Currently, global use of prebiotic compounds has increased considerably. This study aims to analyse the effect of complementing the rations of rainbow trout with different concentrations of Celmanax® prebiotic, which contains Saccharomyces cerevisia associated compounds with Mannan-oligosaccharide on gill and liver histology during the growing period and experimental challenge with yersiniosis. Four concentration levels of prebiotic (0, 0.1, 0.5 and 1%) were mixed into fish feed pellets. The fish (with mean body weight of 19.08±1.45 gr) were fed a supplemented commercial diet for 60-days.On day 60 of the study, experimental yersiniosis was induced in all treatment groups by intraperitoneal injection of bacterial suspension. Tissue samples were taken on days 0, 30 and 60 and also after induction of experimental yersiniosis. The results showed that complementing rainbow trout rations with different concentrations of Celmanax® improved the gill and liver injuries on days 30 and 60 of the study. The best tissue effects in the growing period were observed in treatment groups which received 0.1% and 0.5% of the prebiotic respectively, and after experimental challenge with yersiniosis, the lowest lesions of liver and gill pathology were seen in the treatment group fed with 0.1% prebiotic which was significantly different (p<0.05) from all other treatments. According to the results of this study, adding Celmanax® to rainbow trout diet at 0.1% concentration improves tissue parameters during breeding period and decreases tissue lesions when faced with yersiniosis.

Yersinia ruckeri is the causative agent of yersiniosis, one of the most serious bacterial diseases in rainbow trout culture industry with high economic losses. Outbreaks of clinical forms of the disease have been considerable in Iranian rainbow trout farms. This study was aimed to evaluate the molecular epidemiology of yersiniosis caused by Y. ruckeri, affected farmed trout in Mazandaran (22 farms), Tehran (18 farms), Lorestan (6 farms) and Zanjan (6 farms) provinces during 2011to 2013. Furthermore, biotyping and sequencing of the recovered Iranian isolates was performed. Totally, 34 Y. ruckeri isolates were identified in Mazandaran (14 farms), Tehran (17 farms) and Zanjan (3 farms). All isolates were strongly positive in latex bacterial agglutination using monoclonal antibody to Y. ruckeri. Also, all isolates were identified as biotype 1 showing motility and having lipase activity. In addition, all isolates showed high sequencing similarity (99%). These biochemical, serological and molecular studies all together confirmed the increasing distribution of yersiniosis casued by Y. ruckeri biotype 1 in farmed trout in Iran and so require preventive measures.

Yersinia ruckeri is the etiological agent of Yersinia septicemia or yersiniosis of farmed fishes. In this study, Y. ruckeri isolates were isolated and characterized in the case of phenotype, biotype as well as their patterns of whole cell and outer membrane proteins. Seven isolates were recovered from rainbow trout farms in the Mazandaran, Chaharmahal-va-Bakhtiari, Kohgiluyeh-va-Boyerahamad, and Zanjan provinces during spring and summer 2018.  These isolated Yersinia plus five previously recovered isolates form the North Khorasan and Western Azarbaijan Gharbi were identified as Y. ruckeri based on their phenotype, biotype and molecular characterization. All isolates were biotype one with the high identical patterns of whole cell proteins and outer membrane proteins in electrophoresis. These results illustrated that Y. ruckeri as the cause of yersiniosis in farmed rainbow trout in Iran Y. ruckeri isolates are mostly homogenous showing low diversity and thus, could be useful in further preventive studies such as vaccination.

Yersinia ruckeri is the causative agent of Yersiniosis or Enteric Red mouth Disease that causes huge amount of economic loss in mariculture industry worldwide. Definitive detection and effective treatment for septicemia like Y. ruckeri that outbreak critically, requires rapid and specific diagnosis. Despite the advantages of both PCR and Histopathology techniques in the terms of diagnosis and monitoring they have some defects, the aim of this study is the comparison of PCR and histopathology methods for detection of Yersiniosis in trout fish in Iran.In PCR-based detection, Extracted DNA from suspected Rainbow trout tissue utilized in PCR reaction and polymerase chain products were visualized by gel electrophoresis. In pathological detection, all tissues from live or moribund fish were fixed in 10% formalin saline. Then Samples were embedded in paraffin block and sectioned with digital microtome at 5-7 micrometer thickness. Slides were stained by haematoxillin & eosin, and then treated with mounting media. Differences in the number of positive samples in this comparison demonstrated that each mentioned technique has its advantages so if the advantages of each method exploit and one method supplements the other one, the efficiency and accuracy of monitoring the experiments would boost. In both mentioned methods, all positive results confirmed the existence of yersiniosis infection in Iran, which their comparison is very useful for monitoring and diagnosis of pathogen in the country. Differences in the number of positive samples in this comparison demonstrate that although PCR technique would provide a more rapid and sensitive alternative to traditional diagnosis in detection of harmful pathogens but in some cases such as necrotic and degenerated cells in tissue, PCR ability collapses in the comparison of other detection technique like histopathology. In this study, 20 suspected samples were tested by both techniques that 2 samples were positive and 18 samples were negative in PCR, and 5 samples were positive and 15 samples were negative in pathologic technique .

Streptococcosis and Yersiniosis are important diseases for the aquaculture industry for the rainbow trout (Oncorhynchus mykiss).  In this study, the specific immunological responses of rainbow trout to vaccination with the bivalent vaccine of Streptococcus/ Yersinios were investigated. Three hundred rainbow trout fingerlings (25±2g) were randomly divided into four equal groups in triplicates. Treatments contain Streptococcosis vaccine, Yersiniosis vaccine, bivalent vaccine, and control group.  Fish in vaccinated treatment intraperitoneally injected with 100 microliter vaccine on the first day. The control group was injected with sterile PBS, identical to the vaccinated group. Blood samples were collected from vaccinated and non-vaccinated groups at days 0, 30, and 60 of the study, and antibody titer was subsequently performed. Sixty days after initial immunization, all groups were challenged by a lethal dose of Streptococcus iniae and Yersinia rockeri, mortality rate was calculated and compared among the groups for 14 days. These results indicated high antibody levels in the vaccinated fish at day 30 and 60 post-immunization using both vaccines(p<0.05). However, this amount was fewer at day 60 than day 30. The percentage of trout cumulative mortality after the challenge with Streptococcus iniae and Yersinia rockeri showed a significant decrease in vaccinated groups compared to the control treatment. In general, it can be concluded that the administration of bivalent Streptococosis/Yersiniosis vaccine to the rainbow trout provided appropriate protection against disease and effectively induced the immune response against these two diseases, which is comparable to either of the vaccines separately.

Streptococcosis and Yersiniosis are important diseases for the rainbow trout (Oncorhynchus mykiss) in our country. The aim of this study was to compare the efficacy of divalent vaccine (Streptococcus iniae and Yersinia rockeri) in the immune responses contains, serum lysozyme rate, complement activation, bactericidal, respiratory burst (NBT), total protein, albumin, globulin and some hematological indices contains, RBC and WBC count, hematocrit and haemoglobin in rainbow trout. In this study three hundred rainbow trout fingerlings (25±2g) were randomly divided into four equal groups in triplicates. Treatments contains Streptococcosis vaccine, Yersiniosis vaccine, bivalent vaccine and control group. Fish in vaccinated treatment intraperitonealy injected with 100 microliter vaccine on the first day. The control group was injected with sterile PBS, identical to vaccinated group. Blood samples were collected from vaccinated and non-vaccinated groups at days 0, 30, and 60 of study. The results demonstrated that lysozyme rate in bivalent vaccine were significantly higher at day 60 post-immunization compared to the control group (p<0.05). A significant increase was observed in the complement activation in bivalent vaccine at day 30 and 60 post-vaccination compared to the other groups(p<0.05). Also this results demonstrated that number of WBC in vaccinated groups were higher than control treatment. Generally, it can be concluded that the administration of bivalent Streptococosis/Yersiniosis vaccine provided appropriate protection against disease and effectively induced the immune response against these two diseases which is comparable to either of the vaccines separately. Therefore, investigation of the efficiency of the bivalent vaccine at commercial level is highly warranted.

The aim of this study was to evaluate the effect of edible hot water extraction seaweed, Sargassum angustifoliom, on haematological parameters and survival rate of rainbow trout (O. mykiss) against Yersinia ruckeri. For this purpose, 300 rainbow trout specimens (5.82±0.22 g mean weight) were purchased from a local fish farm and transferred to the laboratory. After 14 days acclimation to the experimental conditions, the fish were randomly divided into five groups with triplicates. Fish were fed with 0 (control), 50, 100, 200 and 400 mg/kg of S. angustifoliom extraction for 56 days. The fish blood samples were takenfor fish exposed with Y. ruckeri bacteria at the end of the experimental period (56 days).The number of red blood cells (RBC), white blood cells (WBC), the percentage of haematocrit and the concentration of haemoglobin were then measured. Results showed that the fish fed with different concentrations of seaweed extraction possessed higher survivability rate and more suitable haematological parameters compared to the control group 56 days after feeding and being exposed to Yersinia bacteria. Meanwhile, the number of RBCs, WBCs, and the percentage of haematocrit and concentration of haemoglobin for the fish fed with 400mg/kg hot extraction of seaweed significantly increased at the end of experimental period. Furthermore, resistance against to the Yersiniosis for these fish increased by using this concentration of seaweed extraction. Therefore the present study suggested that 400mg/kg of seaweed extraction could improve rainbow trout blood parameters and increase the resistance against Yersiniosis.

Enteric red mouth disease (also known as Yersiniosis) is one of the most significant bacterial infections in coldwater fish farms that cause significant mortalities and economical losses in the salmonids fish farms, especially in rainbow trout (Oncorhynchus mykiss). ERM is caused by the gram negative pathogen bacteria Yersinia ruckeri that has five O-serotypes (O1, O2, O5, O6 and O7), five outer membrane protein types (OMP types 1–5) and two biotypes 1 and 2. The disease has a wide geographical distribution in various fresh or sea water fish. More than twenty species mainly of Salmonide origin have been affected and this number is likely to rise in the future following the introduction of new species and the increase of aquaculture trade. The disease can affect fish of all age classes but is most acute in small fish up to fingerling size. Affected fish may reveal different clinical symptoms depending on species, age and temperature. The most characteristic and common clinical signs of the disease include lethargic behavior and inactivity, swimming near the surface, anorexia, and darkening of the skin. The reddening of the throat and mouth, caused by subcutaneous haemorrhaging and exophthalmos are commonly present. Different diagnostic methods have been used for Y. ruckeri, including culturing, serological, biochemical tests, histopathological studies and molecular techniques. This review summarizes the past, present and future state of yersiniosis with emphasis on status of this disese in Iran. Also, some criteria in diagnosis, control and prevention of ERM were discussed.

Yersiniosis is the second important bacterial infections in coldwater fish culture with significant mortalities and economical losses in the Iranian fish farms. In the present study, the effect of extracellular proteins (ECP) on protective immunity of Y. ruckeri vaccine was evaluated in juvenile rainbow trout (7±1.2 g). For this purpose, 540 specimens of juvenile rainbow trout were randomly divided into 6 groups each in triplicates. Group 1 (G1) and Group 2 (G2) were orally administrated with formalin killed cells (FKC) and FKC+ECP, respectively. Groups 3 to 5 received ECP, FKC, ECP+FKC via intraperitoneal route, respectively. Group 6 received phosphate buffer saline as the control group. The humoral antibody responses to bacterial antigens were monitored by ELISA. LD50 of Y. ruckeri was determined used probit method sixty days after vaccination. Then, fish in each treatment were challenged intraperitoneally (I.P) with LD50 of Y. ruckeri virulent registered strain in Iran (KCW 291153). The ELISA results indicated that ECP could increase the serum ELISA antibody titer as the humoral immune response, but ECP with the FKC could increase antibody levels significantly in serum and intestine mucus. Also survival rates in G1 to G6 were 25, 31.25, 37.5, 56.25, 87.5 and 15 percent, respectively. Among I.P immunized fish the survival rate in G5 was significantly higher than the other groups. Although in orally vaccinated fish with FKC (G1) survival rate did not show significant difference with the control group, the FKC /ECP group (G2) showed a significant increase compared to control group (p=0.039). It was concluded that supplementing FKC with ECP increased protective immunity of Yersiniosis vaccine principally in I.P. route. Given the great benefits of the oral vaccine, whole cell/ECP can be considered as a protective antigen to design potential vaccines against this pathogenic micro-organism.

In this study, the efficacy of Streptococcus and Yersinios vaccine in form of bivalent and monovalent was compared in rainbow trout (Oncorhynchus mykiss). Three hundred fishes (25±2g) were randomly divided into four equal groups in triplicates. Treatments contains Streptococcosis vaccine, Yersiniosis vaccine, bivalent vaccine and control group.  Fish in vaccinated treatment intraperitoneal injected with 100 microliter vaccine on the first day. Blood samples were collected from vaccinated and non-vaccinated groups at days 0, 30, and 60 of study and antibody titer were subsequently performed. Sixty days after initial immunization all groups were challenged by lethal dose of Streptococcus iniae and Yersinia rockeri, mortality rate was calculated and compared between the groups for 14 days.
The results demonstrated that lysozyme rate in bivalent vaccine were significantly higher at day 60 post-immunization compared to the control group. A significant increase was observed in the complement activation in bivalent vaccine at day 30 and 60 post-vaccination compared to the other groups(p<0.05). Number of WBC in vaccinated groups were higher than control treatment.  
 High antibody levels were observed in the vaccinated fish at day 30 and 60 post-immunization using both vaccines(p<0.05). The percentage of trout cumulative mortality after the challenge with Streptococcus iniae and Yersinia rockeri showed a significant decrease in vaccinated groups. Generally, it can be concluded that the administration of bivalent Streptococosis/Yersiniosis vaccine to the rainbow trout provided appropriate protection against disease and effectively induced the immune response against these two diseases which is comparable to either of the vaccines separately.