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This article comprises the first presentation of data regarding the growth and distribution of juvenile Atlantic sturgeon, Acipenser oxyrinchus Mitchill, released into the Drwęca River (Vistula drainage basin). In the 2007-2009 period, 2097 sturgeon tagged with Carlin tags were released into the Drwęca River. Information obtained from recapture referred to just under 2.3% of all the fish released. The sturgeon were caught most frequently in the Gdańsk Bay and in the Vistula estuary from March to December, with two periods of more intense catch noted in July and October. The time elapsed between release and capture ranged from 28 to 352 days and depended on the size of the fish at release. The absolute growth of juvenile sturgeon increased throughout the period they spent in open waters; however, this period had no impact on the body length daily growth rate.
Background. Sturgeons have long been extinct in Polish inland waters. A substantial effort has recently been put into their restitution, covering the drainage areas of two major Polish rivers, the Oder and the Vistula. The stocked fishes are clinically healthy, but very little is known about their potential to transmit viral diseases including koi herpes virus (KHV) to healthy fishes of other species, which may pose a threat to the disease-free zones. This study was intended to determine if sturgeons could be asymptomatic carriers of KHV. Materials and Methods. A total of 29 sturgeons (two species; length 8–37 cm) originating from fish farms in northern Poland with a known KHV history in common carp or koi in the area were examined: 15 Russian sturgeons, Acipenser gueldenstaedtii, with clinical signs of a disease and 14 asymptomatic Atlantic sturgeons, A. oxyrinchus. The former were sent to the laboratory alive while the latter were sent fixed in ethanol. As it is required for detection of a latent KHV infection in acipenserids, two independent procedures were applied. The preliminary results were obtained using PCR. Those findings were subsequently confirmation by nested PCR. The latter procedure consists of sequence analysis of PCR products and direct detection of KHV infected cells in tissue materials by in-situ hybridization on nucleic acid level or indirect immunofluorescence on KHV protein level. Results. KHV genome parts were found in nine Russian sturgeons and four Atlantic sturgeons. Comparison of PCR results obtained from three primer pairs used for KHV diagnostic in sturgeon showed that those designed by Bercovier et al. were most sensitive and robust for this purpose. In order to confirm the presence of viral particles the most useful method was in-situ hybridization (ISH), allowing the detection of KHV in gill samples obtained from live sturgeons. Conclusion. This preliminary study shows that sturgeons can be carriers of KHV. Therefore a viral diagnostics is highly recommended not only for sturgeons obtained from the environment but also for fertilized eggs, fry, and fish intended for re-stocking measurements of inland waters.
The movements of individual juvenile sturgeon, Acipenser oxyrinchus Mitchill, during their first stage of downstream migration were observed in the Drawa River, Poland. Two groups of 10 sturgeon each (9 months old, reared in closed recirculation systems) were tagged with internal radio-transmitters. The first group of sturgeon (119-184 g) were tagged with Holohill BD-2N transmitters (weight 0.43 g, operational life 14d) and released on May 7. Fish from the second group (143-206 g) were tagged with BD-2 (weight 1.2 g, operational life 56d) and were released on May 24. The releases took place in the Drawa River below Kamienna Dam, 33 km upstream from the river’s confluence with the Noteć River. All of the fish moved downstream, but migration speeds differed. Seven sturgeon from the first group reached the confluence with the Noteć River, approximately 30 km downstream from the release site, during the first 18 days, which indicated there had been staging intervals in pools. Within four days, six fish from the second group had moved downstream the Drawa River and were located 20 km downstream from the confluence with the Noteć River. The downstream migration speed of the fish correlated with fish size and increased with water temperature.
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