• Journal of fish pathology
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• v.22 no.3
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• pp.253-262
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• 2009

We conducted bacteriological and histopathological analysis for olive flounder Paralichthys olivaceus after experimental infection with Streptococcus parauberis (FP2284) isolated from diseased olive flounder under different stress conditions. Experimental challenge was performed in healthy flounder (40.4 g in average body weight) by intraperitoneal (i.p.) injection with $2{\times}10^{8}$ CFU/fish under normal (no stress) or netting (for 2 min, twice/day) stress condition. The cumulative mortalities of no-stress and netting stress group were 70% and 95%, respectively. The most prevalent changes observed in experimentally infected flounder were darkness of skin and inflammation of the heart. Severe pericarditis, myocarditis and fibrosis were observed in the heart of the affected flounder. The results of viable counts showed the number of bacteria of the heart tissue was maintained over the $10^{4}$ CFU $g^{-1}$ heart for 3 weeks after inoculation. Histological lesions of the heart was more extensive and gradual decrease in bacterial numbers of heart tissue was delayed under stress condition.

• Journal of fish pathology
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• v.34 no.2
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• pp.185-199
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• 2021

Vibriosis is an important septicemic bacterial disease that affects a variety of commercial fish species, including cultured Dicentrarchus labrax. Nanotechnology has become an important modern tool for fish diseases prevention. Furthermore, nanomaterials have the ability to prevent and treat fish diseases. The current study was aimed to identify the causative agent of massive mortality of D. labrax commercial farm in Alexandria, Egypt. Experimental infection and the median lethal dose (LD50) of pathogenic isolate were assessed. Also, the effect of ginger nanoparticles (GNPs) and Sacchromyces cerevisiae as feed additives for prevention of vibriosis in D. labrax was carried out. Similarly, the tissue immunstimulant genes, IL-1β and TLR2 were measured in the spleen of feeding groups. The clinical signs of naturally diseased D. labrax showed corneal opacity and paleness of gills with excessive mucous secretion. The post-mortem abnormalities were severe hemorrhage and adhesion of internal organs. After bacteriological isolation and identification, the causative agent of mortality in the current study was Vibrio alginolyticus. The LD₅₀ of V. alginolyticus was 1.5×10^5.4 CFU/ml. The experimentally infected D. labrax showed ulceration, exophthalmia and skin hemorrhages. The post-mortem findings of the experimentally infected D. labrax revealed internal hemorrhage, spleen darkness and paleness of liver. There is no mortality and 100% RPS in groups fed GNPs then injected with V. alginolyticus, in those fed a combination of GNPs and S. cerevisiae and a group fed normal diet then injected with physiological saline (control negative), respectively. Contrarily, there was 10% mortality and 87.5 RPS in the group fed S. cerevisae then injected with V. alginolyticus. On the other hand, the control positive group showed 79% mortality. The spleen IL-1β and TLR2 immunostimulant genes were significantly increased in groups of fish fed GNNP, S. cerevisiae and a combination of GNPs and S. cerevisiae, respectively compared to control group. The highest stimulation of those immunostimulant genes was found in the group fed a combination of GNPs and S. cerevisiae, while fish fed S. cerevisiae had the lowest level. Dietary combination of GNPs and S. cerevisiae was shown to be efficient in preventing of vibriosis, with greatest stimulation of spleen IL-1β and TLR2 immunostimulant genes.

• Journal of fish pathology
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• v.22 no.3
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• pp.263-273
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• 2009

There is an increasing number of reports describing Streptococcus parauberis as an important pathogen of cultured olive flounder Paralichthys olivaceus and starry flounder Platichthys stellatus in Korea. We tried to determine the effects of water temperature (14${^{\circ}C}$ and 21${^{\circ}C}$) on the pathogenicity in Streptococcal disease caused by S. parauberis. We have challenged 180 olive flounder by i.p injection to $2.0{\times}10^{7}$ live cells/fish. Mortality was monitored for 21 days post challenge. And histopathological characterizations as infection degree, tissue degeneration and/or bacterial distribution were investigated with H&E stain and in situ hybridization technique. Fifty percent and 16.7% of mortality occurred within 21 days at 21${^{\circ}C}$ and 14${^{\circ}C}$ water temperature, respectively. In most cases, the typical symptoms of olive flounder infected with S. parauberis were darkness of the skin, lethargy, mild abdominal distension cause by ascites, splenomegaly, congested liver and internal organs paleness. The pericardial sac contained large amounts of cloudy fluid. Numerous whitish nodules, which were variable in size and often confluent, were randomly scattered throughout the myocardium. Especially, pericarditis and/or myocarditis was observed in all tested fishes after death. Positive in reaction with S. parauberis were found in all tissues in situ hybridization analysis. The relative numbers of S. parauberis in heart were much more than in liver, spleen, kidney and stomach. We evaluated that S. parauberis strain causes serious damage in the pericardium, shortness of breath and the blood disorder. Therefore, pericarditis and myocarditis caused by S. parauberis were closely related to mortality of olive flounder.