Triploidy

Enhancing Stress Resistance of Cultured Hard Clams in Florida by Triploidy

Investigators:
Dr. John Scarpa, Harbor Branch Oceanographic Institution, Division of Aquaculture
Dr. Shirley Baker, University of Florida, Department of Fisheries and Aquatic Sciences
Leslie Sturmer, University of Florida, Cooperative Extension Service
Dr. Chuck Adams, University of Florida, Food and Resource Economics Department

Funding:
U.S. Department of Agriculture Agricultural Research Service
Florida Sea Grant College Program

Time Period:
2003 - 2005

Rationale:
Production of cultured clams in Florida is primarily increasing through expansion of cultivation area and not through better culture practices or strain development. Recently, the need for a hardier clam strain has become evident as clam culturists in south Florida report below average survivals or total losses during the hot summers. At this time, clams that have lost body mass from spawning in the spring encounter reduced food production as water temperature increases beyond the threshold for many phytoplankton species. At the same time, clam metabolism is higher, yet food and dissolved oxygen saturation levels are reduced. Together, these stressors may contribute to low survival and unreliable production.

Strain development through basic breeding takes many years and large financial and physical resources to accomplish. A quicker method to capitalize on genetics is through triploid induction, which has been utilized successfully in oyster aquaculture in the Pacific Northwest. Triploidy is induced by inhibiting polar body extrusion of the oocyte during meiosis. Meiotic maturation of clam oocytes occurs after oocytes are released into the environment and inseminated, thereby making this procedure easily accomplishable. Triploid organisms contain three sets of chromosomes, which inhibits chromosome pairing during gametogenesis. This in turn diverts energy from reproduction (i.e., gametogenesis and loss of body mass during spawning) toward somatic growth, which would be available for metabolism during the summer.

There is a dearth of information regarding the commercial value of triploid hard clams, especially for increased stress resistance rather than increased growth, in Florida and elsewhere. Therefore, a rigorous examination of the utilization of triploid hard clams for increasing survival and quality in Florida waters is warranted. Further information on triploid applications in shellfish aquaculture is included in the January 2004 issue of The Bivalve Bulletin.

Goals and Objectives:
The goal of this research is to improve stress resistance, specifically high temperature and low dissolved oxygen resistance, in the hard clam, which is the basis of an expanding shellfish culture industry in Florida, by utilizing a basic agricultural breeding technique, i.e., triploid induction. It is hypothesized that triploid clams will exhibit reduced gametogenesis and increased body mass that will contribute to higher survival during the summer stressors of heat, reduced dissolved oxygen, and reduced feed availability found in the subtropical waters of Florida.

The objectives of this research are: 1) verify timing of ooycte meiotic maturation for treatment application during spawning, 2) produce triplicate groups of sibling diploid and triploid hard clams, 3) grow a portion of these clams under controlled conditions for laboratory challenges, 4) grow a portion of these clams under commercial nursery conditions in upland systems, 5) grow triploid and diploid families under commercial conditions in natural bodies of water, 6) compare production characteristics in both the nursery and growout phases (e.g., growth and survival) between these families, 7) compare responses of these clams subjected to controlled laboratory environmental challenges, 8) determine the physiological mechanism by which triploidy may improve field survival, and 9) compare and characterize economics of triploid seed production and the financial considerations of nursery and growout of triploid hard clams.

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