In intensive pond farming management, light is considered a “dual” factor that directly affects the development of the algal system and the physiological cycle of shrimp. Light is both an energy source that sustains the ecosystem, but when its intensity is too strong (scorching sunlight), it becomes a serious stressor, directly threatening the health of the shrimp stock.
Below is a detailed analysis of the role and impact of light in the pond environment for farmers to better understand.
1. THE ESSENTIAL ROLE OF LIGHT IN THE POND ECOSYSTEM
Sunlight is not merely for illumination; it also plays a core role in maintaining the pond’s biological balance:
- Maintaining a natural oxygen source: Light is the only energy source for phytoplankton (mainly algae) to carry out photosynthesis. A stable algal system will provide a large amount of dissolved oxygen (DO) during the day.
- Creating a protective layer: The growth of algae creates the characteristic “tea-colored water.” This water color acts as a shield, helping reduce the intensity of light reaching the bottom layer, creating a sense of safety for the shrimp.
- Regulating shrimp physiology: Light supports the biological cycle, stimulates feeding activity, and nutrient metabolism. If light is lacking for a prolonged period, the algal system will collapse (algal die-off), leading to severe oxygen depletion, disrupting the biological rhythm and causing shrimp to become sluggish and reduce feeding.
2. WHY ARE SHRIMP “AFRAID” OF SCORCHING SUN? IMPACT ON LIVESTOCK PHYSIOLOGY
Although they need light, whiteleg shrimp are extremely sensitive to heat radiation when the sun is intense. This suddenly changes the shrimp’s physiological tolerance limits:
- Damage from ultraviolet (UV) rays: Scorching sunlight often comes with high-intensity ultraviolet (UV) rays. These rays can penetrate shallow water layers, causing damage to the epithelium and sensitive organs of shrimp.
- The “double stress” phenomenon: When surface water temperature rises above 32°C, shrimp tend to move down to the bottom layer to find a cooler place. However, the bottom of intensive ponds is often where organic sludge accumulates, oxygen is low, and many pathogenic bacteria are present. Avoiding the heat inadvertently pushes shrimp into a more dangerous situation, under pressure from both temperature and a polluted environment.
3. WATER ENVIRONMENT FLUCTUATIONS: CONSEQUENCES OF PROLONGED HEAT AND SUN
Scorching sunlight not only directly affects shrimp bodies but also causes severe fluctuations in the pond’s physicochemical parameters:
- Increased osmotic pressure: High temperatures cause water to evaporate quickly, making salinity rise sharply and placing heavy osmotic stress on shrimp bodies.
- pH fluctuations and increased toxicity of harmful gases: Under intense sunlight, excessive photosynthesis by algae at midday will push the pH above 8.5. This high pH level inhibits shrimp respiration and also increases the toxicity of NH3 gas present in the water.
- Temperature stratification: A large temperature difference between the surface layer (hot) and the bottom layer (cool) creates water stratification. The hot upper layer prevents oxygen from diffusing downward into deeper layers. As a result, the shrimp’s safe living space is reduced, leading to weakened resistance and a higher risk of hepatopancreatic diseases.
4. SOLUTIONS TO REDUCE HEAT STRESS AND MANAGE THE ENVIRONMENT
To protect shrimp stocks from the negative effects of scorching sunlight, farmers need to proactively apply the following technical measures:
- Shade the pond: Use shade netting with appropriate coverage to reduce direct heat radiation onto the pond surface.
- Manage algal density: Maintain water transparency at 30–40 cm. This helps create a natural biological protective layer, preventing sunlight from penetrating too deeply to the bottom.
- Operate aeration systems: On extremely hot days, increase the operation of paddle wheels and bottom aeration. This helps break up temperature stratification, mix surface and bottom water, and provide enough dissolved oxygen for shrimp respiration.
- Strengthen resistance: Supplement Vitamin C and electrolytes in the feed to help shrimp reduce stress, stabilize osmotic pressure, and improve resilience against environmental fluctuations.
CONCLUSION
In short, in intensive ponds, light is a necessary factor but must be strictly controlled. Understanding shrimp physiology in response to scorching sunlight will help farmers be more proactive in management. The synchronized combination of shading techniques, proper paddle wheel operation, and a resistance-boosting nutritional regimen is the key to helping shrimp stocks overcome harsh weather conditions, ensuring productivity and quality for the crop.
Thùy Dung
Source: tepbac.com
