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1.
Fungal infestation by water mold Saprolegnia spp. causes great losses in aquaculture and fish egg hatching. To find a safe and effective alternative for the fungal prevention, we studied continuous disinfection of the inlet water by UV irradiation and ozonation combined with low concentration hydrogen peroxide (H2O2) treatments in a rainbow trout (Oncorhynchus mykiss) egg hatching system. High dose of UV irradiation (400 mWs/cm2) of the inlet water decreased the mortality of rainbow trout eggs from the 77.3% to 14.3% in a 28 day trial. UV irradiation did not modify water quality parameters, while combination of UV irradiation and H2O2 caused up to fivefold increase in the formate levels, and combination of O3 and H2O2 caused even ten-fold increase in the acetate and formate levels. UV suppressed the gradual increase of the heterotrophic bacterial counts on the fish eggs. Based on the molecular profiling high dose of UV reduced the growth of some of the dominating bacterial groups and combination of UV and H2O2 had a distinctive effect on the overall bacterial community structure on the fish eggs.  相似文献   

2.
The incidence of fish pathogenic oomycetes, Saprolegnia, has increased significantly in aquaculture since the ban of malachite green. For the efficient characterization of anti‐Saprolegnia therapeutics, simple accurate methods are required. However, the current screening methods are limited by time, and none of them are confirming the viability of treated spores or hyphae. In this study, a modified fluorescence‐based assay for the in vitro screening of Saprolegnia inhibitors has been developed. This method involves the use of FUN‐1 viability dye combined with calcofluor white M2R, and is based on the formation of orange‐red cylindrical intravacuolar structures (CIVS) in metabolically active spores, hyphae and biofilms. Heat‐killed and bronopol‐treated Saprolegnia spores, hyphae and biofilms exhibited diffuse bright green fluorescence which confirms complete loss of viability. For boric acid‐treated spores, no germination was observed. However, tiny CIVS were observed in 50% of treated spores which indicated reduction in their viability. Our results proved that FUN‐1 dye is an efficient tool to distinguish between live and dead Saprolegnia spores, hyphae and biofilms and to monitor the change in Saprolegnia viability during qualitative evaluation of potential anti‐Saprolegnia compounds.  相似文献   

3.
Inhibitory concentrations of clove oil and ethanol against growth of Saprolegnia sp. hyphae were screened by a modification of the hemp (Cannabis sativa L.) seed MicroPlate (HeMP) method and their usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss eggs was tested. In vitro experiment showed that in continuous static exposure, clove oil at 100 mg L?1 significantly inhibited the growth of Saprolegnia, whereas in bath exposures, clove oil at 500 mg L?1 had no significant effect at any exposure time tested (15, 60 and 240 min), but clove oil at 10 000 mg L?1 significantly inhibited growth at all exposure times. Clove oil and ethanol treatments had no visible effects on the onset or spread of the fungus during incubation of rainbow trout eggs. Clove oil at 1000 mg L?1 resulted in 95–100% mortality before the eyed stage was reached. Sublethal concentrations of clove oil and ethanol had no effects on the development rate of the embryo or growth and yolk utilization efficiency after hatching. This study suggests that clove oil and ethanol may not be options in controlling aquatic fungi infestations during incubation of rainbow trout eggs.  相似文献   

4.
This study evaluated the probiotic potential of the biofilm formed by the strain Pseudomonas sp. RGM2144 on rainbow trout survival. When challenged with the fish pathogen Flavobacterium psychrophilum, Pseudomonas sp. RGM2144 increased rainbow trout survival to 92.7 ± 1.2% (control: 35.3 ± 9.5%, p < .0001). The draft genome of Pseudomonas sp. RGM2144 is 6.8 Mbp long, with a completeness 100% and a contamination of 0.4%. The genome contains 6122 protein-coding genes of which 3564 (~60%) have known functions. The genome and phylogeny indicate that Pseudomonas sp. RGM2144 is a new species in the Pseudomonas genus, with few virulence factors, plasmids, and genes associated with antimicrobial resistance, suggesting a non-pathogenic bacterium with protective potential. In addition, the genome encodes for 11 secondary metabolite biosynthetic gene clusters that could be involved in the inhibition of F. psychrophilum. We suggest that Pseudomonas sp. RGM2144 may be applied as a probiotic in salmonid fish farming.  相似文献   

5.
In this study, 318 bacterial strains were isolated from the gastrointestinal (GI) tracts of 29 rainbow trout, Oncorhynchus mykiss (Walbaum). These bacteria were screened in vitro for their ability to inhibit growth of Flavobacterium psychrophilum, the causative agent of coldwater disease. Bacteria observed to inhibit F. psychrophilum growth were further screened against rainbow trout bile, as an indicator of their ability to survive in the GI tract. This screening resulted in narrowing the pool to 24 bacterial isolates. Those 24 isolates were then tested for pathogenicity in rainbow trout by intraperitoneal injection. Following a 28‐day challenge, eight isolates were shown to cause direct mortality and were eliminated from further study. As a result, 16 bacterial isolates were identified as probiotic candidates with the potential to control or reduce disease caused by F. psychrophilum.  相似文献   

6.
Major histocompatibility complex (MHC) loci encode glycoproteins that bind to foreign peptides and initiate immune responses through their interaction with T cells. MHC class II molecules are heterodimers consisting of α and β chains encoded by extremely variable genes; variation in exon 2 is responsible for the majority of observed polymorphisms, mostly concentrated in the codons specifying the peptide‐binding region. Lactococcus garvieae is the causative agent of lactococcosis, a warm‐water bacterial infection pathogenic for cultured freshwater and marine fish. It causes considerable economic losses, limiting the profitability and development of fish industries in general and the intensive production of rainbow trout, Oncorhynchus mykiss (Walbaum), in particular. The disease is currently controlled with vaccines and antibiotics; however, vaccines have short‐term efficacy, and increasing concerns regarding antibiotic residues have called for alternative strategies. To explore the involvement of the MHC class II β‐1 domain as a candidate gene for resistance to lactococcosis, we exposed 400 rainbow trout to naturally contaminated water. One single nucleotide polymorphism (SNP) and one haplotype were associated with resistance (P < 0.01). These results are promising for using MHC class IIβ as a molecular marker in breeding rainbow trout resistant to lactococcosis.  相似文献   

7.
In northern Japan, juvenile chum salmon Oncorhynchus keta (Walbaum) are released from hatcheries to enhance the fishery resource. Infections with ectoparasitic protozoans, particularly the flagellate Ichthyobodo salmonis and the ciliate Trichodina truttae, occasionally cause severe mortality among hatchery‐reared juveniles. This study examined the susceptibility of the two parasites to wide‐ranging UV irradiation (experiment 1) and then investigated whether UV disinfection of the rearing water using a commercial device was useful for preventing infections among juveniles in a small‐scale rearing system over a 28‐day period (experiment 2). In experiment 1, parasite mortality reached 100% with UV irradiation doses of ≥9.60 × 105 μW s/cm2 for I. salmonis and ≥8.40 × 105 μW s/cm2 for T. truttae. In experiment 2, disinfection of the rearing water at a UV irradiation dose of 2.2 × 106 μW s/cm2 succeeded in complete prevention of both parasites in the juvenile salmon. These results elucidate the minimum dose of UV irradiation for inactivation of I. salmonis and T. truttae, and demonstrate the usefulness of water disinfection using a commercial UV irradiation device to prevent infections by these parasites in hatchery‐reared juvenile chum salmon.  相似文献   

8.
A quantitative survey of Saprolegnia spp. in the water systems of Norwegian salmon hatcheries was performed. Water samples from 14 salmon hatcheries distributed along the Norwegian coastline were collected during final incubation in the hatcheries. Samples of inlet and effluent water were analyzed to estimate Saprolegnia propagule numbers. Saprolegnia spores were found in all samples at variable abundance. Number of spores retrieved varied from 50 to 3200 L?1 in inlet water and from 30 to >5000 L?1 in effluent water. A significant elevation of spore levels in effluent water compared to inlet water was detected. The estimated spore levels were related to recorded managerial and environmental parameters, and the number of spores in inlet water and temperature was the factor having most influence on the spore concentration in the incubation units (effluent water). Further, the relative impact of spore concentration on hatching rates was investigated by correlation analysis. From this was found that even high spore counts did not impact significantly on hatching success.  相似文献   

9.
The aim of this study was to evaluate probiotic properties and the aflatoxin B1 adsorption ability of yeasts isolated from rainbow trout intestine and fish feed to assess their use in the formulation of feed additives. Growth at pH 2, bacterial pathogens inhibition, bacterial pathogens co‐aggregation, autoaggregation, homologous and heterologous inhibition against lactic acid bacteria were evaluated. Moreover, aflatoxin B1 adsorption was tested. All strains were able to maintain viable (107 cells/ml) at pH 2. All strains isolated from intestine were identified as Kazaschtania exigua, while strains isolated from feed were all identified as Debaryomyces hansenii. Kazaschtania exigua RC035 and RC037 showed the strongest antimicrobial activity while K. exigua RC037 and RC038 were the most efficient co‐aggregating bacterial pathogens. All strains exhibited strong autoaggregation. None of the tested yeast strains showed homologous inhibition towards other yeasts and heterologous inhibition towards lactic acid bacteria strains. Debaryomyces hansenii RC031 demonstrated aflatoxin B1 adsorption capacity (21%). The results of the present study indicate that select strains of Kazaschtania exigua and D. hansenii showed potential to improve the health of rainbow trout by inhibiting pathogens and binding AFB1 and their use as probiotics may improve the production of rainbow trout in aquaculture systems.  相似文献   

10.
Aquaculture production is predicted to increase sharply. In this regard, live feed plays a crucial role in the larval phase of many aquaculture organisms. Hence, a persistent concern in aquaculture is to find low‐cost and eco‐friendly feed sources to culture live feed organisms. Branchinecta orientalis (G. O. Sars 1901), a fresh/brackish water fairy shrimp, was reared using effluent from rainbow trout Oncorhynchus mykiss (Walbaum 1792) ponds, either fresh but supplemented with two species of microalgae, Scenedesmus sp. and Haematococcus sp., or non‐supplemented but after “ageing” of the culture medium. The feeding experiment was designed at a density of 100 individuals L?1 in 2‐L vessels. The results indicated that differences between final length, survival and most reproductive parameters of the treatment with aged medium and the treatment using fresh medium supplemented with Scenedesmus sp. were non‐significant (p > .05). Better results were obtained for a number of reproductive parameters in the treatment supplemented with Haematococcus sp. Thus, for intensive resting egg production of B. orientalis, microalgae can be replaced by aged non‐supplemented effluent from trout ponds as a nutrient‐rich feed source. This consequently can reduce drainage of nutrients into the environment and thus decrease aquatic pollution.  相似文献   

11.
A quantitative and reproducible 96‐well microtiter method that is easily adaptable for the screening of Saprolegnia biofilm inhibitors is described. As opposed to other methods previously developed for the screening of Saprolegnia inhibitors on spore germination or mycelial growth, this technique is of particular significance as it investigates potential inhibitors against surface‐attached mycelial mats of Saprolegnia spp. (biofilm). In this study, we have investigated the effects of propionic acid (PPA) on reducing the viability of induced Saprolegnia biofilms using colorimetric MTS assay based on the reduction of tetrazolium salts. Viability of Saprolegnia hyphae in treated biofilms was reduced significantly following treatment with different PPA concentrations. The effect was enhanced after combining each of the tested PPA concentrations with 500 mg/L of boric acid (BA). However, the percentage of non‐viable hyphae was still higher in 200 mg L–1 bronopol‐treated biofilms (positive control) following 6‐ and 12‐hr exposure. Similar results were observed using other recently described fluorescence‐based assays for viability.  相似文献   

12.
This study investigated the indirect use of silver nanoparticles (AgNPs) for reduction of fungal infections during incubation period of fertilized rainbow trout eggs. Different concentrations of nanosilver-coated zeolite (0.5, 1, and 1.5 % AgNPs) were compared with unmodified zeolite as water filter media in semi-recirculation systems. For testing the effect of AgNPs on reduction of fungal infection, fertilized eggs were transferred in incubators receiving water from filters coated with nanosilver. The eggs in each incubator were inoculated with Saprolegnia-infected trout eggs. Any dead or infected eggs and embryos were periodically removed, while the performance of the filters was assessed by calculating the survival rates from fertilization up to completion of the yolk–sac absorption stage. The results showed that the filters containing 0.5 % AgNPs increased the survival rate by 4.56 % from fertilization to the swim up stage compared to the control (p < 0.05). Also, the additional application of activated carbon (as absorbent media) along with AgNP-coated media in filters caused an increase of about 11.24 % in the survival rate for the larval stage (p < 0.05). In contrast to the control group with about 6 % fungal infection, no infections were observed during the incubation period in the incubators containing nanosilver-coated filters. Therefore, the final results confirmed that the indirect use of AgNPs in the aforementioned filters were significantly effective for preventing fungal infections in semi-recirculation systems for rainbow trout, making them a candidate for replacing the chemical fungicides currently used during egg incubation in hatchery systems.  相似文献   

13.
During a 3‐month period from June to the end of August 2016, ~5% mortalities were observed in a farm with rainbow trout (Oncorhynchus mykiss Walbaum) and one farm of common carp (Cyprinus carpio L.) in Bulgaria. The disease was manifested by gill ulcers/rot, asphyxiation and bloody ascites. Aeromonas hydrophila was isolated from the internal organs of all the diseased fish. Bacillus mycoides or B. pseudomycoides were recovered from the gill lesions on diseased carp and rainbow trout, respectively, with identification achieved by conventional phenotyping and by sequencing of the 16S rRNA gene. In vivo experiments confirmed that all three organisms were pathogenic to rainbow trout.  相似文献   

14.
Proliferative kidney disease (PKD) of salmonids caused by Tetracapsuloides bryosalmonae causes high mortalities of wild brown trout (Salmo trutta fario) and farmed rainbow trout (Oncorhynchus mykiss) at elevated water temperatures. Here the aim was to compare the temperature‐dependent modulation of T. bryosalmonae in the two salmonid host species, which display different temperature optima. We used a novel experimental set‐up in which we exposed brown trout and rainbow trout to an identical quantified low concentration of T. bryosalmonae for a short time period (1 hr). We followed the development of the parasite in the fish hosts for 70 days. PKD prevalence and parasite kinetics were assessed using qPCR. Exposures were performed at temperatures (12°C and 15°C) that reflect an environmental scenario that may occur in the natural habitat of salmonids. T. bryosalmonae infection was confirmed earliest in brown trout kept at 15°C (day 7 post‐exposure) while, in all other groups, T. bryosalmonae was not confirmed until day 15 post‐exposure. Moreover, significantly greater infection prevalence and a faster increase of parasite intensity were observed in brown trout kept at 15°C than in all other groups. These results indicate that PKD is differentially modulated by water temperature in related host species.  相似文献   

15.
The present study investigated the antifungal effects of essential oils of oregano (Origanum onites) and laurel (Laurus nobilis) on Saprolegniasis, a disease that occurs in rainbow trout eggs during the incubation period. Oregano and laurel were ground after drying, and essential oils were obtained by water distillation method using a Clevenger apparatus. The essential oils were added to potato dextrose agar (PDA) at the rates of 1–1000 ppm, and the minimum inhibitory concentration (MIC) was determined as 250 ppm whereas the minimum lethal concentration (MLC) was determined to be 500 ppm for both plants. In the in vivo trials, fertilized eggs were treated with predetermined doses either by bathing during water hardening and incubation period or only during incubation period, and death rates were monitored during embryological development. The best larvae hatching rate was determined in 500 ppm oregano and 500 ppm laurel groups treated during water hardening plus daily as 82.11% and 79.87%, respectively. According to the results, it was determined that oregano and laurel essential oils exhibited better results in all doses compared with the negative control group, and 500 ppm dose had a better effect than the positive control group treated with formalin.  相似文献   

16.
Different antibiotic‐based drugs are being used for the treatment of Aeromonas hydrophila infection in rainbow trout, and several studies emphasize the use of medicinal plants as immunostimulants for prophylactic measure against Aeromoniasis disease. However, therapeutic effects of aqueous methanolic extracts of tetra (Cotinus coggygria) against A. hydrophila in rainbow trout were not investigated. Four different concentrations of tetra extract (0 [control], 4, 8 and 12 mg/100 µl) and also two different positive control groups (florfenicol and doxycycline antibiotics) were administered orally using feeding needles to individual rainbow trout, Oncorhynchus mykiss of all experimental groups twice a day after intramuscular inoculation of A. hydrophila. The study period was for 10 days. On 0th, 3rd, 7th and 10th day, blood and tissues were collected from the fish and changes in humoral immune responses, haematology and immune‐related gene expressions were determined. In the study, superoxide radical production was decreased generally in all experimental groups except in 12 mg tetra and florfenicol treatments compared to control (p < .05). Lysozyme activity was generally decreased (p < .05), or no differences were observed in all experimental groups compared to the control. Myeloperoxidase activity was significantly increased in florfenicol‐treated fish group on 7th day (p < .05). Generally, myeloperoxidase activity showed an increase in almost all tetra‐treated groups. Haematological parameters increased but were not significantly high enough in treatments. Almost all immune‐related gene expressions were significantly enhanced on 3rd and 10th day of the study. Survival rate of 53.33% was found in control group. There were no significant differences in survival between control and 4 mg tetra‐treated group (p > .05). All the other groups' survival rate was significantly increased compared to control. The highest survival rate was found in florfenicol group (80%). In 12 mg tetra‐, doxycycline‐ and 8 mg tetra‐treated groups, survival rate was recorded as 74.44%, 70% and 70%, respectively. Our results suggest that tetra methanolic extract is an effective therapeutic remedy against A. hydrophila infection in rainbow trout at the dose of 24 mg/32.34 g body weight/day.  相似文献   

17.
The probiotic activity of 15 bacterial isolates that inhibit Saprolegnia parasitica in vitro was tested for the biocontrol of saprolegniosis in rainbow trout (Oncorhynchus mykiss Walbaum), adding the bacteria to tank water for 14 days at a concentration of 106 bacteria ml?1 water. Pseudomonas fluorescens LE89 and Pseudomonas fluorescens LE141 were effective in controlling experimental infection with S. parasitica since of the fish treated with LE89, 24.5% ± 16.27% (p < 0.05) became infected, as did 42.8% ± 8.41% (p < 0.05) of those treated with LE141. Given their protective effect when administered in water, their effect was also studied when administered in feed before and after experimental infection. Both bacterial isolates survived low pH levels and the action of bile, grew in skin and intestinal mucus, were resistant to several antibiotics and survived in feed; however, neither of the two isolates prevented S. parasitica infection when administered in feed.  相似文献   

18.
Saprolegnia infections cause severe economic losses among freshwater fish farming. In this study, two known compounds, rhein and aloe‐emodin, were isolated from Rheum palmatum, and the in vitro inhibitory activity of both compounds against mycelial growth and spore germination of Saprolegnia was tested. Both rhein and aloe‐emodin were able to decrease Saprolegnia mycelial growth and spore activity in all tested concentrations after exposure for 48 h. Complete inhibition of mycelial growth was observed at 20 mg/L for rhein and at 50 mg/L for aloe‐emodin, while spore germination was 100% prevented at 16 and 40 mg/L for rhein and aloe‐emodin, respectively. Because rhein showed stronger in vitro anti‐Saprolegnia activity, it was further tested in vivo to measure the prevention and treatment efficacy on Saprolegnia infection of grass carp. Its acute activity to grass carp was also evaluated. The results revealed that exposure to rhein at 20 mg/L for 7 d could prevent 93.3% of infections by Saprolegnia in abraded grass carp, while 67.7% of infected fish could be recovered by treatment with rhein. The 48‐h median lethal concentration (48 h‐LC50) to grass carp was 148.5 mg/L, which is about 7.4 times the effective dose indicating the safety for the use of rhein. This study suggests that rhein has promising anti‐Saprolegnia activity and may be an option in preventing and controlling Saprolegnia infection.  相似文献   

19.
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20.
The objective of this study was to determine if deoxynivalenol (DON) exposure alters the susceptibility of rainbow trout to bacterial coldwater disease caused by Flavobacterium psychrophilum. Rainbow trout were fed a nutritionally complete diet containing corn that was naturally contaminated with DON at a desired concentration of <0.5 (control and pair‐fed treatments), 4 or 6 ppm over 7 weeks to apparent satiation. After 4 weeks, fish were infected by intraperitoneal injection with F. psychrophilum (3.03x106 CFU mL?1) via intraperitoneal injection and monitored for morbidity and mortality. A significant linear reduction in feed intake was associated with increasing dietary levels of DON contamination over the initial 4 weeks. There was a significant reduction (P < 0.05) in cumulative per cent mortality in DON‐fed groups (4.1 ppm, 11%; 5.9 ppm, 7%) in comparison to control (46%) and pair‐fed (25%) groups at 21 days post infection. Mortality of trout pair‐fed the control diet was also significantly lower (P < 0.05) than the control group fed to apparent satiation. A replicate trial using genetically similar fish and the same experimental design produced similar results. These results suggest that DON exposure and restricted feed intake provided a protective effect for rainbow trout infected with F. psychrophilum.  相似文献   

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