Modeling the effect of nitrogen input from feed on the nitrogen dynamics in an enclosed intensive culture pond of black tiger shrimp (Penaeus monodon)

In the present study, a mathematical model was developed to evaluate the effect of nitrogen (N) input from feed on the N dynamics under different feeding scenarios in a well aerated and enclosed culture pond of black tiger shrimp (Penaeus monodon). Three feeding levels were examined: underfeeding, optimum feeding and overfeeding. The model was formulated using field data gathered from an earthen pond (0.69 ha) which was stocked with shrimp post larvae at a density of 340,000 individuals ha(-1) and grown for 151 d. The model suggested that the underfeeding rate 329 kgNha(-1)cycle(-1)) observed from the study pond, which was being underfed, resulted in the ingestion of the natural productivity in the pond. With the underfeeding practice, phytoplankton assimilated ammonia and nitrate+nitrite at the rates of 412 and 52 kgNha(-1)cycle(-1), respectively, while nitrification rate in the water column was 45 kgNha(-1)cycle(-1). The coupled processes of nitrification and denitrification in sediment were nearly equal at rates averaging 207 and 206 kgNha(-1)cycle(-1), respectively. Optimum feeding indicated that the larger N input accelerated the accumulation of N in shrimp and phytoplankton as well as the accumulation of N in the water column and sediment. The coupled processes of nitrification and denitrification were accelerated to the rates of 298 and 292 kgNha(-1)cycle(-1). The overfeeding practice indicated that the extra N did not accelerate the process of N assimilation by phytoplankton due to light limitation, but accelerated the N processes in the sediment resulting in the active removal of N from the enclosed shrimp culture pond through the denitrification process (343 kgNha(-1)cycle(-1)). Thus, the mathematical model developed by the present study proved to be an effective tool in understanding N dynamics and gives informative data for farm management in the enclosed culture pond of black tiger shrimp.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga