BACKGROUND: Nowadays, the tendency to use food packaging with antimicrobial activity of natural origin has increased. The use of edible and biodegradable films has been considered as an appropriate alternative to non-degradable plastic coatings. OBJECTIVES: In this study, the effect of coating with wheat starch and Pennyroyal (Mentha pulegium essential oil was investigated on microbial and physicochemical characteristics of rainbow trout fillet in cold conditions. METHODS: For this purpose, different treatments under the influence of starch, starch and Pennyroyal essential oil (1%), starch and Pennyroyal essential oil (2%) were prepared and physicochemical and microbial changes were evaluated at specified intervals (0, 4, 8, 12 and 16 days). RESULTS: In the microbial test, the count of total bacterial and other bacteria by starch and starch + 1% and 2%, the essential oil was decreased in different days, also the difference between the control group and other treatments was significant (p < /em>≥0.05). The highest effect of pH reduction belonged to starch + 1% and 2% essential oil in different studied days. The level of pH was not different among different treatments on day 0 of storage. However, there was a significant difference between the control group and treatments on the fourth, eighth, twelfth, and sixteenth days of storage (p < /em>≥0.05). The results of the oxidative test showed that on the 16th day of storage, the lowest level of TBA was related to the treatment with starch + 2% essential oil and the highest value was related to the control group. In fact, the application of the coating layer delayed the oxidation process. CONCLUSIONS: This study demonstrated antioxidant and antibacterial properties of the composition of edible starch and pennyroyal essential oil on the increased shelf-life of Rainbow trout fillet.

BACKGROUND: Antimicrobial agents can alter physiological status and immunity system of the host, and use of hematological indices are the appropriate marker for monitoring them. OBJECTIVES: The present study intended assessment of changed hematological indices of rainbow trout challenged with streptococcosis/lactococcosis agents following oral administration of florfenicol. METHODS: The purchased fish (55±7.5 g) were examined through a randomized blocks design in the replicated 6 treatments consisting of without/with the infectious challenge of each pathogen separately and without/with medicated feeding in 15 mg/kg-1 BW for 10 consecutive days. Doses of Streptococcus iniae (2.87×107 CFU/ml) and Lactococcus garvieae (6.8×105 CFU/ml) equal to 30% of LD50 values were applied in the main experiment. At the end of trial, blood was sampled via caudal vein. Measurement of hematocrit and hemoglobin has been accomplished according to standard methods, and the number of blood cells was counted by hematocytometer. RESULTS: Findings pointed out PVC%, Hb value and RBCs count of groups that received the drug were reduced significantly than control (p < /em><0.05). 10-day administration of flornfeicol in the mentioned dosage could cut down lymphocytes statistically (p < /em><0.05). On the other hand, monocytes, neutrophils, and other blood cells were enhanced following administration of therapeutical dosage (p < /em><0.05). CONCLUSIONS: It seems that oral consumption of florfenicol could improve innate immunity, especially through enhancement of hematocytes. However, due to reduced frequency of blood lymphocytes, and as the problem of anemia in fish following drug consumption is still observed, it is recommended that in case of reduction of losses and improvement of clinical symptoms, the lowest FDA-suggested levels of the antibiotic for treatment should be used.

BACKGROUND: It is necessary to potentiate the immune system of fishes against stresses in farms. OBJECTIVES: This study was carried out to address the potential effect of Levamisole on immune system of rainbow trout against density stress. METHODS: 1500 fish (average weight of 50 g) were divided into 5 test groups, in which each test group was repeated three times with average density of 33 kg/m3. They were fed with commercial diet supplemented with Levamisole at concentrations of 0 (control), 100, 250, 500 and 1000 mg / kg for a period of 45 days. The fishes of all groups were then fed with Levamisole free diet and exposed to 2 and 3-fold density stress for the following 15 days. Blood samples were collected on days 0, 15, 30, 45 and 60 to evaluate the serum compliment and lysozyme activity as well as total immunoglobulins. RESULTS: The results showed that all used concentrations of Levamisole just had significant effect on compliment activity after 45 days feeding period (p<0.05). Higher levels of lysozyme and complement activity as well as total immunoglobulin were observed in 1000 mg/kg Levamisole treated group when exposed to density stresses 2 and 3-fold at the end of trial (day 60) (p<0.05). The highest overall survival was found in group which was treated with 1000 mg/kg of Levamisole. CONCLUSIONS: Our results revealed that using 0/1% Levamisole as an immunostimulator in commercial diet could potentiate rainbow trout against outbreak of high density stresses and increase its overall survival.

BACKGROUND: Yersinia ruckeri is the etiological agent of enteric red mouth (ERM) or yersinioisis disease, one of the important bacterial diseases in the cultured salmonids. OBJECTIVES: The purpose of present study was detection of gyrA gene (quinolone resistance) in the Y. ruckeri bacterium. METHODS: In this study fish were evaluated in average size 8-12 cm from six rainbow trout farms in Chahar Mahal va Bakhtiyari province (Iran). In each farm 10 fish (totally 60) suspected to yersinioisis were randomly selected; sampling was done from lower part of intestine and cultured on Trpticase Soy Agar (TSA). The mediums were transferred to incubator and kept at 22 °C for 48 hours. Pure colonies which are grown on the mediums were tested by catalase, oxidase and gram staining, then those of gram-negative, catalase positive and  oxidase negative were diagnosed, and cultured on Waltman- Shots medium (as specific medium for Y. ruckeri). These mediums were incubated at 22 °C for 48 h. Colonies that were grown were tested by PCR method for Y.ruckeri detection. Then, in the identified strains of Y.ruckeri gyrA gene were detected by PCR test. RESULTS: The results of bacteriological, biochemical and molecular tests showed that three cases out of total isolates were identified as Y. ruckeri. In all isolates of Y. ruckeri, gyrA gene was identified by molecular test. CONCLUSIONS: Identification of quinolone resistance gene in Y. ruckeri isolates can be the reason of low efficacy of these classes of antibiotics in the aquaculture. ِTherefore, the policy of treatment should be changed specially in enteric red mouth disease.

BACKGROUND: Today the use of natural substances plays a major role in improving the growth and immunity of aquatic organisms. OBJECTIVES: The purpose of the present study was to evaluate the effects of Iron nanoparticles with Lactobacillus casei as a probiotic on growth parameters and probiotic counts in rainbow trout intestine. METHODS: Seven hundred and twenty fish with 12±0.49 g initial weight were prepared and after acclimatized to the laboratory conditions divided randomly into six groups. First group was selected as control, other groups were fed with a commercial diet supplemented with 108 CFU/g Lactobacillus casei (group 2), 50 µg/kg Iron nanoparticles (group 3), 100 µg/kg Iron nanoparticles (group 4), 50 µg/kg Iron nanoparticles with 108 CFU/g Lactobacillus casei (group 5) and 100 µg/kg Iron nanoparticles with 108 CFU/g Lactobacillus casei (group 6), respectively. Biometry and intestine bacteriologic examination were carried out at days 0 and 60. RESULTS: Results showed that growth parameters (weight gain, body weight gain, specific growth rate, daily growth rate, and condition factor and food conversion rate) were significantly higher in group 5 compared with the other groups. Also, intestine bacterial counts increased by using Iron nanoparticles in combination with Lactobacillus casei. The fish that received 100 µg/kg Iron nanoparticles and probiotic had significantly higher bacterial counts in their intestine compared with the other groups. CONCLUSSIONS: Based on the obtained results we conclude that diet supplementation with Iron nanoparticles and Lactobacillus casei as a probiotic could significantly improve growth parameters in rainbow trout. However, these results would warrant further study on the clinical application of these agents.

BACKGROUND: Zeolites containing silver ion, in combination with synthetic fibers, show antibacterial activity. OBJECTIVES: The purpose of this study was to use silver zeolite indirectly as antimicrobial agents to control Streptococcus iniae infection which recently has caused disease in some of rainbow trout farms in Iran. METHODES: In this context polyurethane foams containing silver zeolite (10 and 20%) were used in water filtration of semi circulation culture system of rainbow trout fry. After addition of Streptococcus iniae (105 Cell/ml) to water in culture systems, the filters were evaluated for efficacy in inhibiting bacteria through measuring bacterial loading in water, monitoring disease symptom and culture of bacteria from kidney and spleen. RESULTS: The results indicated that filters containing silver compounds could significantly reduce load of bacteria from the water to 102 (p<0.05) compared to the control. Filter with 10% silver zeolite had higher efficiency among others. CONCLUSIONS: According to the results of this study, it seems that silver zeolite in combination with polyurethane foams has the sufficient potential to control bacterial infection and disease prevention in semi circulation system of Rainbow trout. Development of these filters and their application in control of aquatic animal diseases can result in reduction of using chemical drugs.