To study the presence and spread of viral fish pathogens in Rainbow Trout Oncorhynchus mykiss in the eastern Black Sea region of Turkey, 172 pooled samples (seven fish per pool) of Rainbow Trout fry from 28 hatcheries were examined from December 2006 to July 2007. Forty-three pools (seven broodfish per pool) of seminal and ovarian fluids from 182 female and 119 male brood Rainbow Trout were also sampled during spawning. Moreover, reproductive fluids (22 pools) of wild trout (Salmo trutta labrax, S. t. caspius, S. t. abanticus, and S. t. macrostigma), captured by electroshocking in the rivers in and around the region, were sampled. Triplicate groups of 40 or 80 Rainbow Trout fry was also challenged with two similar isolates to determine their virulence on trout fry. Enzyme-linked immunosorbent assay was performed on the samples producing cytopathic effect on CHSE-214 cells. The positive results were confirmed with a reverse transcriptase polymerase chain reaction assay. Neither infectious hematopoietic necrosis virus (IHNV) nor viral hemorrhagic septicemia virus (VHSV) was detected during the survey. Of the 28 hatcheries sampled in the Black Sea region, 15 from six provinces tested positive for infectious pancreatic necrosis virus (IPNV) in trout fry. Unexpectedly, all reproductive fluids from both male and female cultured and wild broodstock tested negative for IPNV. Nucleotide sequences of the VP2/NS region of IPNV showed that all isolates collected (n = 38) in the region and surrounding areas belonged to the genogroup III. The findings strongly suggest that IPNV is endemic in the fry of farmed Rainbow Trout within the region. Virus prevention measures should be taken to prevent in-farm spread of these highly contagious, low-virulence isolates.
In this study, the age-dependent reproductive performance of 4 th generation of hatchery-origin Black Sea trout (Salmo labrax Pallas, 1814) females was determined with the aim of understanding breeding characteristics of ideal broodstock management plan for Black Sea trout. The 2 + , 3 + , 4 + and 5 + years old females (n=131, 104, 63 and 28, respectively) with weights ranging from 919.45±36.22g to 2439.21±139.28g were used. Reproductive rates of females (2 + , 3 + , 4 + and 5 + years old) were determined as 22.14%, 60.30% and 17.56% for 2 + , 17.47%, 72.82% and 9.71% for 3 + , and 19.05%, 68.25%, and 12.70% for 4 + years old in November, December and January, respectively. Fertilization rates were obtained 94.31%, 95.02%, 96.03% and 93.39%, respectively. The total fecundity was positively correlated with the age and weight (r=0.84) but negatively with the relative fecundity (r=-0.24). The difference between 2 + and 3 + age groups' total fecundities was insignificant, and the 4 + and 5 + age groups were different from all groups. In addition, there was no significant difference in fertilization rates among all age groups' rates but the 5 + age group had slightly lower value (P<0.05). For ideal broodstock management in Black Sea trout production, based on the results of this study, it is recommended to use 3 + and 4 + years old females with high breeding efficiency and remove 5 + years and older females from the broodstock.
This study assessed the effects of Hexamita salmonis (Moore) on metabolism of rainbow trout Oncorhynchus mykiss (Walbaum) and its effect on the host's susceptibility to infectious pancreatic necrosis virus (IPNV) after antiparasitic treatment. Rainbow trout naturally infected with H. salmonis were treated with 10 mg metronidazole kg fish(-1) per day, and their physiological recovery was assessed through measuring resting metabolism on the 7th, 14th, 21st and 28th day after treatment. In addition, we exposed the naïve fish to H. salmonis and measured the resting metabolism (oxygen consumption as mg O2 kg(-1) per hour) on the 10th, 20th and 30th day after the exposure to assess the variation in metabolic rates after infection. Significantly lower rates of metabolic activity (P < 0.05) were anticipated 20 days after infection with H. salmonis compared with the fish infected with H. salmonis for 10 days or with the parasite-free fish. Similarly, the treated fish needed about 20 days to fully recover from hexamitiasis. The susceptibility of rainbow trout to IPNV remained unchanged in the presence of H. salmonis. Weight loss was significantly higher (P < 0.05) in infected than that in the parasite-free fish. Fish should be examined regularly for H. salmonis and treated immediately whether found to prevent economic losses and excessive size variation.
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