The White Shrimp, Litopenaeus vannamei, is a Cornerstone of Global Aquaculture. However, in recent years, a significant threat to this industry has emerged: the microsporidian Enterocytozoon hepatopenaei (EHP). This intracellular fungus, often accompanied by White Feces Syndrome (WFS), has caused considerable economic losses worldwide. WFS, characterized by floating white feces, reduced feed intake, and growth retardation, has devastating effects on shrimp populations.
To address this pressing issue, researchers from Benchmark Genetics As and Benchmark Advanced Nutrition have delved into the genetic composition of shrimp, aiming to identify key factors contributing to resistance against Enterocytozoon hepatopenaei (EHP) + White Feces Syndrome (WFS). By analyzing a pedigreed shrimp population, they discovered that genetic factors play a crucial role in determining an individual’s susceptibility to this deadly disease.
Understanding the Threat
EHP, a microsporidian parasite, weakens shrimp and makes them more susceptible to other infections, such as Acute Hepatopancreatic Necrosis Disease (AHPND). While WFS is not yet fully understood, it is often linked to secondary bacterial infections, particularly from Vibrio species, which can exploit the compromised gut health of shrimp infected with EHP.
EHP has spread globally, affecting shrimp farming regions in Asia and Latin America. Economic losses due to EHP were especially high in India’s main white shrimp farming states during the 2018-2019 production periods.
Selective Breeding as a Cost-Effective Approach
A complementary and cost-effective approach to mitigate EHP + WFS infection is the development of shrimp lines with enhanced resistance through selective breeding. Selective breeding is an effective tool for controlling disease resistance. However, understanding the genetic variation and architecture of the target trait is essential before implementing selective breeding.
Genomic Selection: A Promising Alternative
Genomic selection (GS) can complement family-based breeding to improve the accuracy of predicting breeding values. GS improves selection decisions by increasing accuracy through the exploitation of within-family variance, particularly for traits typically measured in the siblings of selection candidates. This GS approach allows siblings to undergo challenge tests, while core breeding candidates are kept in a biosecure hatchery environment, providing accurate breeding values for candidates.
A Shrimp Population Undergoes a Challenge Test
According to a study published in the journal Aquaculture, researchers conducted a challenge test using a pedigreed shrimp population from the Benchmark Genetics breeding program in Colombia. Of the genotyped animals, 1,436 individuals from 47 families passed quality control, underwent relationship analysis, had phenotypic records, and were available for further analysis.
Heritability and Genetic Correlation
Moderate heritabilities were estimated for binary survival to EHP + WFS using pedigree-based (0.31 ± 0.04) and genomic-based (0.41 ± 0.06) analyses. Additionally, a low genetic correlation between body weight and EHP + WFS survival traits in the challenge test was observed, suggesting that genetic improvement of EHP + WFS resistance can be achieved without compromising growth performance.
Genome-Wide Association Analysis
Genome-wide association studies (GWAS) indicated that resistance to Enterocytozoon hepatopenaei (EHP) + White Feces Syndrome (WFS) is a polygenic trait, meaning that multiple genes with small effects contribute to the overall phenotype. This complex genetic architecture suggests that a genomic selection approach, which considers the combined effects of many genes, is the most promising strategy for genetic improvement.
Genomic Selection Strategy
Cross-validation analysis showed a prediction accuracy of 0.54 ± 0.01 for genomic analysis and 0.49 ± 0.001 for pedigree analysis, indicating the relevance of a genomic selection strategy to achieve genetic improvement of EHP + WFS resistance in L. vannamei. This approach can help breeders select shrimp with higher resistance to EHP + WFS, ultimately reducing the economic impact of this disease on the industry.
Implications for the Shrimp Industry
The insights gained from this study have significant implications for the shrimp aquaculture industry. By implementing genomic selection programs, breeders can develop shrimp lines that are highly resistant to Enterocytozoon hepatopenaei (EHP) + White Feces Syndrome (WFS). This will not only reduce economic losses but also contribute to sustainable and environmentally friendly aquaculture practices.
Conclusion
This study aimed to investigate the underlying genetic basis of resistance to EHP + WFS in white shrimp (L. vannamei). The findings provide valuable insights into the genetic mechanisms underlying EHP + WFS resistance and highlight the potential of genomic selection as a promising alternative for disease management in the shrimp industry.
By understanding the genetic basis of resistance, breeders can develop targeted breeding programs to reduce the impact of EHP + WFS on the industry.
Contact
Kahsay Nirea
Benchmark Genetics As
Email: kahsay.nirea@bmkgenetics.com
Reference
Nirea, K., Salazar, M., Erazo, E. C., Suarez, A., DeCock, B., Penaloza, C., Houston, R. D., Yazdi, M. H., & Lozano, C. (2024). The genetic basis of resistance to Enterocytozoon hepatopenaei (EHP) and White feces syndrome (WFS) in the whiteleg shrimp (Litopenaeus vannamei). Aquaculture, 741789. https://doi.org/10.1016/j.aquaculture.2024.741789
