Effects of Size Grading on Growth and Non-Specific Immunity Factors of the Shrimp Litopenaeus vannamei Boone

The study aims to determine the effects of graded farming on growth performance and non-specific immunity factors of shrimp Litopenaeus vannamei Boone. Three size groups of shrimp, i.e., the small size group [GS, with an average body length (BL) of (3.04 ± 0.36) cm and body weight (BW) (0.412 ± 0.35) g], the large group [GL, with a BL of (4.29 ± 0.55) cm and BW of (1.098 ± 0.42) g], and the ungraded group [Gm, with a BL of (3.47 ± 0.81) cm and BW of (0.611 ± 0.79) g], were reared under the same conditions for 8 wk. Growth performance and non-specific immunity factors were measured. The results showed that BW gain, biomass gain and the specific growth rate of body length (SGRL) were significantly influenced by size grading (one-way ANOVA, P <0.05). The peroxidase (POD) and antibacterial (Ua) activities of GL were lower than those of Gm. Superoxide dismutase (SOD) and lysozyme (Ul) activities of Gm were lower than those of Gs. No significant difference (P = 0.121 > 0.05) was found on phenoloxidase (PO) activity among the three size groups. Synthetically, size grading could enhance growth and rearing efficiency, and did not have a significant influence on the immunity of L. vannamei Boone. Therefore, graded farming in L. vannamei Boone was feasible in the culture practice.