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Lipid content and fatty acids composition of non-predatory fish: roach, Rutilus rutilus (L.), bream, Abramis brama (L.), vendace, Coregonus albula (L.), and of predatory fish: Eurasian perch, Perca fluviatilis L., pike, Esox lucius L. and burbot, Lota lota (L.) were examined. These fish were caught from three lakes of Mazurian Great Lakes (Kisajno, Dargin, Niegocin). The content of total lipid and some fatty acids varied widely within and among species. Generally, the lipid content was low (0.56-2.78%). Among the saturated and monounsaturated fatty acids, the predominant fatty acids were palmitic C16:0 (19.24-33.44%), stearic C18:0 (4.37-6.87%), palmitoleic C16:1 (4.51-12.93%), and oleic C18:1 n-9 (6.85-14.49%). Arachidonic C20:4 n-6 (3.17-6.55%), eicosapentaenoic C20:5 n-3 (4.14-8.91%), and docosahexaenoic C22:6 n-3 (5.91-24.67%) acids were the most abundant polyunsaturated fatty acids. In the case of all the freshwater fish, with the exception of bream, higher contents of saturated fatty acids than monounsaturated fatty acids were noted. Among the fish studied, the highest value of total n-3 polyunsaturated fatty acids (43.86%) was noted in vendace, whereas bream contained the highest content of total n-6 polyunsaturated fatty acids (11.21%). The ratio of n-3/n-6 ranged between 1.50 (burbot) and 4.40 (vendace). Differences in the content of fatty acids in fish with different feeding strategies (non-predatory and predatory) were measured. Non-predatory fish were found to have lower values of saturated fatty acids than predatory fish (P mniejsze równe 0.05). Non-predatory fish contained significantly more eicosapentaenoic acid (EPA) than predatory fish (P mniejsze równe 0.01), whereas the amounts of monounsaturated and n-3 and n-6 polyunsaturated fatty acids in non-predatory and predatory fish were not statistically significant (P > 0.05). The total n-3 polyunsaturated fatty acids was higher in non-predatory fish, but not statistically significant (P > 0.05). Similarly, the differences in DHA and n-3/n-6 ratio in muscles of predatory and non-predatory fish were not statistically significant (P > 0.05).
In this study, the total mercury concentration was determined in the muscles, liver and gills of six fish species (rainbow trout Oncorhynchus mykiss Walb., carp Cyprinus carpio L., bream Abramis brama L., perch Perca fluviatilis L., ide Leuciscus idus L. and flounder Platichthys flesus L.). The fish were acquired from October to November 2012. Mercury was analyzed by atomic absorption spectrometry using thermal decomposition, compounds of mercury and amalgamation. The mercury content in fish organs reached 0.006-0.168 (in mg kgˉ¹ wet weight) in muscles, 0.001-0.027 in gills and 0.003-0.045 in the liver. The muscles of perch and ide had significantly more Hg compared to the other fish’s muscles (P≤0.05). The liver and gills of perch, ide and flounder contained more Hg than the same tissues of the other fish (P≤0.05). Generally, the highest Hg content was determined in muscles (except rainbow trout) (P≤0.05), whereas the lowest Hg content was found in gills (except perch) (P≤0.05). The content of Hg in gills of perch did not differ from the one in the liver (P>0.05). There was a positive correlation between the weight or length of a fish and the Hg concentration in its tissues, except for the length and Hg in the gills of carp. However, a statistically significant positive correlation between the body weight and the Hg levels in fish appeared only in the case of the organs of ide (P≤0.004) and muscles of carp (P≤0.038). The correlation between the factor condition and the content of Hg, albeit positive (0.106 < r < 0.811) except for the organs of flounder, was not statistically significant (P>0.05).
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