Biochemical measures of health of farmed tuna using surrogate species
Tuna farming at Port Lincoln involves the transfer of wild caught tuna to holding pens at Boston Bay where they are maintained until harvest. Water quality in Boston Bay may be affected by a variety of contamination sources including urban pollutants, agricultural run-off, and nutrients and debris associated with the fish feeds and excreta. These factors may affect the health of tuna, making them more susceptible to infection or to the stresses caused by other environmental factors. This may reduce the farming yield through increased mortality or reduction in flesh quality. This project will fulfil 3 major needs of the aquaculture industry; 1. the needs for a non-invasive indicator for the assessment of farmed fish health or stress status. 2. a means of achieving a reduction in the mortality of farmed tuna by identifying stress-related effects at a point at which intervention will reduce stress exposure. 3. improving yield and quality from tuna farming activities. Project 95/082, currently funded by FRDC, has measured biochemical endpoints as indicators of stress in farmed tuna. These markers are also evaluated in wild fish and mussels which cohabit with the tuna in the nets to determine whether these indicators predict the responses in tuna. This project has involved both aquarium studies of surrogate species exposed to environmental factors and field studies of these biochemical indicators in tuna and cohabiting species in Boston Bay. In April 1996, high mortalities of tuna (up to 70%) were recorded at Boston Bay, thought to be due to sediment stirred up by a storm surge. This interrupted the project and delayed the monthly collection of field samples. In addition, it may suggest that the 1996 season was abnormal and that collection for a complete season in 1997 would provide a clearer conclusion to this project. One consequence of the high fish mortality in 1996 has been the decision to relocate some of the tuna farming nets outside Boston Bay. The application of the biomarkers measured in this project to fish in nets at these new, and nominally 'better' sites is essential for the understanding of these tests as health performance indicators. In addition, biochemical markers examined in project 95/082 were correlated with indicators of tuna quality such as mortality and market value. These are crude measures of tuna 'health' and may not be sufficiently sensitive to the response of tuna to confinement and exposure to other stresses. In 1997, Dr Carragher, a new appointment at Flinders University, will begin collaborative research with this project group. He will introduce the measurement of objective independent markers of tuna stress based on plasma cortisol concentrations measured in the same individuals sampled for adenylate and ATPase activities. This project clearly satisfies the key requirements for FRDC project funding since; 1. it is fully concordant with the strategic goals of the FRDC described in its research and development plan, 1996 - 2001. 2. it is research which is industry directed, industry centred and industry supported. 3. it satisfies FRDC requirements for industry collaboration and participation through in-kind contribution support.
1. To compare biochemical methods of assessing the effects of stress in farmed tuna with methods currently used. Biochemical methods include measurement of adenylates and ATPase in tuna tissues.
2. To determine the relationship between biochemical markers in tuna and the markers measured in fish and molluscs cohabiting with tuna in farm nets in order to determine whether biomarkers in surrogate species predict the health status of tuna.
3. To compare the findings of the 1997 season with the 1996 season to determine whether high-mortality events have longer term impacts (i.e. effects persisting to later in the farming season) on markers of stress.
4. To compare the 1996 and 1997 season findings and their relationships with farming net locations either within or outside of Boston Bay.
5. To evaluate serum cortisol as a marker of long-term stress in tuna and in cohabiting species.
Principal Investigator: K.L. Soole, J.W. Edwards, P. Hone, S. Clarke & J. Carragher