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From the estimation of the mass balance model, which can also be
classified as “black box” model, it is possible to infer the impact of
management on the system considered. This study aimed to evaluate water
pollution generated by wastewater from a polyculture system of tilapia and
shrimp and discuss the management employee and their relation to the quality of
the effluent released. It used a pond measuring 1500 m2, average
depth 1.6 meters, where 12 cages of 1 m3 populated with tilapia
juveniles were installed 33 days after the shrimps’ population. The tilapia
juveniles were distributed in densities from 200 to 400 fish per cubic meter,
reaching the density of 2.4 fish per square meter within the total pond area.
Shrimp post-larvae were released outside the cages within the pond area in a
density of 3.3 organisms per square meter. Total density considering fish and
shrimps was of 5.7 organisms per square meter in the pond area. Water samples
were taken weekly in affluent and effluent of the pond (January-August/2009).
The mass balance model was calculated from the difference between the estimated
load for the output and input of the pond. The average flow rate was 4.46 L/s.
The average loads nitrogen was 0.072 Kg/day (affluent) and 0.179 Kg/day
(effluent) and phosphorus 0.0136 Kg/day (affluent) and 0.031 Kg/day (effluent).
The mass balance resulted in mean values of 0.11 ± 0.06 Kg/day for total
nitrogen and 0.017 ± 0.010 Kg/day for total phosphorus indicating that the
system exported nutrients. The use of Best Management Practices (BMP) likes
better feed and water management as a way to minimize nutrient export.