Pond preparation

Pond preparation is essential to reduce risks of disease outbreaks, obtain a conducive environment for the growth of the stock, and therefore attaining better productivity.
All surveyed farms treated pond bottom before a new culture cycle. The fallow period varied between farms (2-45 days), However, majority of farms have the fallow period of either 7 days, 10 days, 15 days or 30 days. But in exceptional years the farmers may have to wait longer until seed becomes available.

Almost all farms removed the sludge during the fallow period, which was followed by the application of lime. Some farms dried the ponds. Other treatments included application of salt or filling water then treating with chlorine before draining. All farms did not screen the supply water. In fact this is necessary to minimise the introduction of unwanted materials and organisms. Farms also did not have water sedimentation before supplying water into the ponds – this is although ideal but considering the amount of water use every day, it is difficult to comply.

The following factors/steps are recommended to significantly improve pond environment.

Step 1. Removal of the bottom sludge between culture cycles

Removal of bottom sludge ensures better water quality when the pond is refilled and stocked for the next cycle. The sludge contains organic matter which will get transformed in to harmful gases such H2S (also NH3, NO2-, CH4). Aerobic bacterial decomposition of organic matter is also an important drain on dissolved oxygen in the pond.

Removal of bottom sludge should preferably be undertaken after every harvest but compulsory after every second harvest. The sludge must be disposed away from the pond site, so that it does not seep back into waterways, ponds, or cause other environmental problems.

The catfish farming system in the Delta has to, in due course, evolve strategies, as groups or clusters, to use the sludge as a fertilizer for the vast acreage of crops (e.g. rice and fruit) in the Delta.

Step 2: Ploughing

Ponds located inland and or on high ground may dry easily. On removal of the sludge, light ploughing of the soil when wet, is desired. This step is generally lacking in the current practice. The main purpose of ploughing is to expose the black soil layer(s) underneath to sunlight and atmospheric oxygen, which assist the breakdown and oxidation of the organic waste (sludge) into less harmful substances.

Presence of moisture in soil (i.e., under wet soil conditions) during ploughing allows bacteria to work better in breaking down the black organic matter, thus making the ploughing process more effective. After ploughing, dry the pond bottom for 5 to 7 days.

Ploughing the pond bottom may lead to turbid water conditions during the culture period. Therefore, compaction of the bottom using heavy rollers after the whole process of pond preparation, i.e., before water intake, can avoid the turbid water condition. This step is not applicable to ponds located on the river bank or those that can not be drained completely.

Step 3: Liming Liming during pond preparation, a common and low cost practice, is useful for optimising the pH and alkalinity conditions of soil and water. The type and amount of lime to be added depends mainly on the soil pH and also on pond water pH, which ideally should be checked before lime application.

Recommended lime application during pond preparation

Where a disinfectant such as bleach (calcium hypochlorite) is used apply lime only 3-4 days after the application of the disinfectant. If lime is used earlier to disinfect, then the effectiveness of the disinfectant is reduced.

Step 4: Pond filling

When ponds are filled/ or water is added care needs to be taken to filter the water using small mesh at the inlet pipe to prevent undesirable organisms entering the pond. Admittedly, this will not stop all organisms entering the pond this practice at least offers some control.

Updated on : Feb 2015