BIVALVE AQUACULTURE

Enhancing Stress Resistance Of Cultured Hard Clams In Florida By Triploidy

Research Team:
John Scarpa (HBOI) - Principle Investigator
Shirley M. Baker (Univ. of Florida - Dept. Fish. & Aquatic Sciences) - Co-Principle Investigator
Leslie Sturmer (Univ. of Florida - IFAS/Coop. Exten. Serv.) - Associate Investigator
Charles Adams (Univ. of Florida - Food & Resources Economics) - Associate Investigator

Florida has approximately 350 active hard clam growers producing a crop worth $18.2 million in 2001. 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 southwest 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. Concomitantly, 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 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 resistance of triploid hard clams to high temperatures, low dissolved oxygen and reduced food availability 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. However, before field trials of triploids may proceed, methods for producing triploid hard clams need to be verified and controlled laboratory experiments on juveniles performed for comparison to field grown clams.

Harbor Branch, working in collaboration with the University of Florida, is currently engaged in research to investigate the potential of triploidy as a strategy for improving the stress resistance of cultured hard clams. Specific objectives of this research include:

1) verify timing of ooycte meiotic maturation for treatment application,
2) examine production of triploids using standard commercial hatchery spawning methods
3) produce replicate groups of sibling diploid and triploid hard clam Mercenaria mercenaria,
4) compare production data (e.g., growth and survival) between these groups in a commercial nursery system, and
5) determine physiological responses of these clams in laboratory challenges of temperature and oxygen.