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Fish communities of streams and rivers might be substantially subsidized by terrestrial insects that fall into the water. Although such animal‐mediated fluxes are increasingly recognized, little is known about how anthropogenic perturbations may influence the strength of such exchanges. Intense land use, such as lignite mining, may impact a river ecosystem due to the flocculation of iron (III) oxides, thus altering food web dynamics. We compared sections of the Spree River in North‐East Germany that were greatly influenced by iron oxides with sections located downstream of a dam where passive remediation technologies are applied. Compared to locations downstream of the dam, the abundance of benthic macroinvertebrates at locations of high iron concentrations upstream of the dam was significantly reduced. Similarly, catch per unit effort of all fish was significantly higher in locations downstream of the dam compared to locations upstream of the dam, and the condition of juvenile and adult piscivorous pike Esox lucius was significantly lower in sections of high iron concentrations. Using an estimate of short‐term (i.e., metabarcoding of the gut content) as well as longer‐term (i.e., hydrogen stable isotopes) resource use, we could demonstrate that the three most abundant fish species, perch Perca fluviatilis, roach Rutilus rutilus, and bleak Alburnus alburnus, received higher contributions of terrestrial insects to their diet at locations of high iron concentration. In summary, lotic food webs upstream and downstream of the dam greatly differed in the overall structure with respect to the energy available for the highest tropic levels and the contribution of terrestrial insects to the diet of omnivorous fish. Therefore, human‐induced environmental perturbations, such as river damming and mining activities, represent strong pressures that can alter the flow of energy between aquatic and terrestrial systems, indicating a broad impact on the landscape level. [ABSTRACT FROM AUTHOR]

Recent studies have incorporated behavioural aspects into the analysis of animal invasion processes, citing high activity and boldness as typical traits of successful invaders. The topmouth gudgeon Pseudorasbora parva is arguably the world's most widespread freshwater fish invader currently listed as a pest species on the list of invasive alien species of Union concern. The study aimed at elucidating whether behavioural traits of P. parva contribute to its invasive success. Laboratory experiments contrasting P. parva activity levels, habitat choice and boldness with that of native competitors Eurasian perch Perca fluviatilus and three‐spined stickleback Gasterosteus aculeatus showed P. parva to be relatively shy and avoiding direct competition for prey. An additional field study in a pond in central Germany demonstrated that P. parva was able to establish and maintain a small population, co‐existing with a much higher density of P. fluviatilis. The study suggests that the invasive success of P. parva may be a result of its flexible life‐history traits, while behavioural traits such as boldness and competitive dominance for food may only play a minor role. [ABSTRACT FROM AUTHOR]

Growth of fish is an important contributor to individual fitness as well as fish production. Explaining and predicting growth variation across populations is thus important from fundamental and applied perspectives, which requires knowledge about the ecological factors involved in shaping growth. To that end, we estimated environment‐dependent von Bertalanffy growth models for 13 gravel pit lake populations of Eurasian perch (Perca fluviatilis) from north‐western Germany. To identify the main drivers of perch growth, we evaluated the performance of 16 different biotic or abiotic lake variables in explaining growth variation among lakes. In addition, we compared growth predictions from the best‐performing model incorporating "complex" variables that require intensive sampling effort, with a model using only "simple", easily measurable lake variables (e.g. shoreline development factor). The derivation of a simple model aimed at future applications in typically data‐poor inland fisheries, predicting expected growth potential from easily measurable lake variables. A model combining metabolic biomass of predators, maximum depth and shoreline development factor performed best in predicting perch growth variation across gravel pits. All three parameters in this model were positively related to perch growth. The best‐performing simple model consisted only of the shoreline development factor. Length‐at‐age predictions from both models were largely identical, highlighting the utility of shoreline development factor in approximating growth potential of perch in gravel pits similar to our study lakes. Our results can be used to inform fisheries management and restoration efforts at existing or newly excavated gravel pit lakes. [ABSTRACT FROM AUTHOR]

All individuals of the species Gallus gallus, also broiler breeders, have a preference of resting on elevated areas but only few studies have focused on the resting behaviour of broiler breeders. The aim of the present study was to determine the status quo of perch use on conventional broiler breeder farms. Therefore, nine commercial broiler breeder flocks with the fast growing genetics Ross 308 and Ross 708 and the slow growing genetics Ross Ranger in Lower Saxony, Germany, were investigated. Observations were conducted at two different times during the production phase. The different types of perches and their use were examined by means of photo-based behavioural observations. In total, seven different types of perches were provided. Perches were available in the slatted area as well as in the littered area. They were made of plastic, wood or metal and they were of various heights (38.0-48.0 cm above the littered area, and 0.0-15.5 cm above the raised slatted area). Complying with their natural behaviour, broiler breeders, both of the slow growing hybrid Ross Ranger and the fast growing hybrids Ross 308 and Ross 708, used all types of perches with a higher intensity during the dark-period (2.07 birds/m perch versus 0.73 birds/m in the light period). The study showed that all perch types were used. However, broiler breeders seemed to prefer perches with a height of at least 5.5 cm. [ABSTRACT FROM AUTHOR]

Background: Bioaccumulating contaminants in surface waters are preferably monitored in fish for assessing the related risks to and via the aquatic environment. Consequently, the European Water Framework Directive (WFD) requires a monitoring of certain priority substances such as mercury, polybrominated diphenyl ethers (PBDE), perfluorooctane sulfonic acid and its derivatives (PFOS), hexachlorobenzene (HCB), hexabromocyclododecanes (HBCDD) and polychlorinated dioxins/dioxin-like compounds (dioxins) in freshwater and coastal fish. Tissue levels have to comply with biota environmental quality standards (EQSs) given in Directive 2013/39/EU. EQSs are justified either by risks for human health (assessed on the basis of fillet) or secondary poisoning of wildlife (based on whole fish). To support the practical implementation of the WFD biota monitoring in Germany, comparative investigations of target fish species caught at six sites were performed. Results: At each site, at least three fish species listed in a national guidance document were sampled (e.g., chub, roach, bream, perch). Beside biometric data, concentrations of seven priority substances were determined in pooled fillet and carcass samples and whole fish data were calculated. The EQSs for PBDE and mercury were exceeded in nearly all fillet and whole fish samples. PFOS was above the EQS at several sites especially in perch, while HCB exceeded the EQS only at one site (Elbe River). All fillet and whole fish samples complied with the EQSs for dioxins and HBCDD. Based on wet weight concentrations of a homogeneous set of 20 composite sample pairs of 3–5 year-old fish, the following fillet-to-whole fish conversion factors were derived: mercury 0.81, PBDE 5.4, HCB 3.6, PFOS 2.7, dioxins 5.3, and HBCDD 1.8. Conclusions: Recommendations on selection of target fish species, age or tissue given by EU and national guidance documents are practical and feasible. However, further adjustments of the samplings such as the determination of site-specific length–age relationships are required from both ecological and risk assessment perspectives. The derived conversion factors allow the translation of fillet-to-whole fish concentrations (and vice versa), and thus the EQS compliance assessment for the appropriate tissue (fillet for human health, whole fish for wildlife risks) if only one tissue is investigated. [ABSTRACT FROM AUTHOR]

The article discusses the outbreak of gill worm (Ancyrocephalus percae) affecting Eurasian perch (Perca fluviatilis L.) in Lake Constance in Germany. It says that 539 perch from three age classes were sampled in Upper Lake Contance and a necropsy of the gills and isthmus for Ancyrocephalus was performed. It states that the isthmus of perch was found to be almost exclusively infected by A. percae.

The article explores the impact of the aquatic contamination on the reproductive health of the perch and roach in German surface waters. It notes that deviation of endogenous sexual attributes on wild fish is a warning signal. Moreover, ontogenetic integrity of gonadal development and recrudescence are bioindicators of pollution on animal species.

The parasitological studies were carried out on bream and perch from brackish water of Pomeranian Bay and the Szczecin Lagoon — a mouth of the Odra River. Bream and perch hosted 21 and 13 parasitic species, respectively. The species richness and diversity of parasites were much higher for bream and the abundance of parasites in bream was nearly four-fold higher than that in perch. Faunistic similarity of both parasite communities was low. The dominant group of parasites in both fish hosts was digeneans. Five species were specialists of bream, while only one species was a perch specialist. Five new host records have been reported in Poland for the following species: Myxobolus dispar, Hysterothylacium aduncum, Khawia sinensis, Echinorhynchus gadi and Pomphorhynchus laevis. [ABSTRACT FROM AUTHOR]

In the presence of size-selective fish daphnids were shown to exhibit two alternative inducible defence strategies: They may either escape predation by active migration or adopt a life history strategy, e.g., reproduce earlier and at a smaller size. Depending on the type of habitat, migration may either be vertically (in deep stratified lakes) or horizontally (in shallow lakes with macrophytes) oriented. Concerning behavioural defence strategies, daphnids living in medium-deep, weakly stratified water bodies with a poorly developed littoral face a dilemma, since the littoral provides no shelter and the availability of a deep-water refuge is unpredictable. We studied the population dynamics, life history changes (size at maturity) and daytime vertical distribution of Daphnia galeata in a weakly stratified reservoir in relation to predation by juvenile fish during 6 years. While temperature gradients were usually small, oxygen concentrations suggest that a low-oxygen refuge for daphnids was available in every year to some extent. Our results indicate that, depending on predation intensity and stratification patterns, daphnids exhibit both, behavioural and life history defences. In years with a high biomass of young-of-the-year (YOY) perch Daphnia abundance declined rapidly at the end of the clear water stage while at the same time the vertical distribution at daytime shifted to deep strata providing a low-oxygen refuge and the size at maturity decreased. However, while the life history response in some years lasted throughout most of the summer period, a shift in daytime vertical distribution was exhibited for much shorter periods. Both traits were much less expressed in years with low YOY fish densities and no negative correlation between them could be verified. We suggest that under high predation pressure in this relatively shallow reservoir no strictly alternative (either behavioural or life history) strategies exist, but that daphnids make use of the full range of possible anti-predator defences available, at least during short periods when predation is most intense. [ABSTRACT FROM AUTHOR]

Focuses on the pikeperch stocking used in the biomanipulation strategy in Feldberger Haussee, Germany. Results of study determining population development, growth and diet composition of pikeperch in Feldberger Haussee; Climate conditions leading to successful recruitment from 0+ fish to older age-classes; Impact of the high depth of the lake on the spawning period; Results indicating 0+ pikeperch cannot benefit from the spring maximum of the zooplankton; Reason for the slow growth, which hampers the switch to piscivory for the majority of 0+ pikeperch; Growth rates of pikeperch after becoming piscivorous; How predation was mainly directed towards roach and 0+ perch, the major planktivores; Results confirming the role of pikeperch as an efficient predator of zooplanktivorous fish in open-water dominated lakes; View that the probability of successful recruitment of pikeperch in deeper, stratified lakes is reduced; Results suggesting that stable self-sustaining pikeperch populations cannot be expected in such deeper lakes and regular stocking measures may be necessary even if a potential spawning stock exists.

Abstract: Contrasting to predictions, roach (Rutilus rutilus) are more abundant than perch (Perca fluviatilis) in a number of mesotrophic lakes in the Baltic lake region of northeastern Germany. To reveal underlying mechanisms, roach and perch habitat use were analysed on a diel and seasonal scale, and piscivorous fish predation was quantified in one of those lakes, Lake Großer Vätersee (Brandenburg). For the latter point, piscivorous and non-piscivorous fish population sizes were assessed by multiple mark-recapture experiments and piscivorous consumption was quantified by bioenergetics modelling. Piscivorous fish biomass accounted for about 30% of total fish biomass, and top-down control of third trophic level biomass was intense. Fish habitat shifts closely linked the littoral and pelagic habitat, and were an integral component of the fish species interactions. While pike predation was mainly restricted to the littoral zone, piscivorous perch foraged in the open water during daytime. Roach ≥ age-1 counteracted the pelagic predation risk by diel horizontal migrations. So they could prey on pelagic zooplankton, and at the same time kept their predation risk in the pelagic zone as low as possible. In the littoral zone, roach extensively used non-animal resources not accessible to perch. Non-piscivorous perch were almost exclusively restricted to the littoral habitat; only age-0 perch had an initial pelagic stage. They didn't experience a juvenile competitive bottleneck. Overall, perch were relatively more affected by piscivorous fish predation than roach. This might be decisive for roach dominance under mesotrophic conditions. Additionally, Orconectes limosus, an introduced crayfish species, played a decisive role both as alternative prey for piscivorous fish and as a potential structuring force in the littoral habitat. [Copyright &y& Elsevier]

1. According to previous field studies in the biomanipulated Bautzen reservoir (Germany), a midsummer decline of the dominating zooplankter, Daphnia galeata, was suggested to be initiated by a simultaneous occurrence of low fecundity of the daphnids and a selective feeding of underyearling fish on mature daphnids. The timing of both processes was assumed to be triggered by spring water temperature. However, the field data were not appropriate for testing whether yearly differences in spring warming are strong enough to control the predation rate of underyearling fish on daphnids. 2. By combining field data on fish growth, feeding and population mortality, the daily uptake of Daphnia by a virtual population of underyearling perch (Perca fluviatilis) was simulated. In addition, the daily predatory mortality of mature daphnids was calculated independently. Scenarios with a warm and a cold spring were compared. Furthermore, the delayed warming of a pelagic zone of a lake versus a littoral one was simulated. Sensitivity of the simulation to changes in five parameters was tested. 3. In both the warm spring scenario and the littoral warming scenario, more daphnids in general and more mature daphnids in particular were eaten, compared with the cold spring and pelagic scenarios. The predatory mortality of mature daphnids was driven by the increasing gape size of growing fish such that in warmer years the fish reach earlier the size at which they can eat mature daphnids. 4. The simulation was most sensitive to changes in daily mortality rate of the fish and to the size at maturity of the daphnids. Since at least the fish mortality is also temperature-dependent via the growth rates of fish, the predation rate of perch on D. galeata in Bautzen reservoir is substantially increased during a warm spring. This underlines the assumption that even a slight global warming may have a decisive influence on food web processes due to the fine-scaled patterns of trophic interactions in lakes. [ABSTRACT FROM AUTHOR]