Ograniczanie wyników

Czasopisma help
Autorzy help
Lata help
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 29

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  hatching
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
Background. Hatching is a process in which the embryo emerges from the egg by breaking the protective egg shell. Our preliminary observations indicate that hatching duration and time-distribution may vary among and within the fish species, and that some embryos fail to hatch or hatch incompletely, probably due to the “incorrect” hatching way. So the aim of this study was a detailed description of hatching of three fish species: common carp, barbel, and rainbow trout. Materials and methods. Three species of fish: common carp, Cyprinus carpio; barbel, Barbus barbus; and rainbow trout, Oncorhynchus mykiss; were examined for their hatching modes. The mode and the time of hatching of each larva were noted. Newly hatched larvae were counted and examined. The malformations were classified. Observations of embryos and larvae were done using the stereoscopic microscope Nikon connected to the computer with the MultiScan 8.4 image analysis system; the hatching embryos and larvae were photographed. Results. Three modes of hatching were observed, two of them similar in all three fish species. Some fish started hatching tail first from the egg shell, others head first or—specifically for barbel—yolk sac first. The data obtained in the present study showed that tail hatching was the most successful in all fish species, and shown by most good quality larvae. The majority of tail-hatched larvae developed normally and were viable, and only some of them were deformed and showed slight morphological defects, mainly single vertebral malformations that in most cases were negligible. Head hatching was the precarious in carp, and in all fish species less common and successful comparing to the tail hatching. Conclusion. The hatching mode could be used as another good parameter for estimation of quality of eggs and larvae.
During laboratory studies on the reproductive biology of Vallonia pulchella and V. costata we observed an unusual behaviour in adults and juveniles of both species. The snails moved with their heads and radulae over the egg surface as if feeding. The examination of the egg shell revealed the presence of the fungus Arthrobotrys oligospora, which commonly occurs in the soil and has multiple lifestyles: it is known as a nematode pathogen, a saprophyte and a coloniser of plant roots. The extraordinary behaviour of Vallonia may be associated with the presence of mycelium on the egg surface. We hypothesise three possible explanations of egg grooming: (1) parental care, (2) trophic behaviour and (3) the infection can constitute a means of defence against nematodes, which are known to be predators of snails and slugs as well as their eggs. The removal of the fungus is not associated with overcrowding, but may be a selective advantage when combined with feeding.
In this study, fertilized mirror carp eggs were allowed to develop in fresh water with various magnesium concentrations (0.05, 0.2 and 2 mg l⁻¹). The percentage of dead (eggs+prelarvae) and deformed prelarvae increased sharply to 94% at an ambient magnesium concentration of 0.05 mg l⁻¹ compared with 22 and 10% at ambient magnesium concentrations of 0.2 mg l⁻¹ and 2.0 mg l⁻¹, respectively. Mirror carp require more than a 0.05 mg l⁻¹ ambient magnesium concentration for survival and successful development during the early life stage. The whole body magnesium and calcium concentrations of the developing prelarvae were dependent on the ambient magnesium concentration. The uptake of magnesium by animals decreased and the uptake of calcium increased with decreasing ambient magnesium concentrations. However, the uptake of the sum of these two divalent ions seemed to be independent of ambient magnesium concentration. This indicates that there is competition between magnesium and calcium for uptake into developing embryos.
In this study, nest characteristics (size and proportions of basic components) were not correlated with the timing of breeding. Clutch size was negatively correlated with total nest mass but positively correlated with the proportion of the mass of the lining in the total nest mass. Analyses of hatching and fledging success showed that the quantity and proportion of moss in the nest structure as well as the nest size influenced the performance of eggs and nestlings at the nest. We suggest that variation in nest size and composition may be due to several contradictory pressures associated with the need to keep the moisture and temperature in the nest relatively constant, to protect the brood from predation, and to control sanitary standards.
An account has been given of the egg variability, egg development, egg hatching and behaviour and anatomy of the oncomiracidia of three species of the genus Quadriacanthus, monogeneans parasitizing the gills of the catfish Clarias gariepinus inhabiting Nile Delta waters in Egypt. Each of the three species of the genus Quadriacanthus produces eggs of different shapes and sizes. Quadriacanthus clariadis clariadis and Q. allobychowskiella produce four types of eggs while Q. aegypticus produces nine types of eggs. All types of eggs differ from each other in the presence or absence, size and shape of the appendages. It is suggested that eggs of different types are not genetically determined or functionally different. There is no significant increase in the egg size during incubation. Fluid-filled sacs are found only in the fully developed eggs of Q. c. clariadis and Q. aegypticus; they are absent from eggs of Q. allobychowskiella. It is suggested that opening of the operculum and emergence of the oncomiracidium are brought about by a mechanical, chemical and/or osmotic hatching mechanism. The glandular system of the oncomiracidia of the genus Quadriacanthus includes two anterior median head glands, at least six lateral head glands constituting the anterior adhesive apparatus and four posterior body glands. Two crescent-shaped sclerites, representing the precursors of the ventral hamuli, are present in the haptor of the oncomiracidium of Q. allobychowskiella but these sclerites were not observed in the oncomiracidia of Q. c. clariadis and Q. aegypticus.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.