• Journal of Microbiology and Biotechnology
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• v.33 no.5
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• pp.668-679
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• 2023

Edwardsiella tarda is one of the most significant fish pathogens, causes edwardsiellosis in a variety of freshwater fish species, and its antibiotic resistance against multiple drugs has made it a health risk worldwide. In this study, we aimed to investigate the antibiotic resistance (ABR) genes of E. tarda and establish its antibiotic susceptibility. Thus, 540 fish (299 Oreochromis niloticus, 138 O. mossambicus, and 103 O. aureus) were collected randomly from twelve fish farms in three districts of Punjab in Pakistan. E. tarda was recovered from 147 fish showing symptoms of exophthalmia, hemorrhages, skin depigmentation, ascites, and bacteria-filled nodules in enlarged liver and kidney. Antimicrobial susceptibility testing proved chloramphenicol, ciprofloxacin, and streptomycin effective, but amoxicillin, erythromycin, and flumequine ineffective in controlling edwardsiellosis. Maximum occurrence of qnrA, blaTEM, and sul3 genes of E. tarda was detected in 45% in the liver, 58%, and 42% respectively in the intestine; 46.5%, 67.2%, and 55.9% respectively in O. niloticus; 24%, 36%, and 23% respectively in summer with respect to fish organs, species, and season, respectively. Motility, H₂S, indole, methyl red, and glucose tests gave positive results. Overall, E. tarda infected 27.2% of fish, which ultimately caused 7.69% mortality. The Chi-squared test of independence showed a significant difference in the occurrence of ABR genes of E. tarda with respect to sampling sites. In conclusion, the misuse of antibacterial agents has led to the emergence of ABR genes in E. tarda, which in association with high temperatures cause multiple abnormalities in infected fish and ultimately resulting in massive mortality.

• Journal of fish pathology
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• v.28 no.3
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• pp.145-155
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• 2015

The pathogenecity of atypical Aeromonas salmonicida was studied in healthy Oreochromis niloticus. Inoculum at concentration of $1.5{\times}10^8CFU/ml$ and $3{\times}10^8CFU/ml$ was injected into healthy fish through intramuscular and intraperitoneal injections. Experimentally infected Oreochromis niloticus showed ulceration at the dorsal musculature and trunk region in addition to black coloration, congested gills, exophthalmia, and ocular hemorrhage. Congested liver and kidney were recorded in post-mortem examination. Mortality of the experimentally infected Oreochromis niloticus reached 100% after intramuscular injection at concentration of $3{\times}10^8CFU/ml$. Histopathological investigation of infected organs was also performed. There was a focal area of bundles of skeletal musculature showing hyalinization. In addition, hyperplasia, congestion, and fusion were noticed in the gill lamellae. There was also congestion in the blood vessels in the ocular chamber. Severe congestion was also noticed in the central vein of liver associated with focal aggregation of the melanin pigmented cells in the parenchyma. Degenerative changes were noticed in the epithelial cells lining of kidney tubules. Plant extracts carvacrol and its biological precursor cymene were found to be effective in treating experimentally infected Oreochromis niloticus at concentration of 100 or 200 ppm.

• Journal of fish pathology
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• v.21 no.3
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• pp.209-217
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• 2008

A disease with mass mortality characterized exophthalmia and abdominal distension by ascites occurred in farmed starry flounder, Platichthys stellatus in Pohang since October of 2007. Severe necrosis and infiltration of inflammatory cells were observed in tissue histopathological sections from liver, kidney, spleen and heart of the diseased fish. The catalase-negative and gram positive cocci with -hemolysis were isolated from moribund fish. Analysis of the API profiles and the multiplex PCR of the isolates showed that strains were identified as Streptococcus parauberis. In API profiles, S. parauberis isolated from starry flounder differed from those of olive flounder, Paralichthys olivaceus to the test of arginine dihydrolase, D-mannitol, D-sorbitol and α-lactose. And the strains, PH0710 and PH0711, were strongly lethal for starry flounder (LD50 ranging from 4.2×103~4.2×102 cfu/fish at 7 days after intraperitoneally inoculation). This is the first report on a S. parauberis infection in starry flounder.

• Journal of fish pathology
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• v.16 no.3
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• pp.153-159
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• 2003

The high mortality of cultured juvenile turbot, Scophthalmus maximus occurred in Gochang on June, 2003. The diseased fish was lethargic with reduced feed intake. Grossly, these fish showed pale body, abdominal extension and exophthalmia. The dominant internal gross features of diseased fish were severely enlarged spleen, pale gills and/ or liver. Diseased fish histologically showed basophilic enlarged cells in the kidney, spleen, gill, heart, stomach, intestine, liver, pancreas and adipose tissue. Transmission electron microscopy (TEM) reveled hexagonal virions in the cytoplasm of necrotic cells. The viral particles lead a central electron-dense core and an electron translucent zone, and were 136-159 nm in diameter. These results suggest that the virus belonging to the iridoviridae was responsible for the mortality of cultured juvenile turbot.

• Journal of fish pathology
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• v.34 no.2
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• pp.255-259
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• 2021

This is the first report describing acute mass mortality occurred in juvenile olive flounder (Paralichthys olivaceus) caused by gas bubble disease (GBD). A total of 610 fish (average weight = 35 g), which were more than half of the fish acclimated at 17℃ in an aquarium, were killed within two days of acclimation. The dead and moribund fish showed excessively opened opercula and mouths, and occasionally, severe exophthalmia. Through microscopic observation, numerous gas emboli were found in the gills of the dead and live fish, while the fish were not infected with any microbial pathogens. The dissolved oxygen (DO) saturation level of the rearing water and seawater nearby the facility reached 145% and 286%, respectively, whereas other water quality parameters (such as salinity, pH, and chemical oxygen demand) were normal. The extreme saturation rate of seawater in the shore nearby seemed to be due to an enormous algal bloom that occurred there. Through molecular identification based on 18S rDNA sequences, the most dominant algal species was most closely related to Ulva californica (99.87% sequence identity) followed by U. prolifera, U. linza, and U. curvata (99.81%). Therefore, it can be concluded that supersaturated seawater due to mass algal bloom caused gas bubble disease in the olive flounder, leading to mass mortality. After technical adjustment, such as increased aeration, lowered water circulation rate, and inlet water filtration using micro-pore carbon filters, the DO level became normal, no further mortality occurred and the status of the fish was stabilized.

• Journal of fish pathology
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• v.34 no.1
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• pp.105-110
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• 2021

We experienced mortality of dark-banded rockfish (Sebastes inermis) maintained in the rearing facility located in Gangneung, after transportation. Moribund fish showed various symptoms such as exophthalmia, skin ulcers, tail rots, gill rots, discoloration of liver with petechiae, yellowish fluid in intestines and ascites. Two different colonies were dominantly appeared after spreading the lesions on the agar plates and incubation. One isolate (SI_1) showed swarming movement on TSA, and formed yellow colonies on TCBS agar. The other (SI_2) showed no swarming motility and green colonies on TCBS agar. Both of them were Gram-negative. All of these results are similar with those of Genus Vibrio. They were identified as V. harveyi and V. gigantis by PCR with subsequent sequencing of 3 different genes (16 rDNA, recA, rpoA). V. harveyi is well-known as a serious pathogen of marine fish and invertebrates, while V. gigantis is known to be often isolated from marine invertebrates, but the pathogenicity is still unknown. We suspect V. harveyi as the cause of the mortality of dark-banded rockfish, but challenge experiments with these 2 Vibrio species are thought to be necessary to make a clear conclusion.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.4
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• pp.365-369
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• 2001

Streptococcus spp. of bacterial pathogen of fish were isolated from the cultured flounder (Paralichthys olivaceus) in fish farm of Jeju Island. Clinical signs of the infected flounder which are the most commons symptoms are as follows: erratic swimming, darkening of the body colour, unilateral or bilateral exophthalmia, corneal opacity, hemorrhages in the opercular and the bases of the fins, and the ulceration of the body surface. Biochemical characteristics of pathogenic fish Streptococcus spp, were gram positive, spherical form, catalase negative, oxidase negative and $\beta$-haemolytic, respectively, The viable cells counted from the tissue of the diseased flounder were the largest in the order of the ulcer, the kidney, the blood and the brain, The drugs used were ampicillin, ciprofloxacin, doxycycline, gentamycin, tetracycline, erythromycin, streptomycin and oxytetracycline, Streptococcus spp. were found to be sensitive to ampicillin, ciprofloxacin, doxycycline and gentamycin, but were resistant to tetracycline, erythromycin, streptomycin and oxytetracycline. The pathogenicity of Streptococcus spp. on the cultured flounder with an abdominal cavity injection was high. The haemolytic activity of the toxin against the sheep red blood cells reached the maximum after 30 min incubation at $37^{\circ}C$ or $50^{\circ}C$. The toxin showed highest activity at pH $5.5\sim6.5$.

• Journal of fish pathology
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• v.14 no.2
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• pp.71-80
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• 2001

The purpose of this study was to investigate the microbiological characteristics and the distributions of the bacteria causing streptococcicosis occurred in marine fish farm, Korea. Many kinds of cultures fishes suffered from the disease accompanied with typical symptoms, including darkening of the skin, exophthalmia, petechiae inside of the opercula and distended abdomen. The isolates from the diseased fishes were compared with Lactococcus garvieae by biochmical, biophysical and serological methods and polymerase chain reaction(PCR) assay. We isolated 35 strains of the geuns Streptococcus from the diseased olive flounder, Paralichthys olivaceus, yellow tail, Seriola quinqueradiata and Korean rockfish, Sebastes schlegeli. 15 strains out of the isolates were identified to L. garvieae and the others were not because of their different biochemical and biophysical charateristics. Seven strains of the isolates were agglutinated by rabbit serum raised against L. garvieae $KG^+$ phenotypic cells(ATCC49156)as a reference strain. Twenty-one strains of the isolates identified to L. garvieae since they were formed the expected band through performing PCR assay using specific primers, pLG-1(5'-CATAACAATGAGATCGC-3') and pLG-2(5'-GCACCCCGCGGTTG-3'). In the present study, it showed that L. garvieae was a dominant strain causing streptococcicosis in the tested area due to occurrence of 21 strains as L. garvieae out of all the isolates, 9 atrains as Streptococcus sp. and 5 strains as Enterococcus sp.

• 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.