The Vital Breath: Dissolved Oxygen in Aquaculture

In aquaculture, the quality of water is paramount to the health and growth of cultured species. Among all water parameters, Dissolved Oxygen (DO) is arguably the most critical. It is the lifeline for fish, shrimp, and other aquatic organisms, directly influencing their metabolism, feed conversion, immunity, and overall survival.

What is the Standard Value?

While the optimal DO level can vary slightly depending on the species, life stage, and water temperature, a general standard is widely accepted.

• Adequate Level: The recommended DO concentration for most farmed fish and shrimp is above 5 mg/L (or 5 ppm).

• Optimal Level: For promoting good growth, feed efficiency, and overall health, maintaining a level between 6 mg/L and 8 mg/L is ideal.

• Stress Level: When DO falls below 3-4 mg/L, most aquatic animals become stressed. They may reduce feeding, exhibit slower growth, and become more susceptible to diseases.

• Lethal Level: A further drop below 2 mg/L can be lethal, causing mass mortality in a very short time.

Why is Maintaining Proper DO So Important?

1. Respiration and Metabolism: Fish "breathe" oxygen dissolved in water through their gills. Sufficient DO is essential for their basic metabolic functions and energy production.

2. Feed Conversion Efficiency: In an oxygen-rich environment, fish can better digest and utilize feed, leading to improved growth rates and lower Feed Conversion Ratios (FCR), which directly impacts profitability.

3. Water Quality: Adequate DO supports beneficial nitrifying bacteria that break down toxic ammonia and nitrite, crucial for maintaining a healthy ecosystem within the culture pond or tank.

Monitoring and Management

Regular monitoring of DO, especially during early morning when levels are typically at their lowest, is essential. Farmers use aerators, paddlewheels, and diffused air systems to replenish oxygen, particularly in intensive farming systems.

In conclusion, maintaining dissolved oxygen above 5 mg/L is a non-negotiable standard for successful and sustainable aquaculture. It is the invisible fuel that drives productivity and ensures the well-being of the stock.