Aquaculture begins with raising fish, and good water is essential for their growth. In recent years, as eutrophication in aquaculture has worsened, water quality has deteriorated, leading to an increase in difficult-to-treat diseases. As a result, water quality management has become the top priority for farmers.
**1. Characteristics of Water Quality Management in Aquaculture During Summer**
Water quality changes gradually during summer. At the early stage of aquaculture, the pond has low biomass and limited organic matter, allowing sufficient dissolved oxygen. Microbial decomposition occurs under aerobic conditions, maintaining a balanced ecosystem. However, as the breeding period progresses, more organic matter accumulates due to increased feeding, fish excretion, and algae growth and death. Rising water temperatures further intensify these issues.
With higher stocking densities and continuous feeding from seedlings to harvest, excess feed, fish waste, and dead organisms accumulate in the water. These substances build up over time, leading to pH fluctuations, increased ammonia and nitrite levels, reduced water clarity, and the proliferation of harmful bacteria. This results in poor water quality and frequent outbreaks of fish diseases, often peaking in July and August.
**2. Key Points in Managing Water Quality During Summer Farming**
**1) pH: A Vital Indicator of Water Quality**
pH is a crucial factor in determining water quality. For most aquaculture systems, the ideal range is 7.5 to 8.5, while freshwater systems typically maintain a pH between 6.5 and 9.0. If the pH is too low (below 6.5), it can reduce the blood's oxygen-carrying capacity, causing physiological anoxia in aquatic animals. Even with high dissolved oxygen, fish and shrimp may exhibit abnormal behavior like floating at the surface. Conversely, if the pH is too high, it can damage gill tissues, leading to respiratory failure and mass mortality.
**2) Dissolved Oxygen: The Lifeblood of Aquatic Animals**
Dissolved oxygen is essential for the survival of aquatic species. Levels should be maintained between 5 and 8 mg/L, with a minimum of 4 mg/L. Low oxygen levels cause stress, rapid breathing, and slowed growth. Excess oxygen, on the other hand, can lead to gas bubble disease in fish and shrimp.
**3) Controlling Ammonia Nitrogen Toxicity**
Ammonia nitrogen comes from uneaten feed, animal waste, and decomposing plant and animal matter. It is highly toxic to aquatic life. At low concentrations (0.01–0.02 mg/L), it can cause chronic poisoning and hinder growth. At higher levels (0.05–0.2 mg/L), it damages internal organs and causes bleeding. At lethal concentrations (0.2–0.5 mg/L), it leads to acute poisoning and death.
To prevent ammonia buildup, farmers should clean ponds, manage stocking density, use quality feed, avoid overfeeding, and regularly aerate the water. Zeolite powder and biological treatments can also help absorb ammonia and improve water quality.
**4) Managing Nitrite Levels to Prevent Disease Outbreaks**
Nitrite is an intermediate product of the nitrification process. High levels can oxidize hemoglobin in fish and shrimp, reducing their ability to carry oxygen and causing "yellow blood disease." Nitrite levels should remain below 0.1 mg/L. If levels are high, partial water changes, zeolite application, and bacterial treatments are recommended to lower nitrite concentration and restore water balance.
**5) Improving Poor Water Color**
Cloudy or white water is often caused by excessive zooplankton or the death of phytoplankton. To address this, farmers should control feed, use ammonia-removing agents, and introduce fresh water. Biological fertilizers can help restore healthy algae growth. During sudden water quality changes, providing health supplements like vitamins and allicin can support recovery and strengthen immune systems.
In summary, effective water quality management in summer requires constant monitoring and timely interventions. By maintaining proper pH, dissolved oxygen, and nutrient levels, farmers can reduce disease risks and ensure healthier, more productive aquaculture systems.
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