Study of efficacy of vaccination against yersinosis in rainbow trout using local strains of Yersinia ruckeri

Outbreak and development of yersiniosis in rainbow trout farms in Iran has caused a serious problem over the last years. The purpose of this study was to evaluate the efficacy of immersion vaccination with Yersinia ruckeri in rainbow trout. Prior to antigen preparation, the phenotypic, molecular and serological features of a number of Yersinia ruckeri isolates obtained from affected trout farms were studied. The virulent of these isolates were then evaluated using intra peritoneal injection route. Trout were vaccinated by immersion route [3 min at 12 °C] using Yersinia ruckeri bacterin of the virulent strains. The efficacy of vaccine antibody titer within 2, 4, 6, 8 and 10 weeks post vaccination were evaluated using relative percent survival. The phenotyping, serological and molecular studies have led to identification of 8 isolates of Yersinia ruckeri and all the isolates produced bands 409 bp, which is indicative of Yersinia ruckeri. In pathogenicity test 3 isolates caused above 50% mortality, while 5 isolates reached 16%. The RPS of vaccinated fish reached 72.7, 80, 80, 82.2 and 83.3% within 2, 4, 6, 8 and 10 weeks post vaccination, respectively. In the other words, the mortality level in vaccinated groups was in range of 10-20% within 10 weeks post vaccination, while those of control group was in range 56.7 - 73.3% [p<0.05] .The lowest and the highest antibody titers in immunized groups were 32 +/- 4.50 and 164.57 +/- 9.37 respectively, obtained after 4 and 10 weeks of immunization, whereas the control group had no measurable titer of antibody. The results of this study clearly show that this vaccine can remarkably protect the trout from yersiniosis outbreaks inside Iran

[Pathogenicity of Streptococcus iniae in Persian sturgeon [Acipenser persicus] fingerling]

Streptococcosis caused by Streptococcus iniae is one the most important bacterial diseases in aquaculture industry worldwide. This study was aimed to assess the experimental pathogenicity of Streptococcus iniae in Persian sturgeon [Acipenser persicus] fingerling. A number of 400 Persian sturgeon [Acipenser persicus] fingerling weighting 17 +/- 3 g were used. Fish were challenged with a virulent strain of Streptococcus iniae via both intraperitoneal and intramuscular injections at dosage of 4.7×106, 4.7×105, 4.7×104, 4.7×103, 4.7×102 cells/fish. Each treatment group included 12 fish in two replicates. Control fish received 0.1 mL per fish sterile normal saline [0.9% NaCl]. Clinically mortality started after 24 hours post-challenge and the affected fish showed listless, spiral swimming, spot haemorrhages on different parts of bodies particularly at the base of fins, the lateral line around the bone columns, on the base of barbells, mouth and around anal area. Also signs of abdominal distention, hyperemia of intestine, accumulation of bloody fluid in abdominal cavity, lordosis and scoliosis as well as hemorrhages in eyes were seen. The lethal concentration [LD50] of intraperitoneal injection was calculated 1.1×103, 8×103, 3.7×106 cells/fish after 48, 72 and 96 hours post-challenge, respectively. The LD50 of intramuscular injection was 4.8×102, 1.8×103 and 6.4×105 cells/fish at 48, 72 and 96 hours post-challenge, respectively [p<0.05]. No mortality or abnormal signs was seen in control fish up to 14 days post-experiment. The results of this study showed that Parisian sturgeon fingerling is highly susceptible to Streptococcosis

Red-pink colony-producing Pseudomonas sp. is the causative agent of mass mortality in larvae and post-larvae of Litopenaeus vannamei raised in hatcheries in south Iran

This study aimed to identify the causative of the mass mortality observed in zoeal to post-larval shrimp raised in hatcheries in south Iran. For three consecutive months, samples of nauplii and zoea of Litopenaeus vannamei were collected from an affected hatchery located in the province of Bushehr. Upon culture on marine agar, bacterial colonies that produced white, orange, yellow and red pigments were identified. In the hatcheries in which mass mortality was observed, the water columns of the affected tanks exhibited a red-pink color. Therefore, the bacteria that produced red pigment were selected for further phenotypic characterization using polymerase chain reaction [PCR] and virulence bioassays. Our results indicate that this bacterium belonged the genus Pseudomonas and that it was identical to P. mesophilica and/ anguilliseptica. PCR analysis of this bacterium revealed the production of a 150-bp band that was consistent with the Pseudomonas genus. To determine the pathogenicity of the isolated bacteria in nauplii and post-larvae of L vannamei, we performed bioassay experiments by bath immersion at 27-28°C. Our results showed that culture of nauplii and post-larvae of L. vannamei with the bacteria at a concentration of 1.5-2.0[x] 10[5] CFU/mL in marine broth resulted in a 100% mortality rate 24-48 h post-challenge. In contrast, there was no mortality in the nauplii and post-larvae that were cultured in the absence of bacteria. Upon pathological examination, we found that the color of the larvae was abnormal and pink, with acute necrosis of the entire body 48 h post-challenge

[Study on hematology and serum biochemistry of common carp [Cyprinus carpio] after low cadmium concentration exposure]

High concentration of heavy metals or long time exposure to low concentrations of these metals can usually decrease the hematological indices in fish. Therefore the aim of this study was to indicate changes in hematology and serum chemistry of common carp [cyprinus carpio] after low cadmium concentration exposure. 60 apparently healthy common carp [mean weight of 700g] divided in two groups and transfred to 1000 liter indoor fiberglass tanks under controlled conditions. Treatment group was exposed to low concentration of cadmium [30ppb]. Blood were exsanguinated randomly from 5 fish in each group through the caudal vein at days 15 and 30 of exposure. The hematological and biochemical parameters [WBC, RBC, different count, hematocrit, total protein, albumin and globulin concentrations, albumin: globulin ratio, LDH, ALT, and AST] were determined. Results revealed that WBC counts decreased significantly on the 15th day of exposure [p<0.05]. Furthermore, WBC counts decreased significantly on the 30th day of exposure [p<0.05]. The levels of LDH after day 30 of exposure, significantly increased in the test group compared to the control. In the test group, LDH levels significantly increased at the 30th day of exposure. No significant differences have been observed between control and test groups in respect to the other parameters. This study showed that the exposure time for sublethal concentration of cadmium is an important factor for increasing the LDH levels in common carp

[Evaluation of geranium herbarum escence application in control of fungal contamination in rainbow trout eggs]

Assessment of the capability of Geranium herbarum escence in control of fungal contamination rainbow trout eggs. Experimental study. About 16 kg eggs of 3-4 years old Oncorhynchus mykiss brooders [232464 eggs]. The effects of this escence [1,5,10,25,50 and 100ppm] was daily evaluated until the eyed egg stage [about 18-20 days]. The positive control was treated with 1 ppm malachite green and the negative one assessed without any drugs. Analysis of Variance and t-student by SPSS. Culturing of affected eggs showed a contamination of Saprolegnia parasitica and Fusarium solani was obsereved. MIC valuse of Geranium escence against Saprolegnia and Fusarium were 4.8 and 18.2 ppm respectively. The geranium escence specially at 25, 50 and 100 ppm had significant difference compare to negative control [p<0.05]