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Feature title: Extending the shelf life of farmed juvenile Southern Bluefin Tuna (Thunnus maccoyii)
The International magazine for the aquaculture feed industry
International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2009 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058
In 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 qual-ity 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 (raw-fish) 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
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 condi-tion 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 approxi-
mately 15 – 20 kg from December to
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 approxi-mately six to nine months.
The tuna are fed baitfish six days a week twice per day. This is done by feed-ing 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
Extending the shelf life of farmed juvenile Southern Bluefin Tuna (Thunnus maccoyii) by Dr Philip Thomas, University of New England, New South Wales, Australia
26 | InternatIonal AquAFeed | May-June 2010 May-June 2010 | InternatIonal AquAFeed | 27
F: Tuna
BioDr 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.
IAF10-03.indd 26 30/04/2010 16:21
has resulted in a recently renewed effort by feed manufactures to produce larval, juvenile and grow-out feeds tailored spe-cifically for tuna.
During the ongrowing phase the farmed SBT will gain greater weights and have a higher condition index (CI >25) than their
wild counterparts (CI<20). Condition index can be expressed as
CI = Weight (Kg)
Length (m3)
and is a measure of SBT fatness. As the muscle fat content increases
the girth of the fish also increases. A large girth relative to the length of the fish indicates a fish with high muscle fat content. High condition equates to larger amounts of high value cuts of fatty muscle and therefore a more valuable carcass.
26 | InternatIonal AquAFeed | May-June 2010 May-June 2010 | InternatIonal AquAFeed | 27
F: Tuna
Figure 1: Commercial cuts of meat Figure 2: The role of glutahione peroxidase in the reduction of lipid organic peroxide-hyperoxides
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Global production of crude palm oil (CPO) exceeded 43 million tonnes and together with about nine million tonnes of coconut and palm kernel oils, constitutes a highly available and sustainable source of lipids for the aquafeed industry.
When freshly extracted, CPO is the richest known natural source of β-carotene and is also a rich source of vitamin E, consisting of tocopherols and tocotrienols. Several studies have shown that various palm oil fractions can be successfully used either singly or in combination with other plant oils in the aquafeeds of commercially farmed species. The limited PUFA content, combined with the presence of natural antioxidants (in the case of CPO), has been reported to impart enhanced pellet and fillet oxidative stability.
Furthermore, the overall fatty acid modi-fication of the fish fillet is less detrimentally affected by SFA-rich oils, when compared to other alternative lipid sources.
Nevertheless, concerns have been expressed on its potential negative effect on nutrient digestibility, particularly when fed to cold water fish species during the winter season.
High quality sources of dietary energy
Soybean, corn, safflower, cottonseed and sunflower oils are the main n-6 PUFA-rich (namely linoleic acid, 18:2n-6) oils produced.
When incorporated into aquafeeds, these n-6 PUFA-rich plant oils have been reported to be high quality sources of dietary energy and fatty acids during the grow-out cycle in most fish tested to date.
However, a major concern of using these oils is that linoleic acid is abundantly and preferentially deposited in the fish fillet. Since our human diets already contain too much n-6 PUFA, some scientists believe that a good fish oil substitute should limit the deposition of these less desirable fatty acids in fish fillets.
Once deposited, linoleic acid is also known to be selectively retained in fish fillets and resistant to ‘dilution’ even after switching to a fish oil finishing diet. This may be problematic in the context of using fish oil finishing diet strategies to restore beneficial n-3 to n-6 PUFA ratios in farmed fish fillets.
Several selected cultivars of these oilseeds have been recently developed to contain significantly lower concentrations of linoleic acid.
The major monounsaturated fatty acid
(MUFA)-rich oil produced is rapeseed (canola) oil with olive, peanut and rice bran oils making up the rest of this class of lipids. Oleic acid (18:1n-9) and other MUFA are readily digested and β-oxidized by fish to produce energy and have been reported to have no known adverse effect on fish growth performance.
Depending on market prices, rape-seed oil is cur-rently one of the commonly utilized lipid alternatives in c o m m e r c i a l a q u a f e e d s , especially those formulated for cold water and temperate species.
Plant oils rich in n-3 PUFA [namely α-linolenic acid, ALA (18:3n-3), and steari-donic acid, SDA (18:4n-3)] has generated much research interest due to the ability of these fatty acids to be bio-converted into the longer chain, more un s a t u r a t ed ,
physiologically important n-3 LC-PUFA by many farmed species, albeit mostly at lim-ited capabilities.
Despite encouraging evidence of poten-tial bio-conversion of ALA and SDA into n-3 LC-PUFA, the inclusion of these oils (i.e. linseed/flaxseed, camelina, perilla and echium) in aquafeeds is limited, as they are
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A new generation of omega-3 lipids with a broader spectrum of health bene� ts.
- High DHA contents, preferably in easily digestible and highly bio available form for aquaculture use.
- Numerous bene� ts on improving the immune response, better weight gain and physical conditions of land animals.
Marine phospholipids
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999_AD_IAF0904V3.indd 1 22/06/2009 14:01
Figure 3: Palm oil is the most produced and fractionated oil in the world and many fractions have been successfully evaluated in aquafeeds
10 | InternatIonal AquAFeed | May-June 2010 May-June 2010 | InternatIonal AquAFeed | 11
F: Lipid
IAF10-03.indd 11 30/04/2010 16:19
recent advances in the nutrition of fin fish and crustacean species. A dedicated session chaired by Diane Bellis, Delber t Gatlin, Michael Rust, Jeffrey Silverstein and Frederick Barrows concerned alternative feedstuffs for aquaculture.
The quest for replacing fish meal or at least reducing our burden on meal and oil from oceanic sources seems eternal but major steps have been taken. Although it may seem that such plant by- products as soya bean meal and oil seed rape meal and various protein concentrates derived from corn, rapeseed etc have been fully studied, there is much more information to be gained from con-tinuing processing developments. Improved nutritional quality has resulted for fish such as trout and salmon with refinements such as enzyme treatments and enhanced milling technology to remove non-starch polysac-charides and anti- nutritional factors.
Similar ly, there was much discussion regarding the use of oils and lipid sources in general in aquafeeds in a session under the chair of Jesse Trushenski, Rebecca Lochman, Ron Hardy and Giovanni Turchini. Most of the presentations examined the role of lipids in relation to the physiological as well as met-abolic requirements of fish with new insights into the use of novel sources from algae and macro-algae (seaweeds) for a variety of species. Speakers reported effects on carcass composition, fillet quality, as well as on growth, health and immune function. Advances in the use of alternative terrestrial plant oils were also featured.
However, another area of interest seemed to be the relevance of feed additives which warranted a separate session. This was chaired by Delbert Gatlin and Ann Gannam and it was pleasing to be directly involved with presentations from myself, my PhD student Carly Daniels and work presented by John Sweetman involving Plymouth. There was a review on functional dietary compo-nents such as MOS, FOS and various algal, microbial and yeast extracts as well as pro-biotic applications. Rebecca Lochman from the University of Arkansas gave an inter-esting review on various dairy yeast prebi-otic agents on golden shiners, goldfish and channel catfish culture with a very southern USA theme.
John Sweetman spoke on mannan oligosac-charides (Bio-Mos) and their benefits from a commercial standpoint with sound scientific evidence for their positive effects on gastro-intestinal function, growth and health poten-tial in experiments conducted across Europe form several universities and institutions. This
work addressed trout, salmon and sea bass. Carly Daniels (UK) gave a splendid first talk at such a large venue on her work with the European lobster examining the use of prebi-otic and probiotics in larval diets for different stages of development and survivability. Carly is based at the National Lobster Hatchery in Padstow, Cornwall which is devoted to the release of juvenile lobsters for a conser-vation and stock enh an cemen t scheme.
P r o f e s s o r Simon Davies presented an overview on the complexities of the ver tebrate gut and how the fish intes-tine is as compli-cated as higher an ima l s w i th distinct involve-ments in immu-nology, endo-crine function as well as nutrient absorption. The effects of various feed additives as modulators of gut immune function, micro-biology and gut integr ity were stated and the role of com-merc ia l MOS repor ted for a range of fish species.
Live foods and their use in aquaculture has always been a key aspect of the hatchery phase of fish and shrimp production. The conference sessions addressed this area with examples of improvements in husbandry, nutritional quality of artemia and new
There is resurgence in interest in algae at present and this relates as much to algal based bio-fuel applications as well as fish
14 | InternatIonal AquAFeed | May-June 2010 May-June 2010 | InternatIonal AquAFeed | 15
F: Aquaculture 2010
IAF10-03.indd 15 30/04/2010 16:19
specifically in place of methionine, which provides tissue reserves of this critical trace element. Normal cell and protein turnover releases the required selenium, a process that escalates during periods of increased demand such as oxidative stress.
The farming success in any aquaculture operation is dependant on optimal growth and performance with the product qual-ity meeting the consumer preferences. In Atlantic salmon farming, fillet colour and texture are two very important characteris-tics. Fillets with a soft texture or fillets with slits or holes in the surface (gaping) cannot be satisfactorily processed resulting in poor appearance and downgrading by customers. Fillet gaping is responsible for 38 percent of the downgraded material in the second-ary processing of salmon (Mitchie, 2001). The inclusion of selenium as a selenoyeast in salmon diets has been demonstrated to improve product quality in terms of decreased gaping and resulted in a higher content of selenium in the fillet.
In terrestrial animals drip loss has been associated with the oxidative process that promotes post-mortem development of compromised cell membranes and facili-tates increased moisture loss from proc-essed meat. The use of organic selenium has been shown to significantly reduce the drip loss in poultry (Naylor et al. 2000).
Shelf lifeAs with terrestrial red meats, shelf life
is an important product quality feature of farmed Southern Bluefin Tuna (SBT). Also in common with beef, the bright red colour of SBT is due to the myoglobin content of
process begins, which leads to peroxidation of susceptible polyunsaturated fatty acids and ultimately membrane damage.
The occurrence of selenium (Se) in the enzymes involved in controlling or reducing oxidative and free radical damage to the cell membranes is critical in fish. Fish under a state of stress may draw on tissue reserves of selenium to prevent oxidative damage and membrane lipid peroxidation through the glutathione peroxidase (GSH-Px) pathways. Davies et al. 2008 describe the biochemical function of GSH-Px and its role in reducing lipid organic peroxide-hyperoxides to their corresponding alcohols and reducing the free hydrogen peroxide to water.
For the GSH-Px to be active it must be in the reduced state. The major inter and intracellular reducing capability of ascorbic acid can provide the required proton to expedite the reduction of the GSH-Px from
the oxidized form back to the reduced form. This interrupts phospholipid peroxidation and reduces further cell membrane structural damage (Figure 2)
The role of organic selenium
Substituting an organic sele-nium yeast source for inorganic sodium selenite has been dem-onstrated to improve uniformity and product quality. The reason for this is that the organoseleni-um compounds formed by yeast are more easily metabolized and can be taken up into tissue proteins, such as muscle non-
Farmed fish also have much higher levels of tissue fat in comparison to the wild SBT. The differences in condition index and tissue fat levels in the different cuts of meat from wild and farmed SBT are shown in Figure 1.
Flesh quality and antioxidant protection
Oxidative metabolism in aerobic tissues results in the continuous production of superoxide radicals and hydrogen peroxide. However oxidative stress occurs when the generation of reactive oxygen species (ROS) exceeds their normal removal. As fish contain a high percentage of polyun-saturated fatty acids they are particularly vulnerable to attack by free radicals and are very dependant on antioxidants for protec-tion. Under conditions of oxidative stress, induced by ROS, the lipid peroxidation
28 | InternatIonal AquAFeed | May-June 2010 May-June 2010 | InternatIonal AquAFeed | 29
Figure 3
F: Tuna
Traditionally tuna are caught at approximately 15 – 20 kg from December to March along the Great Australian Bight region and transferred in specialized tow pontoons to the farm pontoons off Port Lincoln
IAF10-03.indd 28 30/04/2010 16:21
for farmed SBT has been evaluated to determine whether a muscle dose response could be achieved and result in improved antioxidant defence and extend the colour shelf life of farmed SBT.
For five years, from the 2001 farming season and up to and including the 2004 season, our research group ran experiments that were designed to investigate and evaluate the use of feeds (baitfish and pelleted) fortified
the meat. During storage, the myoglobin is oxidised to met-myoglobin and gradually changes from red to brown.
In addition, and unlike beef, the high lev-els of highly unsaturated fatty acids found in SBT meat in the presence of ROS can start the lipid peroxidation process resulting in unstable highly reactive lipid hydroperox-ides which can threaten cell integrity and increase the rate of post mortem browning.
Within the wild fishery, capture stress is unavoidable and hard to control while aqua-culture offers the opportunity to manage all aspects of the ongrowing, pre-harvest and harvest practices, thereby minimizing stress and any negative effect that this will have on product quality. In addition it has been shown that pre-mortem conditions that can alter the physiology of the fish can in turn affect the post-mortem tissue biochemistry, which is then directly related to product quality (Thomas et al.1999).
The use of antioxidant fortified diets
28 | InternatIonal AquAFeed | May-June 2010 May-June 2010 | InternatIonal AquAFeed | 29
F: Tuna
Figure 4
Figure 5
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IAF10-03.indd 29 30/04/2010 16:21
CRC participants. The author wishes to thank DSM Nutritional Products for their ongoing support of this research and Alltech® for providing the organoselenium from Sel-Plex selenium.
ReferencesBuchanan J and Thomas P. 2008. Improving the colour shelf-life of farmed Southern Bluefin Tuna (Thunnus maccoyii) flesh with dietary supplements of vitamins E & C and selenium. Journal of Applied Food Product Technology, 17 : 3.
Davies S, Rider S and Sweetman. 2008. The nature of selenium and its role in fish nutrition. International Aquafeed, July/August issue, p28-33.
Douglas A, Carragher J, Thomas P and Patterson B. 2000. Flesh quality and market price determination of farmed fresh Southern Bluefin Tuna in Japan. In Responsible Aquaculture in the New Millenium, European Aquaculture Society Special publication, No 28.
Mitchie I. 2001. Causes of down grading in the salmon farming industry. In; Kestin, S.C., Warris, P.D, (Eds.) Farmed fish quality. Oxford: Blackwell Science, Fishing New Books. Pp 129-136.
Morkore T and Austreng E. 2004. Temporal changes in texture, gaping, composition and copper status of Atlantic salmon (Salmo salar, L.) fed moist feed or extruded dry diet. Aquaculture 230: 425-437.
Naylor A, Choct M and Jacques K. 2000. Effects of selenium source and level on performance and meat quality in male broilers. Poultry Science 79 (suppl), 17.
Thomas P, Pankhurst N and Bremner H. 1999. The effect of stress and exercise on post-mortem biochemistry of Atlantic salmon and rainbow trout. Journal of Fish Biology, 54, 1177-1196.
Thomas P. 2007. Aquafin CRC - Southern bluefin tuna Aquaculture Subprogram: Maximising the control of quality in farmed SBT (Aquafin CRC Project 2.2 FRDC Project No. 2001/248) Final Report.
Thomas P, Thomas M, Schuller K and D'Antignan T. 2009. Aquafin CRC - Southern bluefin tuna Aquaculture Subprogram: Application of the use of dietary supplement for improving flesh quality attributes of farmed SBT. (Aquafin CRC Project 2.2(2) FRDC Project No. 2004/209) Final Report.
http://www.daff.gov.au/brs/fisheries
in the fish fed the fortified diets (Figure 4).
Higher levels of these antioxi-dants in the fish muscle consist-ently result in an extension of the colour shelf life of sashimi grade tuna meat as illus-trated in Figure 5.
By slowing the oxidation process in SBT meat it is possible to extend the window of sale opportunity at the market and reduce the losses that may current-ly be experienced through the prac-tice of trimming portioned car-casses during cold storage. These benefits obviously have the capacity to improve the reputation of this valuable product.
Pellet diets fortified with antioxidants are by far the most effective delivery system for these nutrients and therefore the most effective way to improve the shelf life of
farmed SBT flesh. In other work, not illus-trated here, it was shown that feeding SBT pellets fortified with a higher level of vitamin E alone may not be as effective in extending the shelf life of SBT meat as a combination of higher levels of vitamins E and C plus selenium as Sel-Plex.
Acknowledgements This work formed part of a project
of the Cooperative Research Centre for the Sustainable Aquaculture of Finfish (Aquafin CRC), and received funds from the Australian Government’s CRCs Program, the Fisheries R&D Corporation and other
with the natural antioxidants vitamin E (dl-α-tocopherol acetate), vitamin C (l - ascorbic acid monophosphate) and selenium, initially as sodium selenate (Buchanan & Thomas 2008) and then selenomethionine as Sel-Plex® (Alltech), organic selenium based on the strain Saccharomyces cerevisiae CNCM I-3060 (Thomas 2007 and Thomas et al. 2009).
When standard baitfish or pellet feed were coated or fortified with boosted levels of vitamins E and C and selenium, as Sel-Plex, significantly higher selenium levels were recorded in the muscle of SBT (Figure 3). This reduced the muscle oxidation status
"The farming success in any aquaculture
operation is dependant on optimal growth
and performance with the product quality
meeting the consumer preferences"
More inforMation:Email: [email protected]
30 | InternatIonal AquAFeed | May-June 2010
F: Tuna
Selenium is an essential nutrient for all aquatic diets. The form used
directly impacts performance in and out of the water.
Sel-Plex® from Alltech® is the only FDA reviewed and EU approved
organic selenium source on the market. Sel-Plex supports better,
health, performance and product quality of aquatic species.
Sel-Plex is an esSential™ part of aqua diets worldwide.
Carcass Quality, Growth, Safety, HeTraceability, Genetic Potential, RelHealth, Profitability, Oxidative StreShelf Life, Nutritional Value of Food
www.alltech.com
For more information, visit www.Sel-Plex.com or e-mail [email protected].
IAF10-03.indd 30 30/04/2010 16:22
Selenium is an essential nutrient for all aquatic diets. The form used
directly impacts performance in and out of the water.
Sel-Plex® from Alltech® is the only FDA reviewed and EU approved
organic selenium source on the market. Sel-Plex supports better
health, performance and product quality of aquatic species.
Sel-Plex is an esSential™ part of aqua diets worldwide.
Carcass Quality, Growth, Safety, HeTraceability, Genetic Potential, RelHealth, Profitability, Oxidative StreShelf Life, Nutritional Value of Food
www.alltech.com
For more information, visit www.Sel-Plex.com or e-mail [email protected].
www.aquafeed.co.uk
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VOLUME 13 I S SUE 3 2 010
Alternative Lipid Sources
in Aquafeeds
Phytobiotics and Prebiotics:
- a new alternative for sustainable aquaculture
Innovative approaches to reduce feed cost in
aquaculture: - Optimizing nutrient utilization and gut health
IAF10-03.indd 1 30/04/2010 16:17
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