This study aimed to identify the aetiological agent that leads to the newly identified phenomenon of “Chalky back” in Banana prawns (Fenneropenaeus merguiensis) farmed in far North Queensland. The phenomenon presents itself as a localised white discoloured segmentation, arising between the cephalothorax and the upper back; which after cooking causes prawns to explode making them unfit for commercial sales. Histological examination revealed physical signs of trauma with some moribund specimens showing slight atrophy (necrosis) of the gut and significant breakdown and wasting of abdominal muscle tissue. These findings suggested that pathogenic bacteria may be involved. Three healthy and six chalky back specimens were initially chosen for selective targeting of Vibrio spp. which are well documented disease causing agents in prawns. Isolated bacteria were then identified using 16S rRNA sequencing and typed biochemically. These isolates were then probed for the presence of 13 virulence genes (VGs), known for their involvement in biofilm production, adhesion and cytotoxicity. The isolates identified belonged to the Vibrio clade, including V. harveyi, V. owensii, V. sinaloensis, V. campbellii, V. shilonii, Vibrio sp. as well as Photobacterium damselae. All V. harveyi isolates identified carried VGs coding for haemolysin, toxR and flaB, and demonstrated adherence to cells in vitro. A similar set of VGs was also seen in the V. sinaloensis strains. Importantly this species is well documented as an opportunistic pathogen in prawns and was consistently isolated only in Chalky back specimens. Despite the low number of prawns tested in this study, our data suggests that V. sinaloensis may play a role in the pathogenesis of Chalky back. This study is the first report of Chalky back in farmed prawns, and given its rise in the industry, such conditions need to be closely monitored and disseminated.