Detailed Explanation of Key Technical Points for Freshwater Farming of Whiteleg Shrimp (Litopenaeus vannamei)
AbstractThe most suitable water temperature for the survival of whiteleg shrimp is 28-32°C. Release them when the weather is clear or in the evening; the most suitable water temperature for releasing fry is 20°C or above. Select high-quality fry with good vitality, quick responses, and a transparent body. Before releasing them into the freshwater farming pond, carry out desalination and extensive conditioning to increase the survival rate. Properly control the salinity content, pH value, dissolved oxygen level and content of other chemical substances in the farming pond.
1. Stocking of shrimp fry and selection of fry
Whiteleg shrimp can survive in water temperatures of 15-35°C, but the most suitable water temperature for their growth is 28-32°C. Shrimp fry living at this water temperature have very robust constitutions and grow quickly. Avoid stocking on rainy days when the water is turbid or at noon when the sun is directly shining; choose clear days or the evening for releasing fry, and the water temperature at stocking should be above 20°C.
In the Huanggang area of China, the annual fry release time is around late May. At this time the water temperature is relatively stable, generally around 25°C. Releasing fry at this time can effectively avoid the low-temperature stimulation brought by cold currents. During stocking, in order to make the temperature difference between the water in the shrimp bag and the water in the pond smaller, you can first place the bag containing the shrimp fry into the pond for about 30 minutes.
When selecting shrimp fry, choose fry with good vitality, agile movement, a transparent body without redness, gills that are not black, and fully opened tail fans.
2. Desalination and pre-growing treatment
Shrimp fry hatched at seedling farms are usually hatched in seawater with a salinity content of 20‰. Although they have undergone a short period of desalination treatment, releasing them directly will affect the survival rate, and in serious cases it may lead to total loss. In order not to affect the survival rate of whiteleg shrimp, in the early stage of farming the shrimp fry need to undergo a gradual desalination and temporary holding treatment.
Before releasing the fry, use colored cloth strips or earthen dams to enclose a temporary holding pond in one corner of the pond for desalination and pre-growing treatment. Place 500 shrimp fry per square meter in the temporary holding pond; if there is aeration equipment, 1000 can be placed. Then add sea salt essence or coarse salt to the water in the temporary holding pond, and adjust the salinity to be similar to the salinity of the water in the fry release pond. When releasing the fry, the salinity difference in the water must not exceed 3‰-5‰, the temperature difference must not exceed 3°C, and the pH value should be 7.8-8.6.
Four days after releasing the fry, add about 3-5cm of pond water to the temporary holding pond every day, so that the salinity of the water in the temporary holding pond gradually decreases, while keeping the water depth in the pond at about 1m, and pay attention to adjusting the pH value and water color in time. After half a month of desalination and pre-growing treatment, the salinity content in the temporary holding pond will be comparable to that in the farming pond.
When the shrimp fry in the temporary holding pond grow to a body size of more than 2cm, stop feeding, dig several gaps in the pond embankment of the temporary holding pond to connect it with the farming pond, and let the shrimp fry swim out on their own. On the evening of the same day the fry enter the farming pond, feed them bait, and 4 days later feed them feed. The first feeding amount is 5-10 grams per 10,000 fry, and the daily feeding frequency is 5-6 times, gradually increasing each day, with a daily increase of 20%-30% of the feed amount. The stocking density in the farming pond should be reasonable, about 100,000 fry per mu.
3. Water quality requirements
Whiteleg shrimp is a marine shrimp, so the salinity variation range of the pond water in the farming pond must not exceed 5%, the pH value should be between 7.5-9.0, and the daily variation range must not exceed 0.5 units, the dissolved oxygen content should be above 4mg/L, the nitrite nitrogen content must not exceed 0.1mg/L, the ammonia nitrogen content must not exceed 0.02mg/L, and the hydrogen sulfide content at the bottom layer of the pond must not exceed 0.1mg/L.
There are relatively high requirements for algae in the pond water. The most suitable water color is tea-brown or yellow-green formed by green algae and diatoms, with a transparency of 25-40cm.