Simulation of phosphorus dynamics in an intensive shrimp culture system: effects of feed formulations and feeding strategies

The rapid expansion of shrimp culture has brought concern about potential e nvironmental-impacts caused by phosphorus wastes discharged from shrimp far ms. This study describes development of a simulation model representing the effect of feed nutritional quality, feed physical characteristics, and fee ding strategies on phosphorus dynamics in intensive Pacific white shrimp (L itopenaeus 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 metaboli sm by shrimp, and its loss in uneaten feed, particulate feed, feces, and di ssolved in the water. The model was quantified using published information and unpublished research results conducted at the Shrimp Mariculture Resear ch Laboratory of Texas A&M University. The model is multivariate, determini stic, 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 feedi ng parameters on total reactive phosphorus (TRP) concentration in the water . Simulated TRP generally agreed with indoor experimental results, but it w as overestimated by 0.13 ppm when compared to the outdoor experiment, proba bly due to lack of phytoplankton representation in the model. Simulations i nvestigating a range of possible inorganic phosphorus availabilities sugges ted that when apparent availability is low either animals are using other s ources of phosphorus or published values are underestimated and when appare nt availability is high either animals are metabolically eliminating excess assimilated phosphorus or published values are overestimated. (C) 2000 Els evier Science B.V. All rights reserved.