Total Organic Matter is a water quality parameter in shrimp farms which reflects the amount of organic matter from uneaten feed, feces, and metabolic byproducts. This parameter is usually seen as waste at the bottom of the pond or in water suspensions. The quality standard for total organic matter (TOM) in cultivation water is < 55 ppm. In water which has undergone treatment in tanks, the recommended TOM is < 20 ppm.
A high TOM concentration may occur due to death of plankton and overfeeding. Increase in leftover feed can be observed from the increase in total organic matter suspended in water or at the bottom of the pond. Dirt foams in pond water also indicate high organic matter. High organic matter and its consequences towards water quality parameters may impact the amount of feed consumed by shrimp.
High organic matter concentration also decreases DO. In water, a low dissolved oxygen (DO) level, or < 4 mg/l, causes various problems for shrimp, such as decreased appetite, emergence of disease, and even mortality. With high TOM, there is more materials to be utilized by microorganisms at the bottom of the pond, increasing biological oxygen demand (BOD) and decreasing DO. BOD is the total oxygen used by microorganisms to decompose organic matter.
A low DO is caused by the decomposition of organic matter by bacteria which requires it, causing the bottom of the pond to be in anaerobic conditions. High BOD indicates a high amount of organic waste in the pond. The excessive accumulation of waste due to the drastic drop in DO usually occurs at night or in the morning.
The combined effect of high TOM at the bottom and lack of oxygen causes the formation of hydrogen sulfide (H2S). Hydrogen sulfide is the byproduct of sulfate-digesting bacteria from organic matter in anaerobic conditions, usually at the pond bottom or mud. H2S can inhibit shrimp from absorbing oxygen.
If the TOM value is too high, some actions farmers can take are evaluating feed amount, disposing dead plankton, increasing siphoning, administering probiotics and replacing the water. These steps can be taken to maintain the amount of organic matter:
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