Chytrid Batrachochytrium dendrobatidis fungal infection in freshwater prawn, Macrobrachium rosenbergii (de Man) - A new report

For the first time the occurrence of a chytrid, Batrachochytrium dendrobatidis (Bd) fungus infection in the fresh water prawn, Macrobrachium rosenbergii in grow out farms is reported. An extensive survey carried out between 2007 and 2011 in 15 farms (F) indicates that B. dendrobatidis is responsible for major pandemics in M. rosenbergii culture ponds as evidenced by the unique characteristics of the presence of fungal hyphae in claws and other features in the infected prawn. The pathogenicity of the fungus, LD50, histopathology, hematology and immunological response of the infected prawn is reported; the clinical symptoms include dull body color, abnormal protrusion associated with a grayish white color, wooly appearance with radiating grayish white fungal filaments on claw. Histopathology studies revealed that the infection resulted in faded eye color, occurrence of dark spots and melanization on the cephalothorax and muscles, translucent musculature, cuticular erosion, tissue atrophy with proliferated and infiltrated cells causing distension and gross enlargement of gill lamellae. An optimum dose of 105 zoospores/prawn (LD50) resulted in 50% mortality from 4 to 6days. At high dose of 108 zoospores/prawn, the infection caused total mortality from 2 to 4days. After 2nd week the total hemocyte counts (THCs) significantly decreased while the phenoloxidase (PO) level, relative superoxide anion production level, and superoxide dismutase (SOD) activity registered a significant increase (p