Dissolved oxygen of water in shrimp pond

Dissolved oxygen (DO) is an important factor in aquaculture production. Low dissolved oxygen in the water can cause deaths in shrimp and fish.

Dissolved oxygen (ppm)	Effects on shrimp
0.3	Shrimp die
1.0	Anoxia in shrimp, shrimp may die
2.0	Shrimp cannot grow up
3.0	Shrimp grows slowly
4.0	Shrimp grows normally
5.0 - 7.0	Shrimp grows healthily and rapidly

Thus, the best levels of dissolved oxygen for shrimp are equal or higher than 5 ppm.

Oxygen concentration decreases depending on the depth of water. Dissolved oxygen decreases when temperature and salinity decrease.

During the day, with sunlight, algae and plankton photosynthesize and create oxygen dissolved in water.

At night, on days without sunlight or with overcast weather and rain, water will not have enough dissolved oxygen for shrimp. At this time, dissolved oxygen should be increased by using paddlewheel aerator, aeration blower, or changing a part of water.

Excessive use of chemicals to remove algae or insecticides that make aquatic plants die can also cause a shortage of dissolved oxygen.

Some symptoms of shrimp when water with dissolved oxygen is lacked: Shrimp concentrates near water surface, edges of ponds, near position where water comes in; lethargic shrimp with strong respiratory rate, coma and possible death in shrimp.

In water which is saturated air, dissolved air will invade the circulatory system of shrimp and form bubbles impeding shrimp blood flow. This creates "gas bubble disease" that causes deaths in shrimp.

The water is saturated air when:

• Photosynthesis of phytoplankton is too much (transparency measured by Secchi disk is read at 10cm or less).

• The water temperature increased.

• Disturbance strong between water layers (at positions fan, water pump)

Overcome the lack of oxygen in the pond:

- Pond needs aeration. If drop waterhyacinth, duckweed or water spinach to make shelter when it's sunny, them gather together in a corner of the pond, do not drop more than 1/3 of the pond surface.

- Do not feed and fertilize with excess doses. This will reduce the concentration of dissolved oxygen. Died algae consumes oxygen and generates CO2, NH3, H2S...

- Change the water with other good quality water.

- When a mass of shrimp, fish swim on water surface and weak active (swimming lethargically, swimming near edges of ponds, no reaction to sound): need aeration, turn on water fan, supply new water.

- Use hydrogen peroxide H2O2: 2H2O2 → 2H2O + O2

When dissolved oxygen is less than 4 ppm, shrimps swim on the water surface: need more aeration and water changes; check and the adjustment feed intake; avoid fresh food, add vitamins, minerals and supplements to food; manage quality of water carefully.

If the dissolved oxygen is too low in morning and too high in afternoon, this makes algae thrive. We must control the feed, use 10 - 20kg CaCO3 / 1600 m2, turn on aeration in night, manage quality of water.

When the dissolved oxygen is too low, use more air blowers.