| Abstract | Experiments to estimate organic matter budget in closed intensive culture system of P. monodon were conducted in 4-m³ (2x2x1 m) concrete ponds with three shrimp stocking densities (20, 40, and 60/m²). The experiment was set up using completely randomize design with three treatments plus control. Each density treatment was in triplicate. Experimental period was 15 weeks. In this closed culture system there was no water exchange but small amount of water was added into the ponds to maintain water salinity at 20 ppt, feeding was done in feeding tray, and leftover feed was removed from the ponds. Photosynthetic rate of pond water and respiration rate of pond bottom soil and pond water as well as some water quality parameters were measured weekly in experimental ponds. Respiration rate of shrimp was studied separately in laboratory. The study of shrimp molt was done in small floating cages. Organic carbon of pond water, pond bottom soil, shrimp postlarva, harvested shrimp, shrimp feed, and shrimp molt were analyzed. Data obtained were used to calculated organic matter budget in shrimp ponds. Total organic matter input in ponds stocking with 20, 40, and 60 shrimp/m² were 620.74, 756.45, and 983.93 gC/m². Shrimp feed accounted for 42.8-51.5% of organic matter input. Fixation of carbon by photosynthesis of photoplankton and bethic algae accounted for 37.0-54-4% and 0.9-10.1% of total organic matter input respectively. Water supply contributed to 1.3-1.8% of total organic matter input and shrimp postlarva contributed to 0.1% of total organic matter input. During culture periods of 15 weeks, the total amount of organic matter of 197.07, 183.44 and 394.02 gC/m² accumulated in bottom soil of ponds stocked with 20, 40, and 60 shrimp/m², water respiration and pond bottom soil respiration used up 28.4-36.1% and 11.7-19.7% of total organic matter input, respectively. Shrimp respiration accounted for the loss of 7.9-12.6% of total organic matter input. Only 5.6-6.8% of organic matter input was removed as harvested shrimp. A small amount, 2.1-3.4%, of the total organic matter input accumulated in pond water and were released with the effluent. The remaining 24.2-40.0% of total organic matter input was left to accumulate in pond bottom soil or lost through anaerobic decomposition. There were positive correlations between stocking density of shrimp and organic matter input through algae photosynthesis. The increase in stocking density to the level of 60 shrimp/m² resulted in high organic matter input and the accumulation of large amount of organic matter in pond which resulted in significantly (P<0.05) lower growth rates, lower survival rates, and higher feed conversion ratio (FCR) of shrimp. Respiration rate of shrimp was significantly affected by temperature, water current velocity, and type of bottom materials. Shrimp assimilated 31.9-38.3% of ingested feed in which 18.4-25.0% were used for shrimp respiration and 11.7-13.5% remaining as shrimp tissue that was harvested from the ponds. Total amount of 61.7-68-1% of organic matter of ingested feed became shrimp molt and shrimp faces. Production of shrimp were 290.9, 409.5, and 442.9 g/m² for the stocking rates of 20, 40, and 60 shrimp/m², respectively |