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Aeration technology for aquiculture
Public Time:2010-03-21 10:47:33 Read Times:2790
 

The change of Dissolved Oxygen (DO)

         The change trend of DO in the pond is mainly determined by the plankton photosynthesis and illumination. From the start of sunrise, as the sunshine increases, the photosynthesis increases, dissolved oxygen increases, about 2 ~ 3 p.m. the dissolved oxygen is at highest level, each liter has more than 10 mg of DO.  Then the illumination decreases gradually, the photosynthesis stops at night, dissolved oxygen is consumed and not increased, so the dissolved oxygen drops quickly, before dawn, the dissolved oxygen is at the lowest level, usually it can be as low as 1 mg/l.

The dissolved oxygen in the pond is mainly from the plankton photosynthesis and the oxygen in the air solved in the water. The consumption of the dissolved oxygen is mainly by the phytoplankton respiration organic decomposition. The dissolved oxygen is effected by illumination, wind, air pressure and plankton etc. Though there is some variation, but we can not rely on experience to accurately judge of the dissolved oxygen content in ponds.

How to control the dissolved oxygen?

      At present, aquaculture ponds rely mainly on the manual control aerator, it effectively solves the problem of adding oxygen in the ponds. Because the dissolved oxygen content can not be accurately checked, manually controlled aerator still has certain blindness, it is difficult to achieve the purpose on energy saving and moderation of oxygen, hypoxia phenomenon occurs happen from time to time.

The new apparatus can accurate detect the dissolved oxygen content in the water. The operator can set the top and bottom limits to start or stop the aerators. When the dissolved oxygen is under bottom limits, it will alarm audibly and visually, when the dissolved oxygen reaches top limit, it will stop the aerators, so it can keep the dissolved oxygen at the high point. This apparatus can detect water temperature, alarm when no electricity and have manual control function.

Correctly use the instrument can keep the dissolved oxygen content in ponds at a proper level to ensure fish grow normally and reduce the fish disease. It can raise feed coefficient, save manpower, saving energy. The instrument is especially for automatic control of dissolved oxygen for fish ponds.   

Aquatic animal life elements – oxygen

Like human being, aquatic livings must live in aerobic conditions, hypoxia can make fish gasp for air, when the hypoxia is serious, fish will die extensively in the pond. Generally, the aquaculture breeding needs dissolved oxygen 5-8mg/l. At least it shall above 4mg/L. All sorts of fish need dissolved oxygen conditions as follows:

variety

Dissolved Oxygen (mg/l)

fish hypoxia

(mg/l)

Suffocation deaths (mg/l)

mandarin fish

6-8

1.5

0.8

silurus meridionalis

6-9

1.4

0.7

chub

5.5-8

1.75

0.6

terch

4-8

1.55

0.4

grass carp

5-8

1.6

0.5

carp

5-8

1.5

0.3

dace

4-8

1.6

0.5

japanese eel

4-9

1.4

0.6

megalobrama amblycephala

5.5-8

1.7

0.6

tilapia

6-9

1.5

0.2

snoek

5-8

1.8

0.7

crucian

4-5

1.0

0.1

chinese shrimp

6-8

1.4

0.4

sugpo prawn

5-8

1.2

0.3

macrobrachium rosenbergii

7-9

1.5

0.5

river crab

5

2.5

1.5

How to reasonably increase oxygen?

1.      Ensure no fish gasping for air: if fish often gasp for air, it will consume a lot of energy. “once it gasp for air, the fish will not grow in 3 days”. The fish’s appetite will decrease and bait use ratio will drop, so the fish is easily to be ill and grow slowly.  If the oxygen in the water is too small, the plankton will die in big quantity, so the water quality will deteriorate.  So when the dissolved oxygen is close to the bottom level, the aerator shall start work. It is better to start the aerator when the oxygen is 1-2 mg/l above the bottom limit.  This can increase the bait use ratio and reduce feed ratio, keep the fish energetic and reduce illness of fish. It can keep the water quality.

2.      avoid to increase oxygen in vain: when the dissolved oxygen is enough (usually it is above 3—4mg/l), it shall stop aerator to avoid energy waste

3.      supplement oxygen at noon :

                 It is necessary to supplement oxygen at noon. When the sunshine is strongest at noon, the dissolved oxygen on the top water layer is saturated. Usually the figure can be above 10 mg/l, at this moment, to start the aerator can mix the top water with bottom water, which can increase the whole oxygen in the pond, this can prevent the dissolved oxygen drops too quickly at night. It can speed up the decomposition of organic matters and oxygenation of inorganic substance, it can suppress ammonia, nitrites and Hydrogen sulphide. It is good for water quality. So it is necessary to supplement oxygen at noon. If the top water is not saturated with oxygen, it is not ideal to supplement. When the oxygen is saturated, it is most efficient to supplement oxygen.

The application effect of the controller

To properly use the controller, it can perfectly perform automatic and reasonable aeration. It saves labor, money, electricity, feed and reduce fish illness and increases aquatic output. It can save about 30% electricity than manual aeration, the feed ratio can reduce by 5—10%, the production can increase by about 5% and the effect is obvious.  

 

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