The survival rate and the opening rate of seedlings have long been a concern for farmers, as these factors directly impact the success of aquaculture operations. Improving both the survival and opening ratios is a critical challenge that needs urgent attention in the industry. Several factors influence these outcomes, including water quality, climate conditions, timing of unloading, seedling quality, stocking methods, transportation, grading, aquatic vegetation in cages, water maintenance, carcass management, farming concepts, feeding practices, and the use of check boxes and feeding tables. The following points outline key considerations before and during the stocking process.
First, water quality is crucial. Dianchi water must be soft, live, and cool, with dissolved oxygen levels above 5 mg/L. The pH should be maintained between 7.2 and 7.6. Toxic ammonia, hydrogen sulfide, and nitrite levels must not exceed 0.02 mg/L, 0.1 mg/L, and 0.05 mg/L respectively. Water testing should be conducted before stocking, and adjustments made if necessary. The water depth should be kept around 40 cm to ensure optimal conditions.
Second, the water temperature in the next box should remain stable at 25°C, with a daily temperature fluctuation of no more than 5°C. Avoiding extreme temperatures is important—maximum water temperature should not exceed 34°C. These conditions help ensure that seedlings can adapt effectively.
Third, farmers should closely monitor weather changes before stocking. It's recommended to check long-term forecasts and aim for at least four consecutive sunny days after stocking. Day-to-night temperature differences should also stay within 5°C to prevent stress on the seedlings.
Fourth, aquatic vegetation in the cages, such as water hyacinth, should be lush to provide a natural habitat for the seedlings. This helps reduce stress and the occurrence of jaundice. Mixing 5% oil grass with water hyacinth can further improve the environment.
Fifth, seedling quality depends on several factors: fishing methods, source, holding time, handling techniques, and transport methods. When purchasing, it’s essential to understand these aspects thoroughly. Locally sourced seedlings are often the best choice, as they are better adapted to the environment. Seedlings should be vibrated (electrolyzed) for improved vitality, but this should be done carefully. Avoid handling them too much or keeping them in mucus, as this can cause dizziness and brain damage. Do not stun them; instead, use a net to gently remove surface jaundice. Proper identification of the "mountain bar" is important, as it can be difficult to distinguish visually. Look for muscle fullness—seedlings from lake areas tend to be fatter, while those from other sources may appear thinner.
Sixth, temporary holding of seedlings should be done in clean, clear water, avoiding well water or tap water. The temperature difference between new and existing water should not exceed 2°C. The fish-to-water ratio should be at least 1:2, and water should be changed at least four times a day. The holding period should not exceed four days to maintain health.
Seventh, during transportation, seedlings should be handled quickly and carefully. A fish-to-water ratio of 1:2 or higher is strongly recommended. Povidone iodine should be used in the transport water at a rate of 6 drops per 100 kg (fish + water). Transport duration should be limited to no more than 10 hours to avoid excessive stress.
Eighth, when returning seedlings from the lower box, they should be acclimated gradually to the water temperature of Dianchi Lake. This ensures a smooth transition and reduces shock. Seedlings should be graded into three or four categories, ensuring quick and accurate sorting. Remove any weak or injured individuals. If transported via a medicine bath, avoid using chemical baths. Instead, opt for an electrolytic multidimensional solution, which can temporarily boost vitality without compromising immunity. Always keep detailed delivery records for traceability.
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