Simulation of nitrogen dynamics and shrimp growth in an intensive shrimp culture system: effects of feed and feeding parameters

Worldwide increases in shrimp culture have caused concern about potential e nvironmental impacts, particularly water pollution resulting from discharge of nitrogenous wastes 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 nitrogen dynamics and growth of the Pacific white shrimp, Litopenaeus vannamei, in intensive systems receiving dry feeds in the absence of natural productivity except b acteria. The model represents the addition of nitrogen to the culture syste m as dry feed, its consumption and metabolism by shrimp, and its loss in un eaten feed, particulate feed, feces, and excretion as ammonia. Shrimp somat ic growth is based on the amount of nitrogen incorporated into whole body. The model was quantified using unpublished research results conducted at th e Shrimp Mariculture Research Laboratory of Texas A&M University and publis hed information on the species. The model is multivariate, deterministic, a nd uses a compartment model structure based on difference equations. Evalua tion of the model consisted of simulating six indoor and one outdoor experi ments that examined the effect of various feed and feeding parameters on sh rimp growth. Simulated shrimp growth dynamics generally agreed with indoor experimental results but at low dietary protein levers (below 11%) and low feeding frequencies (below 2 times per day) simulated final biomass was und erestimated by 22 and 50%, respectively. Simulated final biomass was overes timated by 15% when compared to the outdoor experiment. Simulations investi gating a range of possible consumption rates suggested that either experime ntal animals used other sources of food or consumption rates for 2 g animal s are underestimated in the literature. (C) 1999 Elsevier Science B.V. All rights reserved.