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.
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