How can you control Vibrio bacteria?
After Dr. Lightner confirmed its virulence using Koch’s postulate, it was found that some strains of Vibrio parahaemolyticus that is the cause of EMS in Asia. Most recently it has also been found to cause EMS in Mexico, which is far away from Asia. It is possible that someone brought brooder shrimp from an Asian country where EMS is prevalent into Mexico for breeding purposes and the weak postlarvae got EMS, or perhaps they used very fast-growing breeding stock and the postlarvae were so weak they got large numbers of Vibrio bacteria growing in their hepatopancreas. It would probably be impossible for V. parahaemolyticus to suddenly become more virulent, because it is a normal flora commonly found in sea water and brackish water. More likely the cause is that the postlarvae shrimp got weaker and more susceptible to Vibrio bacteria.
A major cause for concern is that when shrimp breeders and shrimp farmers learn from the report that EMS is caused by Vibrio bacteria they may decide to use more antibiotics in their shrimp farms and nurseries to reduce and control Vibrio bacteria. That is not desirable for the marine shrimp industry, which needs to reduce antibiotic residues in shrimp. Also, long-term use of antibiotics, particularly during the nursery period, can make the shrimp become weak when the antibiotics treatment is stopped. Shrimp producers should use other methods to control Vibrio bacteria, such as probiotic bacteria, some kinds of which synthesize chemicals similar to antibiotics that can inhibit Vibrio bacteria. The probiotic approach is probably preferable to using antibiotics. However, when Nauplius or postlarvae shrimp are raised at a high population density in the nursery, then the amount of feed they require is quite high. This tends to increase the population of Vibrio bacteria. In that case using probiotic bacteria alone might not be enough to control the Vibrio bacteria and it would be advisable to change the water frequently. That would likely be a better way to keep the Vibrio bacteria in check.
The stocking density in nurseries should not be too high because it will have a direct impact on the amount of Vibrio bacteria, which is related to the amount of feed given. If the amount of feed given is too little, then the shrimp will eat each other and will be weak, but if the amount of feed given is too much, the water quality will drop and the amount of Vibrio bacteria will rise. The most appropriate population density for nurseries is 100,000 nauplius per cubic meter of water.
Postlarvae that has been nursed for 30 days before release into the pond.
Water temperature is also important in shrimp nurseries. The most appropriate temperature is 30 + 1oC. At this temperature the nauplius will eat normally. At lower temperatures the Nauplius will eat less and develop more slowly. On the other hand, if the temperature is high, such as up to 33oC, then the nauplius will eat more and grow very quickly from stage to stage, but they will be weaker, and the higher temperature is also favorable for the growth of Vibrio bacteria, which will increase rapidly and difficult to control. If it is necessary to use a higher temperature to eliminate WSSV that might be presenting the nursery, then it is best to elevate the water to just 32oC for 7 days before the postlarvae shrimp are transferred to the culture pond.
Source: Chalor Limsuwan, Ph.D., Aquaculture Business Research Center (ABRC), Faculty of Fisheries, Kasetsart University, Thailand – Oct./ Dec. 2013