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Title: Studies on shell disease in the edible crab, Cancer pagurus
Author: Vogan, C. L.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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The current study investigates the levels of shell disease in Cancer pagurus from various sites on the Gower Peninsula. Generally, it was found that (i) male crabs displayed higher levels of the disease then females, (ii) the proportion of lesioned carapace increased with crab size, (iii) exoskeletal areas subjected to abrasion were most commonly infected and (iv) male crabs from Rhossili were less severely affected than their Langland counterparts. The observed sexual differences in shell disease were attributed largely to behavioural difference whereas, regional (site) differences were explained by variations in substratum type and chitinolytic bacterial populations. Histologically, diseased crabs showed indications of systemic bacterial infections. The thin cuticular lining over the gills appeared to be particularly vulnerable to microbial degradation and penetration. Extensive hepatopancreatic atrophy in severely diseased crabs suggested shell disease is a significant source of crab mortality. Chitinolytic bacteria were isolated from both lesioned and non-lesioned areas of crab exoskeleton. Nine isolates (I1-I9) were partially identified and used for future investigations into the causative agents of the disease. In liquid culture, their extracellular chitinase production/activity was found to vary with chitinous substrate, with C. pagurus shell pieces found to be the strongest inducers of chitinase activity. Zinc and mercury were found to inhibit chitinase activity, whilst iron and copper had the potential to enhance activity. Injections of the bacterial isolates (I4 and I7) into healthy crabs, revealed differential pathogenicities suggesting that shell disease mortalities are highly dependent on the virulence of the exoskeletal penetrator.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available