Brian Jones

The study of molluscan diseases has a long history. The first publication on the redial stages of a trematode appeared in the 18th century; early papers on molluscan phagocytosis appeared in the last half of the 19th century and yet much work published before about 1975 does not appear in electronic abstract databases and is effectively “lost”. By contrast, a recent search of a leading abstract database for the terms “mollusc” and “disease” shows that the number of publications has exploded in the last eight years and the exponential trend looks set to continue. Much of the increase has been driven by the introduction of molecular technologies, the rediscovery that the immunology of invertebrates generally is a rich hunting ground for new biochemical defence systems and thus potential medical breakthroughs and the desire to publish multiple papers from the same project. As this publication trend continues, it will become increasingly difficult to be knowledgeable on all aspects of molluscan diseases and considerable specialisation is inevitable. It is not only our knowledge about known mollusc diseases that has grown, since new diseases continue to be reported as: aquaculture becomes more intensive; the Asia/Pacific regional skills base develops; and international reporting becomes more accurate. Transfer of disease between jurisdictions is also becoming more rapid as products are sent live around the world both as broodstock and for human consumption. Thus, the work of the Network of Aquaculture Centres in the Asia and the Pacific and the Food and Agriculture Organization of the United Nations in awareness raising and skills development will continue to make an impact. It is inevitable that, as the initial work on mollusc diseases developed around shellfish growing areas in Europe and America, the next generation of molluscan disease experts will be based in the Asia and the Pacific region.

Many governments are under increasing pressure from international trading partners to provide better information on the health status of exported aquatic animal commodities, particularly live animals. A central factor in this situation involves the training and certification of various links in the Competent Authority chain-of-command, including aquatic health service providers, aquatic pathogen detection laboratories, aquatic species pathologists, veterinarians and personnel who facilitate the endorsement of aquatic animal certificates of inspection. Standardized methods to ensure the competence of those people charged with providing and interpreting information on the health status of aquatic animals and/or their products for export is imperative to maintain the confidence of international trading partners. A thorough and logical certification protocol for aquatic animal health personnel would lend additional credibility and assuredness/peace of mind to the importer/consumer in the quality of the product and the production of health certificates of instantly recognizable meaning. Existing professional certification programs for aquatic animal health providers will be reviewed. These programs could provide guidance as a Professional Standards establishing mechanism for veterinarians and non-veterinary personnel in Asia who currently provide aquatic animal health services. This paper proposes a professional standards mechanism, developed through NACA and the Asian Fisheries Society-Fish Health Section (AFS-FHS), to promote and authorize a certification protocol for aquatic animal health providers in Asia as highly useful in improving this situation.

Biosecurity can be defined as the protection of plants, animals (including humans and associated activities) and the wider environment from the unwanted impacts of biological agents including diseases and pests. As a discipline, biosecurity can be applied at various levels. In the context of aquatic animal disease, this can range from managing the health of individual animals, through whole commercial enterprise to national or international biosecurity. The last three decades or so have seen an increase in the farming of aquatic animals worldwide – a situation compounded from a biosecurity perspective by a quantum leap in aquaculture technologies, countries and species new to aquaculture, increased international movement of juvenile animals and broodstock; all in an environment of little knowledge of the health status of source populations and the frequent emergence of new diseases. The end-result of this change has been significant farm level production losses well documented in the scientific and lay literature. The focus on increased farm level biosecurity in recent times has been in direct response to this very real threat. All aquaculture operations rely on trade (commercial exchanges) to some extent. Trade provides stock, genetic material, inputs (such as feeds, vaccines, treatments, etc.) and takes the outputs (product). Aquaculture operations are not isolated from the realities of trade and the associated biosecurity risks. This paper describes the various elements that make for good farm level biosecurity and assesses the resourcing needs against net long- and short-term benefits to production. This paper also examines the role that farm biosecurity plays in overall regional or national biosecurity systems, with particular emphasis on the Australian experience. Farm level biosecurity is placed in context with inter- or intra-national disease zoning (and compartmentalisation), national quarantine control and global biosecurity initiatives such as international disease reporting and standards setting. The necessity for on-farm biosecurity as a complement to zoning and the more traditional country quarantine requirements is emphasized.

Two epizootics have occurred in populations of the Australasian pilchard Sardinops sagax neopilchardus in waters of southern Australia. The first occurred between March and September 1995. It is thought to be the largest fish kill ever recorded and is also unique in the geographic extent of the mortalities. The economic loss attributed to the 1995 mortality event was in excess of A$ 12 million. The second occurred in 1998-1999 when approximately 60% of the total pilchard biomass in Southern and Western Australian waters was lost. After the 1998-1999 epizootic, two of the three pilchard fisheries of Western Australia were closed for a season and although the national economic impact has not been formally assessed, it exceeded A$ 15 million in Western Australia alone (Gaut, 2001). In 1995 mortalities occurred along more than 5000 km of the Australian coastline (Fig. 1) and also affected pilchards in New Zealand. The disease front spread from its origin in South Australia at about 30 km/day, often against prevailing currents and was not impeded by storm events. Thus it was not caused by planktonic toxins/pathogens. Likewise, there was no consistent association of the mortalities with environmental parameters such as temperature or salinity.

There is a widespread perception that the practice of importing untreated frozen fish for use as bait is a 'high risk' activity. The problem has been that there has been no quantifiable data on which to evaluate that perception. In 1997 the Western Australian Rock Lobster Industry commissioned a quantitative risk assessment, based on OIE principles, to assess the risk posed by bait in rock lobster pots. Several novel approaches were used to quantitatively assess the risk, based on historical patterns of usage. The resulting conclusion was that the risk of introducing disease with rock lobster bait was extremely low, or did not exist at all. In 1998 the WTO ruled on the Canadian dispute with Australia over salmon. In the Report of the Appellate Body, the definition of risk assessment was explored in detail. Their rulings indicate that risk assessments should be based on a threefold test: Identification of the diseases; evaluation of the likelihood of entry; and evaluation of the effect of SPS measures which might be applied to reduce risk. These were all met in the 1997 report. However, there are serious questions about disease identification in the absence of data and the meaning of "appropriate level of risk". These issues still need to be addressed by the international community.

This paper presents a review of the cellular defense mechanisms of spiny lobsters. These mechanisms can be divided, for convenience, into three broad groupings: maintenance of exoskeleton integrity; foreign agent recognition, inactivation and elimination from the internal organs; and repair of damage by toxins. Cellular defense mechanisms are dependent on circulating haemocytes and phagocytes, fixed phagocytes and fibrocytes. The process or processes by which these cell types are generated and mature in the animal have not yet been adequately described for spiny lobsters. In addition, attention has only recently focused on the way in which cellular defence responses are influenced by environmental stress and by the nutritional and moult status of the lobster. These are areas of critical importance to animal husbandry and production in aquaculture. While rapid advances are being made in the understanding of humoral defense mechanisms of crustaceans there are still large gaps in our understanding of the cellular components of the system in spiny lobsters.

In March 1995 a mass mortality of pilchard started to occur in South Australia; this spread very rapidly throughout the Australian pilchard's range, later reaching New Zealand. In November 1998 a si1nilar mass 1norta1ity broke out in South Australia and also spread, at a slower rate, throughout the Australian range. The mortality appeared to be caused by a herpesvirus. The mortality spread as a classical epidemic front, but its speed of progress and the brief duration of mortalities at a given location are extreme. We apply simple epidemic 1nodelling techniques, SIR and SEIR modelling, to exa1nine the factors behind the spread of this mortality and the differences between the 1995 and 1998/9 epidemics. We discuss biological factors influencing the critical processes of long-distance (D) and local (β) transmission of infection.