Hamdi Ogut

Seasonal dynamics of Trichodina spp. on whiting (Merlangius merlangus) in relation to organic pollution on the eastern Black Sea coast of Turkey

It was determined that there is a relationship between prevalence and mean densities of Trichodina spp. on Merlangius merlangus and organic pollution, measured as levels of nitrite, nitrate and phosphate in the surrounding environment. Monthly, two left anterior gill arcs of 60 M. merlangus (unless otherwise stated) captured with hook and line were fixed in 10% formalin. The number of Trichodina spp. was determined by counting all of the cells with a grid slide. The two right anterior gill arcs were used to prepare dry smears to picture the morphology of the trichodinids and to determine species composition. High levels of prevalence and densities of the protozoan were observed during the late fall, winter and early spring months. Then, prevalence decreased to lower levels but never below 60%, an indication of the important role of M. merlangus for Trichodina spp. in the studied region. A multivariate analysis revealed that the magnitude of prevalence was related to the level of all three parameters: nitrite, nitrate and phosphate (r2=0.59). However, a much stronger relationship between prevalence and nitrate, phosphate, oxygen and temperature (r2=0.89) was detected. Consequently, the seasonal parasite prevalence and density were affected by organic pollution. The timing for a high prevalence and mean densities of this parasite also suggests that primary production may be responsible for the observed seasonal variation in prevalence and mean densities. By using the model describing the relationship between the water quality parameters and the prevalence data of Trichodina spp. recalculated values and observed field data corresponded closely.

Effect of fasting on feed intake, growth and mortality of chinook salmon, Oncorhynchus tshawytscha, during an induced Aeromonas salmonicida epizootic

Anorexia is a common sign of bacterial and viral diseases and is thought to be a negative consequence of the disease process. However, this inappetence may be an active portion of the host defence system. We tested this idea by withdrawing food for 32 days from juvenile chinook salmon (Oncorhynchus tshawytscha) during an Aeromonas salmonicida epizootic, induced by cohabitation. Disease-specific mortality was low (5.0% and 12.5% in fed and fasted groups, respectively); there was no mortality in uninfected control fish. While only very few fish had detectable A. salmonicida in the kidney, at the termination of the experiment, an average of 18.5% and 65.0% of the fish in fed and fasted groups, respectively, had this bacterium in or on mucus, but these mean values were not statistically different because of high variation between replicates. Feed intake was measured by X-radiography at days 16 (fed groups) and 32 (all groups). Feed intake as well as growth were unaffected by exposure to bacteria. However, food consumption was greater when fasted fish exposed to A. salmonicida were offered a meal than in those infected individuals that had been eating. This result may be relevant for application of medicated diet, as it seems possible that fasting of sick fish before administration of medicated ration could increase the probability that sick individuals would also eat.

Prevalence of Furunculosis in Chinook Salmon Depends on Density of the Host Exposed by Cohabitation

Abstract Chinook salmon Oncorhynchus tshawytscha were experimentally infected with Aeromonas salmonicida to determine the dependence of initiation and spread of a furunculosis epizootic on host density. Groups of 30 and 60 recipient Chinook salmon (1.7 ± 0.14 g) were held in various volumes of water at a wide range of densities (15.52, 7.76, 1.23, 0.61, 0.32, 0.15, and 0.047 g fish/L) for 23–33 d, and each were exposed to a single infectious individual by cohabitation. Significant relationships (r 2 = 0.55) were found between host density (g fish/L) and survival from furunculosis. No pathogen transmission occurred at the lowest density. Acute and chronic patterns of furunculosis were obtained by adjusting densities. It took longer to observe disease-specific mortality among recipient fish at lower densities compared with higher densities even when donors were similarly infectious. The results have important implications for stocking salmonids regarding natural route of transmission and in understanding th...

Early Kinetics of Infectious Hematopoietic Necrosis Virus (IHNV) Infection in Rainbow Trout

Abstract A series of experiments was carried out with infectious hematopoietic necrosis virus (IHNV; 193-110 isolate) in rainbow trout Oncorhynchus mykiss (weight, ∼1.2 g) to determine the duration of the patent period and the timing of onset of the infectious periods. We first attempted to transmit IHNV to recipient fish from infected rainbow trout 2–3 d after they had been exposed. No infection transfer occurred despite high titers (104.79 to 104.91 plaque-forming units 5–8 d postexposure (dpe). To determine the number of secondary cases produced by one infectious individual, we exposed approximately 50 rainbow trout (weight, ∼1.5 g) in each of seven replicate tanks to a donor fish that had been infected with virus by bath exposure 3 d earlier. The prevalence of infection in recipient fish rose from 0.84% at 2 dpe to 7.9% at 6 dpe. Maximum incidence (22 cases) occurred between 2 and 4 dpe. No disease-specific mortalities occurred in recipient fish during the experiment. The titer of virus in both recipi...

Viral Surveillance of Cultured Rainbow Trout in the Eastern Black Sea, Turkey

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.

A comparison of ectoparasite prevalence and occurrence of viral haemorrhagic septicemia virus (VHSV) in whiting Merlangius merlangus euxinus

Seven hundred and eighty-four whiting ( Merlangius merlangus euxinus ) were individually sampled for virological and parasitological examination to assess th...

Monthly variation in the morphological characteristics of Trichodina sp. (Ciliophora: Peritrichida) found on whiting Merlangius merlangus euxinus

To determine the existence and extent of seasonal variation in morphological characteristics of Trichodina sp., sixty whiting Merlangius merlangus euxinus were sampled monthly for one year, from the Eastern Black Sea coast of Turkey, using a line and hook. Strong seasonal morphological variations were detected; the denticle span, blade length and ray length showed significant seasonal variation, especially in June. The timing of primary production in the Black Sea and the changes in cellular organelles suggested a negative relationship between the body diameter of trichodinids and food availability in the surrounding environment.

A survey of viral haemorrhagic septicaemia virus in cultured sea bass and its virulence on juveniles of sea bass, Dicentrarchus labrax (Actinopterygii: Perciformes: Moronidae) and gilthead sea bream, Sparus aurata (Sparidae)

Background. Turkey is one of the major European seed producers of European sea bass, Dicentrarchus labrax (Linnaeus, 1758), and gilthead sea bream Sparus aurata Linnaeus, 1758. Determination of susceptibility to viral haemorrhagic septicaemia (VHS), a notifiable disease in Europe, is crucial particularly for sea bass and sea bream seed production to develop control measures and to take necessary actions in case of a VHS outbreak. We hypothesized that VHS virus does not replicate at 16°C and above—the temperature range typical for hatcheries in the Aegean region . Materials and methods. To assess the seasonal occurrence and virulence of viral haemorrhagic septicaemia virus genogroup Ie (VHSV-Ie), a virological survey was conducted in cultured sea bass in the Black Sea. Thirty- five sea bass were sampled monthly from a local marine farm, and examined virologically. Triplicate groups of juvenile of sea bass ( n = 30 per replicate or n = 40 per replicate) and gilthead sea bream ( n = 20 per replicate) were challenged by immersion with VHSV-Ie at 12°C and 16°C to determine the occurrence of pathogen trans - fer and viral replication . Results. VHSV-Ie, or any other viral pathogen able to infect BF-2 and CHSE-214 cells, did not occur in cultured sea bass of the Turkish Black Sea region. It was impossible to infect sea bass at 16°C but moderate levels of mortality occurred at 12°C. Sea bream, however, were susceptible to VHSV-Ie, presenting low levels of mortality (15%) . Conclusion. VHSV-Ie poses no risk to the production of sea bass seed carried out at 16°C and above, but sea bass and sea bream should be monitored for VHSV-Ie where ambient water temperature is below 16°C since the risk of introduction is present .