Stressing stocking density and rearing time effect on whiteleg shrimp (Penaeus vannamei) reared intensively in floating cages

The stressing effect of stocking density and rearing time was assessed on shrimp Penaeus vannamei reared intensively in floating cages. Juvenile shrimp were stocked in 9 m2 cages at 200, 250, and 300 ind m-2 for a 25-day grow-out period. Total soluble protein concentration, superoxide dismutase (SOD), and catalase (CAT) activities were used as stress indicators in shrimp muscle, hepatopancreas, and hemocytes. Two-way ANOVA showed that protein content in hepatopancreas significantly decreased as stocking rate increased (from 3.81 to 2.26 mg mL-1). Density and rearing time interacted significantly to determine SOD activity in muscle and hemocytes where the maximum activity occurred at the densest rate by the end of the study (10.21 and 122.41 U mg-1); CAT activity in hepatopancreas was significantly lower when the highest density (4.1 U mg-1) was used. Final shrimp weight (5.28-5.49 g), survival (90.2-91.9%), feed conversion ratio (0.75-0.78), specific (0.058-0.063), and absolute (1.17-1.30 g week-1) growth rates were not significantly affected by density, although yields varied significantly (0.99-1.49 kg m-2). To conclude, despite the stocking rate causing a stressing effect on shrimp, its antioxidant enzymatic activity prevented such development from negatively affecting shrimp growth, survival, feed conversion ratio, and production.