Epidemiology of bitter crab disease (Hematodinium sp.) in snow crabs Chionoecetes opilio from Newfoundland, Canada

Abstract

The parasitic dinoflagellate Hematodinium sp. causes a condition known as bitter crab disease (BCD) in snow crabs Chionoecetes opilio and Tanner crabs C. bairdi. As the name of the condition implies, crabs infected with BCD are unmarketable due to their bitter flavor. We surveyed the distribution of BCD in 3 regions within the snow crab fishery of Newfoundland from 1997 to 2003. Over time, the disease has become firmly established in Conception and Bonavista Bays and persists at low levels on the Avalon fishing grounds. An epizootic occurred within Bonavista and Conception Bays in 1999 and persisted in Conception Bay in 2000, reaching prevalences of over 2% to 9% in trapped and trawled male crabs and from 19 to 26% in trawled and trapped female crabs, respectively. Infections were highest in females and small males, i.e. the unfished and pre-recruit portions of the fishery. In a mortality study, all of the naturally infected crabs died and 50% of the experimentally inoculated crabs died. Patterns in the molting cycle and prevalence of infection indicate that transmission occurs during the post-molt condition, and that overt infections probably develop 2 to 4 mo later with mortalities occurring at least 3 to 4 mo thereafter. The hydrography of this bay may have contributed to the epizootic as infections were centered within the deeper confines of the bay. Analysis of various abiotic factors uncovered a significant positive association between prevalence, depth and mud/sand substrates; the nature of this relationship was not apparent but may be related to diet or alternate hosts. Lastly, given the increase in BCD in snow crabs in Newfoundland, we recommend that fishery management programs for Chionoecetes fisheries employ non-selective gear to monitor for Hematodinium infections in female and juvenile crabs because these under-sampled members of the population may forewarn of impending recruitment declines that might otherwise remain unexplained.

A review of the parasitic dinoflagellates Hematodinium species and Hematodinium-like infections in marine crustaceans

“…Thus, the simplest diagnostic method involves an external assessment of the opaquely discoloured carapace that can be performed rapidly in the field. This method has been used as a field diagnostic tool for Hematodinium infection of Nephrops norvegicus in Scottish, Swedish and Irish waters (see Field et al 1992, Tärnlund et al 2000, Stentiford et al 2001c, Briggs & McAliskey 2002, for Cancer pagurus in the English Channel (Stentiford et al 2002), for Chionoecetes bairdi from Alaskan waters (see Meyers et al 1987Meyers et al , 1990) and for C. opilio from Newfoundland (Taylor & Khan 1995, Dawe 2002, Pestal et al 2003, Shields et al 2005. However, while this method remains useful for the detection of advanced cases in heavily infected hosts, it does not detect low-level 'sub-patent' or potentially sub-patent (low-level, tissue-based) infections (see Meyers et al 1987, Shields & Squyars 2000, Stentiford et al 2001c, Pestal et al 2003, nor is it useful for infections in temperate species such as Callinectes sapidus (J. D. Shields pers.…”

“…For example, at the commercial level, biochemical alterations to the meat of patently infected Tanner crabs C. bairdi and snow crabs causes a condition known as bitter crab disease (BCD) or bitter crab syndrome that renders them unmarketable, with a single infected crab ruining the flavor of an entire batch of processed crabs (Meyers et al 1987, Taylor & Khan 1995. At the population level, infections often have extremely high prevalences in juvenile and female hosts, with the potential for dramatic, but cryptic effects on host populations (Meyers et al 1987, Wilhelm & Mialhe 1996, Messick & Shields 2000, Stentiford et al 2000a, 2001b,c,d, Pestal et al 2003, Shields et al 2005. At the organismal level, physiological and biochemical disruptions to the muscles and other organs substantially alter the metabolism of infected hosts providing insights into the host's physiology as well as immune defences (Taylor et al 1996, Stentiford et al 2000a,b, 2001a,b, 2003.…”

Transmission of Panulirus argus virus 1 (PaV1) and its effect on the survival of juvenile Caribbean spiny lobster

“…For example, juvenile snow crabs Chionoecetes oplio have higher prevalences of infection by a parasitic dinoflagellate than do adults, which cease molting and are therefore no longer susceptible (Shields et al 2005. Juvenile false king crabs Paralomis granulosa are susceptible to infection by a parasitic isopod, whereas adults are not, and this may be due to host size and the efficacy of gill cleaners in larger hosts (Roccatagliata & Lovrich 1999).…”

Epidemiological determinants in outbreaks of bitter crab disease (Hematodinium sp.) in snow crabs Chionoecetes opilio from Conception Bay, Newfoundland, Canada

“…Crabs were captured with either a modified shrimp trawl or a fleet of traps with different mesh sizes (primarily 2.5, 13.3, or 14 cm). Details of the trawling and trapping are given in Pestal et al (2003) and Shields et al (2005). Note that trawls represent a more unbiased sampling method compared to traps.…”