Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish

Hematodinium sp. (Bitter Crab Disease)

Category | Common Name | Scientific Name | Distribution | Host Species
Impact on Host | Diagnostic Technique | Methods of Control | References | Citation

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Category

Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Bitter crab disease, Bitter crab syndrome.

Scientific name or taxonomic affiliation

Hematodinium-like dinoflagellate. Nucleotide sequence analysis of the partial small subunit (SSU) rDNA gene and ITS1 region of several isolates indicated that the Hematodinium sp. in Chionoecetes sp. is a different species from Hematodinium perezi in Callinectes sapidus and from the Hematodinium sp. in Nephrops norvegicus (Hudson and Adlard 1996).

Geographic distribution

Southeastern Alaska, USA; Bering Sea; boundary area of the Chukchi Sea and the Arctic Ocean (for details see Meyers et al. 1996); west coast of Vancouver Island, British Columbia, Canada (Bower et al. 2003); and east coast of Newfoundland, Canada (Taylor and Khan 1995).

Host species

Chionoecetes bairdi, Chionoecetes opilio and Chionoecetes tanneri (Bower et al. 2003).
Note: Hematodinium spp. have been described from other marine crustaceans including other species of crabs from the Atlantic Ocean and crabs from the vicinity of Australia, and from lobsters.

Impact on the host

Infected crabs have drooping limbs and mouthparts, milky-white haemolymph and when cooked, the muscle has a chalky texture and an astringent after-taste. Prevalence and intensity of infection are highest between July through October with peak mortalities in August and September. Prevalence of infection is usually zero by mid-winter. Severe economic losses (estimated to be as high as $3 million US) have been attributed to this parasite on the C. bairdi fishery in Alaska (Meyers et al. 1987). High prevalence of infection (50-80%) were common in C. opilio from Norton Sound and west of St Lawerence Island but the parasite was relatively rare in C. bairdi (about 2%) and C. opilio (about 4%) in the Eastern Bering Sea (Morado et al. 2000). Surveys in Newfoundland indicated that fewer infected male C. opilio were collected in traps (0.57%) than in trawls (1.59%) and in trawls, female C. opilio had a significantly higher prevalence of macroscopically diagnosed infection (6.34%) than males (Pestal et al. 2003). Morado et al. (2000) also noted a slightly higher prevalence of infection in female crabs from Alaska but of more significance was the higher prevalence of infection observed in small crabs less than 60 mm in carapace width suggesting that this parasite may have an impact on crab recruitment.

Diagnostic techniques

Gross Observations: The cuticle often with a slightly different red colour in comparison to cohorts and with a pinkish white discolouration at the appendage joints. Opaque cloudy haemolymph and milky emaciated musculature.

Wet Mounts: Numerous non-motile trophonts (vegetative stage) in the haemolymph. Although the trophonts are similar in size and shape to some crab haemolymph cells, their sheer abundance and highly granular appearance in heavily infected crabs are clues to diagnosis.  During July through October, prespores and two types of motile dinospores occur in the haemolymph. Sporulation is the last stage of infection resulting in Tanner crab death.

Histology: Four distinct morphological forms occur in the haemal spaces of all tissues. The two most commonly occurring forms are the single cell trophonts (6 to 20 µm in diameter) and multinucleate plasmodia (with 2 to about 30 nuclei per plasmodium). Both these forms have distinctive dinokaryon nuclei (6.3 ± 0.7 µm in diameter with condensed and darkly staining chromatin) and frothy cytoplasm. Plasmodia with less than 6 nuclei are often spheroid but occasionally vermiform in shape. Plasmodia with more than 6 nuclei are usually polymorphous with a lobular surface consisting of separating trophonts. The other two morphological forms are two different sizes of biflagellated dinospores that occur only during the terminal stage of the infection. In Alaska, dinospores were observed in naturally infected crabs during the summer (Love et al. 1993).

DNA Probes: The development of a PCR-based diagnostic test is being investigated in the Department of Parasitology, University of Queensland, Brisbane, Queensland 4072, Australia (Hudson and Adlard 1994). The SSU rDNA sequence of the Hematodinium sp. from C. tanneri was nearly identical to the Hematodinium spp. sequences in GenBank (Bower et al. 2003). Thus, this segment of the genome may provide a useful sequence for genus specific probes but will not be applicable to differentiating between species.

Methods of control

Management of bitter crab syndrome may be possible by harvesting Chionoecetes spp. in the winter when fewer crabs are severely parasitized and meats are more marketable. Proper disposal of infected crabs is essential in controlling dissemination of the parasite.

 

References

Bower, S.M., G.R. Meyer, A. Phillips, G. Workman and D. Clark. 2003. New host and range extension of bitter crab syndrome in Chionoecetes spp. caused by Hematodinium sp. Bulletin of the European Association of Fish Pathologists 23: 86-91.

Dawe, E.G. 2001. Trends in prevalence of bitter crab dosease (Hematodinium spp.) in snow crab (Chionoecetes opilio) at Newfoundland and Labrador, Canada. Abstract. 19th Lowell Wakefiekd Symposium, Crabs in Cold Water Regions: Biology, Management, and Economics. Sea Grant, University of Alaska, Anchorage, Alaska, USA, January 17-20, 2001. pg. 41.

Eaton, W.D., D.C. Love, C. Botelho, T.R. Meyers, K. Imamura and T. Koeneman. 1991. Preliminary results on the seasonality and life cycle of the parasitic dinoflagellate causing bitter crab disease in Alaskan Tanner crabs (Chionoecetes bairdi). Journal of Invertebrate Pathology 57: 426­434.

Hudson, D.A. and R.D. Adlard. 1994. PCR techniques applied to Hematodinium spp. and Hematodinium-like dinoflagellates in decapod crustaceans. Diseases of Aquatic Organisms 20: 203-206.

Hudson, D.A. and R.D. Adlard. 1996. Nucleotide sequence determination of the partial SSU rDNA gene and ITS1 region of Hematodinium cf. perezi and Hematodinium-like dinoflagellates. Diseases of Aquatic Organisms 24: 55-60.

Love, D.C., S.D. Rice, D.A. Moles and W.D. Eaton. 1993. Seasonal prevalence and intensity of bitter crab dinoflagellate infection and host mortality in Alaskan Tanner crabs Chionoecetes bairdi from Auke Bay, Alaska, USA. Diseases of Aquatic Organisms 15: 1-7.

Meyers, T.R. 1990. Diseases of Crustacea. Diseases caused by protistans and metazoans. In: O. Kinne (ed.). Diseases of Marine Animals. Volume III: Introduction, Cephalopoda, Annelida, Crustacea, Chaetognatha, Echinodermata, Urochordata. Biologische Anstalt Helgoland, Hamburg, p. 350-423.

Meyers, T.R., C. Botelho, T.M. Koeneman, S. Short and K. Imamura. 1990. Distribution of bitter crab dinoflagellate syndrome in southeast Alaskan Tanner crabs Chionoecetes bairdi. Diseases of Aquatic Organisms 9: 37­43.

Meyers, T.R., T.M. Koeneman, C. Botelho and S. Short. 1987. Bitter crab disease: a fatal dinoflagellate infection and marketing problem for Alaskan Tanner crabs Chionoecetes bairdi. Diseases of Aquatic Organisms 3: 195­216.

Meyers, T.R., J.F. Morado, A.K. Sparks, G.H. Bishop, T. Pearson, D. Urban and D. Jackson. 1996. Distribution of bitter crab syndrome in Tanner crabs (Chionoecetes bairdi, C. opilio) from the Gulf of Alaska and the Bering Sea. Diseases of Aquatic Organisms 26: 221-227.

Morado, J.F., T.R. Meyers and R.S. Otto. 2000. Distribution and prevalence of bitter crab syndrome in snow (Chionoecetes opilio) and tanner (C. bairdi) crabs of the Bering Sea, 1988-1996. Journal of Shellfish Research 19: 646-647. (Abstract).

Pestal, G.P., D.M. Taylor, J.M. Hoenig, J.D. Shields and R. Pickavance. 2003. Monitoring the prevalence of the parasitic dinoflagellate Hematodinium sp. in snow crabs Chionoecetes opilio from Conception Bay, Newfoundland. Diseases of Aquatic Organisms 53: 67-75.

Shields, J.D. 1994. The parasitic dinoflagellates of marine crustaceans. Annual Review of Fish Diseases 4: 241-271.

Taylor, D.M. and R.A. Khan. 1995. Observations on the occurrence of Hematodinium sp. (Dinoflagellata: Syndinidae), the causative agent of bitter crab disease in Newfoundland snow crab (Chionoecetes opilio). Journal of Invertebrate Pathology 65: 283-288.

 

Citation Information

Bower, S.M. (2003): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Hematodinium sp. (Bitter Crab Disease).

URL: http://www.pac.dfo-mpo.gc.ca/science/species-especes/shellfish-coquillages/diseases-maladies/pages/hematcb-eng.htm

Date last revised:  May 2003
Comments to Susan Bower