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Cheshmehkileh River and adjacent mountainous streams, play a strategic role as a historical axis for anthropogenic civilization, human welfare also habitat and migration pathway of commercial – biologic valuable fishes e.g. Caspian trout, Caspian kuttum, members of Cyprinidae family in south Caspian Sea drainage. Treats such as overfishing of Caspian trout and Red spotted trout stocks in mountainous headwaters, barriers construction and manipulations those are out of river carrying capacity developed by human activities, affected normal function of river as well. Sand mining big factories establishment next to the river, legal and illegal trade of river sediments, direct entry of Tonekabon landfill leakage into the river, development of Rainbow trout farms since 3 decades and huge effluents into the river containing dead fish and types of solids, escapement of cultured Rainbow trouts into the river, … are major minimum factors which needs basic information for integrating inclusively drainage management system. Cheshmehkileh River contains Headwaters of Dohezar (Daryasar & Nusha), Sehezar and Valamroud rivers during 13 monthly sampling phases between September 2009 and October 2010 based on macrozoobenthoses investigations by EPT, EPT/C EPA protocols, measurements of nominated physic-chemical and microbiologic parameters. Probability of Rainbow trouts escapement and invasion, existence, nutrition in Cheshmehkileh environment indeed investigated. Data analysis explained significant differences (P

The aim of this study is the feasibility of introducing suitable species of fish (native and exotic) for rearing in cages in the southern region of the Caspian Sea. This study from the perspective of economic efficiency and maintaining ecology were analyzed. The results showed that the southern Caspian Sea has the ability to aquaculture fish. However, due to the yearly temperature variations of water (from surface to a depth of 50 meters), the talent of aquaculture area is preferred for fish in cold water than warm water fish due to possibility rearing over the years. The survey showed that the current conditions and due to unfavorable changes in the ecology of the area in the last decade, the use of non-native fish culture in cages is not recommended. Many species of native fish are suitable for rearing in cages. Nevertheless, there is no infrastructure suitable for the production of all of them. Therefore, respectively species of Salmo caspius, Huso huso and Common carp of Caspian Sea for cultivation of in cages was suggested. In the current situation, this fish for their ability to grow faster than the need for selectivity. It is noteworthy that detailed environmental assessments and species risk assessments before the final introduction of any fish species (native and exotic) for rearing in cages in the Caspian Sea ecosystem is essential.

The The Shahid Rajaei Reservoir- Sari is an important and large reservoir in Iran. The major objectives of dam instruction are flood control, irrigation purposes, and electricity power. However the dam is going to supply drinking water for the people. In order to prevent threats of unsuitable water to human health risks and economic losses, it is necessary to monitor the water quality before offering it to people. In this study, some of the physicochemical parameters and Chlorophyl- a, phytoplankton, microb and fungi of Shahid Rajaei reservoir were measured at 4 stations (Shirin Roud branch, Sefid Roud branch, the crossing point of branches, near the tower) during six sampling months (June, July, August, September, November and February) in 2012-2013. In order to water quality classification, the water quality index, trophic status, Shanoon and saproby indices of reservoir calculated and the results compared to different criteria and standards. The results showed that the mean (±Standard Error) of temperature, dissolved oxygen, pH, phosohate, amonium and nitrate concentrations and Chlorophyl a were 21.35 (±1.30)ºC, 10.48 (±0.37), 8.54 (±0.04), 0.050 (±0.004), 0.036 (±0.004), 0.75 (±0.03) mg/l and 18.00 (±7.23) mg/m^3, respectively. In the present study, temperature between surface and deep layer was stratified in June and July, which the stratification was registerd 0.47 and 0.69 °C decreases with increasing of each meter depth in 15 to 30 meter culumn. But, these changes for each increasing meter of water depth were 0.2 to 0.26 °C in August and September, respectively, and finally was close to zero in November. In the warm months (July, August and September) with the formation of thermal stratification in the reservoir was formed oxygen stratification, but in the cold season (November and February), with vertical mixing of water oxygen and percent saturation of the reservoir was nearly homogeneous. TSI showed the maximum and minimum values at stations 4 (oligotrophic condition) and 2 (mesotrophic condition), respectively. The maximum and minimum monthly values of TSI obtained in July, August (eutrophic level) and September, February (oligotrophic level) respectively. Based on the Water Quality Index (WQI), the reservoir was in the “good” quality in whole months, .This class shows that the reservoir is suitable as source of drinking water through routine treatment of drinking water and the quality of water is rarely is low. Meanwhile the water is suitable for swimming and water recreation and survives of .sensitive fish and other aquatic species. Based on the results, 107 phytoplankton species were identified during the period of study. The species were classified in 8 divisions. Maximum and minimum values of mean (SE) abundance observed in July and January, 661 (±286) and 10 (±2) million cells/m^3 respectively at the surface layer. The One way analysis of abundance and biomass data showed temporal significant variances (P< 0/05), however the spatial variances of data were not significant (P> 0/05). Bacillariophyta and Pyrrophyta formed more than 95% of phytoplankton. 3 dominant species namely, Cyclotella meneghiniana, Goniaulax polyedra and Ceratium hirundinella formed about 70% of phytoplankton aboundance. Comparison of diversity indices (Shannon and Evenness) showed higher values in May and January; however the indices reached its lowest level (0.58 and 0.16) in August. Water quality assessment using Shannon index showed the lowest quality of water (moderately to high polluted) in July and August. This index demonstrated the highest water quality (slightly polluted) at station 1 and 4 respectively. The results of the water quality assessment using Saproby index (based on the resistant phytoplankton species to organic pollution) also indicated to organic pollution of water in the months of summer. The saproby assessment in stations categorized most of the stations in “moderately polluted” class of organic pollution except at station 4 which was in "slightly polluted" class. In conclusion, the removal (transfer) place and time of water to the water treatment plants.are impratnt because of temporal and spatial variation of water quality due to changes of phytoplankton structure in Shahid Rajaee Reservoir. Meanwhile, the survey showed that physico-chemical parameters alone did not reflect the actual conditions of aquatic water bodies. Monitoring of aquatic ecosystems must be complemented by biological monitoring. Microbial survey showed that the maximum and minimum geometric mean of the total number of bacteria, in September (6101559 CFU/100ml) and February (3310 CFU/100ml) respectively. However in stations, the maximum and minimum count of this parameter obtained at stations 2 (455316 CFU/100ml) and 3 (40964 CFU/100ml) respectively. There were no viable count of total coliform in the months of May and June. However it’s counting reach to the maximum value in September. Clostridium perfrigens showed viable count in water sample during September. The results also showed no proportion of fecal streptococci in microbe account in the Shahid Rajaei Reservoir. It might be good sign of suitable water quality in term of no-contamination by old and resistant fecal microbes. Base on the total coliform count, water quality was suitable for swimming and source of drinking water in most stations and months. The coliform count increased in August and September in stations 3 and 4. In these 2 months the probability of new fecal contamination increased by warm blood animals in the reservoir. It seems that the environment in September is suitable for accession of old and resistant microbes such as Clostridium perfrigens. The results of sample analysis revealed that the fungal colony counts in the station 4 and 5 were significantly higher than those the other stations. Moreover, the minimum and maximum of the fungal colony counts wereobserved in August and February, respectively. The most commonly isolated genera were Aspergillus, yeasts (especially candida) Penicillium, Cladosporium, Mucor, Fusarium, Althernariya, sterile hyafe and Paecilomyces respectively. Finally, in order to prevent of occurrence of eutrophication, algal bloom, and control of microbial activities and organic phosphorus loading it is necessary to control the activities of the human societies around the dam or the rivers tributary.

This study was conducted for the first time and the effects of probiotic bacteria isolated from the gut of Rainbow trout (Oncorhynchus mykiss). In the first step, after the purification of the isolated bacteria, probiotic properties in vitro was assessed with injection to healthy fish and challenge with three species of pathogenic bacteria in culture media. The second phase of the bacteria isolated in 5 treatments (log 7, 8 and 9 of the lactic bacteria (LAB), Vibrio sp and Pseudomonas sp) and a control treatment on growth and survival, hematological parameters (RBC and WBC cells), immunology and physiology parameters tested during the 60 days of the above parameters after 30 and 60 days and finally at the end, the final assessment was Streptococcosis resistance in fish. The results showed that the isolated bacteria were able to enhance the growth parameters (weight, feed conversion, feed fat, protein efficiency ratio and specific growth rate) and survival. The results showed that log 8 LAB was significant difference with other treatments and control. When using log 8 LAB and Vibrio, the MCV, MCH and MCHC were decreased with no significant difference. The log 8 has the greatest effect on the amount of liver enzyme (AST), IgM and complement component C3, and had significant difference with other treatments. The challenge examination to Streptococcus iniae showed the highest survival in treatments with log 8 (96.66%), and Vibrio (93.33%) and then subjected to other treatments and control are also the least survival (25.38%). The conclusion of that study is the first probiotic properties of bacteria isolated from trout to changes in quality indicators are in particular the LAB bacteria and the second log 8 of LAB had significant positive of changes development and safety, and the fish are resistanted against Streptococcosis.

One of the most important bacterial fish diseases which has caused some outbreaks in rainbow trout farms in Iran is streptococcusis .The farmers were suffering from huge economic losses due to the disease outbreaks in different rainbow trout farms in Iran. The aim of our study was to determine rate of streptococcusis incidence in different stage of growth in farmed rainbow trout in Haraze River, Mazandaran province. Fish and water samples were randomly collected and measured of randomly in10 selected farms, monthly throughout a year. After clinical observations, Isolation and recognition of strep strains were made using biochemical tests. Some Environmental factors include Nitrate, Nitrite, Temperature, pH, Ammonia and DO measured during sampling periods. According to our results 4.6% of juvenile samples showed clinical singe of streptococcusis while only0.7% of them had strep. Contamination .These rates in adult samples were 8.9 and 1 percent respectively. Major isolated bacterial strain was Streptococcus uberis. Incidence of streptococcusis in rainbow trout 20% affected by fluctuation of Nitrite, temperature and DO. Management of these factors can decrease rate of disease outbreaks.

In this study, 11 male of Caspian trout (Salmo truta caspius) (with mean length and weight 37/8 ± 5/3 cm and 523/3 ± 24/7 respectively) and 23 male of Caspian kutum (Rutilus frisii kutum) (with mean length and weight 36/1 ± 7/1 cm and 631/3 ± 21/6 g respectively) were evaluated. All the fish were good at the initial examination of sexual maturity. After sperm sampling, their quality were tested. In this step, the parameters such as motility, duration of mobility, density, pH and osmolality were measured. After this stage, the sperm samples of Caspian trout in the ratio 1: 3 were diluted with the aqueous solution containing compounds (0.3M Glucose, 10% Methanol, 10% egg yolk) and the freezing process was done manually and the sperm was frozen in liquid nitrogen. The sperm samples of Caspian kutums were diluted (ratio of 1: 3) with two soluble diluent containing compounds (350 mM glucose, 30 mM Tris and 4% Polyethylene glycol) and (350 mM glucose, 30 mM Tris and 2% Glycerol) and were frizzed automatically by Planner Kryo instrument and placed in liquid nitrogen. The sperm samples were thawed 1 to 3 months after the date of first freezing and their quality were assessed by measuring percent and timing motility. The results showed that the obtained semen volume of Caspian trout was more than Caspian kutum. Moreover, percentage of motile sperm, timing motility and sperm density of Caspian trout were higher than those of Caspian kutum but osmolality and pH of Caspian trout were lower than those of Caspian kutum. Over time, the percentage of sperm motility and mobility for both species declined compared with fresh samples. After thawing, percentage of motile sperm and timing motility of Caspian kutum were lower than those factors Caspian trout. The results showed that the sample of Caspian kutum sperm that were diluted by ethylene glycol after thawing and were immotile ll of them. However, the samples were diluted by glycerol, after thawing, were alive and motile. According to the results, it seems very important species differences that must be fully considered in the process of freezing sperm. The use of a single protocol would not be successful in cryopreservation because the reaction of sperm against to chemical agents is variable. Therefore, it is essential to get the right information to protect valuable Caspian fish by using cryopreservation. Further studies on the characteristics of each species, as well as the freezing process take appropriate diluent.

The water quality provides the valuable information about the available resources for human usage. The reservoirs are the important resources of surface water which could be considered as an appropriate water resource for irrigation, drinking water and also fish culturing. The Shahid Rajaei Reservoir- Sari is an important reservoir in Iran, which conducted to study on its water quality in this survey. In this study, some of the physicochemical parameters and Chlorophyl- a of Shahid Rajaei reservoir were measured at 4 stations (Shirin Roud branch, Sefid Roud branch, the crossing point of branches, near the tower) during six sampling months (June, July, August, September, November and February) in 2012-2013. The water quality and trophic status of reservoir calculated based on some reference values and the modified Carlson formula. The results showed that the mean (±Standard Error) of temperature, dissolved oxygen, pH, phosohate, amonium and nitrate concentrations and Chlorophyl a were 21.35 (±1.30) ºC, 10.48 (±0.37), 8.54 (±0.04), 0.050 (±0.004), 0.036 (±0.004), 0.75 (±0.03) mg/l and 18.00 (±7.23) mg/m^3 , respectively. In the present study, temperature between surface and deep layer was stratified in June and July, which the stratification was registerd 0.47 and 0.69 °C decreases with increasing of each meter depth in 15 to 30 meter culumn. But, these changes for each increasing meter of water depth were 0.2 to 0.26 °C in August and September, respectively, and finally was close to zero in November. In the warm months (July, August and September) with the formation of thermal stratification in the reservoir was formed oxygen stratification, but in the cold season (November and February), with vertical mixing of water oxygen and percent saturation of the reservoir was nearly homogeneous. The results showed that the European authorities (OECD) trophic status varied between mezotrophic to hypertrophic during the sampling period at all stations. The comparison with the values listed in the references of Iranian dams based on transparency and chlorophyll variables showed similar results. However, phosphorus variable (due to limited for phytoplankton) was not showing the true conditions of trophic status. As a conlusion, trophic status of Shahid Rajaei dam based on Carlson trophic index (TSI) was obtained oligotrophic (May and October), mezotrophic (February) and eutrophic (August and September) condintion during diferent months. Therefore, water management of the reservoir was more attention during warm months.

Due to the increased bacterial resistance to common antibiotics, there is a tendency towards using herbal extracts in order to increase the non-specific immune system. This study was conducted to evaluate the effects of different levels of Mentha piperita extract on hematological, biochemical and immune parameters of Oncorhynchus mykiss. For this purpose, fish with mean (±SD) weight of 32.2± 0.12 g were raised for 8 weeks in Vniro tanks (1800 l water), 80 fish to each tank and feeding with different levels of M. piperita (with concentrations of % 0, % 1, % 2.0 and % 3.0, three replicates were used for each concentration). At the end of the trial, blood samples were collected to determine some hematological, biochemical and immunity parameters in different groups and compared to one another. Results showed significant differences in RBC and WBC count, neutrophil percentage, haemoglobin (Hb), haematocrit (HCT) value, total protein (TP), IgM and lysozyme activity in fish fed M. piperita (especially with 2 and 3.0% concentrations) when compared with control group. The results suggest that M. piperita extract may enhance the non-specific immune system of O. mykiss. Thus, using this supplement especially at of 3.0% level as immunostimulants were recommended in O. mykiss diet.

One of the important problems in Rainbow trout production industry is egg fungal infection especially saprolegniasis which is the most important mortality factor in Rainbow trout hatcheries. Controlling saprolegniasis in hatcheries was done using green malachite in the past years, which is a very effective fungicide. Nowadays, due to the prohibition of using green malachite, effort is done to replace it with other materials as an effective fungicide. Some of the most important materials which have been examined are formalin, sodium chloride and hydrogen peroxide etc. The aim of this study was to evaluate the effects of neutral anolyte on the mortality percent of rainbow trout eggs and produced larvae in point of view of growth indices and survival until yolk sac absorption and larvae active feeding in incubation phase comparing with green malachite to be able to introduce a suitable alternative. This study was carried out in a complete randomly plan with 7 treatments and 3 replications (21 troughs in general), in 20*35*70 cm (length*width*depth) Californian troughs containing an incubator. Treatments included anolyte solutions constant bathing with 0.5 and 0.25 ppm concentrations and periodic anolyte treatments with 2 ppm concentrations (every 2 days), positive control infected with fungus without any disinfectant and negative control without any infection or disinfectant. 300 grams of newly propagated green eggs of rainbow trout which were provided from one of the fish hatcheries in Haraz Road and acclimated with the trough’s water temperature, were distributed in one layer at the bottom of the trough basket. All treatments, except negative control, were infected with saprolegnia, taken from infected eggs of rainbow trout which were previously provided from one of the fish hatcheries of 2000 Road in Tonekabon. The treatments took one month to complete. The studied variables included hatching percent, percent of eyed eggs, abnormality percent and percent of unfertilized eggs, from which percent of eyed eggs was calculated and recorded in the middle and the rest of the variables at the end of the test. In this study Paired-sample T-student test, Levene’s test, one-way ANOVA and Bonferroni’s test was used. For examining egg abnormality, hatching, fungus infection and eyed eggs, first the percent of the variables were specified and then for comparing the rate of abnormality in one of the anolyte treatments (which had the least abnormality) and green malachite, Mann-Whitney test was carried out. This comparison was done to analyze the rate of hatching, fungus infections, eyed eggs, resulting from the materials used in different treatments, using one-way ANOVA Bonferroni’s tests. Results showed that in lower anolyte concentrations (0.5 and 0.25 ppm), the number of fungal colonies of hatchery water and the percent of egg fungus infection were significantly higher than higher concentrations of anolyte (100 ppm and 30 ppm) and green malachite. In other words with concentration increase, the fungicidal effect has also increased. In evaluating the percent of eyed eggs, statistical results showed that eyed eggs percent in 0.25 ppm treatment and green malachite treatment were significantly higher than the other three anolyte treatments. This result can explain egg hatching in 0.25 ppm concentrations and not seeing hatching in the (other) remaining three doses. Between the treatments of 0.25 ppm and green malachite, the group of 0.25 ppm anolyte can be a better disinfectant for rainbow trout eggs compared to green malachite, for fish farmers, due to the high percent of eyed eggs and the low total count of fungus. The results of this study showed that the amount of abnormality in 0.25 ppm treatment has been higher compared to the green malachite group. Because this study was the first research on using anolyte as a fungicide in rainbow trout hatcheries, therefore for more specific study of the concentrations, the timing of usage and the factors affecting these two, more vast and general research is needed.

The genus of saprolegnia is one of the most important pathogenic aquatic fungi in farmed and wild fish. In the present study, fungal infected egss were collected from rainbow trout (Oncorhyncus mykiss) and Caspian trout (Salmo trutta caspius). After purification, 16 isolates were obtained (8 isolates from rainbow trout and 8 isolates from Caspian salmon, respectively). The isolates were then coded as R2 – R9 (rainbow trout) and S2 – S9 (Caspian trout).The registered DNA for S. parasitica (ACTT # 200048) and S. diclina (ACTT # 4206) were used and coded as R1 and S1, respectively. Based on the RAPD profile obtained all samples were divided to 3 groups and members of each group had more than 90% similarity among themselves. According to matrix of similarity and reference strains, the isolates were classified as three groups. Therefore, all of isolates in group 1 and 3 were S. parasitica and S. diclina, respectively, and the members of group 2 were known as Saprolegnia sp. The results of thermal resistance assessment showed that the isolates of rainbow trout and Caspian salmon eggs had slow growth in the temperature between 18 – 20 °C. Thus, R2 and S8 isolates had the lowest radial growth compared to other isolates. The isolates categorized in S. parasitica (group 1) created secoundry zoospores but not observed in two other groups. Thus, catenulated gamme was found in 78% and 55.55% isolates of rainbow trout and Caspian trout eggs, respectively. This study indicated that molecular methods were the best methods for identification of Saprolegnia spp. and it could be applied as a supplementary confirming method.

The project of survey on health status of ornamental fishes in Mazenderan , Golestan and Khorasan Razavi carried out with association of 5 , 2 and 6 centers in orderly. The main aims of this survey were identification and distribution local infectious of epizootic diseases, identification positive and negative points, offers management applicable guidelines to prevent of diseases.The results of survey showed that important virologically agent identified was Lymphocystis virus in Angel fish. Also, main bacteriologically agents were Aeromonas spp, Pseudomonas spp and vibrio. As well as, from the fungal agents that were identified can mentioned to Aspergilus flavus, Mucor, Penicilium and Alternaria. The important parasitic agents also were Trichodina, Ichthyophytrius, tetrahymena, Dactylogyrus, Gyrodactylus and capillaria. In the health management part of this survey positive points include non-application of antibiotic and cooperative of hatchery directors with executive organizations to sampling examination periodically. The negative points were non familiarity and training about fish disease, were not technical director, prepairing feeds without familiarity with principals of diets, non-quarantine units before fishes entrance to production cycles, non existens good food storage rooms, non existens foot bath in entrance gate to the hatchery systems and ets.

Study of survey health management and diseases in hatcheries and fish farms can help us to knowledge and application control methods such as: prevention, treatment and increase high levels of production in hatchery and farms, finally. This survey carried out from 2005 to 2008 for 4 years in sturgeon hatcheries and farms of Golestan province. Sturgeon fishes include Huso Huso, Ship sturgeon, Acipenser persicus collected and for virology, bacteriology, fungius and hematology examined. Also, physicochemical parameters measured and recorded in different stages of culture. Results of this study showed that all of samples in virology was negative and did not observe any doubetful causes. In bacteriology CFU was variation from 3/9 ×105 to 6/9×10. The most parasites that detected in this survey was Cocolanus espherolanus, Sceria binopsulus semiarmatus and Amphilina fuliacea that separates from Acipenser Percicus, especially. The results about hematology parameters some important hematological indices of ship sturgeon include: The total RBC for female and mail specimens measured as 5.3±1.5 ×10^5, 4.8±0.5×10^5 per mm^3 respectively. The amount of haematocrit and hemoglobin for female and mail determined: 34.3±2.8, 35±1.4 percent and 10.3±0.9, 8.9±0.8 gr/dl .The MCV: 216.3± 96.2, 736.5± 102.5, MCH: 720.2±309.5, 186±0.7 and MCHC: 30±0.8, 25.5±3.4 percent respectively.The total WBC were (female, male): 21320±1054, 20580±777 per mm^3 and neutrophil: 16.4±2.5, 17±1.4 percent and lymphocyte: 74.4±2.4, 73.5± 0.7 percent and eosinophil: 6±1.4, 6.4±0.5 percent, monocyte: 2.8±0.8, 3.5±0.7 percent. There was not any significant differences (p>0.05) between mentioned parameters in male and female (students t-test). Also evaluation of hematological parameters in bluga ( Huso huso) include: total RBC were (male , female) 5±0.3 ×105 , 4.9±0.6 ×105 per mm^3 ,respectively and hematocrit: 33.2±6.7 , 35.4±3.4 percent and hemoglobin: 11.2±1.5 , 12.2±1gr/dl and MCV: 669.9±172.2, 723.9±982.4 and MCH: 226.2±42.5, 249.5±35.4 and MCHC: 34.1±2.4, 34.6±3.6 percent respectively. The totals WBC were (male, female): 24800±707.1, 23042±1375.4 per mm^3 and neutrophil: 18.5±0.7, 21.4±1.1 percent and lymphocyte: 73.5±1.4, 68.4±1.1 percent and eosinophil: 5±2.8, 7±1.2 percent and monocyte: 3.5±3.5, 3.2±0.8 percent. According to statistically study the count of lymphocyte had significant difference between male and female fish and this count in male was higher than female. (p≥0.05).

The present study was conducted on 428 moribund mullet fish samples to isolate and identify the causative agent of a mysterious acute mortality which recently occurred in wild mullets in Iranian waters of Caspian Sea, suspected to be due to viral nervous necrosis (VNN) disease. Disease investigation was carried out employing various diagnostic procedures such as virology, bacteriology, parasitology, haematology, histopathology, IFAT, IHC and nested RT-PCR. Brain and eye samples of affected fishes were collected in sterile conditions and then kept at -80 °C for cell culture isolation and nested RT-PCR detection of the causative agent. Other tissue samples were also collected and fixed for histopathology, IHC and EM examinations. CPE was observed in cell cultures at 6 days after inoculation. Nine samples were found positive with virological assay. Nested RT-PCR, performed on suspected tissues and CPE positive samples, showed that about 21 tissue samples and all the CPE positive samples were positive for VNN virus (VNNV). IFAT was selected as a confirmatory method for detecting the presence of Betanodavirus antigen, cell culture isolation results and nested RT-PCR findings. Moreover, VNNV particles with 25-30 nm in diameter were also visualized in the infected brain and retina. In pathogenicity studies, guppy fishes bathed in VNNV-infected tissue culture (10-4 TCID50) showed clinical signs similar to naturally infected mullet after 15 days post infection (dpi), with mortality rates reaching up to 100% at 30 dpi. Affected organ samples as examined by cell culture isolation, IFAT, IHC and histopathology, revealed the presence of VNNV in the guppy fishes. In conclusion, it was confirmed that VNNV was the main causative agent for the disease outbreak in mullet fish in the Caspian Sea, and this is such first official report of VNN disease from Iran.