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Vliv teplotních a hyperoxických podmínek na růst, příjem krmiva a fyziologii hybrida sivena arktického (Salvelinus alpinus Linnaeus, 1758) a sivena amerického (Salvelinus fontinalis Mitchill, 1815)
ČEJKA, Jakub
This diploma thesis should have tested growth abilities during different temperature and oxygen regime in hybrid between brook trout (Salvelinus fontinalis) and arctic charr (Salvelinus alpinus) culture. There were survival, growth, feed conversion, weight heterogeneity of fish and somatic indexes as followed indicators. The hypothesis was discovery of differences in growth and mentioned indicators during rearing in water with different temperature and oxygen regime. This thesis consists of two done experiments. There were tested five temperature regimes (7, 10, 13, 16 and 19 °C) in the first experiment. Each of tested groups was repeated four times. The experiment took place 84 days and biometric data were measured always after 21 days period. Results showed that the highest weight growth was achieved in fish reared at 13 °C as specific growth rate achieved 4,12 ? 0,21 % × day-1. Higher temperature regimes (16, 19 °C) are not suitable for rearing of Salvelinus hybrid. Survival of tested group reared at 19 °C were only 41,4 ? 27,3 % after the end of the first experiment. At lower temperatures efficient feed conversion were not managed and specific growth rate were lower than at mentioned temperature 13 °C. There were four tested groups permanent hyperoxia (120 130 %), hyperoxia only during a light part of a day, oscillating hyperoxia/normoxia and permanent normoxia (85 95 %) in the second experiment. Each of tested groups was repeated three times. The experiment took place 63 days and biometric data were measured always after 21 days. There were no difference in survival among tested groups and after the end of the second experiment survival was 86,0 ? 1,4 %. The highest specific growth rate were achieved at the normoxia group 1,48 ? 0,05 % × day-1 and at the group where fish were reared under hyperoxia only during a light part of a day - 1,38 ? 0,10 % × day-1. The most efficient feed conversion was mentioned at the fish reared in permanent normoxia and permanent hyperoxia.
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Reciprocal predation between non-native crayfish and salmonids Who eats whom?
MÜLLEROVÁ, Lucie
Signal crayfish (Pacifastacus leniusculus) is important invasive species in European freshwaters. Its influence on other freshwater organisms is well known from the literature, as well as direct and indirect impact on fish assemblages. This work was focused on the experimental evaluation of non-indigenous signal crayfish as a predator of salmonids compared to indigenous noble crayfish (Astacus astacus). Moreover, the possible importance of young-of-the-year signal crayfish as a prey for salmonids was assessed. There were carried out experiments using eggs and hatchings of grayling (Thymallus thymallus) as a prey for adult and subadult specimens of both, signal and noble crayfish. Next experiment used young-of-the-year signal crayfish as a prey for young-of-the-year of brown trout (Salmo trutta). Results showed that the danger of signal crayfish for grayling eggs is slightly higher. However, detected differences were surprisingly lower and in the majority of parameters even insignificant. In the case of grayling hatchings, was not detected any significant difference at all. The abilities of both tested species to prey on eggs and hatchings are therefore very similar, comparable. Even so, the effect of signal crayfish can be importantly higher in natural conditions because of its more dense populations, higher growth rate and fast maturation. In accordance to our findings, it is evident that brown trout has no so high effect of crayfish juveniles compared with crayfish effect on salmonids early developmental stages. Crayfish are therefore more likely able to limit salmonids than conversely.
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