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

[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

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