Asia contributes more than 90% to the world's aquaculture production. Like other farming systems, aquaculture is plagued with disease problems resulting from its intensification and commercialization. This paper describes the various factors, providing specific examples, which have contributed to the current disease problems faced by what is now the fastest growing food-producing sector globally. These include increased globalization of trade and markets; the intensification of fish-farming practices through the movement of broodstock, postlarvae, fry and fingerlings; the introduction of new species for aquaculture development; the expansion of the ornamental fish trade; the enhancement of marine and coastal areas through the stocking of aquatic animals raised in hatcheries; the unanticipated interactions between cultured and wild populations of aquatic animals; poor or lack of effective biosecurity measures; slow awareness on emerging diseases; the misunderstanding and misuse of specific pathogen free (SPF) stocks; climate change; other human-mediated movements of aquaculture commodities. Data on the socio-economic impacts of aquatic animal diseases are also presented, including estimates of losses in production, direct and indirect income and employment, market access or share of investment, and consumer confidence; food availability; industry failures. Examples of costs of investment in aquatic animal health-related activities, including national strategies, research, surveillance, control and other health management programmes are also provided. Finally, the strategies currently being implemented in the Asian region to deal with transboundary diseases affecting the aquaculture sector are highlighted. These include compliance with international codes, and development and implementation of regional guidelines and national aquatic animal health strategies; new diagnostic and therapeutic techniques and new information technology; new biosecurity measures including risk analysis, epidemiology, surveillance, reporting and planning for emergency response to epizootics; targeted research; institutional strengthening and manpower development (education, training and extension research and diagnostic services).

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The monogenean Neobenedenia girellae (Hargis, 1955) Yamaguti, 1963 is redescribed and reported for the first time in Japan. The parasite was recovered from the body surface, fins, and occasionally from the eyes of 14 species, comprising 5 families of cultured marine fishes from several localities in southwestern Japan. Neobenedenia melleni (MacCallum, 1927) sensu Kaneko et al. (1988) from tilapia (Oreochromis mossambicus) in Hawaii is synonymized with this species. Examination of original specimens (syntypes) of N. melleni sensu MacCallum (1927) revealed differences with N. girellae in having a wide and rounded body, a prominently large anterior hamuli, and absence of glands of Goto. This Neobenedenia from Japanese fishes sometimes showed an unusual morphology of the individual parts of the median sclerites. The potential threat of N. girellae to the health of cultured Japanese fishes is indicated by its low host specificity, wide distribution, and ability to cause mortality due to heavy infection. Unregulated importation of amberjack fry (Seriola dumerili) to Japan appears to be the source of N. girellae infection in Japanese fishes since 1991.

Shrimp domestication and genetic improvement programmes began in late 1980s, in the United States of America, under the United States Marine Shrimp Farming Program (USMSFP), using the Pacific whiteleg shrimp Penaeus vannamei. The USMSFP was based on proven concepts from the livestock and poultry industries and began with establishing a specific pathogen‐free (SPF) shrimp stock. The original shrimp stock was obtained using rigorous screening of captured wild shrimp for selection of individuals naturally free of major shrimp pathogens. Although the concept of SPF animals was well defined for terrestrial animals, it was relatively new for aquaculture, and it took some time to be adopted by the aquaculture community. In the early 1990s, parallel to USMSFP, several other programmes on genetic improvement of shrimp were also initiated in Latin America. Subsequently, several new terminologies and products, such as specific pathogen resistant (SPR) shrimp, specific pathogen tolerant (SPT) shrimp and even ‘all pathogen exposed’ (APE) shrimp, entered the shrimp industry vocabulary and became commercial. This led to confusion in the shrimp industry about the meaning, relationship and significance of these new terms with respect to SPF. This position paper attempts to clarify these concepts, provide science‐based definitions, reconfirms the importance of developing, maintaining and using domesticated, specific pathogen‐free (SPF) shrimp stocks (which may also achieve SPR and/or SPT status) to reduce the risk of disease outbreaks and increase production and profit. The same principles would apply to development of domesticated SPF stocks for other species used in aquaculture. The paper also discusses the difficulties of confirming and certifying SPF status due to the presence of endogenous viral elements (EVEs) and calls for internationally agreed science and evidence‐based technical guidelines for producing healthy shrimp.