Hematodinium spp. of Crabs in Australia and China

Category

Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Dinoflagellate blood disease, Milky disease.

Scientific name or taxonomic affiliation

Hematodinium spp. in the family Syndiniceae, Order Syndinida (Syndiniales to botanists)can be identified as dinoflagellates on the basis of their: typical dinokaryon (or mesokaryon); the alveolate pellicle; the presence of naked, athecate gymnodinoid dinospores (or zoospores); and the classic form of mitosis known as dinomitosis (Stentiford and Shields 2005). Although Hematodinium spp. have been reported from a broad range of brachyuran crabs (Stentiford and Shields 2005, Morado 2011), only two species (H. australis and Hematodinium perezi) have been described because of their lack of distinct characteristics and poorly understood life cycles.

Reports on Hematodinium from the vacinity of Australia and China are presented below under subsections a) and b), respectively. This separation may be significant because of the possible presence of different species of Hematodinium in crabs along the coasts of the two countries.

  1. Hematodinium australis and possibly other species of Hematodinium.
  2. Hematodinium sp.

Geographic distribution

  1. Queensland, Australia.
  2. Coast of southern and eastern China

Host species

  1. Hematodinium australis was described from Portunus pelagicus. However, Hematodinium have also been reported from other crabs including Trapezia areolata, Trapezia spp. and Scylla serrata for the same area. The parasite from P. pelagicus was experimentally transmitted by injection (with a 16 day pre-patent period) to P. pelagicus and S. serrata whereas the parasite from S. serrata could not be transmitted to S. serrata nor to P. pelagicus in one laboratory experiment. (Hudson and Shields 1994).
  2. The crabs Scylla serrata and Portunus trituberculatus (Li et al. 2008, Small 2012), and the ridgetail white prawn Exopalaemon carinicauda (Xu et al. 2010).

    Note: Hematodinium spp. have been reported from other marine crustaceans including other species of crabs from the Atlantic Ocean and Chionecetes spp. and other crabs from the North Pacific and North Atlantic oceans, as well as from Norway lobsters (Stentford 2006, Morado 2011, Small 2012). A morphologically similar but genetically distinct parasite, that was initially thought to be a species of Hematodinium, was reported from shrimp.

Impact on the host

  1. Prevalence usually low (0.9 to 4.0%) (Shields 1992, Hudson and Shields 1994, Hudson 1995). Heavily infected sand crabs (Portunus pelagicus) were mordiund on capture and died within 24 hours. Heavily infected crabs have non-clotting, cloudy haemolymph containing very few haemocytes, numerous H. australis. Also, six haemolymph parameters (urea, potassium (K+), creatinine, glucose, phosphate (P043-), and aspartate amino transferase enzyme) were higher than the normal range (Hudson 1995).
  2. In Zhejiang Province, eastern China, disease outbreaks caused by Hematodinium affected greater than 3000 acres of culture ponds in several aquaculture facilities around the coastal areas of Zhoushan, with mortalities of up to 60% in P. trituberculatus stocks (Small 2012). High mortalities also occurred in farmed S. serrata from the Sanmen area of Zhejiang Provence (Small 2012). In aquaculture facilities along the coast of southeastern China (in Shantou, Guangdong Provence), Hematodinium caused acute epizootics in S. serrata often affecting greater than 60% of the stocks and usually occurring from September to November as the crabs were nearing maturity (Li et al. 2008). The salinity in these affected aquaculture ponds was less than 9 ppt, unusually low because Hematodinium spp. in wild populations of crustacea from other parts of the world usually occur where salinity was greater than 11 ppt (Li et al. 2008). Infection in farmed Exopalaemon carinicauda resulted in up to 100% mortality in affected polyculture ponds in Zhoushan, Zhejiang province, China (Xu et al. 2010).

Diagnostic techniques

Gross Observations:

  1. Sternae and ventral surfaces of heavily infected sand crabs (Portunus pelagicus) appeared chalky white whereas heavily infected mud crabs (Scylla serrata) showed no external signs of the disease (Hudson and Shields 1994).
  2. Clinical signs include a lethargic, moribund behaviour, a cooked appearance (often with a pinkish carapace discoloration), milky body fluids, death shortly after capture or during transit and are generally similar to those reported for bitter crab disease and pink crab disease (Li et al. 2008, Small 2012). Infected prawns Exopalaemon carinicauda usually failed to school with healthy prawns (Xu et al. 2010).

Wet mount:

  1. Haemolymph poorly clotting, devoid of haemocytes, and containing numerous nonmotile, trophonts (circular cells, vegetative stage, 7.9 to 11.9 µm in diameter) or ovoid plasmodia (dividing cells, 20.1 to 47.5 µm in diameter). Trophonts and plasmodia usually contain many refractile granules (Hudson and Shields 1994).
  2. Haemolymph with decreased haemocyte count and numerour parasites of various shapes or putative developmental stages and usually containing many refractile granules (Li et al. 2008). Occasionally motile biflagellated dinospores (7 to 9 µm in diameter) were observed in the unclotted haemolymph (Xu et al. 2010).

Histology:

  1. Trophonts contain one nucleus and vacuoles with larger vacuoles in larger parasites. Plasmodia contain 2 to 5 nuclei. The nuclei of trophonts and plasmodia have irregularly dispersed nucleoplasm and chromatin condensed into small beads in larger (> 10 µm in diameter) parasites. Infection caused separation of the muscel bundles, and degeneration and rupture of the connective tissue in the hepatopancrease, gills and gonad with numerous parasite filling the spaces (Hudson and Shields 1994).
  2. The parasite caused profound pathological changes in gills, hepatopancreas, heart, and muscles of infected hosts (Xu et al. 2010). In heavily infected crabs and prawns, all tissues were conjested with Hematodinium displacing the connective tissue in conjunction with atrophy of epithelial cells in the hepatopancrease and gills and coagulative necrosis in the myocardium (Li et al. 2008, Xu et al. 2010).

Electron Microscopy:

  1. Cytoplasm of H. australis from Portunus pelagicus contained trichocysts whereas no trichocysts were observed in the Hematodinium from Scylla serrata (Hudson and Shields 1994).
  2. The ultrastructure of the Hematodinium in the prawn Exopalaemon carinicauda was similar to that from Portunus trituberculatus including beaded or lobed chromatin, dinokaryotic structures typical of dinoflagellate, and the presence of trichocysts (electron dense bodies) in the cytoplasm (Xu et al. 2010).

Immunological Assays:

  1. None reported.
  2. The Hematodinium sp. from the prawn Exopalaemon carinicauda shared similar antigenic determinants with the Hematodinium sp. identified in the Chinese swimming crab Portunus trituberculatus (Xu et al. 2010).

DNA Probes: For Hematodinium spp., all published efforts have exclusively focused upon segments of the ribosomal RNA gene complex (rDNA), which is present in the nuclear genome of eukaryotes as tandemly repeated clusters of highly conserved genes encoding the small subunit (SSU or 18S), 5.8S, and large subunit (LSU) genes, which are separated by highly variable spacer sequences, the first and second internal transcribed spacers (ITS1 and ITS2) (Small 2012).

  1. A polymerase chain reaction (PCR) based diagnostic test was development by Hudson and Adlard (1994).
  2. The PCR assay as described by Gruebl et al.(2002) amplified an expected band of about 187 base pairs in tissue samples from Scylla serrata with milky disease (Li et al. 2008). Partial sequences of the 18S and full sequence of ITS1 of Hematodinium sp. from E. carinicauda were 99% similar to equivalent sequences from Hematodinium in P. trituberculatus and S. serrata in Zhoushan, China (Xu et al. 2010). Preliminarily phylogenetic analysis based on sequences of the ITS1 of Hematodinium rDNA indicated that the parasite from E. carinicauda is closely related to the Hematodinium sp. identified in Callinectes sapidus from the east coast of the United States and has distinct genetic distance from the Hematodinium sp. identified in Nephrops norvegicus, Cancer pagurus, Pagurus bernhardus, and Chionoecetes opilio from the northern areas of the North Atlantic (Xu et al. 2010). In agreement, Jensen et al. (2010) concluded that the Hematodinium sp. infecting the portunoid crabs, S. serrata from China, Callinectes sapidus from the east coast of the United States, and Liocarcinus depurator from the English Channel belonged in a clade separate from Hematodinium in other widley distributed decapods (such as Nephrops norvegicus, Hyas coarctatus, Pagurus bernhardus, Pagurus prideaux, Munida rugosa, Cancer pagurus and Carcinus maenas, Chionoecetes angulatus, Chionoecetes bairdi, Chionoecetes tanneri, Chionoecetes opilio, Lithodes couesi and Paralithodes camchaticus) from the North Atlantic and North Pacific oceans. Small et al. (2012) suggested that the Hematodinium infecting C. sapidus from the United States, and P. trituberculatus and S. serrata from China are different genotypes of Hematodinium perezi based on molecular analysis of the ITS rDNA regions from H. perezi infecting L. depurator from the English Channel. Small (2012) proposed that the ITS1 region be used to designate three different H. perezi genotypes from the following locations and hosts: genotype I (English Channel, L. depurator); genotype II (east China, P. trituberculatus and S. serrata), and genotype III (east coast US, C. sapidus).

Methods of control

No known methods of prevention or control.

References

Gruebl, T., M.E. Frischer, M. Sheppard, M. Neumann, A.N. Maurer and R.F. Lee. 2002. Development of an 18SrRNA gene-targeted PCR-based diagnostic for the blue crab parasite Hematodinium sp. Diseases of Aquatic Organisms 49: 61-70.

Hudson, D.A. 1995. Biochemical parameters of the serum of the sand crab, Portunus pelagicus, with reference to the parasitic dinoflagellate, Hematodinium australis. Bulletin of the European Association of Fish Pathologists 15: 202-205.

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.J.G. Lester. 1994. Parasites and symbionts of wild mud crabs Scylla serrata (Forskal) of potential significance in aquaculture. Aquaculture 120: 183-199.

Hudson, D.A. and J.D. Shields. 1994. Hematodinium australis n. sp., a parasitic dinoflagellate of the sand crab Portunus pelagicus from Moreton Bay, Australia. Diseases of Aquatic Organisms 19: 109-119.

Hudson, D.A., N.B. Hudson and J.D. Shields. 1993. Infection of Trapezia spp. (Decapoda: Xanthidae) by Hematodinium sp. (Duboscquodinida: Syndinidae): a new family record of infection. Journal of Fish Diseases 16: 273-276.

Jensen, P.C., K. Califf, V. Lowe, L. Hauser and J.F. Morado. 2010. Molecular detection of Hematodinium sp. in Northeast Pacific Chionoecetes spp. and evidence of two species in the Northern Hemisphere. Diseases of Aquatic Organisms 89: 155-166.

Li, Y.Y., X.A. Xia, Q.Y. Wu, W.H. Liu and Y.S. Lin. 2008. Infection with Hematodinium sp. in mud crabs Scylla serrata cultured in low salinity water in southern China. Diseases of Aquatic Organisms 82: 145-150.

Shields, J.D. 1992. Parasites and symbionts of the crab Portunus pelagicus from Moreton Bay, Eastern Australia. Journal of Crustacean Biology 12: 94-100.

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

Small, H.J. 2012. Advances in our understanding of the global diversity and distribution of Hematodinium spp. – Significant pathogens of commercially exploited crustaceans. Journal of Invertebrate Pathology 110: 234-246.

Small, H.J., J.D. Shields, K.S. Reece, K. Bateman and G.D. Stentiford. 2012. Morphological and molecular characterization of Hematodinium perezi (Dinophyceae: Syndiniales), a dinoflagellate parasite of the harbour crab, Liocarcinus depurator. Journal of Eukaryotic Microbiology 59: 54-66.

Xu, W., J. Xie, H. Shi and C. Li. 2010. Hematodinium infections in cultured ridgetail white prawns, Exopalaemon carinicauda, in eastern China. Aquaculture 300: 25-31.

Citation Information

Bower, S.M. (2013): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Hematodinium spp. of Crabs in Australia and China.

Date last revised: February 2013
Comments to Susan Bower

Date modified: