Aquaculture begins with raising fish, and good water is essential for their growth. In recent years, as the degree of eutrophication in aquaculture has increased, water quality has deteriorated, leading to a rise in disease outbreaks. As a result, water quality management has become the top priority for farmers.
In summer, water quality changes continuously. At the beginning of the farming cycle, the pond has low biomass, limited organic matter, and sufficient dissolved oxygen. Organic matter is broken down by aerobic bacteria, maintaining a stable ecological balance. However, as the breeding period progresses, more organic waste accumulates due to feeding, excretion, and algae growth and decay. Rising water temperatures, combined with continuous feeding from fry to harvest, lead to higher stocking densities and excessive feed input. This results in large amounts of uneaten feed, feces, and dead organisms settling at the bottom, increasing organic load and reducing water clarity. Over time, this leads to elevated ammonia and nitrite levels, lower pH, and the proliferation of harmful bacteria, often culminating in fish disease outbreaks in July and August.
Effective summer water quality management involves several key points:
1. **pH Balance**: pH is a critical indicator of water quality. For most aquaculture systems, it should be maintained between 7.5 and 8.5. If the pH is too low (below 6.5), it can impair oxygen transport in fish blood, causing physiological anoxia. Conversely, high pH can damage fish gills, leading to mass mortality.
2. **Dissolved Oxygen Levels**: Aquatic animals require adequate dissolved oxygen to survive. Levels should remain between 5-8 mg/L, with a minimum of 4 mg/L. Low oxygen can cause fish to float, while excessively high levels may lead to gas bubble disease.
3. **Ammonia Nitrogen Control**: Ammonia comes from feed, animal waste, and decaying plant material. Even low concentrations can harm aquatic life, while high levels are lethal. To prevent accumulation, farmers should maintain proper stocking density, use quality feed, and regularly clean the pond bottom. Zeolite powder and biological treatments can also help absorb excess ammonia.
4. **Nitrite Management**: Nitrite is a toxic intermediate in the nitrogen cycle. It oxidizes hemoglobin in fish, reducing oxygen-carrying capacity and causing "yellow blood disease." Nitrite levels should stay below 0.1 mg/L. Regular water exchange, disinfection, and zeolite use are effective solutions.
5. **Water Color and Clarity**: Poor water color, such as milky or greenish hues, often indicates algal imbalances or overfeeding. Solutions include aerating the water, replacing some of the old water, using biological treatments, and reintroducing beneficial algae through live fertilizers.
Proper water management not only prevents disease but also improves growth rates and overall productivity. Farmers must remain vigilant, monitor water parameters regularly, and take prompt action when issues arise. With careful attention, aquaculture can thrive even under challenging summer conditions.
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