Hinge Ligament Disease of Juvenile Oysters
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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 spp. ("gliding") bacteria.
Geographic distribution
Ubiquitous.
Host species
It has been observed in all species of cultured oysters examined and in many other bivalve molluscs including juvenile Crassostrea gigas, Crassostrea virginica, and Ostrea edulis; (also isolated from cultivated clams Mercenaria mercenaria, Tapes philippinarum and Siliqua patula).
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 for various reasons. Any bivalve species or size 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. Although predisposing conditions are not fully understood, the disease has been associated with poor sanitation of cultures and with small spat that were sufficiently stressed to cease growth for a period of time. The disease has little to no effect on healthy growing juvenile bivalves.
References
Dungan, C.F. and R.A. Elston. 1988. Histopathological and ultrastructural characteristics of bacterial destruction of the hinge ligaments of cultured juvenile Pacific oyster, Crassostrea gigas. Aquaculture 72: 1-14.
Dungan, C.F., R.A. Elston and M.H. Schiewe. 1989. Evidence for colonisation and destruction in hinge ligaments of cultured juvenile Pacific oysters (Crassostrea gigas) by Cytophaga-like bacteria. Applied Environmental Microbiology 55: 1128-1135.
Elston, R.A. 1984. Prevention and management of infectious diseases in intensive mollusc husbandry. Journal of the World Mariculture Society 15: 284-300.
Elston, R.A. 1999. Health management, development and histology of seed oysters. Chapter 14. Hinge ligament disease of juvenile oysters. pp. 83-85. World Aquaculture Society, Baton Rouge, Louisiana, USA. 110 pp.
Citation Information
Bower, S.M. (2001): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Hinge Ligament Disease of Juvenile Oysters.
Date last revised: April 2001
Comments to Susan Bower
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