Pathology of shell disease in the blue crab, Callinectes sapidus Rathbun, (Decapoda : Portunidae)

Blue crabs affected with shell disease displayed a wide array of pathologie s in response to this very common affliction. Grossly, shell disease lesion s most commonly presented as variably sized brown to black foci. Such lesio ns ranged from very small (1 mm(2)) to locally extensive (up to 200 mm(2) i n area). The larger of the melanized lesions sometimes appeared ulcerated. The most severe lesions observed (Pamlico River shell disease-PRSD) resulte d in loss of up to 25% of the entire carapace. A diverse bacterial flora co nsisting of aeromonads, vibrios and five other genera were isolated as the predominant organisms from shell disease lesions. Fungi were rarely observe d in larger lesions. Protozoa and algae were also rarely observed on the su rface of some lesions. Histologically, lesions ranged from mild erosion of the epicuticle and outermost: layers of the calcified endocuticle to more e xtensive endocuticle erosion with accompanying inflammation. In the most, s evere cases, there was total loss of the endocuticle and epidermis, with ps eudomembrane formation, intense haemocyte infiltration, and involvement of adjacent viscera. There was no apparent relationship between the size of gr oss lesions and their histological severity (as defined by the extent of ti ssue damage), suggesting that gross examination pf shell disease lesions is not a reliable method for assessing the damage to affected blue crabs.