WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2025 79 in gill or lymphoid tissues, while EHP requires hepatopancreatic tissue. Latent and Dormant Infections Many pathogens, such as IHHNV and EHP, can remain latent. These infections evade immune responses and are often undetectable until activated by stress or environmental shifts (Flegel 2006). PCR cannot distinguish between active and latent infections, nor can it predict flare-ups. Thus, overreliance on PCR as a standalone measure is dangerous. Negative results should not be treated as a clean bill of health but rather as one component in a broader diagnostic toolkit. Broodstock Management: A Critical Vector for Vertical Transmission Comparative Management in L. vannamei vs P. monodon Broodstock management differs significantly between species. In L. vannamei hatcheries, high-density systems often place hundreds of animals in communal tanks. While cost-effective, this setup facilitates rapid horizontal and vertical transmission. Infected individuals can easily contaminate the system, and even low-level infections may be sufficient to infect egg masses or larvae (Moss et al. 2012). By contrast, P. monodon hatcheries often maintain broodstock in lower densities, sometimes even isolating individuals in separate tanks. While more labor-intensive, this approach allows for better monitoring and reduces the risk of undetected crosscontamination (Chakraborty and Thakur 2017). Breakdown of Biosecurity Common maturation practices such as eyestalk ablation, used to induce spawning, can also weaken immunity, making animals more susceptible to latent infections. Moreover, communal spawning and the reuse of tanks or spawning equipment further increase the chances of horizontal transmission, especially if sanitation protocols are inadequate. In some cases, hatchery managers claim that they sold post-larvae (PL) from the same batch to multiple farmers, and only one experienced disease. This is possible due to uneven infection load, environmental triggers, or secondary stressors at the grow-out stage. However, it often signals a failure in broodstock screening and batch segregation. When SPF shrimp are brought into local countries, certain local practices may compromise their SPF status. Many broodstock facilities may not be aware that the feed provided to broodstock can act as a disease carrier. Common feed items such as polychaetes and squid can harbor various pathogens. If the feed is not properly processed to eliminate these pathogens, there is a high risk of introducing diseases into the broodstock population. Implications of Vertical Transmission WSSV, IHHNV, EHP, and potentially other pathogens can be vertically transmitted via gametes or egg surfaces (Hoa et al. 2011). Inadequate broodstock management allows these infections to propagate silently through the larval and post-larval phases and reach farms already primed for outbreak. This emphasizes the need for high-resolution, individual-based diagnostics and improved hatchery biosecurity. The Need for a Paradigm Shift in Industry Thinking Shrimp farming has long operated under assumptions that SPF status, regular PCR testing, and standard hatchery practices are sufficient. These assumptions are no longer tenable. Integration of Advanced Diagnostics The industry must move beyond single-tool diagnostics. Histopathology, LAMP, immunofluorescence, and sequencing technologies can reveal pathogen presence, tissue damage, and community-level dynamics that PCR alone cannot (Notomi et al. 2000). Environmental DNA (eDNA) analysis can detect pathogens in the water column before clinical signs emerge. Smarter Biosecurity Protocols Effective biosecurity demands more than disinfectants and entry barriers. It requires system-wide discipline from water source control and larval batch tracking to full traceability of broodstock origin. Investments in recirculating systems, physical barriers, and real-time monitoring should be seen as essential, not optional. (CONTINUED ON PAGE 80) PHOTO 2. High-resolution digital PCR for precise nucleic acid quantification in pathogen detection. Photo by Pipitpan Lerdpipitpon PHOTO 3. Specific Pathogen Free (SPF) Litopenaeus vannamei broodstock. Photo by Nik Siti Zaimah Binti Safiin
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