Histopathological analysis of golden pompano Trachinotus ovatus infected with Photobacterium damselae subsp. piscicida

The pathogen Photobacterium damselae subsp.piscicida was isolated from the diseased Trachinotus ovatus.The aim of the study is to observe the pathological changes in T.ovatus after intraperitoneal injection or immersion routes of infection with Photobacterium damselae subsp.piscicida.The infected fishes exhibited acute and/or chronic symptoms,according to the lesional degree.The acute lesions includes slight hemorrhage around the gill covers,abdominal dropsy and multifocal necrosis in the internal organs.The chronic lesions are mainly small white miliary lesions with 0.5~1 mm in diameter observed in spleen,kidney and heart.The histopathological changes were observed under optical microscope and transmission electron microscope.In fishes with acute lesions,degeneration and coagulation necrosis in the gill,liver and kidney,microvillus disorder and mitochondrial cristae destruction in renal tubule,hyperplasia of macrophages and chromatin clumping of lymphocytes in the spleen,and hyperplasia of mitochondrion or multifocal necrosis in the heart were most pronounced in infected fish.Few or no lesions were observed in intestine.Fishes with chronic lesions suffered necrosis of the gill epithelium,disaggregation of mitochondria,Golgi body and endoplasmic reticulum in the spleen.The renal tubule epithelium microvillus underwent desquamation,meanwhile,the Z bands in myofibrils became disorder and mitochondria underwent denaturation in the heart.Typical chronic granulomatous lesions were also observed mainly in spleen,kidney,heart,liver and intestine.Generally,the most significant histopathological changes were detected in spleen,kidney and heart.