Dynamics of shell disease in the edible crab Cancer pagurus: a comparative study between two sites on the Gower Peninsula, South Wales, UK (original) (raw)
Related papers
Diseases of Aquatic Organisms, 1999
The prevalence and severity of shell disease in the edible crab Cancer pagurus (L.) was investigated in animals collected from Langland Bay, Gower, South Wales, UK, at monthly intervals from 1997 to 1998. Shell disease is the progressive degradation of exoskeletal chitin accompanied by melanisation of the affected region. Over 50% of the crabs sampled had 1 or more black-spot lesions. The proportion of exoskeleton affected increased with the size of the crab. Male crabs showed significantly higher levels of the disease than females, a higher prevalence of black-spot lesions (63% in males, 40% in females) and a higher mean percentage of body covered by lesions (1 % in males, 0.2% in females). This difference between the sexes corresponded to an increase in ventral surface and chela infection in males. For both sexes, the dorsal carapace was the area most affected by the disease. Dorsal carapace regional breakdown revealed the areas most commonly affected were located to the posterior of the crab. Lesion location patterns suggested that sand abrasion injuries during back-burrowing behaviour of C. pagurus lead to the formation of shell disease lesions. Seasonal trends in shell disease were seen to be dependent on the onshore migration patterns of the different size classes and sexes over the sampling period.
Chitinolytic bacteria are believed to be the primary aetiological agents of shell disease syndrome in marine crustaceans. The disease principally results from the breakdown of their chitinous exoskeletons by the shell disease pathogens, but pathogenicity may also manifest internally should a breach of the carapace occur. The current study looks at the pathogenicity of a number of bacteria (predominantly from the genus Vibrio) isolated from the edible crab, Cancer pagurus. All chitinase-producing bacteria investigated were capable of growth in a minimal medium consisting of chitin powder from crab shells, but differed in their speed of growth and nature of chitinolytic activity, suggesting that they have different roles within the lesion community. Two isolates (designated I4 and I7) were chosen for studies on internal pathogenicity, which included the effect of the pathogen on crab tissues, the ability of the host to remove the bacteria from circulation and the antibacterial activity of crab blood. Initially, I4 was rapidly removed from circulation, but began to reappear in the blood after 24 h. By 100 h, 100 % of crabs were moribund. The septicaemic effects of the isolate were reflected in the low levels of its killing by blood-cell lysate and serum. By contrast, I7 was only slowly removed from circulation and caused the rapid mortality of all crabs in T 3 h. A large decline in the number of circulating blood cells following injection of I7 was mirrored by an accumulation of these cells in the gills. Initial experiments suggest that the death of the crabs following injection with I7 may be caused by toxic extracellular bacterial products that exert their effects on the blood cells and nervous system of the crabs.
A histological study of shell disease syndrome in the edible crab Cancer pagurus
Diseases of Aquatic Organisms, 2001
Shell disease syndrome is characterised by the external manifestation of black spot lesions in the exoskeletons of crustaceans. In the present study, gills, hepatopancreas and hearts from healthy (< 0.05% black spot coverage) and diseased (5 to 15% coverage) edible crabs, Cancer pagurus, were examined histologically to determine whether this disease can cause internal damage to such crabs. There was clear evidence of cuticular damage in the gills of diseased crabs leading to the formation of haemocyte plugs termed nodules. Nephrocytes found within the branchial septa of the gills showed an increase in the accumulation of dark material in their vacuoles in response to disease. In the hepatopancreas, various stages of tubular degradation were apparent that correlated with the severity of external disease. Similarly, there was a positive correlation between the number of viable bacteria in the haemolymph and the degree of shell disease severity. Approximately 21% of the haemolymph-isolated bacteria displayed chitinolytic activity. Overall, these findings suggest that shell disease syndrome should not be considered as a disease of the cuticle alone. Furthermore, it shows that in wild populations of crabs shell perforations may lead to limited septicaemia potentially resulting in damage of internal tissues. Whether such natural infections lead to significant fatalities in crabs is still uncertain.
Journal of Invertebrate Pathology, 2015
The prevalence of disease in edible crabs (Cancer pagurus) was assessed at two sites in South West Wales; one estuarine (Pembroke Ferry) and another facing open water (Freshwater East). Diseases included pink crab disease caused by Hematodinium sp., an infection of the antennal gland caused by Paramikrocytos canceri and an idiopathic inflammatory condition of the connective tissue surrounding the anterior ganglionic masses. This latter condition was only found in crabs from Pembroke Ferry. There was a significantly higher prevalence of pink crab disease at Freshwater East than Pembroke Ferry, although both sites had similar levels of infection by P. canceri.
Shell disease in the Freshwater crab, Barytelphusa cunicularis
International Journal of Fisheries and Aquatic Studies, 2014
The current study deals with the isolation and identification of bacterial and fungal pathogens, from lesioned carapace and limb of the freshwater crab Barytelphusa cunicularis, inhabiting the paddy fields of Mananthavady, Wayanad, Kerala. The bacterial flora was isolated by pour plate method and phenotypic identification was made based on morphological features and biochemical tests. The fungal pathogen was isolated from Sabouraud dextrose agar medium and morphologically identified using Lactophenol cotton blue stain. From the infested carapace, bacteria belonging to nine genera Aeromonas, Alcaligenes, Bacillus, Chromobacterium, Enterobacter, Escherichia, Klebsiella, Micrococcus and Pseudomonas and one fungal pathogen Aspergillus sp. were identified. Infested limb showed the presence of Pseudomonas and Escherichia coli. The present study on the isolation and identification of microbes from infested carapace and limb will aid in understanding the pathogen profile and its prevalence ...
Aquaculture, 2002
Crustaceans affected by shell disease syndrome display characteristic black-spot lesions in regions of exoskeletal degradation. Vogan et al. [Dis. Aquat. Org. (2001)] have shown that the severity of shell disease in the edible crab, Cancer pagurus, correlates with an increase in haemocoelic bacterial infections and may therefore serve as an external marker for the internal health of the animal. Therefore, this present study examined if the same crabs with shell disease lesions and varying degrees of bacterial septicaemia also displayed differences in the haemogramme, haemolymph phenoloxidase activity, total protein, copper and urea, as well as haemolymph-derived antibacterial activity, compared to uninfected individuals. A strong correlation was found between the severity of shell disease and a reduction in serum protein, which was further indicative of haemocoelic infection. Levels of copper, urea, phenoloxidase, and antibacterial activity in the haemolymph showed no correlations with the proportion of exoskeletal lesion cover. However, the degree of melanisation of haemolymph samples taken from shell-diseased individuals was less than that seen in disease-free crabs. Total haemocyte counts were unaffected by the disease, although some minor changes were found in the differential counts. Overall, despite having intrahaemocoelic infections, shell disease-affected individuals displayed few changes in the cellular or humoral defence parameters examined. D
Shell disease in crustaceans – just chitin recycling gone wrong?
Environmental Microbiology, 2008
The exoskeletons of aquatic crustaceans and other arthropods contain chitin, a biopolymer of b-(1,4)linked N-acetylglucosamine together with associated proteins. Despite the vast amounts of chitin within such animals little is found in sediments and open water because microorganisms rapidly degrade this following its loss after moulting or upon the animals' death. Shell disease syndrome is a worldwide disease condition that affects a wide range of crustaceans. It comes about as a result of bacterial degradation of the exoskeleton leading to unsightly lesions and even death if the underlying tissues become infected. There are at least two potential forms of the disease; one that appears to centre around chitin degradation and an additional form termed 'epizootic' shell disease, in which chitin degradation is of less significance. This account reviews our current understanding of the causative agents of this syndrome, assesses the potential economic consequences of the disease, and critically examines whether it is associated with anthropogenic disturbances including pollution. Overall, despite extensive studies during the last few decades, the potential links between faecal, heavy metal and insecticide pollution and shell disease are still unclear.
Marine Biology Research - MAR BIOL RES, 2006
Crabs infected by rhizocephalans usually do not moult. Because moulting is the ultimate defence against fouling epibionts, infected as opposed to uninfected crabs can be expected to harbour a diversity of hard-bottom organisms on their cuticula. Here we provide unequivocal evidence that this is the case in the Carcinus maenas ÁSacculina carcini association. In a Danish sample of shore crabs, 75% of sacculinized individuals harboured macroscopic epibionts, whereas only 29% of the uninfected crabs were colonized. The mean numbers of fouling barnacles and serpulid tubeworms per individual were 7.7 and 47.3 for uninfected and infected crabs, respectively, corresponding to coverage of the cuticula by 0.7 and 5.4%. Infected crabs were 12% lower in tissue dry weight than uninfected individuals, which may be a factor causing the moult of sacculinized crabs to be postponed. Finally, a laboratory experiment suggested that infected crabs are less likely to bury than uninfected specimens. Because burying is an important fouling defence, such a parasite-induced behavioural change will favour the colonization by epibionts. It is argued that rhizocephalans infecting crabs from soft-bottom communities may indirectly affect the structure of the free-living benthic community by adding hard-bottom species that otherwise would be absent.