Sylon (Rhizocephalan Disease) of Shrimp and Prawns
Category 2 (In Canada and of Regional Concern)
Common, generally accepted names of the organism or disease agent
Sylon infection, Rhizocephalan disease of shrimps.
Scientific name or taxonomic affiliation
Sylon sp.; the only recognized species is Sylon hippolytes.
Widely distributed in shrimp and prawn populations of the northern hemisphere: North Atlantic Ocean including the coasts of Iceland, Spitzbergen, Greenland, Shetland Isles, and Franz Josef Land; coastal areas of the North Pacific Ocean including the adjacent Bering Sea, Chukchi Sea, Sea of Okhotsh and North Sea of Japan.
Known from 21 species of Caridea shrimp belonging to three families: Crangonidae, Pandalidae and Hippolytidae.
Impact on the host
Roots of the parasite invade all tissues of the cephalothorax. Infection causes stunting of growth, modification of the secondary sexual characteristics (i.e. morphological alterations of the appendix masculina and appendix interna on the endopod of the second pleopods) and castration. Infected prawns usually die when the parasite has completed its life cycle. The few surviving prawns are marked by obvious brownish to black scars in tissues formerly inhabited by the parasite. Sylon sp. usually occurs in low prevalences (less than 5%) on many species of shrimp throughout the northern hemisphere. However, high prevalences (up to 47%) were found on some stocks of prawns (Pandalus platyceros) in northern British Columbia while stocks of P. platyceros in southern British Columbia are not infected.
Gross Observations: The externa is usually attached to the ventral surface of the abdomen and depending on the stage of infection can be a pinkish to white coloured plump ovoid sac (growing to about 1.5 cm in length and 1.0 cm in width) or can be grayish coloured and wrinkled when spent. Mature cyprid larvae expelled from the externa are ovoid in shape and approximately 170µm long, this stage has been observed to swim rapidly with a flicking action of the posterior appendages and to walk on solid surfaces using its antennal appendages with their suction cup-like extremities.
Histology: Parasite roots called interna can be observed within and around the organs of the cephalothorax. If the parasite is intact, there is usually no cellular response by the host to the infection. When the externa is lost, a massive melanotic inflammatory response occurs around the interna causing the interna to die and acquire a brown colour.
Methods of control
No known methods of prevention or control. In British Columbia, there is great concern that the Sylon infecting prawns (P. platyceros) is different from that affecting other species of shrimp. Until the risk of introducing the abundant prawn Sylon found in prawn stocks from northern B.C. to uninfected southern prawn stocks can be accurately assessed, there will have to be restrictions/controls placed on commercial fisherman who wish to transport live prawns from northern stocks to southern markets.
Bower, S.M. and J.A. Boutillier. 1988. Enigma of Sylon (Crustacea: Rhizocephala) infections on the shrimp Pandalus platyceros, in British Columbia. Abstracts Third International Colloqium on Pathology of Marine Aquaculture, Gloucester Point, VA. 2-6 October 1988, p. 59-60.
Bower, S.M. and J.A. Boutillier. 1989. Extent of castration of prawns (Pandalus platyceros) by Sylon (Crustacea: Rhizocephala). Abstract. Journal of Shellfish Research 8(2): 467.
Bower, S.M. and J.A. Boutillier. 1990. Sylon (Crustacea: Rhizocephala) infections on the shrimp in British Columbia. In: F.O. Perkins and T.C. Cheng (eds.). Pathology in Marine Science. Academic Press, p. 267-275.
Butler, T.H. 1980. Shrimps of the Pacific coast of Canada. Canadian Bulletin of Fisheries and Aquatic Sciences 202, p. 11-15.
Høeg, J. and J. Lützen. 1985. Marine Invertebrates of Scandinavia, No. 6. Crustacea Rhizocephala. Norwegian University Press, Oslo, p. 24-27.
Jensen, P.G., J.T. Høeg, S. Bower and A.V. Rybakov. 1994. Scanning electron microscopy of lattice organs in cyprids of the Rhizocephala Akentrogonida (Crustacea: Cirripedia). Canadian Journal of Zoology 72: 1018-1026.
Lützen, J. 1981. Observations on the rhizocephalan barnacle Sylon hippolytes M. Sars parasitic on the prawn Spirontocaris lilljeborgi (Danielssen). Journal of Experimental Biology and Ecology 50: 334-347.
Bower, S.M., Meyer, G.R. (1998): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Sylon (Rhizocephalan Disease) of Shrimp and Prawns.
Date last revised: August 1998
Comments to Susan Bower
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