Assessment of Potential Pathogenicity of Emergent marine bacterium, Tenacibaculum maritimum to Thin lipped grey mullet (Mugil capito) farmed in Egypt

Abstract

The pathogenicity of marine bacterium, Tenacibaculum maritimum (T. maritimum) in cultured Mugil capito (M. capito) was determined through conducting experimental infection using immersion bath for 18 hours only with different concentrations of the bacterium and observed for one week to determine the median lethal dose (LD50). Another experiment was operated to determine the clinicopathological picture of M. capito when experimentally infected with suspension containing 1/10 of the LD50 of tested bacterium and then observed for another four weeks. The clinical signs postmortem (PM) lesions and mortalities were recorded daily. Kidney, gills, liver and spleen were sampled and examined for any histopathological alterations. Results indicated that the LD50 of T. maritimum for M. capito was (1.5 × 105 CFUs mL-1). The infected fish has dark skin color, hemorrhages with different degrees at the base of all fins especially the pectoral and pelvic ones, hemorrhagic inflamed swollen vent, extensive hemorrhagic skin ulceration and severe congestion in visceral organs with copious amounts of bloody hemorrhagic ascetic fluids in the abdomen. The lesions concluded that T. maritimum is a serious pathogenic bacterium and can cause septicemic lesions in cultured fish with high economic losses.