Chitinolytic Bacterial Shell Disease of Crayfish
Category 4 (Negligible Regulatory Significance in Canada)
Common, generally accepted names of the organism or disease agent
Shell disease, Burn spot disease, Chitinolytic or chitinoclastic bacterial disease.
Scientific name or taxonomic affiliation
Chitinolytic bacteria including species of Aeromonas, Pseudomonas, and Citrobacter.
Impact on the host
Necrotic bacterial disease of the integument including the gills. If underlying tissues are invaded may lead to septicemia and death. Systemic infections are usually facilitated by stressful environmental conditions (e.g., high temperatures) and/or wounds in the cuticle (Vey 1986). Fungi may also be involved in the lesions (Geasa 2003b). Low virulence; shell lesions usually lost at molting but renders shell unsightly and reduces market value.
Gross Observations: Melanized, eroded lesions on exoskeleton.
Histology: Heavy infestation of bacteria can result in partial erosion of the cuticle, retraction of epidermis from the cuticle, accumulation of granulated haemocytes under the epithelia and possibly epithelial degeneration.In progressed cases, the bacterial colonies can produce indentations in the cuticle, pigmentation (melanization), and necrotic lesions.
Culture: Causative bacteria difficult to separate from opportunistic invaders, but may be recovered and cultured from surface-sterilised exoskeleton. Test for chitinolytic activity in saline solution with thin chitin strips.
Methods of control
Poor water quality or crowding predispose stocks to infection.
Alderman, D.J. and J.L. Polglase. 1988. Pathogens, parasites and commensals. In: D.M. Holdrich and R.S. Lowery (eds.). Freshwater Crayfish Biology, Management and Exploitation. Timber Press, OR., pp. 174-175.
Geasa, N.M.S. 2003a. Pathological changes in the exotic crayfish Procambarus clarkii (Crustacea, Decapoda) induced by gill bacterial infestation. Journal of the Egyptian German Society of Zoology 40D (Invertebrate zoology & Parasitology): 15-27.
Geasa, N.M.S. 2003b. Histopathological and SEM studies on cuticular changes in the exotic crayfish Procambarus clarkii (Crustacea, Decapoda) infected by shell disease. Journal of the Egyptian German Society of Zoology 40D (Invertebrate Zoology & Parasitology): 63-76.
Sparks, A.K. 1985. Synopsis of Invertebrate Pathology Exclusive of Insects. Elsevier Science Publishing Co. Inc., Amsterdam. p. 201.
Vey, A. 1986. Disease problems during aquaculture of freshwater crustacea. In: Brink, P. (ed.), Freshwater Crayfish VI, Papers from the Sixth International Symposium of Astacology. International Association of Astacology, Lund, pp. 212-222.
Bower, S.M. (2005): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Shell Disease (Chitinolytic Bacterial Disease) of Crayfish.
Date last revised: September 2005
Comments to Susan Bower
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