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Port Lincoln tuna sea cages The birds arrive for tucker time Bluefin Tuna: FOOD FOR THOUGHT BY PETER HUTCHINSON, E.N. HUTCHINSON, NEW ZEALAND AND JOE KEARNS, WENGER MANUFACTURING, INC., USA B luefi n tuna aquaculture has grown into an industry worth hundreds of millions annually, with farms located in the Mediterranean, Japan, Australia and Mexico. Currently these farms are based on "ranching", which in aquaculture terms is used to describe the fattening of wild caught fi sh in pens. The tuna are fed bait fi sh and held in ocean cages until they reach ideal market size. This holding time varies from place to place primarily depending on water temperatures. In cooler regions of the Med fi sh may be held for several years, whereas in South Australia fi sh are caught at 15-20kg and fattened to 40-50kg over 8-10 months before winter temperatures make holding the fi sh unviable. The last decade has seen a big investment in breeding of bluefi n to secure reliable supply of juveniles, reduce pressure on wild stocks, and to grow the industry. Dealing with broodstock fi sh weighing in at several hundred kilogams clearly has its challenges, and it would be fair to say that hatchery success has been slow in coming. There has been some success over recent years however. Japan's Kinki University lead the hatchery charge and have been the most successful in terms of numbers in sea cages to date, with tens of thousands of animals making it through to grow out over the previous two years. Australia's Clean Seas Tuna has been close on the heels of Kinki, although are struggling to get good numbers. Hatchery development in the Med has been quickly catching up with the formation of SELFDOTT (now morphed into TRANSDOTT or, translation of domestication of Thunnus thynnus into an innovative commercial application), a group formed with funding from stake-holding nations and industry working together to reach a common goal: millions of tuna juveniles per season. Another hurdle the industry must rapidly overcome once numbers start leaving hatcheries, is the supply of bait fi sh. Bait fi sh are limited, and their use is seen as a waste of fi sh resources. Furthermore, it does not allow for nutritional development and increases in growth are only attainable through the use of compounded feeds. The problem is that tuna can be fussy, particularly wild fi sh, and they haven't performed well in long 6 ■ NZ AQUACULTURE ■ SEPTEMBER/OCTOBER 2012 term trials with compounded feeds to date. The size of the pellets required also presents some challenges when compared with the standard extrusion technology used to manufacture fi sh feeds. In the early 2000's EN Hutchinson Ltd in NZ began work to produce extruded broodstock feeds for large marine fi sh. The challenges faced in producing these feeds (primarily palatability and size), were the same challenges facing the tuna industry. In Mid 2010 during an informal discussion with members of the Australian tuna industry, Joe Kearns from Wenger Manufacturing, and Peter Hutchinson from EN Hutchinson Ltd, the solution became clear: the feed must be simple and cost effective to produce, unlike other tuna feeds which had been developed. To this extent extrusion was clearly the front runner. It must also be palatable, and ideally be shelf stable without having to be dried as the costs involved with drying large pellets may be uneconomic. ENH Ltd had already resolved these issues with broodstock feeds it was manufacturing and had on sale in Australia. Within weeks of the discussion a bag of "BroodMax" pellets were delivered to Port Lincoln in South Australia. When tossed into the sea cages, the tuna had no hesitation in slamming the pellets despite mid winter temps supposedly making them "fussy feeders". The palatability problem had been resolved through use of wet fi sh in the extrusion process. Wet fi sh included in the extrusion process increases palatability enormously, the protein is more digestible due to reduced processing, more sustainable due to reduced production energy requirements, and has the potential for greater utilisation of waste/by-products. The problem now, was that ENH Ltd's small research and development plant was limited in both capacity to produce volume for commercial on-farm growth trials, and its ability to include signifi cant percentages of wet fi sh to make the ideal product for tuna requirements. This is where Wenger Manufacturing picked up the ball with a newly developed extrusion cooker, the Thermal