In recent years, despite a certain deceleration of the process, evident decrease or even extinction of many local populations of the majority of rheophilic fish species including dace Leuciscus leuciscus (L.), ide L. idus (L.), and chub L. cephalus (L.) -the only representatives of the genus Leuciscus in Polish ichthyofauna -has still been observed. Invariably, the major reasons for that situation are ) and chub L. cephalus (L.) were obtained from rivers belonging to the Pasleka River basin (northeastern Poland) and next transported to a hatchery for the purpose of conducting artificial reproduction. The obtained eggs were fertilized and next incubated under a variety of thermal protocols: slow gradual heating of water (M1), rapid increase in temperature at the end of incubation (M2), fluctuating temperature (M3) and two constant temperatures (optimum and sublethal). Variable thermal changes of water were also continued after hatching, up to the yolk sac resorption by larvae. During the study it was shown that relative to incubation at optimal temperatures (12.3°C for dace, 15.7°C for ide and 19.0°C for chub), thermal modifications had no clear influence on a decrease in survival rates (differences among regimes did not exceed 5%) and increase in developmental deformations (differences below 1.0%) observed among the hatched embryos. The duration of egg incubation and developmental rate increased with increasing temperature. In the systems with modified temperature the embryonic development of dace (from fertilisation to commencement of exogenous food intake) took from 9.5 to 22.5 days, for ide from 6.1 to 12 days and for chub from 5.0 to 10.5 days. The yolk sac resorption stage in the particular species occurred from 11.7 to 23 days for dace, 7.5 to 13.2 days for ide and 5.5 to 12.8 days for chub. Different time of hatching was also reflected in the level of ontogeny of hatched embryos. Among the fish hatched at modified temperatures the largest sizes, similar to those characteristic of fish incubated at optimum temperatures, were observed in individuals originating from variants where the temperature fluctuated. The developmental disproportions among the embryos of studied species originating from different thermal regimes observed at the time of leaving the egg shells were definitely larger than during the following development stages. This study also confirmed that the embryos of studied species can adapt to increasing water temperature due to global warming up to 19.0 (dace), 23.0°C (ide) and 27.5°C (chub). The obtained results are very important not only for practical purposes but also from physiological and ecological aspects.

This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in preovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and di¡erent oil droplet coalescence rates. This categorization covered seven stages (from I to VII)^from the end of vitellogenesis to ovulation. The categorization was veri¢ed by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 1C), which extended the latency time. In addition, some morphological indicators (pseudo-gonadosomatic index, Fulton's condition coe⁄cient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ine¡ective for this purpose, further highlighting the need to determine the maturational stages in pre-ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical di¡erences were found in terms of latency time between experimental groups at di¡erent maturity stages (II^789 8 h; III^57^78 h; IV^48^58 h; V^32^49 h; VI^5^30 h) according to the proposed classi¢cation. This classi¢cation and the results presented in the study signi¢cantly improved the synchronization of ovulation, which may positively a¡ect the e¡ectiveness of pikeperch production under controlled conditions.

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Research into arti¢cial reproduction of chub was studied during three subsequent reproductive seasons. Chub reproduction was conducted in two di¡erent variations. In the ¢rst experiment di¡erent hormonal agents were given to ¢sh, such as CPE, hCG, or an analogue of GnRH with dopamine antagonist (ovopel). In the second one, the optimum moment of applying of arti¢cial reproduction was sought and the ¢sh were only obtained an analogue of GnRH in di¡erent periods. The results obtained in two ¢rst seasons indicated that ovopel is the most e¡ective agent for the arti¢cial reproduction of chub. Consequently, it was decided that the ¢sh would obtain only this agent in the ¢nal year of research. In last year (experiment II), chub spawners were taken to the hatchery under controlled conditions every few weeks from February to the beginning of June. Periodically, the maturity of oocytes was checked. As soon as the oocytes had achieved stage 2^3 of maturity, ¢sh were obtained ovopel. It was noted that there was no problem with collecting semen. Obtaining oocytes was much more di⁄cult. Most frequently, they were not obtained at all or obtained in very small amounts. It was also observed that the administration of hormones caused a very quick maturation of gonads and their over-maturation.