Global Aquaculture Alliance —
Before discussing organic matter decomposition, it will be helpful to mention organic matter production by plants. The end product of photosynthesis is simple sugar (C6H12O6). Plants use some of this sugar directly for energy or convert it to starch for a reserve energy source. They also use the sugar from photosynthesis to make proteins, hemicellulose, cellulose, lignin, fats, waxes, etc. that comprise plant biomass. The composition of plant parts differ and the average composition of entire plants vary among species.
Plants and organic matter
Plants are harvested and used for human and animal food and for other purposes. Plants harvested for human use are processed with resulting wastes and plants die and enter the environment as dead organic matter. The composition of organic matter is chemically complex, and livestock manures have been greatly altered from their original form by passing through the gastrointestinal tracts of animals.
Organic matter added to aquaculture production systems is some combination of organic fertilizer, uneaten feed, feces and remains of plankton and other dead organisms. Decomposition of organic matter exerts an oxygen demand and too much organic matter may lead to dissolved oxygen depletion, which is of concern in feed-based aquaculture. In fertilized ponds, organic matter is a source of food for benthic organisms that can also be eaten directly by some fish and shrimp.