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The parasite fauna of autochthonous Cyprinus carpio and introduced Ctenopharyngodon idella, Hypophthalmichthys molitrix and Aristichthys nobilis, cultured together in fish ponds, was analyzed. In common carp four introduced parasites were found, while in introduced fishes 19 autochthonous parasite species occurred. The transfer of parasites between native and introduced fishes requires that the parasites have a rather wide circle of hosts. The autochthonous parasites which occurred in both autochthonous and introduced fishes were generally more frequent in introduced fishes, and vice versa. This fact can indicate a greater susceptibility of new hosts toward non specific parasites, and lack of balance in new host-parasite systems.
The effect of two types of modified atmosphere (MA1: 69% N2, 25% CO2, 5%O2, 1% CO; MA2: 70% N2, 30% CO2) on changes in physical and chemical parameters (pH, aw - water activity, TVBN - total volatile basic nitrogen, TMA - trimethylamine, FFA - free fatty acids, PV - peroxide value, TBA - thiobarbituric acid) in muscle tissues of the silver carp was monitored in the study. The samples were stored at temperatures +2 ± 2oC for 18 days. Changes in gas volumes (CO2 and O2) in MAs were also monitored. CO2 levels increased in MA1 but decreased in MA2. At the end of 18 days of storage, a significantly (P < 0.01) lower water activity (aw) levels were found in samples packaged under MA1, in contrast to samples packaged under MA2 where water activity values showed considerable fluctuation. Variations in pH values in the two types of MA showed similar trends. Sample pH gradually decreased until day 9 of storage. On day 11, muscle tissue pH increased markedly and then began to decrease again. The overall decrease in pH values was more profound in samples packaged under MA1. TVBN and TMA levels in samples packaged under the two types of MAs remained almost identical until day 9 of the experiment. Later, however, significantly (P < 0.01) higher levels of both parameters were found in muscle tissues packaged under MA1. FFA concentrations in silver carp samples in MA1 were significantly lower (P < 0.01) throughout the experiment. The PV increased significantly in both muscle samples tested. Greater fluctuations in this parameter’s values throughout the experiment were observed in samples packaged under MA2. Faster rates of oxidation (P < 0.01) were found in samples packaged under MA1 starting on day 9. Maximum TBA values in MA1 and MA2 were observed on days 14 and 18 of the experiment, respectively. From the course of proteolytic and oxidative changes point of view, the more appropriate combination of gases for silver carp storage seems to be the mixture of 70% N2 and 30% CO2 (MA2), which allows for muscle storage of up to 9 days. We recommend TVBN as a suitable indicator of freshness, and TBA assay as a suitable indicator of the extent of oxidative processes.
Migration behavior of carp (Cyprinus carpio L.), bream (Abramis brama L.), roach (Rutilus rutilus L.), nase (Chondrostoma nasus L.), barbel (Barbus barbus L.), ide (Leuciscus idus L.), and silver carp (Hypophthalmichthys molitrix L.) is presented. Fishes migrate in different periods of life. The main migrations are spawning migrations, feeding migrations, and wintering migrations. The distances covered by cyprinids differ, and range from several meters to many kilometers. Many species return to spawn in the same places each year, which is known as “homing” or “site fidelity”. Spawning grounds are chosen by fish near shore, where water is well oxygenated, warmer, and provides good food resources. Conditions in these waters are good for the development of fish eggs and then fish larvae.
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