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Title: Studies on the diseases and culture of brachyuran decapods
Author: Powell, A.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2006
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Several diseases were studied in the shore crab, Carcinus maenas, and the edible crab, Cancer pagurus. The most commercially important disease included a novel, systemic disease of C. maenas, (christened “milky disease”). Infected crabs displayed white haemolymph with reduced clotting abilities, and was infected with small Gram-negative bacteria. This was accompanied by changes in serum chemistry, and cell necrosis in the gill and hepatopancreas. The present dynamics of another commercially important syndrome, shell disease, were studied after recent improvement in local sewage treatment. C. pagurus were surveyed in 2003 in Langland Bay (post-sewage treatment change) and compared to similar data collected in 1997 (pre-sewage treatment change). Significant results included a decrease in shell disease lesion severity in certain anatomical areas, and in small crab class sizes in 2003-4, compared with 1997-8. Cost effective feeds were optimised for adult C. maenas, which incorporated a range of possible immunostimulants (chitin powder, yeast extract, polychaete extract). Chitin fed crabs showed significantly reduced tissue bacterial load, possibly because of the bacterial purging effect of the chitin as it passed through the gut. This resulted in significantly less mortality in experimental animals.  Yeast fed animals experienced significantly increased haemocyte counts and haemocyte phagocytic activity. This may be due to the immunosimulating nature of the β-1, 3-glucans found in yeast extract. Crabs fed polychaete extract showed significantly increased phenoloxidase activity and granular cell counts. Observations of an enhanced feeding response suggest that polychaete extract has beneficial nutritive value, and has the possibility to enhance feed palatability and reduce feed wastage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available