Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts

Introduction

The geoduck (pronounced gooey duck) clam is a member of the Phylum Mollusca, Class Bivalvia, Subclass Lamellibranchia, Order Myoida, Family: Hiatellidae, Genus Panopea, and Species generosa originally named by Gould in 1850. Vadopalas et al. (2010) indicated that over time and a series of publications, P. generosa became incorrectly synonymized with Panopea abrupta (for example see Coan et al. (2000), page 490) a fossil bivalve collected from Miocene deposits along the banks of the Columbia River near Astoria, Oregon that was originally named Mya abrupta by Conrad (1849). Leyva-Valencia et al. (2015) also disagreed with this synonymy and indicated that Panopea generosa is unquestionably the proper name for the Pacific geoduck clam. This clam is the largest burrowing clam in its natural range throughout Alaska, British Columbia, Washington and as far south as the northwestern area of Baja California, Mexico (Leyva-Valencia et al. 2015). Although a few individuals weigh up to 4.5 kg (10 lbs.), the average whole body wet weight is about 1 kg. (2.2 lbs.) with an average shell length of about 195 mm (7 ¾ inches) (Harbo 1997). To the first-time observer, this clam could be considered as rather grotesque because its shell is not capable of encompassing the huge body.

Despite their appearance, the commercial value of this clam has significantly increased in recent years giving geoduck clams the current honour of being one of the most valuable commercial shellfish species harvested in British Columbia. Historically, geoduck clams were harvested for food in the Pacific Northwest by the native population and the clams currently support a prosperous commercial fishery in Alaska, British Columbia, and Washington. For example, in British Columbia landed value peaked at $42 million (ex-vessel price) in 1995 but since declined to about $33 million. Landings peaked in 1987 at 5,735 tonnes and steadily declined to 1,817 tonnes (about 4 million pounds) in 1996 and since then has remained at about that level (DFO 2000). The maximum yearly harvest quotas have been set in an attempt to conserve stocks thereby assuring the long term viability of the geoduck harvest industry in British Columbia. Although geoduck clams are very long lived, with a reported life span of up to 146 years (Harbo 1997), natural recruitment is poor. Thus, the commercial harvest of wild stocks is carefully controlled and curtailed. The proposed method of increasing the landings of geoduck clams without jeopardising the long term survival of the industry is to increase the numbers of geoduck clams available for harvest through enhancement and/or aquaculture.

Currently there is increasing interest by the industry to actively culture and enhance geoduck stocks. Initial research and field trials in Washington State and British Columbia indicate a significant potential in geoduck clam culture for both farming and enhancement purposes. The need to transplant animals between various locations will arise as development of a geoduck clam culture industry progresses. However, many geoduck clams stocks within the natural range of this species probably have been separated from each other for hundreds of thousands of years. For example, geoduck clams from the Strait of Georgia side of Vancouver Island have not had contact with geoduck clams on the Pacific Ocean side of Vancouver Island for as long as Vancouver Island has been in place. Thus, the possibility that these stocks are genetically different and have developed mechanisms of dealing with different environmental conditions, including different associated organisms such as parasites, must be acknowledged.

It is well established that the movement of shellfish stocks across natural geographic barriers incurs the risk of transmitting diseases that are endemic in any isolated population. In British Columbia, information available on the few native shellfish species that have been examined indicate that parasites and diseases occur in stocks from some areas that are not seen in others. For example, 1) Sylon sp. a parasite of shrimp that castrates its host occurs in up to 33% of the spot prawns in northern British Columbia but is not known to occur in waters adjacent to Vancouver Island where the spot prawn stocks support a viable commercial harvest (for details see Sylon (Rhizocephalan Disease) of Shrimp and Prawns) and 2) stained prawn disease, that was associated with significant reductions in spot prawn populations in Thornbrough Channel, Howe Sound and causes high mortalities among prawns in the laboratory, is not known to occur outside of the Strait of Georgia and associated inlets (for details see Rickettsia-like Infection of Pandalid Shrimp). Unfortunately almost nothing is known about the disease and parasites of geoduck clams. A cautious approach to the transplantation of animals into and around the province will reduce the risks involved and maximise the possibilities of success. Repercussions of the indiscriminate transplantation of geoduck clams around the province could be devastating and irreparable.

To help reduce the risk of inadvertent transfer of diseases of aquatic animals into and within British Columbia, a Federal / Provincial Fish Introductions and Transfers Committee was established. This Committee is bound by existing government legislation and policies regarding movements of live fish into and within the Province of British Columbia (see https://www.dfo-mpo.gc.ca/aquaculture/management-gestion/licen-permi-eng.htm). Thus, all proposed shellfish transplants must be submitted to the Committee for prior approval. Further details including contact information for the Committee are available via the Internet at https://www.dfo-mpo.gc.ca/aquaculture/management-gestion/contact-intro-eng.htm.

In order to ascertain the risk associated with indiscriminate movements of geoduck clams through enhancement/culture efforts, the acquisition of information pertaining to normal morphology and distribution of abnormalities including diseases as well as parasites and symbionts in geoduck clams was initiated. To date, all activities involving geoduck clam culture and enhancement in British Columbia have been confined to the Strait of Georgia in order to avoid the potential harm resulting from mixing of stocks and accidental transfer of pathogens. In recognition of the requirements of transplantation for future expansion of geoduck culture, the industry (Underwater Harvesters Association (Web site http://www.geoduck.org), FAN Seafoods Ltd., Island Scallops Ltd. and Unique Sea Farms Ltd.) and government (Diseases of Shellfish Program of the Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo) with previous funding assistance from the National Research Council of Canada Industrial Research Assistance Program Research and Development (NRC/IRAP) and the British Columbia Information, Science and Technology Agency's Technology Assistance Program (TAP) addressed issues relevant to geoduck clam health.

In 1993, the geoduck industry in British Columbia (Under Water Harvesters Association, and Fan Seafoods Ltd.) in conjunction with a commercial hatchery (Island Scallops Ltd.) initiated geoduck clam culture for both farming and enhancement purposes. Because little is known about the biology of geoduck clams, studies were initiated in collaboration with the Fisheries and Oceans Canada to collect base line information, which included:

1. describing the development, anatomy and histology of normal, healthy clams,
2. assaying the symbionts, parasites and diseases detected during a survey of cultured geoduck clams of the 1995 and 1996 year classes,
3. examination of abnormal and/or diseased geoduck clams submitted by the commercial fisheries during the period from August 1996 through August 1998, and
4. conduct experimental investigations into the cause of geoduck ‘warts’ and the fungus associated with the dark discolouration of the siphon and exposed mantle surface.

The web pages on this site present the results of this study and are arranged with each topic on its own page. All pages are listed in the Table of Contents and grouped firstly by subject. Within each subject grouping, pages detailing specific features are listed with appropriate access (link) to the detailed description with illustrations. Appropriate references are located at the bottom of each page.

References

Breen, P.A., and T.L. Shields. 1983. Age and size structure in five populations of geoduck clams (Panope generosa) in British Columbia. Can. Tech. Rep. Fish. Aquat. Sci. 1169: 62 p.

Coan, E.V., P.V. Scott and F.R. Bernard. 2000. Bivalve Seashells of Western North America. Marine Bivalve Mollusks from Arctic Alaska to Baja California. Santa Barbara Museum of Natural History. Santa Barbara, CA.

Conrad, TA. 1849. Mollusca. Pp. 723-728 pls 17-21. In: J.D. Dana (editor) Geology. United States Exploring Expedition. During the years 1838 ... 1842. Under the command of Charles Wilkes, U.S.N., Vol. 10: Appendix 1 (Descriptions of fossils), III. Fossils from northwestern America. Philadelphia (Sherman). [as sited by Coan, E.V., P.V. Scott and F.R. Bernard. 2000. Bivalve Seashells of Western North America. Marine Bivalve Mollusks from Arctic Alaska to Baja California. Santa Barbara Museum of Natural History. Santa Barbara, CA. Pp 605.]

DFO 2000. Geoduck Clam. DFO Science Stock Status Report C6-05 (2000). Web site: https://waves-vagues.dfo-mpo.gc.ca/library-bibliotheque/331771.pdf

Fisheries and Oceans Canada, Fisheries Management, Geoduck Fishery - Pacific Region. Web site contains information on an overview of the geoduck clam fishery in British Columbia, Canada: http://www.pac.dfo-mpo.gc.ca/fm-gp/commercial/shellfish-mollusques/geoduck-panope/index-eng.html.

Fitch, J.E. 1953. Common marine bivalves of California. Calif. Dep. Fish Game Fish Bull. 90: 102 p.

Goodwin, C.L. 1973. Subtidal geoducks of Puget Sound, Washington. Wash. Dep. Fish. Tech. Rep. 13: 64 p.

Harbo, R.M.1997. Shells & Shellfish of the Pacific Northwest, A Field Guide. Harbour Publishing, Madeira Park, B.C. Canada.

Jamieson, G.S., and K. Francis. 1986. Geoducks, p. 18-22. In G.S. Jamieson and K. Francis. Invertebrate and marine plant fishery resources of British Columbia. Can. Spec. Publ. Fish. Aquat. Sci. 91.

Leyva-Valencia, I., P. Cruz-Hernández, S.T. Álvarez-Castañeda, D.I. Rojas-Posadas, M.M. Correa-Ramírez, B. Vadopalas and D.B. Lluch-Cota. 2015. Phylogeny and phylogeography of the geoduck Panopea (Bivalvia: Hiatellidae). Journal of Shellfish Research 34: 11-20.

Quayle, D.B. 1978. The intertidal bivalves of British Columbia. B.C. Prov. Mus. Handbook 17: 84-85.

Ricketts, E.F., J. Calvin, and J.W. Hedgpeth. 1985. Between Pacific Tides. 5th ed. Stanford Univ. Press, Stanford, Calif.: 325-328.

Underwater Harvesters Association. Geoduck from Canada web site see: http://www.geoduck.org

Vadopalas, B., T.W. Pietsch and C.S. Friedman. 2010. The proper name for the geoduck: resurrection of Panopea generosa Gould, 1850, from the synonymy of Panopea abrupta (Conrad, 1849) (Bivalvia: Myoida: Hiatellidae). Malacologia 52: 169-173.

Citation Information

Bower, S.M. and Blackbourn, J. (2003): Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts: Introduction.

Date last revised: August 2020
Comments to: Susan Bower