Estimating Genetic Parameters for Weight and Body Size of Pacific White Shrimp (Litopenaeus vannamei ) by Restricted Maximum Likelihood Method

This study was designed to estimate genetic parameters for weight and body size at tagging (77 d post hatch) and at harvest (124 d post hatch) of Litopenaeus vannamei. At harvest, a total of 1,664 individuals from 12 full-sib families reared under three different pond conditions were measured, with mean ± SD of 18.70 ± 3.00 g for body weight (BW), 11.67 ± 1.14 cm for body length (BL), 8.72 ± 1.03 cm for abdominal length (AL), 2.9 ± 0.2 cm for carapace length (CL), 74.62 ± 1.85 for percent tail length, and 25.38 ± 1.85 for percent carapace length. Body ratio was 1.60 ± 0.15 g/cm for BW/BL. Sex, days post hatch and pond had significant effects on weight and size traits (P < 0.05). Variance components were estimated by a restricted maximum likelihood procedure with animal mixed linear models. At harvest, estimates of heritability ± SE were 0.37 ± 0.14 for BW, 0.34 ± 0.13 for BL, 0.35 ± 0.13 for AL, 0.13 ± 0.06 for CL, 0.05 ± 0.03 for percent tail length and percent carapace length, and 0.34 ± 0.13 for BW/BL. The results suggested that a high amount of genetic response would be obtained through selection for body weight and size traits as the estimates of heritability for these traits were relatively high. Furthermore, the high genetic correlations between body weight and size traits (BL, AL and BW/ BL) imply that an improvement in body weight will cause simultaneous changes in abdominal length as well as the ratio of body weight to body length. The study demonstrated the application of a mixed linear model technique and restricted maximum likelihood procedure for estimating variance components in shrimp with a small set of experimental data.