Water-heating therapy can increase the survival rate of shrimp. When studying the effect of water temperature on Penaeus vannamei infection with white spot disease (WSSV), it was found that the shrimp continued to be cultured at a temperature of 321°C or the water temperature dropped to 281°C after being raised at this temperature for 7 days. Shrimp infected with white spot disease did not show symptoms of disease and death. The use of water-enhancing therapies in Thailand and Latin America has greatly increased the survival rate of shrimp.
In the study by the authors of this paper, the shrimps used in the study were collected from the province of Chantanburi, Thailand. These shrimps infect WSSV through bathing and oral routes. During the experiment, the relationship between water temperature and the related reactions they produced was evaluated.
The virus capable of reinfecting SPF broodstock was stored at -80°C. The inoculum was obtained from head thoracic tissues infected with WSSV prawn, including tendons and muscles.
WSSV experiment
Bath treatment. In the bath treatment, 180 5 g shrimp were transferred to 21 90 L aeration and heating tanks, and then the tank was filled with 90 mL of WSSV inoculum.
After inoculation, one group of shrimp lived at a temperature of 321°C and the control group lived at a temperature of 281°C. Other shrimp lived at a temperature of 321°C, but at 1, 3, 5, and 7 days respectively, the water temperature dropped to 281°C. Another group is a blank control group. Each group has 3 repeated experiments.
Oral treatment. In the oral route, another 180 shrimp were also transferred to 21 90L aeration and heating tanks. First, the subjects were fed a diseased shrimp with WSSV at a shrimp body weight of 10%, and then the pellets were fed twice a day in a ratio of 5% of the shrimp body weight.
One group of shrimps in the experimental group was cultured at 321°C and the control group was cultured at 281°C. In the other experimental groups, the initial culture temperature was 321°C. After 1, 3, 5, and 7 days, the water temperature dropped to 281°C. Another group is a blank control group. Each group has 3 repeated experiments.
Observe symptoms and death every 12 hours until the end of the experiment. The status of sudden death and survival of shrimp was confirmed by nested PCR test and histopathology.
Experimental results
Whether WSSV-infected shrimps were immersed in the bath or the oral route, those who continued to live at 321°C and those who had lived at these temperatures after infection for 7 days then lowered the temperature to 281°C did not show WSSV symptoms and death. . Using nested PCR and histopathology, these surviving shrimps were found to be negative for WSSV. Tables 1 and 2 show the initial time of death observed in the other experimental groups within 42-66 hours after treatment with the bath and oral route of infection. The total time of death observed between 114-168 hours.
Improves survival rate
In the rearing pool, even if a greenhouse is used, it is unlikely to solve the water temperature problem. However, during the hatchery nursery, using the heater, it is relatively easy to maintain the water temperature at 321 °C. But at present, there are not a few hatchery water temperatures that reach this level. In comparison, their water temperature is usually 28-30°C. Even in some hatcheries without heating processors, their water temperature will be lower during the wintering period. .
Although WSSV PCR testing was performed on juvenile shrimp before shrimp production, it was discovered in many farms in Latin America and Thailand that when the water temperature is lower than 30°C, WSSV will explode. Of course, this is only a random sampling of shrimp samples rather than all of them. Prawns. Even in the conditions of bio-safety and circulating water equipment, there will be deaths from WSSV 60 days after the initial release. Some farms have investigated and decided to use water for warming treatment for 7 days. The effect is significant and the survival rate is improved.
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