WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2025 39 documented in commercial ponds. Although the exact cause of WFD remains unknown, the disease has been reproduced by co-infecting P. vannamei with EHP followed by specific strains of Vibrio parahemolyticus or Vibrio alginolyticus. This mimics what occurs in commercial ponds, where shrimp first exhibit the presence of EHP, and later, during the grow-out cycle, develop white discoloration of the gastrointestinal (GI) tract, with characteristic floating white fecal strings associated with WFD appearing in the pond (Tang et al., 2016). Prevention and management of EHP should begin at maturation facilities by using EHP-free breeders and feed. In larviculture, disinfection, surveillance, and the use of high-quality feeds are also critical tools for controlling EHP. However, controlling EHP is challenging because its spores are highly resistant to disinfection, and horizontal transmission is highly effective, requiring no intermediate host — unlike the microsporidia that cause cotton shrimp disease. Genetic selection is another strategy to address diseases in the shrimp industry. Family and within-family selection have proven highly effective in creating resistant populations against the Taura Syndrome Virus (TSV), but not against WSSV (Cock et al., 2009). In recent years, genomic selection has been increasingly employed in aquaculture species, driven by advances in next-generation sequencing and the availability of reference genomes and SNP arrays for most commercially valuable species, including P. vannamei. In traditional family breeding programs, animals are selected based on the performance of their siblings in challenge tests, but the specific resistance of each animal is unknown. By combining genomic selection with challenge testing in the siblings, it is possible to predict individual genomic breeding values (GEBVs) for disease traits in the genotyped breeding candidates. This enables the breeding of resistant stocks without compromising the biosecurity of the breeding nucleus (Houston et al., 2020). Since 2018, Benchmark Genetics has been using genomic information to enhance the resistance of animals from their Breeding Nucleus against key pathogens. The first experiment was focused on resistance to WSSV (Lillehammer et al., 2020), demonstrating that genomic selection holds significant potential for further genetic improvement of WSSV resistance in the evaluated P. vannamei population. In this study we evaluated the power of genomic Diseases have traditionally been considered one of the main limitations to the expansion and profitability of the P. vannamei industry, as modern intensive shrimp farming systems provide nearly ideal conditions for disease propagation. Shrimp are often cultivated yearround without breaks between production cycles; they are raised in ponds, tanks, or raceways at high densities. Water exchange is limited, and moribund animals are not easily culled from the system. This latter point is particularly important, as cannibalism is common, effectively disseminating pathogens. After the era of viral infections (IHHNV, TSV, and WSSV) and bacterial diseases (AHPND, NHP), a new threat has emerged: microsporidia, specifically Enterocytozoon hepatopenaei, now referred to as Ecytonucleospora hepatopenaei (EHP). EHP was initially reported in 2004 in P. monodon in Thailand (Chayaburakul et al., 2004) and 5 years later it was described as a microsporidia (EHP) based on histological, ultrastructural and phylogenetic data (Tourtip et al., 2009). Although initially it was considered a pathogen of minimum risk, the expansion of the industry and the higher stocking densities used in the past decade have led to an increased impact in the P. vannamei industry worldwide in recent years. Microsporidia are parasites that reproduce via spores and are classified within the fungus kingdom. They can infect hosts across all animal taxa, from protists to humans. Aquaculture species are particularly affected, as nearly half of the known microsporidian genera infect aquatic hosts, with more than 50 genera shown to infect aquatic arthropods (Stentiford et al., 2016). In decapod shrimp, apart from EHP, five species of microsporidia have been associated with cotton shrimp disease, which affects the muscles of the animals with very low mortality. In the case of EHP, this pathogen affects the hepatopancreas, leading to hepatopancreatic microsporidiosis (HPM). Although EHP by itself is not associated with high mortality, it damages the hepatopancreas, resulting in severe growth retardation and significant size dispersion among the affected shrimp in the ponds. Additionally, it has been suggested that EHP facilitates bacterial colonization in the hepatopancreas of the affected shrimp. A relationship between EHP and white feces disease (WFD) characterized by the presence of floating white feces and the detection of EHP spores in the feces of shrimp has been widely Breeding for disease resistance to control Enterocytozoon hepatopenaei and White Feces Disease in Whiteleg Shrimp (Penaeus vannamei) Marcela Salazar, Kahsay Nirea, Edna C. Erazo, Andres Suarez, Bruno DeCock, Carolina Peñaloza, Ross D. Houston, M. Hossein Yazdi and Carlos Lozano (CONTINUED ON PAGE 40) Diseases have traditionally been considered one of the main limitations to the expansion and profitability of the P. vannamei industry, as modern intensive shrimp farming systems provide nearly ideal conditions for disease propagation. Shrimp are often cultivated year-round without breaks between production cycles; they are raised in ponds, tanks, or raceways at high densities. Water exchange is limited, and moribund animals are not easily culled from the system.
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