Simulation of phosphorus dynamics in an intensive shrimp culture system: effects of feed formulations and feeding strategies
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The rapid expansion of shrimp culture has brought concern about potential environmental impacts caused by phosphorus wastes discharged from shrimp farms. This study describes development of a simulation model representing the effect of feed nutritional quality, feed physical characteristics, and feeding strategies on phosphorus dynamics in intensive Pacific white shrimp (Litopenaeus vannamei) culture systems, receiving dry feeds in the absence of natural productivity except bacteria. The model represents the addition of phosphorus to the culture system as dry feed, its consumption and metabolism by shrimp, and its loss in uneaten feed, particulate feed, feces, and dissolved in the water. The model was quantified using published information and unpublished research results conducted at the Shrimp Mariculture Research Laboratory of Texas A and M University. The model is multivariate, deterministic, and uses a compartment model structure based on difference equations. Evaluation of the model consisted of simulating two indoor and one outdoor experiments that examined the effect of various feed formulation and feeding parameters on total reactive phosphorus (TRP) concentration in the water. Simulated TRP generally agreed with indoor experimental results, but it was overestimated by 0.13 ppm when compared to the outdoor experiment, probably due to lack of phytoplankton representation in the model. Simulations investigating a range of possible inorganic phosphorus availabilities suggested that when apparent availability is low either animals are using other sources of phosphorus or published values are underestimated and when apparent availability is high either animals are metabolically eliminating excess assimilated phosphorus or published values are overestimated. (C) 2000 Elsevier Science B.V.
