for feeding and monitoring throughout the winter.
Winter management of Brazilian fish focuses on several key areas:
**(I) Transition from Rearing Pond to Wintering Pool**
At the start of winter, fish are often vulnerable due to handling and transportation. To minimize stress and prevent disease, they should be treated with a 1–2 mg/l methylene blue bath for 30 minutes before being introduced into the wintering pool. If possible, gradually increase the water temperature to around 25°C so that the fish can adapt to their new environment. Once they begin eating normally, adjust the water temperature to match the wintering conditions. The fingerling pool should be maintained at approximately 20–23°C, while broodstock pools can be kept at 22–26°C depending on specific needs. Within the first week after transfer, mortality peaks, so dead fish must be removed promptly to prevent water quality degradation and potential disease outbreaks. Daily water changes of about 30% are recommended, but care must be taken to avoid large temperature fluctuations.
**(II) Daily Management**
1. **Feeding Practices**
Brazilian fish are omnivorous, so their feed requirements are relatively low. They can be fed specialized feed or general squid-based diets. The amount of food depends on water temperature and growth stage. For overwintering juveniles, maintain water temperatures between 20–23°C, and feed them 3% of their body weight per day, divided into three meals at 8 AM, 12 PM, and 4 PM. For adult fish, keep the water temperature at 18–21°C and feed 1–2% of their body weight twice daily, at 9 AM and 3 PM. Broodstock require more attention, as proper nutrition supports successful reproduction. Maintain water temperatures between 22–26°C, and feed 3–5% of their body weight daily, with 1/3 in the morning and 2/3 in the afternoon. Feeding should follow the "four timing" principle: fixed time, location, quantity, and quality. Set up feeding platforms and monitor intake daily, adjusting feed amounts based on water quality and temperature.
2. **Water Quality Control**
Maintaining good water quality is crucial for fish health. During winter, frequent water changes are avoided to retain heat, but waste accumulation can reduce dissolved oxygen and release harmful substances. Regularly remove sludge and uneaten feed using siphoning or draining. Even though Brazilian fish tolerate low oxygen levels, high stocking density increases the risk of poor water quality. Install aerators or oxygenation systems and operate them every four hours for 30 minutes to ensure adequate oxygen levels.
3. **Ongoing Monitoring and Care**
Dedicated staff should be on duty throughout the winter to monitor fish behavior, check feeding patterns, manage water temperature, and clean the pond. Observe for signs of distress, such as fish swimming near the surface or reduced appetite. Promptly test water quality, measure temperature, and address any issues. Early detection of diseases is critical to preventing widespread losses.
4. **Disease Prevention**
Due to high stocking density and fluctuating environmental conditions, disease outbreaks are common. To prevent infections, treat the water with 1 mg/l bleaching powder or 0.2 mg/l methylene blue every other week. These measures help maintain a healthy environment and reduce the risk of illness.
By implementing these strategies, fish farmers can ensure better survival and preparation for the next breeding season.
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