Evaluation of Stocking Density and Light Level on the Growth and Survival of the Pacific White Shrimp, Litopenaeus vannamei, Reared in Zero-Exchange Systems

The objective of this study was to evaluate the effects and interactions of stocking density and light level on the growth and survival of Litopenaeus vannamei in zero-exchange mixed biofloc systems. The necessity of light and its effects on stocking density could provide essential information for efficient system design in temperate regions. Twelve, 3800-L conical-bottom tanks housed in a greenhouse were filled with dechlorinated city water, adjusted to 25 ppt salinity, inoculated with mixed biofloc communities, and randomly assigned to one of four different treatment combinations. The study was a 2 × 2 factorial arrangement with main effects being stocking density (182 shrimp/m2 [low density; LD] vs. 364 shrimp/m2 [high density; HD]) and light (natural light [NL] vs. low level artificial [LL]) with three replicate tanks per treatment. Tanks in the NL treatment received ambient greenhouse light. For the LL treatment black plastic was used to block NL and a single 60-W incandescent bulb was hung over each low-light tank and operated on a 12:12 h schedule. Juvenile L. vannamei (0.40 ± 0.28 g) were stocked in rotation into each tank and fed a 35% protein diet twice daily at an initial 10% of body weight, gradually decreasing to 3% of body weight prior to harvest. After 12 wk, there was a statistically significant (P≤ 0.05) interaction between density and light level; therefore, data were analyzed in terms of treatment combinations. Average harvest weight of shrimp was significantly higher (P≤ 0.05) in the LD/NL treatment (14.5 g) than in the HD/LL treatment (12.4 g), but neither was significantly different from HD/NL (13.6 g) and LD/LL (13.4 g). Survival of shrimp was significantly lower (P≤ 0.05) in the HD/LL treatment (61.8%) than in the LD/NL (89.8%) and LD/LL (89.0%) treatments. Survival in the HD/NL treatment (82.7%) was intermediate and not significantly different (P > 0.05) from the other treatments. Harvest yield was significantly greater (P≤ 0.05) in the HD/NL treatment (4.1 kg/m2) than in the LD/NL, LD/LL, and HD/LL treatments (2.4, 2.2, and 2.8 kg/m2, respectively), which were not significantly different (P > 0.05) from each other. These data indicate that a combination of high stocking rate with high light levels or NL may be needed to achieve maximum production; however, relatively low levels of artificial light may be suitable at low stocking densities. Further research should investigate the type and amount of light needed to achieve optimal results.