How to Maintain Water Quality in Fish Farms

Fish, with their unique features such as gills and fins, require a suitable aquatic environment for their optimal growth and health. Water quality management plays a crucial role in ensuring the well-being of fish in aquaculture systems. This article outlines various aspects of water quality management, including dissolved oxygen, temperature, turbidity, ammonia, nitrite, hydrogen sulfide, pH, and total alkalinity. Additionally, it covers bottom soil management considerations for maintaining a healthy aquatic environment for fish farming.

Water Quality Management

(a) Dissolved Oxygen:

Maintaining an optimal level of dissolved oxygen is essential for fish production, with a recommended concentration of 5 mg/l. Oxygen depletion can be rectified through different aeration methods, such as:

Manual method:

Using bamboo sticks to splash the water surface facilitates oxygen dissolution.

Mechanical method:

Operating a diesel water pump to pump out water and spread it across the water body, aiding atmospheric oxygen dissolution.

Aerator method:

Utilizing floating devices equipped with mechanical rotating blades that churn the water, promoting oxygen development.

(b) Temperature:

Temperature significantly influences the aquatic environment. The recommended temperature ranges from 14 to 18 degrees Celsius for cold water and 24 to 30 degrees Celsius for warm water. Planting trees along pond banks provides shade, reducing stratification. Additionally, wind mixing and the photosynthesis process contribute to favorable conditions.

(c) Turbidity:

Turbidity refers to the cloudiness or haziness of a fluid caused by invisible particles. Measuring turbidity is a crucial test for assessing water quality, done using a Secchi disk. The optimum visibility range for turbidity is 40-60 cm. Organic manure application at 500-1000 kg/ha, gypsum at 250-500 kg, or alum at 25-50 kg can effectively control turbidity.

(d) Ammonia:

Ammonia is generally toxic to fish. To maintain a safe concentration for fish (0.02-0.05 mg of ionized ammonia), the following methods can be employed:

1. Avoid overfeeding.
2. Regulate liming to prevent excess.
3. Use formalin to remove ammonia from the fish pond.
4. Implement water exchange to reduce ammonia concentration.
5. Aeration decreases pH, leading to reduced toxicity.

(e) Nitrite:

To maintain suitable nitrite levels in the water, correct stocking density, feeding, and fertilization practices should be followed. Biofiltration through specialized filters and maintaining well-oxygenated ponds are additional measures for nitrite control.

(f) Hydrogen Sulfide:

Hydrogen sulfide, a toxic compound that stresses fish, forms a thick organic deposit at the pond bottom. To control hydrogen sulfide:

1. Frequent water exchange is necessary.
2. Liming should be applied to reduce its toxicity.

(g) pH:

pH indicates the acidity or basicity of water based on the hydrogen ion concentration. The pH scale range for water quality can be summarized as follows: At a pH of 4, it reaches the acid death point, while in the range of 4 to 6, growth is slowed down. The pH range of 6 to 9 is considered the best for growth. However, at a pH of 9 to 11, growth is again slowed down. Any pH value greater than 11 indicates an alkaline death point.

(h) Total Alkalinity:

Total alkalinity refers to the concentration of bases in water and its capacity to accept acidity. Carbonates and bicarbonates are dominant bases, with an ideal range of 75-300 mg/l for fish. Low alkalinity can be corrected through lime treatment.

(i) Total Hardness:

Water hardness, primarily influenced by calcium and magnesium, affects pond productivity. A level of 60 mg/l promotes productivity, while below 60 mg/l can create stress for fish. Low hardness can be addressed through lime treatment.

Bottom Soil Management

(a) Texture:

The ideal soil texture should not be excessively sandy or clayey.

(b) Soil Acidity:

Maintaining a soil pH range of 6-8 is desirable, with lime application adjusted accordingly.

(c) Soil Aeration:

Proper soil aeration and water circulation are essential for maintaining a healthy aquatic environment. Adequate oxygenation of the soil promotes nutrient availability and prevents the buildup of harmful substances.

(d) Drying Pond Bottom:

Allowing the pond bottom to dry for a period of 2-3 weeks is necessary for effective bottom soil management. This drying period helps in reducing excess moisture, controlling the growth of unwanted organisms, and preparing the soil for subsequent cultivation.

Conclusion

In conclusion, water quality management is vital for successful fish farming. By addressing key factors such as dissolved oxygen, temperature, turbidity, ammonia, nitrite, hydrogen sulfide, pH, total alkalinity, and bottom soil conditions, fish farmers can create a conducive environment for the growth, health, and productivity of their fish stock. Implementing appropriate management strategies ensures optimal results and contributes to the overall success of aquaculture operations.