42 MARCH 2025 • WORLD AQUACULTURE • WWW.WAS.ORG As expected, the combined infection with EHP + WFD, not only affected survival but also severely affected the growth and productivity parameters of the infected animals when compared to the non-infected controls. In both batches 48 and 49, the weight gain of the survivors showed a reduction of 37.26% and 43.40%, respectively, while the food conversion rate and the coefficient of variation in the final weight of the survivors were significantly increased in the infected controls (Figure 3). Notably, as shown in Figure 4, around 7% of the survivors in both challenge tests reached a weight similar to that of non-infected animals, demonstrating the resistance/tolerance of these animals in the challenge test. Genetic parameters Batch 48: Heritability for growth, using genomic information calculated on the randomly sampled animals, was 0.32 ± 0.04 for Colombia and 0.50 ± 0.04 for Vietnam, estimates that were within the expected range for this trait. A moderate genetic correlation of 0.62 ± 0.08 was found between growth in Colombia and growth in Vietnam, indicating a mild interaction of genotypes with the environment across these two locations. This finding suggests that the relationship between the growth of shrimp in Colombia and Vietnam is influenced to some extent by their genetic makeup, responding differently to the respective environments. The heritability estimate for survival in the EHP challenge test was 0.31 ± 0.06. This magnitude of heritability suggests a greater potential for rapid genetic improvement compared to traits like WSSV, which showed very low heritability (0.03) using a similar model (Gitterle et al. 2005). Also, in contrast to other diseases such as WSSV, where the correlation between growth and disease resistance is negative and significant, the genetic correlations between growth (in both Punta Canoa and Vietnam) and survival to the EHP+WFD challenge test were not significantly different from zero. This suggests that integrating EHP survival into the selection index might not significantly affect growth, which continues to be the most economically significant trait (Table 1). Batch 49: In this batch, we found similar genomic heritability for growth in both environments: 0.47 ± 0.05 for Punta Canoa and 0.49 ± 0.06 for Vietnam. In contrast, the genomic heritability for EHP + WFD resistance in this batch was lower, with a value of 0.17 ± 0.03. The genetic correlation for growth between Punta Canoa and Vietnam was 0.74 ± 0.08, and although this is higher than the correlation found for batch 48, it still indicates a mild Genotype x Environment effect between both environments. In contrast, the genetic correlations between survival in the EHP + WFD challenge test and growth in both environments were slightly negative but not significantly different from zero for this batch, at -0.10 ± 0.13 for Punta Canoa and -0.02 ± 0.13 for Vietnam (Table 3). Progeny response based on parental genomic indexes As shown in Figures 4 and 5, EHP+WFD resistance GEBVs of the parents positively correlated with the survival of their progeny. Figure 5 illustrates the regression of mean family EHP survival in batch 49 on the mean family GEBV. Each dot represents a family in batch 49, and the mean family EHP GEBV was estimated solely from batch 48 challenge test results. The figure demonstrates a strong relationship between parental GEBV and offspring survival, with a Pearson correlation of 0.60. Figure 6 shows the average survival of the families originated from the parents classified into different groups. Average survival ranged from 0.1 for the worst groups to 0.33 for the best, demonstrating a clear progression in survival as parental indexes increased. Discussion and Conclusions This study demonstrates that genomic selection is an effective method for breeding P. vannamei shrimp resistant to co-infection with EHP and WFD. Pooling shrimp from different families early on, combined with the use of a SNP array, enabled the assessment of shrimp performance from early life stages and across different environments. Genotyping proved highly reliable, achieving an average 99.2% parent assignment rate across both batches. The growth assessment of shrimp families in two distinct environments—tanks in Punta Canoa and ponds in Vietnam— revealed a genotype-by-environment interaction. This indicates that while selecting breeders in Punta Canoa can promote growth in both settings, treating growth in each environment as separate traits could enhance improvement rates. EHP and WFD resistance in juveniles was found to be moderately heritable, supporting the feasibility of using selective breeding to increase resistance. Several genomic regions were identified as weakly associated with resistance, indicating that numerous genes FIGURE 6. Average EHP survival of progeny (batch 49 families) based on mean parental GEBVs for EHP survival: Worse GEBV from -0.13 to 0.0, bad GEBV from 0.001 to 0.13, good GEBV from 0.131 to 0.26 GEBV and best GEBV above 0.261. FIGURE 5. Regression of mean family GEBVs (based on batch 48 parents) on mean survival to EHP in batch 49.
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