Pathology of tail fan necrosis in the spiny lobster, Jasus edwardsii.

Tail fan necrosis (TFN) is the bacterial infection of the tail fan of spiny lobsters which leads to melanosis and erosion of the tail fan tissues. The condition is commonly found among spiny lobsters in aquaculture and commercial fisheries, and greatly reduces their commercial value. This study describes the pathology of TFN by examining the tail fans (telson, uropods) and internal organs (mid-gut, hepatopancreas, heart and gill) of 29 affected wild spiny lobsters (Jasus edwardsii) and 14 unaffected in New Zealand. Initial signs of TFN were observed around the margins of lacerations to the tail fan, with more extensive signs extending from these presumptive sites of initiation. The establishment of the condition at points of injury is consistent with the penetration of TFN through the cuticle and tissue layers of the affected tail fans, which is rarely seen in other forms of shell disease. Entry into these tissues was characterised initially by caseous necrosis and haemocyte accumulation, followed by the spread of these responses together with melanisation. Additional pathological changes to the tail fans included pseudomembrane formation, detachment of epidermis or cuticle, clotted haemolymph and fibrosis. Among internal organs, pathological changes were found in a total of two mid-gut, four heart and two gill samples from eight lobsters with TFN, while no suspected changes were found in the organs of lobsters without TFN. The causes of internal organ pathology associated with TFN in spiny lobsters warrants more detailed research.