Biofloc system is a new technology that used in intensive and semi intensive systems. The main advantages of this system is the reduction of water consumption, along with increasing the intensity of production based on heterotrophic bacteria instead of any biofilter system . This experiment was conducted for 90 day and with 420 common carp at an initial average body weight of 40 ±5.9 gr. The fish were divided into four groups in three replicates, Groups 1 to 3 were cultured with a Biofloc system with a carbon-to-N ratio (C:N) of 15, 20 and 25, respectively. The fourth group was reared in normal culture situation as a control. Water quality parameters, fish growth and survival rates, digestive enzymes activity, fish welfare indices, histological structure's of some organs, oxidative stress condition, blood parameters, carcass quality of fish were compared between among the groups. Furtheremore, analysis of biofloc biochemical compounds, microorganisms flora and resistance of fish against bacterial infection were compared among the groups.
The results showed that most of water quality parameters in biofloc treatments improved compared to control treatment. Most of the growth indices were significantly improved in the all sampling points (day 30, day 60 and day 90) in biofloc groups compared to control (P < 0.05).
On the other hand, there was a significant increase in the number of microorganisms in the water and intestines of fish in biofloc groups compared to the control (P < 0.05). The biochemical analysis of floc produced in the system showed a high protein ratio. The results of biochemical analysis of carcass showed that carcass protein increased significantly in biofloc groups compared to control. Comparison of blood parameters showed that most blood indices in biofloc groups were significantly improved in comparison with the control group. In histological studies, no significant damage was observed in the vital tissues examined including gills, liver and skin. The results of current research showed that most of the antioxidant defense indices were not affected in biofolc groups (p>0.05). The biochemical factors of stress-related serum including total protein, albumin, glucose, cortisol and cholesterol of biofloc groups in most of the sampling points were better than control group. In the present study, biofloc groups have shown the best performance in immune-related tests, so that treatment with the highest carbon ratio showed the best immune response among other groups and control.
The highest survival rate after Aeromonas hydrophila bacterial challenge were seen in biofloc treatments with the ratio of carbon to nitrogen 25 and the highest mortality were in the control group.
Therefore, it can be concluded that biofolc technology can be used in intsentsive culture of common carp and in addition to improving fish growth in the system, the immunity and welfare indexes of fish are also improved in comparison to intensive culture system without Biofolc technology.

The consumption of probiotics in aquaculture is constantly growing due to the numerous benefits conferred on the fish health. Degradation of probiotics in gasterointestinal tract is one of the most important challenges in probiotic efficacy. Encapsulating of probiotics within a physical barrier has been found to increase probiotic viability in fish gastrointestinal tract. In this study the effect of encapsulation of Lactobacillus bulgaricus with alginate/chitosan nano particles in in vitro situation and their effects in Huso huso were evaluated. Firstly in vitro probiotic potential including: pH and bile resistance, gastrointestinal juice tolerance was evaluated. Then effects of encapsulated probiotic were evaluated in Huso huso. 600 juvenile H.huso were randomly divided into five treatments in triplicates. Fish in T1 were fed with alginate/chitosan enriched free probiotic diet, T2 received encapsulated probiotic via emulsification, T3 received encapsulated probiotic via Ionic gelation, T4 received bacteria without any encapsulation and T5 received basic diet as a control group. All treatments fed with experimental diets for 60 days and study lasted for 15 days with control diet in all fish. Fish Samples were taken on days 30, 60 and 75 and growth performance indices including SGR, RGR, FCR, PER, DWG and CF were compared among the treatments. Immunological parameters including: serum lysozyme and bactericidal activity, complement activity, total protein and globulin were compared among the treatments. Total bacterial count and acid lactic bacterial count of Intestinal content were measured in all groups. Results of first phase of study showed that mostly all probiotic properties of encapsulated bacteria were more appropriate than control treatment (P<0.05). The lowest FCR (1.14±0.06) and highest SGR, PER and FER were seen in T4 which were significantly different from control treatment. Encapsulation of bacteria in both procedure enhanced almost all immunological parameters compare to control treatment (P<0.05). Then it can be concluded that nano encapsulation of lactobacillus bulgaricus with alginate/chitosan not only improved invitro probiotic effects of L.bulgaricus, but also it can increase growth performance incides and immunological parameters of H. huso.

 Infections caused by Aeromonas hydrophila in aquaculture systems are treated with difficulty due to resistance of this pathogen to most current antibiotics, necessitating an alternative approach. Given the immunostimulating, growth-promoting, and antimicrobial properties of phytochemical compounds, they are considered appropriate alternatives for antibiotics and chemicals in this system.
Research carried out in this field in recent years tended towards seeking natural compounds with inhibitory effects on bacterial virulence factors. In this regard, the present study investigated the effects of paracoumaric acid(p-Coumaric acid), as a valuable secondary metabolite in medicinal plants with antibacterial effects, and salt content in the growth medium on the expression of ascV and aopB genes, as essential components of the type III secretion system in A. hydrophila. Among 20 bacterial isolates obtained from isolated in this study from suspected fishes to Aeromonas septicemia, 13 isolates were molecularly confirmed. The minimum inhibitory concentration (MIC) of p-Coumaric acid against these isolates was then determined by disk diffusion and broth microdilution methods. According to the results, the MIC and MBC values of p-Coumaric acid against the tested isolates were 2 and 2.17 mg/mL, respectively, and in 1.8 and 2 mg concentrations of p-Coumaric acid, the mean diameter of inhibition zone was 17 and 20.8 mm, respectively. Quantitative realtime PCR was then performed to investigate the effect of sub-MIC concentrations of p-Coumaric acid on the expression of TTSS genes. For this purpose, the bacteria was cultured in the presence of 1 and 1.8 mg/ml concentrations of p-Coumaric acid and the gene expression levels was assessed at 6, 12, and 24 hours after exposure using the comparative Ct method. In the in vivo phase of the study, 135 number of fish with an average weight of 30±4.53, divided to the 3 groups (treatments) with 3 replicates. Each replicate contain 15 fish. Groups 1 to 3, were fed with commercial diet, diet supplemented with p-Coumaric acid (at a final concentration equal to five times the MIC) , and oxytetracycline(100 mg/kg BW), respectively. On the fifth day of the experiment, three groups were challenged with Aeromonas hydrophila. The mortality of fish in each group was recorded for ten days, and samples of kidney and liver were taken from moribund fish and live fish and examined in terms of the presence of A. hydrophila and changes in expression of ascV and aopB genes. The results of in vitro gene expression indicated the ability of the p-Coumaric acid in reduction of the tested genes expression, so that the lowest level of gene expression in 1 and 1.8 mg/mL p-Coumaric acid treatments was observed at 12 hours after exposure (p<0.05), and regardless of the time, no significant difference was found between the concentrations applied in the majority of sampling steps. On the other hand, increasing the salt concentration to 0.19 and 0.35 M Nacl increased expression of the genes . Oral administration of p-Coumaric acid to fish led to a significant reduction in bacterial gene expression in moribund and live fishes in the p-Coumaric acid treatment compared with the controls, (p<0.05); however, no significant difference was found between the two groups in terms of mortality rate after the challenge. In general, it can be concluded that p-Coumaric acid, an effective part of most medicinal plant, has an inhibitory effect on the virulence of A. hydrophila and can be used in future studies to attenuate virulence in this bacteria.

Aquaculture has been expanded rapidly to become a major commercial and food-producing sector worldwide in recent decade. In parallel, viral diseases rapidly spread among farms causing enormous economic losses. The accurate detection of pathogens at early stages of infection is a key point for disease control in aquaculture. Spring Viraemia of Carp Virus (SVCV) is a very severe pathogen of carp fishes in different parts of the world and is categorized as a reportable listed disease in the annual published list of World Organization for animal Health (OIE). The objective of this study was to develop and evaluate RT- PCR test for detecting SVC virus and also the sensitivity and specificity of this test. A semi nested RT- PCR was designed using combination of three primers: two external (SVCF , SVCR) and one internal (SVCS) primers which based on conserved region of G gen. The specificity of designed primers (only external ones) by examination on Viral Hemorrhagic Septicemia Virus (VHSV) and Infectious Hematopoietic Necrosis Virus (IHNV) was confirmed. For optimizing of the PCR test, primer concentration, primer annealing temperature, cycle number and Mgcl2 concentration were surveyed. Also for validity test, prevention of false negative and Assurance of its accuracy, a competitive internal control (mimic) designed and its suitable concentration was defined. Evaluation of the sensitivity of designed test were conducted first by comparing the different commercially available RNA isolation guidelines, two guidelines: isotiocyanate phenol – chloroform based protocols (RNX – Plus Iran, Iq2000 kit Taiwan ) and two column based protocols (Cinna pure RNA Iran , high pure viral RNA kit, Roche Germany ). The results indicated that the column based protocols (Roche method and Cinna pure), yield 36.77 ng/µl and 16/47 ng/µl RNA concentration respectively, which were significantly higher than other protocols(P<0.05). Then for evaluation of extracted RNA sensitivity, Serial dilution of SVCV strain 56.70 grown in EPC (1.9×105 TCID50/ml) was examined To compare sensitivity. Extracted RNA from serial dilution with stone's primers and commercial IQ-2000 kit were examined simultaneously. The result indicated that designed semi- nested RT- PCR was able to recognize SVC virus to 10-4 dilution and stone's primer recognize to 10-3 dilution whereas Iq-2000 commercial kit didnot recognized in any dilution. In high virus titer in designed test two DNA band (462 bp and 266 bp) produced, And by decreasing virus titer 462 bp was omitted.In low virus titer or lack of virus, just DNA band (mimic) 729 bp can propagate. After designing and optimizing PCR test, a total of 400 suspected cultured Cyprinus carpio with high mortality from 4 aquaculture zone of Khuzestan province were collected and tested for SVCV during 2012- 2013 using developed PCR method and IQ- 2000. The results indicated that SVC virus was not observed in samples using both methods.