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Chitinolytic Bacterial Shell Disease of Lobsters


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Shell disease, Chitinolytic bacterial disease, Epizootic shell disease.

Scientific name or taxonomic affiliation

Initially attributed to chitinolytic Gram-negative bacteria but Chistoserdov et al. (2005) found that chitinoclastic bacteria comprised a very small fraction of the bacteria that were cultured from shell lesions. Various bacteria including species from the genera Pseudomonas, Vibrio, Beneckea and Flavobacteriaceae family have been isolated from the shell lesions of lobsters (Malloy 1978, Chistoserdov et al. 2005). Porter et al. (2001) indicated that many strains/species of Vibrionaceae are associated with the cuticle of normal lobsters as well as those with shell lesions. But Chistoserdov et al. (2005) determined that lesions contained two to four orders of magnitude more bacteria than healthy carapace surfaces.

Geographic distribution

Ubiquitous on the east coast of North America, fairly common among lobsters stored in pounds. Also reported in lobsters from offshore around the 106-Mile Sewage-Sludge Disposition Site (Ziskowski et al. 1996) and more recently reported as an important factor affecting lobster fisheries around Rhode Island and Long Island Sound (Castro and Angell 2000, Chistoserdov et al. 2005).

Host species

Homarus americanus, Panulirus argus, crabs and shrimps. The same or similar shell diseases are reported on Crustacea world wide including crayfish.

Impact on the host

The exoskeleton becomes pitted, eroded, and melanized at the site of infection. The bacteria do not usually invade underlying tissues. However, infected lobsters with cuticular lesions exhibit epicuticle deposition, melanization, haemocyte infiltration and pseudomembrane formation. Lobsters in intermolt and passive premolt stages of cuticular development also had proliferation of the membranous layer in the foci of infection (Smolowitz et al. 1992). Smolowitz et al. (2005) described three main types of shell disease in lobsters: 1. start as round blackened focal erosions around a setae that coalesce as the disease worsens, typically found in impounded lobsters; 2. often referred to as burn spot or rust spot appears as individual circular blackened lesions that seem to begin at pores and pits in the cuticle at various location on the body and are attributed to invasion by several different fungi, reported from lobsters in offshore canyons (Ziskowski et al. 1996) and occasionally from impounded lobsters; 3. severe erosive shell disease (called “epizootic shell disease”) characterized by moderate to deep erosions that leaves cuticular matrix to form skeletonal pillars in the lesions, associated with the current lobster disease outbreak in the northeastern United States. Shell disease prevalence was found to be significantly higher in larger lobsters and ovigerous females suggesting an inverse relationship with molting frequency (Estrella et al. 1991, Castro and Angell 2000).

Disfiguration of the lobster cuticle caused by shell disease reduces market value. Although mild and medium levels of the disease are not lethal, severe cases result in mortality (Laufer et al. 2005). Results of research conducted by Laufer et al. (2005) indicated that shell disease may induce lobsters to alter the systemic levels of ecdysone, possibly serving as a defensive measure, allowing the animal to shed the invasion by moulting.

Diagnostic techniques

Gross Observations: Erosion of chitin demarked by dark brown to black pigmentation.

Culture: Culture lesion on marine agar or equivalent media (Chistoserdov et al. 2005). Test isolated bacteria in saline solution with thin chitin strips for lysis or chitin particles suspended in nutrient poor agar for clearing by bacterial colonies.

DNA Probes: Various procedures and probes are available for the analysis of bacteria isolated from shell disease lesions (Chistoserdov et al. 2005).

Methods of control

Infected animals should be removed from holding facilities. Degraded or crowded conditions seems to exasperate the contagious nature of the disease in lobster holding facilities (Getchell 1989). Experimental results of Prince et al. (1995) suggested that improved nutrition may help impounded lobsters resist shell disease.


Castro, K.M. and T.E. Angell. 2000. Prevalence and progression of shell disease in American lobster, Homarus americanus, from Rhode Island waters and the offshore canyons. Journal of Shellfish Research 19: 691-700.

Chistoserdov, A.Y., R. Smolowitz, F. Mirasol and A. Hsu. 2005. Culture-dependent characterization of the microbial community associated with epizootic shell disease lesions in American lobster, Homarus americanus. Journal of Shellfish Research 24: 741-747.

Estrella, B.T. 1991. Shell disease in American lobster (Homarus americanus, H. Milne Edwards, 1837) from Massachusetts coastal waters with consideration for standardizing sampling. Journal of Shellfish Research 10: 483-488.

Fisher, W.S. 1988. Shell disease of lobsters. In: C.J. Sindermann and D.V. Lightner (eds.). Disease Diagnosis and Control in North American Aquaculture. Developments in Aquaculture and Fisheries Science 17. Elsevier, Amsterdam, p. 236-239.

Getchell, R.G. 1989. Bacterial shell disease in crustaceans: a review. Journal of Shellfish Research 8: 1-6.

Laufer, H., N. Demir and W.J. Biggers. 2005. Response of the American lobster to the stress of shell disease. Journal of Shellfish Research 24: 757-760.

Malloy, S.C. 1978. Bacterial induced shell disease of lobsters (Homarus americanus). Journal of Wildlife Diseases 14: 2-10.

Porter, L., M. Butler and R.H. Reeves. 2001. Normal bacterial flora of the spiny lobster Panulirus argus and its possible role in shell disease. Marine and Freshwater Research 52: 1402-1405.

Prince, L.D., R.C. Bayer, M.L. Gallagher and M. Subramanyam. 1995. Reduction of shell disease with an experimental diet in a Nova Scotian lobster pound. Journal of Shellfish Research 14: 205-207.

Smolowitz, R.M., R.A. Bullis and D.A. Abt. 1992. Pathologic cuticular changes of winter impoundment shell disease preceding and during intermolt in the American lobster, Homarus americanus. The Biological Bulletin (Woods Hole, Mass.) 183: 99-112.

Smolowitz, R., A.Y. Chistoserdov and A. Hsu. 2005. A description of the pathology of epizootic shell disease in the American lobster, Homarus americanus, H. Milne Edwards 1873. Journal of Shellfish Research 24: 749-756.

Ziskowski, J., R. Spallone, D. Kapareiko, R. Robohm, A. Calabrese and J. Pereira. 1996. Shell disease in American lobster (Homarus americanus) in the offshore, northwest-Atlantic Region around the 106-mile sewage-sludge disposal site. Journal of Marine Environmental Engineering 3: 247-271.

Citation Information

Bower, S.M. (2007): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Chitinolytic Bacterial Shell Disease of Lobsters.

Date last revised: September 2007
Comments to Susan Bower

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