Bacterial Fish Diseases Research Articles

ИЗУЧЕНИЕ ЭФФЕКТИВНОСТИ ПРОБИОТИКА НА МОДЕЛИ БАКТЕРИАЛЬНОЙ БОЛЕЗНИ МАЛЬКОВ В ЛАБОРАТОРНЫХ УСЛОВИЯХ

The article focuses on a simulation of a bacterial infection of fingerlings carried out in laboratory conditions in order to determine the effectiveness of the developed probiotic. The conditionally pathogenic strains of the genera Pseudomonas and Aeromonas have acted as an infectious agent. Carp fry were used as the test material for disease modeling and studying the effectiveness of a biological product developed for the prevention and treatment of bacterial diseases of fish. The experiment involved two experimental groups and the control one. The probiotic was given to the first experimental group as a feed additive before and after infection; the probiotic was not given to the second experimental group. Species in the control group were not infected and a biological product was not given. Attempts to infect carp fry with an association of strains Pseudomonas taiwanensis , Pseudomonas aeruginosa did not produce any results: after a 2-week period no deviations in the behavior of the fish were recorded, and no fish were killed. Such a situation could be caused by low pathogenicity or by the absence of pathogenicity in museum conditionally pathogenic strains. In the next experiment there was used a more aggressive strain Aeromonas punctata known as the causative agent of fish aeromonosis. Already on the third day after infecting with the pathogen Aeromonas punctata , fish in the second experimental group were killed, and deviations were observed in the form of low mobility of fish and spinal disorders of the type of twisting, which is a consequence of developing bacteriosis - aeromonosis. In fish of the first experimental group that received the previous dose of probiotic no violations were noted, all the fry remained alive. Thus, the therapeutic effect of the developed probiotic was proved on the aeromonosis model, which was expressed in a decrease in the total fish mortality by 27%.

Berberine Influences Blood Glucose via Modulating the Gut Microbiome in Grass Carp.

Berberine (BBR), an isoquinoline alkaloid, is a major pharmacological component of the Chinese herb Coptis chinensis, which has been listed in the Chinese Fisheries Pharmacopeia as a common drug for the control of bacterial fish diseases. However, BBR is poorly absorbed into the systemic circulation but is significantly accumulated in the intestine. It is difficult to explain the mechanism of clinical effects of BBR based on systemic genes and pathways; it has been proved that the function of BBR in mammals is associated with the host metabolic phenotypes mediated by the structural modulation of gut microbiota. The mechanism of pharmacological effects of BBR in fish remains unclear. Here, we fed grass carp (Ctenopharyngodon idellus) a diet supplemented with BBR at a dose of 30 mg/Kg body weight daily and compared them with grass carp fed a regular fish feed diet. Biochemical analysis revealed that fish fed BBR had significantly reduced serum glucose, total cholesterol (TC), and triglyceride (TG) levels, and increased TC (p < 0.05) and TG (p < 0.01) levels in the liver. Deep amplicon sequencing of the V4 region of 16S rRNA genes of the gut microbiota revealed: (i) the composition of gut microbiota after BBR feeding was more diverse than that in the control group; (ii)before fish were fed BBR, the enriched operational taxonomic units (OTUs) mainly belonged to Firmicutes while most enriched OTUs came from Proteobacteria, Planctomycetes, Bacteroidetes, and Firmicutes during BBR feeding and after BBR feeding stopped; (iii) the ratio of Firmicutes to Bacteroidetes was significantly decreased in fish fed BBR. Spearman’s rank correlation showed that 32 berberine-OTUs were significantly negative correlated with glucose (p < 0.05). It indicates that BBR may affect the levels of serum glucose by the structural modulation of gut microbiota. Our results provide insight into the effect of BBR on fish metabolism and gut microbiomes, which would be beneficial for the fish welfare.

Attenuated Listeria monocytogenes protecting zebrafish (Danio rerio) against Vibrio species challenge

Live attenuated bacteria is a promising candidate vector for the delivery of vaccines in clinic trials. In the field of aquaculture industry, live vector vaccine also could provide long-term and effective protection against fish bacterial diseases. In our previous work, we demonstrated attenuated Listeria monocytogenes (Lm) had the potential to be an aquaculture vaccine vector in cellular level and zebrafish model. To further investigate the potential application of attenuated Lm in aquaculture vaccines, the outer membrane protein K (OmpK) from Vibrio parahaemolyticus (V. parahaemolyticus), as a conservative protective antigen, was fused to a new antigen-delivery system, and introduced into double-gene attenuated Lm strain (EGDe-ΔactA/inlB, Lmdd) to get live-vector vaccine strain Lmdd-OmpK. The strain Lmdd-OmpK showed the stable secrete efficacy of OmpK and was tested the cross-protective immunity against Vibrio species. After intraperitoneal administration in zebrafish, Lmdd and Lmdd-OmpK strain both improved the survival rates of zebrafish infected by V. parahaemolyticus, Vibrio alginolyticus (V. alginolyticus) and Vibrio anguillarum (V. anguillarum), respectively. In summary, attenuated Lm is able to protect zebrafish against Vibrio species challenge, illustrating its potential value for further aquaculture vaccines development.

Antibacterial substances produced by pathogen inhibitory gut bacteria in Labeo rohita: Physico-chemical characterization, purification and identification through MALDI-TOF mass spectrometry

Application of antibiotics to combat bacterial diseases in fish has been criticized due to likely emergence of drug resistance. Therefore, investigation of new bioactive compounds from natural sources has been taken into account. This study was designed to purify and characterize the bioactive compound in the cell free supernatant (CFSs) of autochthonous gut bacteria (Bacillus methylotrophicus KU556164, B. amyloliquefaciens KU556165, Pseudomonas fluorescens KU556166 and B. licheniformis KU556167) isolated from rohu, Labeo rohita. CFSs were antagonistic to fish pathogenic Aeromonas spp., moderately thermo-tolerant and active in wide range of pH (5–11). Antibacterial activity of the CFSs was reduced by the action of proteases (e.g., Proteinase K and Trypsin), indicating proteinaceous nature of the bioactive compound like the bacteriocins. Three-step purification procedure resulted in recovery of 16.97%, 18.04%, 33.33% and 6.38% activity of the antimicrobial protein produced by B. methylotrophicus, B. amyloliquefaciens, P. fluorescens and B. licheniformis, respectively. Purification at each step revealed decrease in protein content with gradual increase in the specific activity of the antimicrobial protein. The purified antibacterial compound ranged between 18.2 and 25.6 kDa. Identification through MALDI-TOF MS/MS and database search through Mascot search engine predicted that the bactericidal compound belonged to either alkaline proteases, or, transcriptional regulator and some hypothetical proteins. Apart from potential technological application of the antibacterial compound, the present study might show promise for application of gut-associated bacteriocinogenic bacteria to control diseases in fish caused by pathogenic bacteria.

Screening of antimicrobial activity of citrus essential oils against pathogenic bacteria and Candida strains

AbstractSeveral studies have indicated that plants are good sources of antimicrobial agents and pharmaceuticals. The present study is focused to evaluate the antimicrobial potential of 11 citrus essential oils (EOs) and terpenes (T), against 18 bacterial pathogenic strains and 4 Candida sp. strains. Volatile compounds present in the citrus EOs were determined by a gas chromatography analysis, allowing the identification of 79 components. Results highlights that lemon, bergamot oil and terpene were effective against more than 54.5% of tested bacteria. Candida spp. strains resulted very sensitive to all terpenes and EOs. Gram negative bacteria showed lower sensitivity than Gram positive ones. Among Gram negative, fish pathogens were sensitive to oils, so we suggested their use as possible alternatives in aquaculture farms to prevent bacterial fish diseases. Moreover, results suggested that citrus oils could be a useful tool in the food industry to prolong the shelf‐life.

Isolation, characterization, and detection of antibacterial activity of a bioactive compound produced by marine Bacillus sp. MH20 from Suez Bay, Egypt

This study focused on isolating and identifying a new bacterial strain from marine water and sediments of Suez bay, Timsah Lake, Egypt; capable of producing a bioactive secondary metabolite. Of the 552 bacterial isolates recovered, only 40 of these isolates exhibited antagonistic activities against different bacterial pathogens. A promising bacterium isolated from Suez bay marine water was identified as Bacillus sp. MH20 using 16S rRNA sequencing, and deposited in GenBank with accession number KM374670. This isolate showed sequence similarity of 88% to B. sonorensis strain NBRC 101234. Well-cut diffusion assay was adopted to determine the in vitro antibacterial activity of the active compound produced by this bacterium; whereas, GC-MS analysis was used to identify the components of this bioactive substance. GC-MS analysis showed that the active principle might be Phthalic acid, octyl 2-pentyl ester with retention time of 23.13 min. Crude extract of Bacillus sp. MK20 at a concentration of 200 mg/l exhibited LC50 of 2.5 ppm against Artemia salina. The aims of the current work were; to isolate and identify one of the promising bacterial strain from marine water, capable of producing bioactive antibacterial compound and evaluating its bio-toxicity, for its potential use in the control of bacterial human, animal and fish diseases.

Characteristics of bacterial isolates in Swiss farmed and ornamental fish from a retrospective study from 2000 to 2017.

Aquaculture is a rapidly growing field of food production of high economic importance. Bacterial infections are an important threat to aquaculture growth and also a common problem in ornamental fish. Some pathogenic agents and aquaculture production types are reported to be associated with increased disease. However, a detailed description of bacterial pathogens causing disease in Swiss aquaculture and ornamental pet fish is still missing. In this study we describe 1448 bacterial isolations originating from 1134 diagnostic laboratory submissions from farmed and ornamental fish in Switzerland for the period from 2000 to 2017. A strong seasonality was observed with submissions peaking in spring and summer. Bacterial isolations in fish submitted from organic farms were approximately six times more frequent than in conventional fish farms. Flavobacteriaceae, aeromonads and Yersinia ruckeri were the most common isolates from aquaculture, and motile aeromonads and Vibrio spp. were most often isolated from ornamental fish. The results of this study provide some interesting hypotheses, but further research is needed to better characterize risk factors for bacterial diseases in both aquaculture and aquarium fish in Switzerland.

Expression Differences of Stress and Immunity Genes in Rainbow Trout (Oncorhynchus mykiss, Walbaum 1792) with Different Bacterial Fish Diseases

The aim of this study was to determine the changes in the mRNA transcription levels of HSP70 and IGF genes related to stress and immunity in Oncorhynchus mykiss obtained from fish farms, to determine the phenotypic and antimicrobial properties of the bacteria isolated in the study and to compare the results according to different diseases. Accordingly, six fish from each fish farm, a total of 30 fish were sampled. Bacterial identification, inoculations were carried out from the tissue samples taken from the kidney and symptomatic surfaces of fish samples in TSA. Primary cultures were obtained after incubation periods at 21 and 37oC. Gram staining, catalase, and oxidase tests were performed. Forty-six biochemical and 26 antimicrobial tests were performed using BD Phoenix ID Panels. Muscle tissue was used to determine mRNA gene expression differences and the tissues were preserved at -80°C in RNAlater storage solution. Following the RNA isolation and cDNA synthesis, a real-time PCR procedure was performed with b-Actin (ACTB), Insuline-like growth factor (IGF) and HSP70 Gene Primer Array system. Enterococcus faecium (E. faecium), Lactococcus garvieae (L. garvieae) and Staphylococcus aureus (S. aureus) agents were isolated in the study. These bacteria were identified with 91-99% similarity ratios. No disease agents in the gene expressions of the fish samples in were isolated and they were therefore used as controls. Compared to the control group, heat shock protein (HSP) mRNA expression was upregulated in fish tissues infected with E. faecium, S. aureus, and L. garvieae whereas no significant increase was determined in fish tissues infected with S. aureus. IGF mRNA gene expression was upregulated in all infected tissues. IGF expression was upregulated at the highest level in fish tissues infected with L. garvieae.

Recent biocontrol measures for fish bacterial diseases, in particular to probiotics, bio-encapsulated vaccines, and phage therapy.

The objective of this review is to control fish bacterial diseases or infections through application of some promising novel biocontrol methods, such as probiotics, bio-encapsulated vaccines, and phage therapy, to avoid the disadvantages of traditional one that potentially affects fish and human health. Bacterial infection in intensive fish farming causes mass mortalities and the treatment of that requires the intensive use of chemicals and antibiotics. Several methods have been tried to control fish diseases including the use of antibiotics, but their haphazard use is associated with potentially negative effects as drug resistance and drug residues. The use of probiotics as biocontrol agents for aquaculture is increasing with the demand for environmental beneficial, eco-friendly alternatives for sustainable aquaculture production. The benefits of such supplements include improved food value, inhibition of pathogenic microorganisms, and increased immune response. The bio-encapsulated vaccine appears to be the most attractive method for releasing of vaccines. Several bioactive molecules which are specific for some diseases have been successfully encapsulated with nanoparticles in order to enhance their availability, bioactivity, and controlled delivery. Recently, “reverse vaccine” by using bio-informatics that aids in designing vaccines against infectious pathogens that are difficult to design, especially the intracellular bacteria. Additionally, the use of bacteriophages for biological control of pathogens in cultured fish has gained much interest. Several bacteriophages have been isolated specific to various pathogenic bacteria. Oral administration of phage cocktail is the most suitable way of application in fish, especially when large number of infected fish should be manipulated. Hence, in the following paragraphs, we will discuss some promising novel biocontrol methods that target the fish pathogens like probiotics, bio-encapsulated vaccines, and phage therapy.

Behavior and Stereotypies of Nile Tilapia (Oreochromis niloticus) in Response to Experimental Infection with Aeromonas hydrophila

DOI: 10.26650/ASE2018407191 Motile Aeromonas septicemia (MAS) is a common bacterial fish disease that may cause severe economic losses. This novel study was conducted to investigate behavioral changes of Nile tilapia (Oreochromis niloticus) in response to experimental induction of MAS. Aeromonas hydrophila, which is the causative agent of MAS, was isolated from diseased O. niloticus and used for the experimental infection of O. niloticus by intraperitoneal and intramuscular injections for inducing MAS. Each injection route had its control group. Fish behavior was recorded daily using a digital video camera for 7 consecutive days post injection in intraperitoneally and intramuscularly injected fish. On day 14 post injection, the behavior of intramuscularly injected fish was recorded again. Experimentally infected O. niloticus showed various clinical signs such as exophthalmia, ocular hemorrhage, congested gills, and skin and fin hemorrhages. The behavior of apparently healthy and experimentally infected O. niloticus was recorded and analyzed by scan observation. The experimentally infected fish exhibited cessation of normal behavior. Buccal-opercular movement and signs of aggression increased, whereas foraging, schooling, and shoaling frequencies decreased. Two abnormal behavioral patterns (stereotypies) of apparently healthy O. niloticus following injections were recorded. Post injection, intraperitoneally injected fish performed circular swimming on day 3 and 7, whereas intramuscularly injected fish exhibited vertical movement on the days 4, 5, 7, and 14. The frequency of circular swimming increased over time; however, vertical swimming frequency decreased by day 14. These results revealed that MAS had a severe effect on the behaviors of apparently healthy fish. Therefore, monitoring the behavior of O. niloticus may provide a useful and noninvasive tool for assessing fish health and diagnosing MAS early.

Probiotics as Means of Diseases Control in Aquaculture, a Review of Current Knowledge and Future Perspectives.

Along with the intensification of culture systems to meet the increasing global demands, there was an elevated risk for diseases outbreak and substantial loss for farmers. In view of several drawbacks caused by prophylactic administration of antibiotics, strict regulations have been established to ban or minimize their application in aquaculture. As an alternative to antibiotics, dietary administration of feed additives has received increasing attention during the past three decades. Probiotics, prebiotics, synbiotics and medicinal plants were among the most promising feed supplements for control or treatments of bacterial, viral and parasitic diseases of fish and shellfish. The present review summarizes and discusses the topic of potential application of probiotics as a means of disease control with comprehensive look at the available literature. The possible mode of action of probiotics (Strengthening immune response, competition for binding sites, production of antibacterial substances, and competition for nutrients) in providing protection against diseases is described. Besides, we have classified different pathogens and separately described the effects of probiotics as protective strategy. Furthermore, we have addressed the gaps of existing knowledge as well as the topics that merit further investigations. Overall, the present review paper revealed potential of different probiont to be used as protective agent against various pathogens.

Bazı Aromatik Bitki Esansiyel Yağlarının Patojenik Balık Bakterilerine Karşı Antibakteriyel Aktivitesi

Essential oils of twenty-four plant species were obtained by hydrodistillation and investigated for their antibacterial effects against seven fish pathogenic bacteria (Aeromonas hydrophila, Aeromonas salmonicida, Vibrio anguillarum, Yersinia ruckeri, Enterococcus faecalis, Lactococcus garvieae and Streptococcus agalactiae). The antibacterial activity results of the essential oils obtained by disc diffussion method showed strong activities against all pathogens. In general, whole essential oils except Artemisia absinthium exhibited strong antibacterial effects against the most of the fish pathogens. However, the essential oil of A. absinthium showed weak antibacterial effect against only A. hydrophila. Mostly seven essential oils of the plants (T. spicata, T. vulgaris, L. nobilis, C. verum, H. plicatum and A. citriodora Paláu) among twenty-four essential oils exhibited good antibacterial activity against all fish pathogens. When compared to the tested antibiotics (furazolidon, oxytetracycline, cephalothin, and trimethoprim/sulfamethoxazole), the antibacterial effects of essential oils were mostly obtained equivalent or stronger. Considering the antibacterial activity results of the essential oils, their alternative use in lieu of antimicrobial agents against bacterial fish diseases might be convenient in the aquaculture.

Development of a multiplex real-time PCR method for early diagnosis of three bacterial diseases in fish: A real-case study in trout aquaculture

Lactococcus garvieae, Yersinia ruckeri and Flavobacterium psychrophilum are three of the most important pathogens in worldwide rainbow trout aquaculture (Oncorrhynchus mykiss Walbaum). In this work, a multiplex quantitative PCR (qPCR) method for the simultaneous detection of the three pathogens was developed and tested in a commercial trout farm. Fifty-four spleen and brain samples from a trout farm were analyzed using both multiplex qPCR and classic microbiological methods. When comparing qPCR results and classic plate diagnostic techniques no negative deviations were observed, which resulted in a 100% relative sensitivity of the multiplex qPCR method developed. In addition, efficiency of the qPCR method ranged between 97.5% and 108.8%. The specificity of the combination of primers and probes was successfully tested in 57 target and non-target bacterial strains Hence, the multiplex qPCR method developed in the present study could be used as a reliable diagnostic tool for the detection of L. garvieae, Y. ruckeri and F. psychrophilum in rainbow trout farms, enabling faster diagnostics (only a few hours) and contributing to a quick response and management of bacterial disease outbreaks.

Dietary Withania sominefera root confers protective and immunotherapeutic effects against Aeromonas hydrophila infection in Nile tilapia (Oreochromis niloticus)

In the present study, effect of dietary Withania sominefera (W. sominefera) root powder was evaluated to modulate immune and antioxidant response against Aeromonas hydrophila (A. hydrophila) infection in Nile tilapia (Oreochromis niloticus). W. sominefera root powder supplemented diets at two concentrations 2.5% (W 2.5%) and 5% (W 5%); fed for 6 weeks prior to the A. hydrophila challenge and continued the same respective diets during the post challenge period (2 weeks). Results showed that fish fed W. sominefera at 5% enhanced immune response in both pre and post-challenge period. NBT level exhibited only significant increase (P < 0.05) in the pre-challenge period compared to control. Malondialdehyde (MDA) levels in liver and muscle revealed significant decrease in both Withania supplemented groups compared to the control in post challenge period. Antioxidant enzymes activities (catalase/CAT/, glutathione S-transferase/GST/, glutathione/GSH; and superoxide dismutase/SOD) were improved in liver and muscle in post challenge period. Glutathione peroxidase (GPx) level in muscle and serum total antioxidant capacity (TAC) showed a significant increase in both Withania supplemented groups compared to the control post challenge. Withania supplementation enhanced disease resistance against A. hydrophila and reduced mortalities (20%), especially at supplemented concentration of 5%. Our findings suggest that W. sominefera root powder may have protective and immunotherapeutic roles in Nile tilapia against A. hydrophila infection which may be useful in controlling important fish bacterial diseases.

Development and validation of a Multiplex-PCR tool for the detection of Vibrio alginolyticus, Vibrio anguillarum and Vibrio harveyi in fish

Development and validation of a Multiplex-PCR tool for the detection of Vibrio alginolyticus, Vibrio anguillarum and Vibrio harveyi in fish

Preliminary Survey of Gram-Negative Bacterial Pathogens from Commonly Caught Fish Species (Oreochromis niloticus, Cyprinus carpio and Clarias gariepinus) in Lake Hayiq, Ethiopia

A cross-sectional study was conducted from October 2016 to May 2017 on Oreochromis niloticus, Cyprinus carpio and Clarias gariepinus fish species at Lake Hayiq, North East Ethiopia with the objective of isolation and identification of major gram-negative bacterial pathogens of commonly catched fish species from Lake Hayik. A total of 98 live fishes (49 Oreochromis niloticus, 30 Cyprinus carpio and 19 Clarias gariepinus) were collected and transported to the laboratory. From the three fish species a total of 384 organ samples (96 skins, 98 gills, 94 intestines, 33 swim bladders, 19 kidneys, and 44 livers) were taken. A systematic random sampling technique was used to select the fish samples after drawn from the water. Among 384 fish organ samples 116 (30.2%) gram negative bacterial isolates were found: 9 (2.3%) Aeromonas species, 24 (6.3%) Pseudomonas species, 6 (1.6%) Enterobacter species, 29 (7.6%) Escherichia species, 4 (1.6%) Edwardsiella species, 11 (2.9%) Klebsiella species, 5 (1.3%) Proteus species, 8 (2.1%) Vibrio species, 14 (3.6%) Flavobacter species and 6 (1.6%) Salmonella species were found. Isolation among organs: Pseudomonas species, skin (33.3%), intestine (33.3%), and swim bladder (12.5%); Escherichia species: intestine (41.4%), skin (24.2%) and gill (24.2%) and Klebsiella species: liver (27.3%), gills (36.4%) were found. All the isolated bacterial species were gram-negative bacteria. From the three fish species, Oreochromis niloticus was the most affected fish species (48.2%) while Clarias gariepinus species were the least affected species (17.2%). In conclusion, majorities of those pathogens isolated and identified were very important for different fish disease outbreaks and also public health importance. But, very few and disintegrated studies with scanty data have been done whereas, it has been nowadays fishery is one of the main growth transformation plan for food security in Ethiopia. Therefore, it needs further integrated investigation on fish bacterial diseases.

Transmission through the water of the bacterial diseases of the euryaline fish cultured in the Mediterranean. Elements of epidemiology and risk factors which concern their spread and transmission of the respective pathogens

Intensive fish culture practiced in the Mediterranean requires fish to live under stressful conditions and high fish densities, something that facilitates transmission and spread of bacterial pathogens within cultured fish populations. One of the most important means of transmission of bacterial diseases of the euryaline fish that are cultured in the Mediterranean is the seawater. The main pathogenic bacteria that infect the euryaline fish species that are cultured in the Mediterranean are: Listonella anguillarum, Photobacterìum damselae subsp piscicida Tenacibaculum marìtimum, Piscirikettsia salmonis, Pseudomonas anguilliseptica as well as various species of the genus Vibrìo, various species of the genera Streptococcus and Lactococcus, and species of the genus Mycobacterium. In the natural environment the bacteria, which are usually shed by infected fish, after surviving for some time in the water column and the bottom of the sea can, under appropriate conditions, infect other, cultured or wild susceptible fish. This review presents the published information that concerns the ability of the various bacterial pathogens of the euryaline fish to spread via water. Most of the published information concerning the bacterial diseases of the Mediterranean cultured euryaline fish deal with the characteristics, resistance and means of transmission of the respective bacteria, as determined in experimental studies. This information is very important for the design and application of prevention and control programs for the respective diseases, however, these programs must also consider epidemiological information concerning risk factors that may affect the onset and severity of the diseases. The investigation of risk factors, in analytical epidemiological studies, focuses on characteristics that relate to the pathogen, the host and the environment, which can concern and be measured at the farm level or at any other level of organization of the population. Especially useful in these cases is the determination of management practices which can be related to increased or decreased morbidity or mortality (total or due to specific diseases). In the current study, reference is made to analytical epidemiological studies in which risk factors that may affect the transmission of several fish pathogens, as well as the occurrence and severity of the respective diseases, have been investigated. Although these studies refer to environments outside the Mediterranean, however, they are particularly interesting because they concern infectious agents that are transmitted by water in conditions and culture environments similar to those of the Mediterranean seawater aquaculture. The approach of prevention of bacterial diseases through management of the populations and their environment is particularly important in the intensive culture of euryaline fish, since the methods that are used, today, for the reduction of the concentration of bacterial pathogens in the water have limited application and effectiveness in such systems. At the farm level, and especially in land-based facilities, three methods are used to decrease the concentration of pathogenic bacteria in the incoming sea water: ozonation, UV radiation and manipulation of the microbial flora of the water using non pathogenic microorganisms, which act antagonistically to the pathogenic bacteria. The first two methods are especially effective in flow-through systems, where water is not recirculated but not so much in closed systems where because the water is re-used fish are infected by the few bacteria that survive the treatment. The alteration of the microbial flora of the incoming water, through antagonism, can be applied in hatcheries during the initial stages of fish culture, but not at the grow out stage in the cages.

Beneficial effects of medicinal plants in fish diseases

Fish are constantly in contact with pathogens inhabiting water. High population density as well as poor hydrodynamic conditions and feeding lead to an increased sensitivity towards infections. In order to prevent major economic losses due to diseases, various medications are used for treatment and prevention of infections. The use of antimicrobial drugs in aquacultures could lead to emergence of resistance in pathogenic microorganisms. Alternatives are being sought over the last few years to replace antibiotics, and medicinal plants are one of available options for this purpose. These plants are rich in secondary metabolites and phytochemical compounds, which have an effect against viral, bacterial, and parasitic diseases in fish. Their main advantage is their natural origin and most of these plants do not represent threat for human health, the fish, and the environment. The goal of this review is to present information on the treatment of viral, bacterial, and parasitic diseases in fish through medicinal plants, with focus on the mechanisms of action of the identified secondary metabolites, fractions, or plant extracts.

Ultra highly sensitive method for detecting Edwardsiella ictaluri using high-gradient immunomagnetic separation with polymerase chain reaction

Edwardsiella ictaluri causes an economically important bacterial disease in farm-raised catfish in the USA and abroad. To elucidate the route of infection for fish bacterial disease, it is important to monitor both fish health and trace bacteria in the water environment. In this study, we applied an ultra highly sensitive method to detect E. ictaluri using high-gradient immunomagnetic separation (HGIMS) with polymerase chain reaction (PCR). HGIMS is a magnetic separation method in which the magnetic force is strengthened by integrating a magnetic gradient between the magnetic filter and nearby column. Immunomagnetic beads were specifically designed to react with the target bacteria, allowing for more efficient collection. The accumulated beads were released from the filter by releasing the magnetic force. After the process, DNA was extracted from the concentrated cells, and PCR was applied to detect E. ictaluri. The HGIMS system had higher detection sensitivity using than the conventional method, and the total assay time, including sample preparation, was about 3.5h. The optimal reaction time of immunomagnetic beads was 15min and the flow rate of the HGIMS system was 10mlmin−1. PCR products of the expected size were obtained from samples concentrated up to 102cfuml−1. The proposed system appears to be suitable for highly sensitive detection of E. ictaluri. Improvements in the bacteria recovery ability of the immunomagnetic beads will further increase the detection limits.

Xanthine oxidase activity affects pro-oxidative and pro-inflammatory profiles in spleen of silver catfish experimentally infected with Aeromonas caviae

Several pieces of evidence have linked the involvement of xanthine oxidase (XO), a source of uric acid and reactive oxygen species (ROS), to pro-oxidative and pro-inflammatory effects observed during bacterial fish diseases. Thus, the aim of this study was to evaluate whether upregulation of splenic XO activity contributes to disease pathogenesis of Aeromonas caviae infection, as well as whether it may be considered a pathway involved in ROS and nitric oxide (NO) production. XO activity increased in the spleen of infected animals, as did the splenic levels of uric acid, ROS and metabolites of nitric oxide (NOx), compared to the uninfected control group. Based on this evidence, upregulation of splenic XO activity induces pro-oxidant and pro-inflammatory profiles in the spleen of fish infected by A. caviae due to excessive formation of uric acid. Moreover, excessive uric acid induces the release of pro-inflammatory mediators, such as ROS and NOx, which contribute to disease pathophysiology. In summary, upregulation of XO activity may be considered a pathway involved in ROS and NOx production.