A four-year study carried out in a lake with perennial water blooms caused by toxigenic Planktothrix agardhii (Oscillatoriales) and Anabaena lemmermanii, Anabaena flos-aquae, Anabaena spp. and Aphanizomenon issatchenkoi (Nostocales) revealed that the lakedwelling fish were threatened by simultaneous exposure to intracellular and extracellular microcystins (MCs) as well as anatoxin-a (ANTX). Higher contents of anatoxin-a and microcystins were found in livers than in fish muscles. This is the first report on ANTX accumulation in the common fish, indigenous to European freshwaters during perennial cyanobacterial blooms. Generally, the omnivorous roach (Rutilus rutilus) and Prussian carp (Carassius gibelio) accumulated higher amounts of MCs in their tissues compared to mostly predacious perch (Perca fluviatilis), and similar amounts of ANTX. The longlasting presence of MCs exceeding the safe levels for consumption was found in fish muscles. ANTX accumulation in fish muscles (up to 30 ng g -1 FW) suggests the probability of its transfer in a food chain.

Three groups (wild-WS, semi-pond-SPS, and pond-cultured-PS) of ide Leuciscus idus (L.) were examined. Each group consisted of 30 females and 10 males, aged 5-8 years. All groups were stimulated with two agents: carp pituitary homogenate (CPH) and a synthetic hormonal preparation Ovopel. The amount of ovulating females decreased in conjunction with females' domestication level, mainly because of very low efficacy of CPH for pond-reared ide stimulation. The percentage of ovulating females stimulated with Ovopel (97.0 %) was significantly higher comparing to CPH (63.0 %). No significant differences were found in latency time between the groups but spawning synchronization increased in conjunction with ide domestication. The positive correlation between domestication level and latency time, i.e., the higher the domestication level, the higher the latency time, was stated. No significant differences were found in PGSI as well as in total volume of obtained eggs, but groups differed significantly in the number of dry eggs and in number of swollen egg. Significant negative correlation between domestication level and number of swollen eggs, i.e., the higher the domestication level, the lower the number of eggs, was detected. The survival rate at the eyed stage was the highest in WS group (60.4 %) and PS group (57.7 %), and was significantly higher than in SPS group (51.8 %). Eggs obtained after CPH stimulation had higher survival rate at the eyed-egg stage

The freshwater habitats of semi‐aquatic carnivores in Europe have undergone substantial alterations due to regulation and construction of artificial watercourses. We compared seasonal estimates of otter Lutra lutra food composition with concomitantly collected data on fish availability and otter holt location in a strongly human‐modified ecosystem comprising the upper stretches of the Wieprz‐Krzna Canal, the longest artificial waterway in Poland, and an associated regulated river. Concrete lining of the canal, extreme water level variation and regular vegetation clearance to enhance water flow substantially limited otter food and shelter resources, yet the canal offered attractive habitats for some fish and hibernating amphibians, while otter resting sites were available at the closely adjacent river. The taxonomic composition of fish in the otter diet, reconstructed based on faecal analysis, was largely reflected in electrofishing catches. Fish communities in our study area were numerically dominated by small‐sized species and otters fed on very small fish (median seasonal total lengths: 46‐54 mm). Either the smaller fish in the population were taken or prey sizes did not differ from those available. The significant contribution of amphibians and waterbirds to otter diet (seasonally 41‐75% in terms of biomass) indicated poor fish supplies for otters in the canal‐river system. High trophic diversity, compared to other otter studies in temperate climatic conditions, indicates that otters facing unstable food conditions exhibit great flexibility in their diet, which may facilitate colonisation of anthropogenic, depauperate environments. Otter occurrence provides little opportunity for conflict with human economic interests in ecosystems that are highly managed for purposes other than fish production. Since anthropogenic habitats are typically poor in some resources, such as shelter structures, their suitability for otters can be enhanced by ensuring good connectivity with nearby less‐disturbed habitats, where the necessary resources can be supplemented.

-The role of environmental factors in aquatic ecosystems results from basic lake characteristics, human disturbances ('cultural eutrophication') and climate-related trends in the physical and chemical components of lakes. Although the influence of environmental factors on the abundance of aquatic animals is fairly well documented, less has been done to research their influence on food web interactions. The aim of the study was to evaluate microbial and classical food webs in lakes, with special emphasis placed on the role of environmental factors as influencing strengths. Variation partitioning, based on redundancy analysis, revealed that environmental factors played the most important role in structuring aquatic communities by accounting for 87.5% of their variation. Among all the factors measured, total solids (TS), transparency (Secchi disc) and temperature were most closely related to the variation in trophic communities. The analyses of food web interactions under low and high levels of those factors revealed that they differently influenced strengths among food web components. The strongest relations among distinct trophic levels were found under conditions of low TS, the lowest number of relations was found under conditions of low temperature. Only in low TS did bacteria correlate significantly with biogenes. Under high TS, bacteria positively influenced plenty of higher trophic levels. Top-down control was observed under conditions of high temperature. Conditions of low and high transparency did not diversify food web interactions. The obtained results can broaden our knowledge of the response of food webs to environmental factors in advanced stages of global eutrophication of water bodies and in the early stage of projected trends of global climate change.

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