Characterization of a highly lethal barramundi (Lates calcarifer) model of Pseudomonas plecoglossicida infection.

Pseudomonas plecoglossicida is a highly lethal causative agent associated with severe economic losses in aquaculture industry. P. plecoglossicida has been documented as a highly alarming pathogen in a wide variety of freshwater cultured fish including ayu (Plecoglossus altivelis), rainbow trout (Oncorhynchus mykiss) and pejerrey (Odontesthes bonariensis), and marine cultured fish such as large yellow croaker (Larimichthys crocea) and orange-spotted grouper (Epinephelus coioides) etc. Fish infected with P. plecoglossicida usually exhibited various symptoms, including lethargy, inappetence, disorientation, abdominal swelling with severe ascites and numerous white spots covered on the surface of spleen tissue. In present study, barramundi, zebrafish, spotted seabass and mandarinfish were investigated as potential hosts of P. plecoglossicida. Among them, barramundi was confirmed the most sensitive host fish species for P. plecoglossicida infection. Dynamic histopathology revealed that P. plecoglossicida caused various histopathological effects to barramundi: a) spleen: granulomas appeared at 2 days post infection (dpi) and matured at 4 dpi; b) liver: steatosis at 1 dpi and fat necrosis over time, and damaged the most compared to spleens and metanephros; c) metanephros: Bowman capsule space became larger and glomerulus shrank were even collapsed at 1 dpi; d) ascites: either bacterium or melanin were wrapped in cells from ascites. All these results indicated that P. plecoglossicida could cause systemic diseases with typical clinical sighs to barramundi and would be an alarming pathogen to barramundi industry.