Idiopathic muscle necrosis in the Norway lobster, Nephrops norvegicus (L.): aetiology, pathology and progression to bacteraemia

Abstract

The pathology and progression of idiopathic muscle necrosis (IMN) in Nephrops norvegicus and possible aetiologies have been investigated. Trawl capture, aerial exposure and handling initiate IMN, and the condition can be induced through periods of aerial exposure alone, in the absence of trawling. Within 24-48 h after trawl capture IMN progresses to a multi-species bacterial septicaemia, with moribund animals exhibiting clinical signs. The aetiology of this condition has been examined using molecular (16S rRNA gene sequencing) and biochemical (standard taxonomic assays, Biolog) criteria to characterize bacterial isolates from moribund and healthy animals. Histopathology of the IMN phase reveals a loss of sarcomeric structure with necrotic lesions containing pyknotic nuclei, fragments of myofibrils and connective tissue elements. In the bacterial phase there is extensive loss of abdominal muscle structure, and the presence of rod-shaped Gram-negative bacteria in the degrading tissues. The results demonstrate that the IMN condition is connected to stressful conditions imposed on N. norvegicus, but involves no pathogenic agents. This is followed by an opportunistic bacterial infection that causes further tissue spoilage. It is believed that the primary cause of both IMN and bacteraemia is imposed stress, but they are expressed in different time courses.

Extracellular proteases and possible disease related virulence mechanisms of two marine bacteria implicated in an opportunistic bacterial infection of Nephrops norvegicus

“…Post capture bacterial septicaemia of N. norvegicus has previously been described by Ridgway et al (2007) and was believed to be associated with fishery losses, especially during the summer months (Ridgway, 2007). Trawl capture, aerial exposure and handling initiate a series of events that culminates in stress induced multi-species bacterial septicaemia.…”

“…These species had been identified as potential causative agents of the pathological condition described by Ridgway et al (2007). The objectives were to identify potential disease virulence mechanisms and to further understand the role of these strains in the spoilage of host muscle tissue.…”

“…During an investigation into the opportunistic bacterial infection described by Ridgway et al (2007) several bacterial strains were isolated from the diseased lobsters. Through biochemical and molecular techniques these were characterised as Vibrio spp.…”

Disease will limit future food supply from the global crustacean fishery and aquaculture sectors

“…in Scottish N. norvegicus which has had direct negative impacts on the post-capture transportation of live animals to market, and has led to altered post-mortem degradation and earlier organoleptic rejection of product (Neil, 2012). Non-infectious conditions have also significantly affected the live trade in N. norvegicus -the cumulative effects of capture, emersion, handling and poor post-capture holding conditions causing so-called Idiopathic Muscle Necrosis (IMN) in a potentially large proportion of the catch (Stentiford and Neil, 2000;Ridgway et al, 2006Ridgway et al, , 2007. It is clear that the current practice of live post-capture storage of crustaceans is generally deemed a high-risk sector of the market and one that leads to significant mortalities and lower prices being paid for live commodity to fishers.…”

Factors affecting post-capture survivability of lobster Homarus americanus

“…Harris & Andrews (2005b) monitored the post-capture effects of trawling and emersion on the physiology and survival of 'discarded' and 'escaped' Nephrops norvegicus by placing them within cages on the seafloor, and then recovering them with divers. Ridgway et al (2007) describes idiopathic muscle necrosis in post-capture N. norvegicus, and Bernasconi & Uglow (2008) compared the effects of emersion and reimmersion on trawled and creel-caught N. norvegicus.…”