The southern Bluefin tuna industry in Australia is limited by catch quota. Increased competitiveness through production efficiency is the main way to improve the value of the industry. Improved performance can be achieved by maintaining a high health status which consequently minimises stress, reduces mortalities and optimises production. Since 2002 there has been a significant fall in revenue (prices down over 50% and strengthening of the Australian dollar). The worsening financial parameters, combined with the intrinsic high ‘value’ of each fish, have placed a greater focus on all aspects of the industry and particularly stress impacts limiting production. Mortality is an obvious area and the current, increased level is not acceptable. Possibly more important, parasites may cause economic costs to the tuna industry in lost growth and condition. There is a potential for increased productivity through the reduction of parasite loads. This can be only achieved through better understanding of the current dynamics of parasitic infections and the cost of parasitic infections to the SBT production.

The use of fish cell lines, both as a research tool and a diagnostic tool, has played a major role in the development of salmonid and cyprinid aquaculture worldwide. The commercial success of these finfish aquaculture industries is due, in part, to the development of fish cell lines which are used to monitor farmed fish populations for the presence of specific viral pathogens. Based on the results of such health surveillance programs disease-free stocks can be kept isolated from infected stock through restrictions in fish movements. The current lack of continuous tuna cell lines suitable for the isolation and growth of viral pathogens of tuna could be a serious obstacle to effective disease control in tuna hatcheries and nurseries which, in turn, could have a significant negative impact on the future development of the tuna aquaculture sector. It is noteworthy that viral infections of a tuna species (Thunnus thynnus) have been documented (1). Moreover, other viral pathogens such as marine nodaviruses (2) and birnaviruses (3) tend to be catholic in their host range and should be considered a significant risk.

Development of diagnostic tools for identification of viral pathogens in other systems has been reliant on the availability of continuous cell lines for virus cultivation. Isolation and growth of viral pathogens in susceptible cell lines provide an almost limitless supply of partially purified virus for the development of improved diagnostic procedures for these pathogens (4). In order to be able to develop similar systems to service the farmed tuna sector, there is a need for continuous tuna cell lines.

The aim of this project is to develop continuous tuna cell lines to improve our capacity to isolate and characterise tuna viruses, and to enhance our response to new pathogens that may threaten farm production. Identification of disease-free broodstock, eggs and fry is essential for the further development of the tuna aquaculture sector.

REFERENCES

1. Matsuoka S, Inouye K & Nakajima K. 1996. Cultured fish species affected by red sea bream iridoviral disease from 1991 to 1995. Fish Pathol. 31: 233-234.

2. Nishizawa T, Furuhashi M, Nagai T, Nakai T & Muroga K. 1997. Genomic classification of fish nodaviruses by molecular phylogenetic analysis of the coat protein gene. Appl. Environ. Microbiol. 63: 1633-1636.

3. Reno PW. 1999. Infectious pancreatic necrosis and associated aquatic birnaviruses. In: Fish Diseases and Disorders vol. 3 Viral, Bacterial and Fungal Infections (Woo PTK & Bruno DW, eds.) CABI Publishing, New York, NY, Pp. 1-55.

4. Crane MStJ & Bernoth, E-M. 1996. Molecular Biology and Fish Disease Diagnosis: Current Status and Future Trends. Recent Advances in Microbiology 4: 41-82.