Małgorzata Pilecka-Rapacz

Summer zooplankton in small rivers in relation to selected conditions

The abundance and the biodiversity of summer zooplankton in the waters of the Drawa drainage (NW Poland) were studied, as was their relation to selected environmental conditions. The conditions upstream, especially in the outlets of lakes, did not affect the zooplankton communities downstream. This was also true of tributaries which had no influence on the shape of the zooplankton communities in the main river. The number of zooplankton in the outlets of eutrophic lakes was greater than in those of mesotrophic lakes. Increased vegetation cover significantly affected mainly the crustacean communities of zooplankton. Larger amounts of zooplankton were observed in rivers where the riparian zone was not covered with vegetation, but this difference was not significant. The hydrological conditions of the rivers and the Secchi depth visibility strongly impacted the composition of the zooplankton. The influence of abiotic factors was most pronounced on the abundance of cladocerans, and least pronounced on the abundance of rotifers.

Zooplankton communities of inter-connected sections of lower River Oder (NW Poland)

The aim of this study was the determination and comparative analysis of the zooplankton communities between the inter-connected sections of the lower Oder river in relation to physicochemical factors. The study was performed at five sites of Oder. Two sites were localized in the main channel of Oder (East Oder), other sites were localized in the west arm of Oder and at the beginning of the canal carrying the post-cooling water from the power plant, and the last site was below at the shallow channel joining the Western Oder with the Eastern Oder. At the channel site in which the two arms of the river are connected a significantly higher taxa number, abundance and biomass of crustaceans was observed than at the other sites. The taxonomic similarity index between all sites was at a rather low level. The Pearson’s coefficient, multiple regression analysis and CCA showed that temperature, conductivity and content of nitrates had the strongest impact on the abundance of zooplankton. Thus, in lower, slowly flowing section of River Oder the physico-chemical variables influenced zooplankton density. Post-cooling water from the power plant influenced the zooplankton communities only in the channel discharging the waters into the river, while its influence on the zooplankton in the Oder is insignificant.

Annual development cycle of gonads of Eurasian ruffe (Gymnocephalus cernuus L.) females from lower Odra River sections differing in the influence of cooling water

The subject of this study was gonadal development of Eurasian ruffe females collected at three sites: the Regalica River carrying natural waters of the Odra River, Warm Canal to which cooling water from a power plant is discharged, and Lake Dąbie in which the waters from East Odra and Warm Canal are mixed. According to histological analysis, under the natural conditions in the lower Odra River, ruffes spawning season usually begins in April and lasts till the end of May. The fish from Lake Dąbie started their spawning season in a similar period, while the fish from Warm Canal started their spawning season in March, a month earlier, and also finished their spawning season earlier. The size of oocytes from the ruffe collected in the Warm Canal at the beginning stage of vitellogenesis was smaller (mean diameter of 184.3 μm) and at the end of vitellogenesis larger (755.3 μm) than the size of oocytes from the fish collected at the other two sites (p < 0.05), although their sizes were within the typical range. In the gonads of the fish caught from June to September at all the sites, the presence of degenerating oocytes was confirmed. Folliculi atresia at the beginning of summer was observed in the last not-laid portion of oocytes, while the degeneration of a part of newly produced vitellogenic September oocytes was caused by a high temperature of the lower Odra River water, of over 20°C at that time. Both types of oocyte degeneration are the natural adaptations to the conditions of a changing natural environment.

Analysis of benthic macroinvertebrate communities from the Lower sections of Large river in relation to different environmental factors

The aim of this study was to make a comparative analysis of macrozoobenthos composition at different sites at selected sections of lower the Odra River with relation to different physicochemical factors. The observations were made on the lower section of Odra River at five study sites: two of them were localized in the main channel, one in the left branch of river, another one in the channel carrying post-cooling water from Dolna Odra power plant, and the last one was in the channel connecting both branches of Odra River. At all sites, 26 taxa were found representing by: Bivalvia, Gastropoda, Oligochaeta, Hirudinea, Malacostraca and Insecta. The greatest biodiversity and the highest abundance of zoobenthos organisms were noted in the channel joining the two branches of the river, site 5, characterised by the lowest water flow rates and the densest coverage of the macrophytes at the bottom. Temperature was the sole parameter to be studied that affected the composition of benthic invertebrates. A clearly negative impact of temperature on the diversity of invertebrates was observed only in the channel with post-cooling water discharged from the power plant.

ANNUAL DEVELOPMENT OF GONADS OF PUMPKINSEED, LEPOMIS GIBBOSUS (ACTINOPTERYGII: PERCIFORMES: CENTRARCHIDAE) FROM A HEATED-WATER DISCHARGE CANAL OF A POWER PLANT IN THE LOWER STRETCH OF THE ODER RIVER, POLAND

The pumpkinseed, Lepomis gibbosus (Linnaeus, 1758), known also as pumpkinseed sunfish, is native to eastern and central North America (Tomeček et al. 2007). Because of its attractive appearance, the species was introduced to Europe in the 19th century as an ornamental fish for aquaria or park ponds, or a prospective sport fish (Vooren 1972, Witkowski and Grabowska 2012). Natural escapes and intentional introduction of the fish into open waters has resulted in fast spreading of the species over Europe and a successful colonisation. The pumpkinseed has been already found in at least 28 European countries and in Asia Minor (Coop and Fox 2007). The fish are found in shallow, weedy, quiet reservoirs, lakes, river inlets, tributaries, and canals, in cool to moderately warm waters (Miller 1963, Tomeček et al. 2007). The range of the species is limited by the water temperature. The optimum temperature for pumpkinseed growth is 20–30oC (Mischke and Morris 2002). For reproduction, they need the critical temperature range of 14–16.5oC (Burns 1976). ACTA ICHTHYOLOGICA ET PISCATORIA (2014) 44 (2): 131–143 DOI: 10.3750/AIP2014.44.2.07

Parasitological survey of smelt, Osmerus eperlanus (Actinopterygii: Osmeridae), from five estuary sites along the southern coast of the Baltic Sea

Abstract This is the first comprehensive study covering the parasite fauna of smelt, Osmerus eperlanus, from five estuary sites of the southern Baltic Sea in a stretch of almost 500 km. We examined 432 smelt from: the Neman River mouth, the Vistula River mouth, Pomeranian Bay, the Oder River, and Lake Dąbie and recovered 13 species/higher-rank taxa of parasites: Diplostomum spp., Posthodiplostomum cuticola, Eubothrium crassum, Proteocephalus longicolis, Cystidicola farionis, Hysterothylacium aduncum, Corynosoma semerme, Pomphorhynchus laevis, Unionidae gen sp., Ergasilus sieboldi, Argulus foliaceus, Piscicola geometra, and Saprolegniaceae gen sp. Basic infection parameters such as prevalence, intensity of infection, mean intensity of infection, and the dominance index were determined. The findings of the presently reported study constitute a number of new faunistic records. There were two new host records (Posthodiplostomum cuticola and Saprolegniaceae gen sp.), five new host records for Poland (Diplostomum spp., Pomphorhynchus laevis, Piscicola geometra, Argulus foliaceus, and Unionidae gen sp.), and two new host records for Lithuania (Argulus foliaceus and Unionidae gen sp.). We carefully analyzed the relevant information from more than 100 publications on smelt parasites to compare the data with our own findings.

Genetic structure of the cisco (Coregonus albula L.) from lakes of glacial origin in northern Poland

Abstract European cisco (Coregonus albula L.) is one of the most precious species of the European lake ichtyofauna, however, due to progressive eutrophication of water, the range of its occurrence has decreased. Deteriorating ecological conditions are the main cause of this decline in population, and most of the existing populations in lakes are maintained thanks to reintroduction. Thus, it is important to determine the genetic structure of the European cisco. The study involved PCR-RFLP-based genetic analysis of C. albula caught in 15 lakes in northern Poland, including four lakes located in national parks. The analysis covered 3 genes located in the mitochondrial DNA: ND1, ND3/4 and cytochrome b, as well as a control region (D-loop). The PCR product was digested with 4 endonucleases (RsaI, MspI, BsuI and HhaI) and the resulting haplotypes were grouped into combinations. Statistical analysis were then performed on these groups. Based on the genetic distance, a phenogram was constructed in which two groups could be distinguished. One group was represented by C. albula populations from most lakes in north-western Poland, including the three protected lakes. The other group consisted of the European cisco population from Lake Wigry (north-eastern Poland) and commercially exploited lakes from the southern part of the investigated north-western Poland area. The results of the study of C. albula from northern Poland present a valuable molecular characterization of the populations and can be a starting point for further genetic monitoring.

Which parameters – rates of survival or growth – determine the best moment for stocking trout larvae?

Abstract The aim of this study was to determine the best moment to stock trout, Salmo trutta L., larvae into the wild. This goal was accomplished by determining weekly changes in the growth parameters of larvae that were fed in seven variants: on the day of 2/3 yolk sac resorption; from the first week after the day of 2/3 yolk sac resorption; from the second week after the day of 2/3 yolk sac resorption; from the third week after the day of 2/3 yolk sac resorption; from the fourth week after the day of 2/3 yolk sac resorption; from the fifth week after the day of 2/3 yolk sac resorption; from the sixth week after the day of 2/3 yolk sac resorption. Based on our results, we concluded the following: 1) trout larvae are ready to start eating at the time of the resorption of 2/3 of the yolk sac; 2) trout larvae can live without food for three weeks following the resorption 2/3 of the yolk sac without any notable losses; 3) the best moment to stock trout larvae into the wild is in the period from the resorption of 2/3 of the yolk sac to the third week after this resorption, so one week after full resorption. This is the optimal period to stock any waters with trout larvae.

Determining the spring biomass peak of the smallest plankters in selected vendace lakes in Western Pomerania

Abstract The aim of this study was to determine the prevalence peak of the smallest plankters that are an adequate food resource for vendace (Coregonus albula L.) larvae. This goal was accomplished by determining weekly changes in zooplankton biomass, especially rotifers and nauplii, against changes in basic physicochemical parameters of lake waters. As the results of this paper show, the highest abundance of the smallest plankters, rotifers and nauplii, occurs at a particular temperature for a period of two weeks. The most important variable that determined the peak of small plankter biomass is temperature. Thus, the period of stocking lakes with vendace larvae should be synchronized with this temperature and the coinciding biomass peak of rotifers and nauplii, which are the basic food of vendace larvae.