Experience in using disinfectants in brackish water shrimp farming

Using disinfectants in the preparation and management of the pond water environment for shrimp to grow well is necessary. However, if the drugs are used incorrectly, it will have a negative impact on the pond environment and shrimp health, even causing shrimp death. Therefore, shrimp farmers need to pay attention.

During the pond preparation stage, shrimp farmers often use Iodine, KMnO4, and Chlorine to disinfect pond water. However, the use of disinfectants must be carried out 3-5 days before releasing shrimp larvae to minimize pathogens caused by bacteria and viruses in the water. During this time, farmers must take advantage of the time when the residual disinfectant decomposes and evaporates (usually before 48 hours), quickly color the water, inoculate microorganisms, and release shrimp larvae.

In the juvenile stage, from the time of stocking the shrimp to 45 days, many cases of shrimp are infected with Vibrio, the shrimp molt quickly (1.5 - 4 days/time), the immune system is weak, susceptible to viral diseases (white spots, yellow heads) and bacteria (hepatopancreatic necrosis). On the other hand, disinfectants also kill algae and zooplankton, causing bottom algae to grow and lack food for the shrimp. At this time, the shrimp are very weak and sensitive to disinfectants, especially when the shrimp are sick. Therefore, farmers only use disinfectants in urgent cases.

From the time the shrimp have been released for 45 days until harvest, this stage the shrimp have a higher resistance to disinfectants. However, farmers still need to be careful with disinfectants such as Chlorine, KMnO4 and Idodine because of their ability to kill algae and zooplankton in the pond, affecting the health, causing death to weak shrimp or shrimp that are being treated for diseases. Disinfectants should be used when there is an epidemic around, the shrimp pond water environment is dirty or near harvest. Note, Chlorine should absolutely not be used in the last month.

In brackish water shrimp farming, farmers often only care about the price and effectiveness of disinfectants but forget about their negative effects. Many disinfectants have the effect of killing algae, so when algae die, they consume a lot of oxygen to decompose, the pH in the pond decreases, toxic gases increase, causing shrimp to eat less. On the other hand, shrimp often stop eating immediately after applying disinfectants due to chemical shock, weakened immune systems and susceptibility to disease. Therefore, disinfectants are considered good for shrimp ponds because they cause little harm to beneficial microorganisms, zooplankton and do not affect shrimp health, especially when shrimp are small, molting or sick.

It should be noted that after disinfecting the water, harmful bacteria will quickly re-emerge. Therefore, farmers need to inoculate microorganisms immediately after 48 hours of use to help beneficial bacillus bacteria create a dominant population first, thereby controlling the density of pathogenic bacteria below dangerous levels. Under normal conditions, the periodic use of biological products can overwhelm harmful bacteria in pond water. In cases of high disease pressure, the use of disinfectants is necessary because it helps control the density of harmful bacteria below dangerous levels.

Some harmful effects of disinfectants:

- Chlorine: when pH is high, the effectiveness will decrease, especially when pH is above 8; When the pond has a lot of organic debris (because part of Chlorine will oxidize organic matter), the dose must be increased, causing toxicity to shrimp and being expensive; Only use Chlorine when renovating the pond; Using Chlorine is difficult to color the water, kill algae, and long-term use will make the pond bottom inert, making the beneficial bacteria system poor.

- Potassium permanganate (KMnO4): not stable, reduces the ability to disinfect under sunlight or at high temperatures, so it needs to be stored in dark brown bottles to avoid direct sunlight, should be used in cool weather; When in water, KMnO4 will combine with water to create MnO2, which is toxic to shrimp.

- Formalin: adversely affects the respiratory system, nervous system and skin.

- Iodine: if used in excess of the allowable level, the pond will lack oxygen, causing shrimp to float and die en masse.

According to Thuysanvietnam