Producing Triploid Oysters

Farming of the Pacific Oyster (Crassostrea gigas) is an important part of the economies and cultures of the West Coast states. Oyster culture supports thousands of jobs in rural areas and provides locally produced seafood at a time when the U.S. imports approximately 90% of its seafood. Oysters are also critical in maintaining water quality and provide other important ecological services in coastal areas. The West Coast oyster industry faces numerous challenges such as ocean acidification impacts, rising labor costs, and permitting difficulties, but now faces a challenge that could almost immediately undermine the entire industry as a key patent expires. The patent (#US5824841 A) on the use of tetraploid oysters expired in January 2015, an event which might otherwise go unnoticed, were it not for the fact that the West Coast industry is heavily dependent on the use of tetraploid oysters to produce triploid oysters, the mainstay of the industry. Triploid oysters (which contain three sets of chromosomes) are essentially sterile, a characteristic that makes them harvestable year-round. These generally sterile oysters do not become “spawny” (e.g. full of eggs or sperm) or flaccid and thin during the warmer months, as do fertile diploid oysters. Without triploid oysters, farmers will not be able to harvest during much of the year, thus threatening the economic viability of the farms, hatcheries, and processors. While the importance of the future availability of triploid oysters cannot be underestimated, neither can the current difficulty and cost of obtaining triploid oyster seed. While triploid oysters can in theory be produced using a combination of chemicals, pressure, heat, and other inducers at a precise moment in oyster embryo development, these methods are not efficacious enough to obtain the benchmark of at least 90% triploid progeny to assure summer harvests. The only reliable method of producing greater than 90% triploid oyster progeny is to utilize tetraploid oyster sperm to fertilize diploid eggs. In order for oyster hatcheries to obtain tetraploid oysters for this purpose, a license must be obtained from the 4C’s company. This company was created by Rutgers University, the assignee of the patent for tetraploid oysters, to manage this valuable intellectual property.

To fully understand the difficulty in which the West Coast oyster industry now finds itself, a bit of history must be recounted. In 1993, Rutgers University was awarded a patent for the tetraploid oysters with Drs. Ximing Guo and Standish Allan as co-inventors. At this point, the evolution of the use of tetraploid oysters on the East Coast and the West Coast diverged. The two inventors went on to develop thriving research programs at Rutgers University and the Virginia Institute of Marine Science (VIMS), respectively. One of the outcomes of their continued research on the genetics of the Eastern Oyster (Crassostrea virginica), East Coast farmers, and hatcheries now has access to improved lines of diploid and triploid oysters that demonstrated high performance and disease resistance in both high and low salinity environments. VIMS regularly produces and distributes genetically selected tetraploid and triploid oysters for use in hatcheries and on farms. In contrast, the intellectual property represented by the patented tetraploid oyster languished on the West Coast. The reasons for this are subject to conjecture, but the outcome is that one partner hatchery has been used by 4C’s to produce and distribute tetraploid oysters to the rest of the industry. The results have been less than ideal. For example, even once a license for tetraploid use has been granted to a West Coast hatchery, obtaining verified tetraploid broodstock from the distributor is difficult. Often none is available. The tetraploids also produce low-viability sperm and the resulting triploid progeny is weak and difficult to raise to maturity in the hatchery. The triploid progeny also exhibit early mortality, often dying en masse by the end of the second summer of growth. The cause of this mortality is unknown, but is suspected to be related to the probable inbreeding of the tetraploid stock. No information is released on the genetics of the broodstock. Moreover, licensees are required to propagate their own tetraploid broodstock after receiving the first animals, which is difficult due to their fragility.

With the expiration of the patent, a team of university and private sector partners came together to conduct research and development efforts to advance the development and use of tetraploid Pacific Oysters, thus making production of triploid oysters more efficient, reliable, and available. The goal was to develop reliable methods of tetraploid production to ensure a readily available supply of higher quality broodstock and thus be able to produce a continuous supply of triploid oysters. This clearly benefits farms that would otherwise have trouble obtaining triploid seed, and moreover, provides some degree of control over the quality.

An additional benefit to developing the capability to produce tetraploids de novo rather than continuing to inbreed existing stocks is that researchers and hatchery managers can now improve tetraploid lines and integrate tetraploids into breeding programs. This will benefit all stakeholders in the West Coast Shellfish industry which depend on the availability of triploid seed, but it also improves the resilience of the industry since breeding can help adapt oysters to climate change impacts and disease and optimize performance traits. The final result of the research and development efforts supported by WSARE is a pool of oysters, of which about 30% will be tetraploid adults that can be used to produce triploids and tetraploids.

Hawaiian Shellfish LLC and Paepae o He`eia are partnering with the Pacific Aquaculture and Coastal Resources Center (PACRC) at the University of Hawaii Hilo (UHH) to execute this work. Hawaiian Shellfish also supplies over 20 West Coast and Hawaii farms with seed, thus multiplying the benefits of the work. The team is fortunate in obtaining the technical assistance of Dr. Ximing Guo, co-inventor of the tetraploid production methods, and Dr. Anu Frank-Lawale, who most recently served as the lead Breeding Manager for the oyster improvement program at VIMS.