An evaluation of intraspecific competition for Pacific white shrimp Penaeus vannamei (Boone) in extensive/semi-intensive ponds

The hypothesis that intraspecific competition affects survival and growth during the culture and harvest at extensive/semi-intensive Penaeus vannamei shrimp ponds was evaluated. Thus, the effect of stocking density on the biomass, shrimp average weight, survival, and economic performance during the culture (133 days) and at the harvest of the P. vannamei shrimp was investigated in 400 m(2) earthen ponds. In order to reduce the likelihood of infectious diseases, shrimp received preventive health treatments (probiotics and beta-1,3/1,6-glucans) during all culture phases. In this way, the effect of density on the intraspecific competition for space/food was isolated. Ponds stocked at 6, 9, and 12 shrimp m(-2) showed competition-dependent growth. Ponds stocked at 12 shrimp m(-2) presented a mortality (12 %) between days 76 and 99. Competition, and accordingly individual growth reduction, could have begun at day 76 at a density of 5 shrimp m(-2). Survival was significantly higher at 6 shrimp m(-2) (84.2 +/- A 6.2 %) compared with the 12 shrimp m(-2) (64.8 +/- A 12.4 %) treatment, while no significant differences in yield were observed between both treatments. Ponds stocked at 3 and 6 shrimp m(-2) presented the best benefit-cost rates. The optimal shrimp density during the experimental culture was 5 shrimp m(-2). Given the experimental conditions and considering the fraction of density-independent mortality observed, the optimum stocking density was found to be 6 shrimp m(-2).