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Triploid Oysters

While attending the World Aquaculture Show in Orlando in January, I shared a booth with 4Cs Breeding Technology of New Jersey. Ann Arsinieau and Standish Allen, both with 4Cs, worked with me for the three days of the show, and as a result I got to learn a lot about the triploid technology that has been developed at Rutgers University.

The value to the industry as a whole makes a lot of sense and is very exciting; to help explain it I asked Stan to co-author this column so we could make sure that I got all the technical facts straight.

Oyster farming has slowly developed from the collection of wild spat for growout to hatchery-based production. As genetic improvements gain value, the trend will continue. An early breakthrough was the development of hatchery induced triploids, which in the past few decades has grown to be an important part of oyster production in the Pacific Northwest. Because of recently commercialized new technology, it is likely that triploid oyster production will be more important than ever, and might even become the cornerstone on genetic improvement for oysters throughout the world. triploid oysters are much bigger than diploid oysters

Typically plants and animals have two sets of chromosomes (diploid). Triploidy refers to a genetic condition in which there are three sets of chromosomes. The general condition of having more than two chromosome sets is called polyploidy, and a number of common agricultural crops have been improved in this way, such as sugar beets, blueberries, bananas, watermelon, and even wheat. These polyploid plants were developed by agronomists to increase the size, reduce seeds, and speed growth. They have become the commercial varieties of vegetables we now take for granted on the supermarket shelves. Researchers have used similar tools to obtain a "better" oyster, which will consistently grow faster, bigger, and meatier (think naval orange of oysters!).

In the mid-1980s researchers at the University of Maine and University of Washington developed methods of creating triploid oysters by coaxing an extra set of chromosomes into a newly fertilized egg. These initial methods of inducing triploids included chemical, heat, and pressure shock. The resulting triploids had the advantages of faster growth and more consistent market qualities. While generally effective in practiced hands, these early methods of triploid induction can be tricky and there are several qualities of induced triploids that are undesirable. For example, induced triploids are never 100% triploid. That is, of the millions of oyster eggs treated after fertilization, many but not all are successfully induced to be triploid. A rate of 80% triploids is often the benchmark for accepting or rejecting a spawn as triploid. Another undesirable trait of chemical or induced triploids is early mortality caused by the triploid treatment, which often results in losses of up to 50-70% of the larvae in the first four days of life. Finally, because of the way the extra chromosome set is coaxed into the egg, there is a likely genetic consequence akin to inbreeding.

Despite the disadvantages of chemical triploids, however, many growers have found value in triploids for the primary reason that triploids are reproductively sterile. They fail to produce significant amounts of gonad containing either eggs or sperm. This sterile condition is an advantage for marketing oysters in the warm seasons of the year when diploids are typically spawny or have spawned out completely. The "triploid advantage" is therefore a boon to marketing oysters year-round, with some growers concentrating on growing triploids exclusively for the half-shell trade.

In 1993, a new type of polyploid oyster (Crassostrea gigas) was invented at Rutgers University - one that contains four sets of chromosomes. This work was the culmination of almost a decade of research. The final process was so novel, it received patent protection in the US, Australia, and Taiwan. Patents are also pending in a number of other important markets including the European Union and China. Not only is the process proprietary, but also the actual tetraploid oysters themselves have received patent protection - the first patent for an animal that is not transgenic (i.e., genetically engineered by inserting genes).

Tetraploids could set off a revolution in the way oysters are cultured. The great advantage of tetraploid oysters is their function as brood stock. Tetraploids are not marketed for consumption. Rather, they are used in the hatchery as a highly efficient tool to produce 100% triploid oysters. Unlike their triploid cousins, tetraploids are fully fertile. Tetraploids produce eggs and sperm that naturally contain two sets of chromosomes. Therefore, mating a tetraploid male with a diploid female creates - instantly and without mortality or lingering treatment effects - 100% triploids. This type of triploid is referred to as "natural (or mated) triploid". Triploids from tetraploids, of course, do not occur in nature but they are derived naturally, without any induction (chemical, heat or pressure).

In 1997 a company was formed to develop tetraploid technology. 4Cs Breeding Technologies, Inc. (4Cs), based in New Jersey, has the exclusive worldwide rights to market and sub-license the tetraploid technology. At the World Aquaculture trade show in Orlando, in January 2001, the company rolled out its product to the aquaculture industry for the first time. 4Cs Breeding Technologies also provided documentation of the results of the last four years of research and development of the tetraploid / triploid technology. 4Cs has been involved in continued research and development of the tetraploid technology since its inception. Working with commercial partners Taylor United and Whiskey Creek Oyster Farm in the Pacific Northwest, the company has been instrumental in taking the labouratory invention and demonstrating its commercial feasibility in the hatchery and in the field. The information provided at the WAS meeting was impressive.

4Cs and their commercial partners have developed a reliable supply of tetraploid brood stock and embarked on a breeding plan to steadily improve their quality. They have demonstrated that larvae produced from tetraploid x diploid crosses are consistently 100% triploid, known as 4Cs Natural Triploids. The larvae so produced suffer no mortality (compared to 50% or greater loss in induced triploids) and are highly robust. 4Cs Natural Triploid larvae have dark color, large size, and high setting efficiency. Tetraploids have lived up to their promise for delivering high quality, reliable 100% spawns of 4Cs Natural Triploid seed. Moreover, there are benefits beyond the hatchery. The company has documented growout data concerning the performance of 4Cs Natural Triploids in the field. In commercial scale field testing with Taylor Shellfish in Puget Sound, 4Cs Natural Triploids yielded 43% more meat than induced triploids. (Yield is a product of survival and meat yield.) Significantly there are advantages to growers of Natural Triploids that go well beyond the advantages to the hatchery.

The company is continuing its research and development on tetraploid technology, including work on cryopreserving tetraploid sperm and extension of tetraploid / triploid production in other species. With the prospect of continued genetic improvement of tetraploids, their reliability in the hatchery, and the surprisingly good performance of 4Cs Natural Triploids in the field, oyster growout culture could be looking at a revolution in the making. Taylor United of the Pacific Northwest, for example, has found 4Cs Natural Triploids useful enough that they already have converted half of their oyster production over to them in only two years. Other creative uses of 4Cs Natural Triploids lie on the horizon. With the advent of 100% 4Cs Natural Triploids from tetraploids, it is reasonable to consider using Natural Triploids as a means to prevent reproduction in a non-native population of oysters. For example, 100% 4Cs Natural Triploids are being considered with the introduction of Suminoe (C. ariakensis) 4Cs Natural Triploid oysters in the Chesapeake Bay. 4Cs can breed any variety or strain of oyster to create unique tetraploid broodstock from which to produce a local variety of triploid with all the consistency and benefits of a 4Cs Natural Triploid.

Faster growing, disease resistant and meatier oysters from tetraploid / triploid technology represent the future of a growing hatchery based oyster industry. This technology offers significant oyster growout and marketing advantages, similar to the growth in year round market of bananas and navel oranges.

There are actually two ways in which 4Cs may transfer the technology to new areas. Assuming the successful completion of the current research, the company expects to soon have the ability to ship vials of frozen Gigas sperm, which might be used to create triploid oysters in any acceptable area. In the alternative, the company can sub-license the technology, and create new stocks of tetraploid oysters in various parts of the world, from local stocks.

More information concerning how to convert cultivated oyster production to 4Cs Natural Triploids can be obtained by contacting 4Cs Breeding Technologies, Inc. Tom Rossi, President by phone 609-729-1333.

Contact Don Bishop at:
Fukui North America
PO Box 669
110-B Bonnechere St.W.
Eganville, Ontario K0J 1T0
Tel: 613-624-1704
Fax: 613-624-2688
Email: kate@fukuina.com

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