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Vliv teploty na oplozenost a líhnivost po krátkodobém skladování neoplozených jiker sumce velkého (Silurus glanis)
PŘIBYL, Tadeáš
The experiment validated the impact of storage of artificially spawned unfertilised eggs of European catfish on fertilization, hatching and the beginning of exogenous food intake throughout the transition from the embryonic to larval life period. The eggs from artificially spawned individuals have been used for this experiment using the induction of ovulation by the carp pituitary system. Sperm from each individual was collected by stripping using a hypodermic needle, that were partially filled with immobilising solution for sperm before artificial spawning of female individuals. Artificial stripping of fish was carried out under anaesthesia (by clove oil). Immediately after artificial hatching, samples of eggs (approximately 50 g) were put into six plastic bowls. Covered with wet cloth, bowls with eggs were placed into tempered, isolating thermo boxes with temperatures of 5, 10, 15, 20, 25 and 30 °C. Subsequently, in time intervals of 0,5, 1, 2, 3, 4, 6, 8 and 10 hours (after spawning) a small amount of eggs (approximately 50 pieces) was taken away from each temperature and put into glass beakers (with three repetitions), then the sperm was added and finally activated by adding water. In beakers with incubated non-sticking eggs and during the consequent storage of hatching embryos through temperature between 19,5-20 °C, water was changed two times a day. Approximately 4 hours after incubation, the exact number of used and fertilised eggs, was calculated. Unfertilised eggs (of white colour) and dead embryos were removed. Hatchery was assessed approximately 100 hours after fertilisation, when all living embryos had been hatched. After another 115 hours, throughout the transition from the embryonic to larval life development, live food (nauplia Artemia) was put into each bowl. Three hours after, individuals that began the food intake were calculated. The highest level of fertilisation was found in eggs stored between 0,5 and 2 hours (95,0?2,2 % - 100,0?0,0 %). The decrease in fertilisation is noticeable in all tested groups after 3 hours from stripping. Statistically significant decrease in fertilization was detected in eggs stored for 6 hours, the storage temperature did not affect the fertilization. Similar results have been maintained also in hatchery, where hatchery decreases as storage time increases. The highest level of hatchery was found in eggs stored in 25 °C (for 0,5 h 61,4?5,5 %), or more precisely 1 h 42,8?12,9 %). Hatching significantly decreases in all storage temperatures when storage time is longer than half an hour. The last parameter concerned how many percent of the individuals began the food intake. The highest level was recorded in eggs stored for half an hour (after spawning) in 25 °C (60,1?5,3 %), 30 °C (54,5?17,7 %) and 20 °C (39,0?12,7 %). On the contrary, storage temperatures 5 °C, 10 °C and 15 °C had results between 8,9?2,8 % and 35,0?18,8 %. Total mortality was detected when the storage time was more than 8 hours. It is necessary to fertilize the eggs as soon as possible (max. up to half an hour) after spawning, and to avoid storage of eggs at low temperatures (below 15 °C), to obtain viable individuals.
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