WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2023 47 How effective is the heat shock method in managing disease risk? For tropical fish, barramundi as well as tilapia and other species, in Asia as well as in Africa, the heat shock method (also called hyperthermia) has been a real game changer for most fish farmers. Nowadays, applying heat shocks to juveniles has become a standard method in many production protocols, even if it is not 100 percent efficient. As demonstrated after Alain Michel discovered the method, it produced significant benefits in survival, provided the protocol is properly applied to animals affected by early stages of a disease. Immunity to the pathogen causing the disease is acquired for the life of the fish. Early detection of disease is not always easy and missing it may have critical consequences. For that reason, some fish farmers apply the heat shock method at juvenile stages, and even in some cases on breeders, every 10 or 15 days, as a preventative low-cost method to enhance immune response, which would only appear with the presence of a pathogen during the heart shock time. The heat shock method does not solve all sanitary issues, but, at low cost, most fish farmers consider it is worthwhile to apply it as a routine preventive protocol that significantly reduces the impacts of several fish pathogens. It also has the advantage of being applicable to small-size juveniles, for which vaccination (when it exists) cannot yet be applied, depending on the vaccination protocols like injection, which requires a minimum size. The use of heat as treatment is also applied with variation to the standard technique, since it needs adjustments to different farmer, husbandry and species needs, but even more importantly, depending on the target pathogen or disease (e.g., columnaris syndrome). All participants in the debate acknowledged that there has been a time before and after the heat shock method discovery and demonstration of its benefits on several fish species against several pathogens. This acknowledgement represented a fitting conclusion to the international tribute to Alain Michel. Editor’s Note For further information about the work and professional legacy of Alain Michel, see the full story as told by Régis Bador on LinkedIn (www.linkedin.com/newsletters/aquaculture-alain-michelstory-6979183084516605952/). A follow-up Special Session on Disease Diagnosis and Management is being organized for World Aquaculture 2023 in Darwin, Australia (29 May – 1 June). Notes Régis Bador: regis.bador@innovaquaculture.com Marc Le Groumellec: le.groumellec@gmail.com Luis Fernando Aranguren: lfarangu@arizona.edu Roberto Cascione: r.cascione87@gmail.com that some Endogenous Viral Elements may be inserted into the shrimp genome (e.g., IHHNV) also tends to indicate that crustaceans have a capacity to accommodate to the permanent presence of viral pathogens, provided they have enough time to allow natural and/or shrimp farmerinduced genetic selection leading subsequently to species evolution. In any case, submitting cultured shrimp to stressful conditions (poor water quality, high density, deficient feed, etc.) and poor animal husbandry is a favorable situation for any pathogen to trigger a disease outbreak. Some shrimp farmers may not pay enough attention to this basic rule-of-thumb. Biosecurity is another key element of disease management, and preventive measures can frequently allow normal production to continue, even in an environment where pathogens are highly prevalent. In case of doubts about a possible disease outbreak on a farm, it must be properly communicated to local authorities and neighboring shrimp farming facilities. When properly applied, early detection and emergency harvest protocols can mitigate the disease impact and avoid its spread in the region. There have been some successful cases but also many failures due to the late exchange of information and reaction. What is the difference in the impact of diseases on the shrimp aquaculture industry between Asia and Latin America? Several Latin American countries, especially Ecuador, have a solid and mature community spirit — mostly regionalist and even nationalist — of the shrimp industry, extending across several generations of shrimp farmers. This mindset contributes to better communication of problems and solutions. Sharing all experiences — the good as well as the bad — is a positive attitude to anticipate or mitigate disease outbreaks. This shrimp farmer community spirit might sometimes appear less present among Asian shrimp producers, despite the long history of aquaculture. The widely adopted strategy in Ecuador to invest in disease resistance/tolerance genetic selection programs, including challenging breeders in the field with all endemic pathogens, has become almost routine and possibly has contributed to produce animals becoming progressively more robust and tolerant of these pathogens. This strategy is clearly different from the commonly adopted SPF strategy promoted throughout Asia. The exclusion strategy — keeping pathogens out of the production area — implies a need for the application of a high standard of biosecurity and which is quite difficult to maintain in regions where shrimp farms are so numerous and so close to each other. Globally, learning to live in the presence of pathogens, one of the constant recommendations of Alain Michel, may be the right strategy for long-term success, targeting strains being at the same time SPR/SPT and SPF. Participants in the session organized in tribute to Alain Michel with dignitaries and session speakers.
RkJQdWJsaXNoZXIy MjExNDY=