Seafood CRC: safe spat rearing experiment
Oysters Australia Ltd
A FRDC funded University Sydney/EMAI project investigating the biological behaviour (epidemiology) of POMS has identified an additional need that falls outside its original project aims. The recent incidence and subsequent loss of the industry in the Hawkesbury River, NSW also devastated test stock placed in the water by ASI. The industry must invest in all options to safeguard national production; breeding resistant oysters and alternate husbandry. The objective of this project is to provide scientific evidence that water treatments can be applied to enable safe rearing of spat in holding tanks in a POMS affected area until the window of infection closes. There is evidence to suggest that a similar approach is used in the French oyster industry to cope with POMS. The project objective is to treat water in land-based tanks holding spat to interrupt putative transmission mechanisms. If successful, this can be used by hatcheries to hold stock in safe rearing conditions adjacent to a potentially infected estuary until the window of infection closes, and then they will be stocked out into the estuary. This is of use for growers with leases in infected waters who require a method for rearing/conditioning hatchery spat on-shore from the time of receipt until it is safe to put them in the estuary. If POMS spreads to affected waters near hatcheries in Tasmania, they will also require a solution for safe spat production.
1. Confirmation of the efficacy of water treatments for maintaining viable spat during a POMS transmission season in an infected environment
2. Information to benefit commercial hatcheries to enable production of spat from eggs through highly susceptible larval stages, in the face of POMS
3. Information to benefit growers who receive spat from hatcheries during a POMS transmission season
4. Information which can be integrated with husbandry (growing height modifications) to reduce mortalities in adult oysters and enable production of C. gigas in the face of POMS
5. Information which can be used to plan trials on how spat might be grown to a specific size (as distinct from just maintained) during a POMS transmission season in an infected environment
The production cycle of Pacific Oysters in Australia currently depends on hatchery production of spat, mainly in Tasmania. Experience in France and other European countries is that OsHV-1 affects mainly hatchery spat and juvenile oysters, with near total losses of affected batches being common. However, the observations in Australia and New Zealand are that oysters from spat through to adult stages are susceptible. The results from trials conducted in FRDC projects 2011/053 and 2012/032 have already revealed that mortality in adult stock can be kept below 50% by placing stock in cultivation structures 300 mm above standard growing height. The trials described in this report are the first to examine strategies to enable survival of spat and juvenile oysters.
The objective of this study was to obtain information about simple and practical methods to treat/disinfect water so as to develop a method for hatcheries to safely produce and rear spat in infected estuaries during the risk period for disease expression, and for hatcheries or farmers to hold spat in land based facilities during the seasonal window of infection.