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In the present paper the detailed biometric characteristics of walleye pollock (involving 25 metric and 12 meristic features) is demonstrated, with regard to both sexes. In addition, the comparison is made between the population studied and population of walleye pollock from the Bering Sea (concerning data available in literature) in order to find out if any differences statistically significant exist.
The influence of age, length and migration pattern of saithe Pollachius virens in relation to infection with external parasites has been studied in three different areas on the west coast of Sweden. A total of six species of parasites were found. The degree of infection was closely connected to the body length and the migration pattern of the saithe. A high degree of infection with Diclidophora denticulata, Caligus elongatus, Lepeophtheirus pollachius, and Clavella adunca was found at the two deeper stations (76 and 71% resp.) while the fish at shallow stations inside the Gullmar Fiord exhibited very few cases of parasites.
A rapid PCR-RFLP analysis was optimized to identify the presence of 3 closely related gadoid fish species: Alaska pollack Theragra chalcogramma, Pacific cod Gadus macrocephalus and Atlantic cod Gadus morhua in commercial seafood products. Gadoid universal primers were designed for PCR amplification of a 558-bp fragment encoding the mitochondrial cytochrome b gene. Without purification of the PCR products, double digestion with Eco32l and Eco1051 restriction enzymes generated reproducible species-specific restriction patterns visualizing 3 fragments (106 bp, 161 bp and 291 bp) in Alaska pollack and 2 fragments (106 bp and 452 bp) in Pacific cod, whereas no cleavage was observed in Atlantic cod. This PCR-RFLP analysis is simple, rapid and reliable, and therefore can be routinely applied to discover fraudulent substitution among 3 economically important gadoid species in commercial seafood products.
Background. The hitherto published records of the parasite fauna of Baltic cod, Gadus morhua callarias cover commercially-caught adult fish. The aim of this study was to determine the composition of the parasite fauna of young Baltic cod, the relevant infection parameters and to relate those data to published records on the diet of cod. Materials and Methods. This survey was carried out on 154 young cod, caught in May and June 2002 in the Gulf of Puck, the Baltic Sea, Poland. The fish were examined using standard methods applied in parasitology. Results. No external parasites were found. In the digestive tracts of 58 cod, 3 species of parasites belonging to 2 higher taxa (Nematoda and Acanthocephala) were found. The dominant parasite was Echinorhynchus gadi Zoega in Müller, 1776. The mean abundance ranged from 0.15 to 2.75. The prevalence ranged from 14.6%, in the smallest fish, to 66.7% in the larger ones. Only two acanthocephalan specimens of Pomphorhynchus laevis (Zoega in Müller, 1776) and five nematode larvae of Hysterothylacium aduncum (Rudolphi, 1802) were found. Conclusion. The parasite fauna of young Baltic cod is significantly sparser than in larger fish examined by other authors. It is suggested that the occurrence of the species found, can be related to the composition of diet available.
Background. Tadpole codling, Salilota australis (Günther, 1878), (known also as red cod) and southern blue whiting, Micromesistius australis Norman, 1937, are two commercially important species, which spawning grounds are situated in the Falkland waters. Nothing is known about duration of the embryonic development in these fish, whereas these data are necessary to study life cycle strategies as well as for stock management. Because of this, experiments with artificial egg fertilisation were carried out onboard a research boat that was the only way to obtain such an information. Materials and Methods. Eggs from each species were taken from running females captured on their spawning grounds and then fertilised. Egg samples were collected every 6 hours and stage of embryonic development was assigned using a dissecting microscope. Results. Tadpole codling eggs are of 1.20–1.55 mm, with an oil globule of 0.29–0.33 mm, incubation takes between 140–150 h at 6–8.5ºC, 40–45 degree-days. Larval size at hatching is ca 2.9 mm TL. Blue whiting eggs are of 1.40–1.55 mm with no oil globule. Development takes from 150 h at a mean temperature of 7.15ºC to 200 h at between 5.5 and 6ºC, 45–50 degree-days. Larval size at hatching is 2.8–3.0 mm. Conclusion. Duration of embryonic development for commercial southwest Atlantic gadiform fish, tadpole codling, Salilota australis, and southern blue whiting, Micromesistius australis, is documented for the first time. It allows to draw some conclusions about possible mortality during this ontogenetic stage (assuming that daily rates are similar to those in other similar species) and to hypothesise about possible egg transport by currents and interannual spawning grounds’ variability.
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