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The aim of this study was to assess the species composition and structure of zooplankton and fish communities in lakes with similar ecological conditions that are connected by periodic streams. This was done by assessing the relative importance of local biotic and abiotic interactions associated with the species composition and structure of the zooplankton and fish communities. The study was conducted in three small, soft water lobelia lakes located in the source area of the Brda River, which were characterized by low trophic statuses and similar depths. A total of 15 Rotifera taxa, 18 Cladocera taxa, and nine Copepoda taxa were identified in the lakes analyzed. The lake zooplankton communities differed in species richness, total density, and biomass, while the Shannon–Wiener diversity indexes of the zooplankton communities were similar. Of the three lakes analyzed, the faunal similarity index was the highest in Lake Smołowe. Comparisons of the three lakes indicated there was greater similarity in the pelagic (42.7–50.0%) than in the littoral (20.1–26.8%) zones. The fish community of the three lakes consisted of eight species, and species richness ranged from two to eight fish species. Only perch (Perca fluviatilis L.) and pike (Esox lucius L.) were present in all three lakes. The fish groups also differed in terms of density and biodiversity indicators. Faunal similarity indicators showed significant similarity in the dominance structure of the fish communities.

The post-stocking dispersal of juvenile Atlantic sturgeon (Acipenser oxyrinchus Mitchill) in the Wis3oka River (southern Poland) was investigated using biotelemetry. Thirty-five hatchery-reared juvenile A. oxyrinchus were tagged with radio or acoustic transmitters and tracked using mobile surveys and fixed receivers. Daily movement patterns were similar in 2009 and 2010. The sturgeon migrated with a mean speed of 1.42 km h-1 in 2009 and of 2.06 km h-1 in 2010. Migration rate was not regarded as being dependent on juvenile sturgeon size. The confirmed survival of individuals from the two field seasons differed slightly over the course of this study. Short-term survival of A. oxyrinchus was 86.7 and 90% in 2009 and 2010, respectively.

The aim of this paper is to present the results of studies on the phenology of the spawning of fish in two lakes with different degrees of heated waters. The studies performed indicated that heating the waters distinctly hastened fish spawning in comparison to the same species of fish inhabiting waters with normal thermal conditions. Spawning usually occurred two to three weeks earlier in the heated Lake Licheńskie than it did in Lake Ślesińskie, which has waters with a natural thermal regime. Additionally, it was noted that fish spawning lasted longer in waters with higher temperatures.

This paper discusses the problem of the occurrence of non-native fish species in a strongly transformed aquatic ecosystem. The changes in this ecosystem are caused by warm water discharges from two electric power plants. Twelve non-native fish species are confirmed to occur in the system of five heated lakes located in central Poland. In total, 30% of the total number of non-native species confirmed in Polish inland waters were noted. Aquaculture and fisheries are the primary sources of non-native species in these lakes. Among the species identified, most reached the lakes or canals by escaping from farming facilities or through commercial stocking. Four species have established stable populations. Pseudorasbora parva (Temminck & Schlegel), Carassius gibelio (Bloch), and Carassius auratus (L.) are invasive species that occur abundantly in all the lakes, while Cyprinus carpio L. reproduces irregularly and only in the most heated lakes. The remaining species do not reproduce in the heated lakes system, or anywhere else in Poland; still, the threat these species pose must not be underestimated.

The aim of the study was to determine the degree of overlap in the feeding niches of early developmental stages of roach, Rutilus rutilus (L.), perch, Perca fluviatilis L., bleak, Alburnus alburnus (L.) and sunbleak, Leucaspius delineatus (Heckel). The hypotheses were that (i) larvae of different fish species of similar body sizes feed on similar food, and that (ii) smaller fish compete with larger ones for similar prey. The results of the analysis was to answer the question of whether the diet overlap of juvenile fish stages decreases with ontogenetic development. The study was conducted for two years (2001-2002) in two shallow, polymictic, eutrophic lakes. The diets of early developmental stages of fish species of similar body sizes differed. The few instances of diet overlap resulted from the abundance of food resources in the environment. However, fish of smaller body sizes exploited the same food resources as did individuals of the same species that belonged to different cohorts.