F: Tuna
Extending the shelf life of
farmed juvenile Southern Bluefin Tuna (Thunnus maccoyii) by Dr Philip Thomas, University of New England, New South Wales, Australia
I
n Australia, ranching of Southern Bluefin Tuna (SBT) (Thunnus maccoyyi), one of the most closely managed fisheries, occurs in the offshore region of Port Lincoln in South Australia. The farming of SBT started in 1991 as a result of diminishing fishery catches and a reduction of fishing quotas, which resulted in the operators allocating a portion of their catch to farming rather than for sale. Over the last 19 years this activity has developed into a commercially significant seafood sector in Australia. Considerable research effort has gone into developing this industry with initiatives from the Fisheries Research and Development Cooperation (FRDC) and Aquafin CRC. These initiatives included a focus on nutrition, health, product quality and marketing and fish husbandry and management. A more recent focus has been research into the propagation of SBT. This endeavour has been driven by Clean Seas Tuna in collaboration The Australian Seafood CRC. SBT currently ongrown in sea based aquaculture facilities are particularly attractive to the Japanese sashimi (rawfish) market due to the high fat content of their muscle and in 2007–08, the value of the fishery’s commercial production was approximately AUD$44.5 million from a
Bio
Dr Philip Thomas is currently principal research fellow in the Business Economics and Public policy group at the University of New England, New South Wales, Australia and the work presented in this article took place while he was senior researcher of biological science at Flinders University as part of Aquafin CRC - Cooperative research centre for sustainable aquaculture of finfish where his research focus was on the relationship between husbandry, production performance and flesh quality in aquaculture.
catch of 5239 tonne (DAFF). Prior to the export of fresh farmed SBT experienced Japanese graders will routinely remove a small redundant section of the tail of individual fish during processing and ascribe a subjective grade to each fish. This opportunity allows them to assess flesh quality, carcass shape and condition thereby allowing the target market, method of sale and the product price to be determined. The price obtained on the auction floor has been shown to be correlated to the subjective quality grades given prior to export. (Douglas et al, 2000)
Culture Traditionally tuna are caught at approximately 15 – 20 kg from December to 26 | International AquaFeed | May-June 2010
March along the Great Australian Bight region and transferred in specialized tow pontoons to the farm pontoons off Port Lincoln. Fish are then on-grown to a weight of 25-40 kg in a period of approximately six to nine months. The tuna are fed baitfish six days a week twice per day. This is done by feeding fresh local pilchards or placing frozen blocks of baitfish in mesh cages within each pontoon. Commercial feed pellets have been developed for SBT but under the current price conditions are unlikely to replace the baitfish as a major feed source. However with the prospect of a closed lifecycle for Bluefin tunas including SBT, there is an associated necessity for a commercially produced pellet feed. This