This research aims to improve the product quality (the colour and flavour shelf-life (shelf-life)) of farmed SBT, which is perceived by the Japanese market to be shorter than wild tuna. The main aim in farming SBT is to produce a product that is high in lipids and this is achieved by feeding baitfish that is itself high in lipids, which may be rancid thus accelerating rancidity in farmed SBT. Improving the shelf-life of farmed SBT will provide an advantage for the Australian product be a high fat product, with the additional benefit of an extended post mortem window of sale (ie shelf life).
Previous experiments on the Tuna Research Farm by Thomas and Buchanan and others, has demonstrated that:
• feeding SBT pellets fortified with boosted levels of vitamin E, C and selenium will raise the level of these natural anti-oxidants in the fish muscle and the appropriate colour of sashimi grade tuna flesh is retained for longer.
• pellet feeds with higher levels of Vitamin E, C, and selenium were more effective in extending the shelf life of SBT flesh than those with a higher level of vitamin E alone.
• baitfish coated with vitamin E, C and selenium was also effective in raising the fish tissue level of vitamin C however, it was less effective at raising the tissue level of vitamin E and selenium.
• SBT with a higher tissue level of vitamin C had a sightly extended shelf life compared to those not fed fortified baitfish.
• a combination of higher levels of Vitamin E, C, and selenium increases colour shelf-life and stabilises the muscle activity of glutathione peroxidase (one of the key antioxidant enzymes).

There is now a need to improve the shelf life of farmed SBT which can be achieved by (1) gaining better understand oxidative protection systems in SBT and (2) adapting our field experiment results and diagnostic tools to the commercial environment.
This can be achieved by:
• developing an alternative method of anti-oxidant delivery which can be used within the existing commercial feeding system.
• use of in vitro cell culture techniques to gain a better understanding of oxidative protection system in SBT and as a rapid and cost-effective method of assessing vitamin supplement formulations that have the potential to improve flesh quality and extend shelf-life.
• use surrogate experiments to obtain basic information on the level of oxidative products that require specific antioxidant feed supplementation use and as an intermediate step in the application of invitro findings to commercial SBT farming.

This research will provide valuable information on the effects of oxidized feed on flesh quality and also baseline information on the oxidative status (i.e. degree of rancidity) of farmed SBT fed currently available feeds. It will provide diagnostic tests for industry to monitor the oxidative status of fish feed and farmed SBT.
The current proposed research is focused on product quality and will continue our investigations into the physiology, nutrition and muscle biochemistry of SBT that underpins developments in tuna husbandry. This project will utilise project 2001/248 results including the current adopted PhD students research. The project recruit a PhD student to the tuna quality project and will continue to support collaborative ties between Flinders University (Adelaide), CSIRO (Geelong), SARDI and the South Australian SBT industry.
This proposed research addresses the South Australian Fisheries and Aquaculture Research and Development Strategy 2002-2007 in the following areas:
Program 2 Industry Production –
Post Harvest enhancement/supply chain management
Farm husbandry and the nutrition of farmed species