The following proofs of Goldfish more powerful reproductive potential are given: high individual and relative fecundity, adequate fractional spawning process resulting in numerous off spring, represented by different generations of hatchlings, little number of individuals not participating in reproduction, prevailing number of fish eggs in females’ ovaries, larger fraction of impregnated roe. All the above mentioned factors allow claiming that the Prussian carp is being replaced due to its low replacement ability. Perhaps for that reason Carassius gibelio (Bloch, 1782) choose small isolated water bodies, where it makes small populations, backed up by successful spawning with a single male of crucian carp, Carassius carassius (Linnaeus, 1758).
The subject of the study was two populations of signal crayfish, Pacifastacus leniusculus (Dana), from Lake Pobłędzie and the Naryjska Struga River. Individual female absolute fecundity was studied. The mean individual fecundity of females from Lake Pobłędzie was 361 eggs, while that of females from the Naryjska Struga River was 371 eggs. The average absolute fecundity of signal crayfish in Poland was higher than that of noble crayfish, similar to that of narrow-clawed crayfish, and lower than that of spiny-cheek crayfish.
Bithynia (Gastropoda: Prosobranchia Bithyniidae) Palaearctic. Russ. Parasitol. J., 2: 29–39  Serbina, E. A. (2013c): Variety dixenic life cycles of trematode from Bithyniidae snails (Mollusca: Gastropoda: Prosobranchia) Palaearctic. Russ. Parasitol. J., 3: 49–57. (In Russian)  Serbina, E. A. (2014): The influence of trematode metacercariae on the individualfecundity of Bithynia troscheli (Gastropoda: Bithyniidae). Parazitologiya, 48,(1): 3–19  Serbina, E. A., Bonina, O. M. (2011): Revealing local nidi of opisthorchidoses in flood-lands of river Ob and in