The first 2 days of each period were used for shrimp acclimation to the feed, and no
feces were collected, to clear the digestive tract of the previous feed. Feces were siphoned
from the tank onto a 200-lm mesh screen, washed with distilled water and centrifuged at
3000 rpm, frozen to -24 C and then dried in an oven. Determinations of Cr2O3 (experimental
diets and feces) were conducted in the Soils Laboratory, UNALM, by the
atomic absorption spectrophotometric method (AOAC 2002).