Hinge Ligament Disease of Juvenile Clams
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Category
Category 4 (Negligible Regulatory Significance in Canada)
Common, generally accepted names of the organism or disease agent
Hinge ligament disease, Cytophaga-like bacteria (CLB).
Scientific name or taxonomic affiliation
Cytophaga-like ("gliding") bacteria.
Geographic distribution
Ubiquitous.
Host species
Juvenile Mercenaria mercenaria, Tapes philippinarum and Siliqua patula (as well as various species of oysters).
Impact on the host
Breakdown of the hinge ligament impedes normal respiration and feeding. Perforation of the ligament allows access of secondary infectious agents to the soft tissues. This disease is particularly severe when growth of juvenile bivalves is retarded. Any bivalve species may be infected but the greatest impact is on individuals smaller than 1 cm shell height. Liquefaction of the normally hard ligament appears to be enhanced as water temperature increases from 10°C to 20°C.
Diagnostic techniques
Histology
Examine the hinge ligament for Cytophaga-like bacteria associated with and aligned at right angles to marked erosion of the hinge ligament. Plastic embedding medium should be used due to the resilient nature of the hinge ligament.
Culture
Bacteria can be isolated from the hinge of most bivalves and grown on agar medium with low nutrient concentrations. Cytophaga colonies are recognized by the rhizoid or fimbriate margins. Characteristics common to this group of bacteria include: ability to move on surfaces by a gliding motion accomplished without benefit of flagellar appendages, long and variable cell lengths ranging from 2.5 to several hundred microns, flexible cell walls of typical Gram-negative structure, and ability to degrade and metabolize recalcitrant biomacromolecules.
Methods of control
Prevention is difficult since the causative organism is believed to be ubiquitous in the marine environment. However, the disease has little to no effect on healthy growing juveniles.
References
Elston, R.A. 1982. Prevention and management of infectious diseases in intensive mollusc husbandry. Journal of the World Mariculture Society 15: 284-300.
Elston, R.A., L. Elliot and R.R. Colwell. 1982. Concholin infection and surface coating Vibrio: shell fragility, growth depression and mortalities in cultured oysters and clams Crassostrea virginica, Ostrea edulis and Mercenaria mercenaria. Journal of Fish Diseases 5: 265-284.
Citation Information
Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Hinge Ligament Disease of Juvenile Clams.
Date last revised: Fall 1994
Comments to Susan Bower
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