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The concentration of mercury, fatty acids and lipid quality indices were determined in three species of fish (European eel, Anguilla anguilla Linnaeus, 1758; Eurasian perch, Perca fluviatilis Linnaeus, 1758; and roach, Rutilus rutilus Linnaeus, 1758). The fish were caught from a reservoir in the Warmia and Mazury region located near Olsztyn (north-eastern Poland). Mercury content was determined by atomic absorption thermal decomposition using Milestone DMA-80 (Italy), whereas fatty acids were measured by gas chromatography using a 7890A Agilent Technologies chromatograph. The total mercury concentration had the following sequence: European perch (0.297 mg/kg) > European eel (0.160 mg/kg) ≈ roach (0.100 mg/kg) (P<0.05). A positive correlation was found between the mercury content and size (the body weight and total length) of these fish (P<0.0001). Based on the THQ, HI (<1.0) and BRQ (1.063), it was concluded that the fish does not pose a health risk and is fit for human consumption. Similarly, low AI and TI values (<1) are beneficial to human health related to reducing the risk of ischemic heart disease. A low OFA index of C12+C14+C18 and a high index of C18+UFA also indicate that these fish are safe from a nutritional point of view. The fatty acid indices HH (32.10–74.30), NVI (0.83–2.14), DI(18) (65.50–89.28), DI(16) (18.45–32.96), UI (131.93–278.64) and PI (88.60–314.90) were also studied. However, higher PUFA/SFA and de minimis EPA+DHA/Hg ratios compared to the recommended ratios suggest further research in this area is needed. [ABSTRACT FROM AUTHOR]

ABSTRACT Understanding patterns of trophic niche overlap in fish communities is important because trophic redundancy can stabilise food webs. δ13C and δ15N in fish can be converted into percent littoral carbon and trophic position, respectively, and subsequently used to estimate isotopic niche size and overlap between species. We hypothesised yellow perch (Perca flavescens) would have the most niche overlap on other species due to their central position in lake food webs and large ontogenetic changes in diet. We also hypothesised variance in niche overlap across lakes would be driven by variance in size structure of perch populations among lakes. Alternatively, variance in perch niche overlap could be driven by food web variables such as mean trophic position. We addressed these questions by sampling fish in 17 Minnesota (USA) lakes. Results showed mean perch niche overlap on other species was significantly larger than all other species, and that perch niche size was positively related to niche overlap. We subsequently found no evidence perch population length structure influenced niche size or overlap, as no metrics of perch size structure were related to either variable. Instead, perch mean trophic position was negatively related to perch niche overlap and marginally related to niche size. Perch mean trophic position, in turn, was positively related to depth of hypoxic water. Our results indicate yellow perch may be important for stabilising lake food webs through high trophic redundancy on other fish species and that the degree of trophic redundancy may be influenced by dissolved oxygen patterns in lakes. [ABSTRACT FROM AUTHOR]

Currently, there are no guidelines on housing or recommendations for practical environmental enrichments for chickens used for research and teaching purposes. This study was conducted to identify optimal enrichment programs to improve the health and welfare of caged hens used for teaching and research purposes. The 24-week-old Hy-line Brown laying hens (n = 168) were allocated at random to six enrichment programs/treatments with 14 replicate cages of two birds per cage during a 5-week experiment. Hens had physical access to the following treatments: no enrichment provided (control); round, wooden perches provided (perch); scratch pads made of wood and covered with sandpaper provided (scratch pad); hanging CDs provided (hanging CD); all three enrichment forms provided (complex environment); and each enrichment form provided on a 2-week rotation (novelty). While the egg quality was consistent, the complex group had a significantly lower feed intake (p < 0.001) but similar egg mass; thus, they also had a lower feed conversion ratio (p < 0.001). Additionally, hens in the complex treatment group had the leanest average body weight at week 5 (p < 0.01). It should be noted that while some measures of welfare did show significant differences, the biological or practical difference may be negligible, as in the case of the body condition score in this study. The results show that providing three different forms of environmental enrichment had positive effects on the welfare, health condition, and laying performance of laying hens relative to no enrichment or only one enrichment item. [ABSTRACT FROM AUTHOR]

Simple Summary: This study investigated the effects of perch provision on the productivity and welfare of broilers in two commercial farms. Broiler houses from each farm were provided with or without perches. The results showed that perches did not consistently affect productivity measures such as weight or uniformity. However, corticosterone levels, as the stress indicator, were lower in the group with perches. While there were no significant differences in some animal welfare indicators, gait scores were affected by perches in one of the farms employed. In conclusion, perches did not significantly improve broiler productivity or welfare, but they did have a positive effect on reducing stress. These findings provide important insights for improving broiler farming environments. This study explored the impact of perches on the productivity and welfare of broilers raised on two animal welfare-certified farms (designated as Farm A and B) in South Korea. Broiler houses in each farm were provided with or without wooden square-shaped perches (2 × 2 cm) at a rate of 2 m per 1000 birds. The study aimed to assess whether perches could influence productivity measures, such as weight and uniformity, and animal welfare indicators, including corticosterone levels and physical health markers. The findings showed that the effects on productivity were inconsistent, varying by farm and period. Corticosterone levels, as an indicator of stress, were significantly lower in the perch group on farm B, but not on farm A. There were no significant differences in welfare indicators such as footpad dermatitis or feather cleanliness, although gait scores improved in farm B with perch provision. Litter moisture was higher in the perch group of farm A, but showed no difference in farm B. The study concluded that while perches did not consistently improve productivity or welfare, they did help reduce stress in broilers, as indicated by lower corticosterone levels. [ABSTRACT FROM AUTHOR]

Purpose. The aim of the study was to investigate morphological and histological features of the gills, liver and blood of percids ­­­– pikeperch (Sander lucioperca Linnaeus, 1758) and perch (Perca fluviatilis Linnaeus, 1758) from different areas of the Zaporizhzhia Reservoir. Methodology. The study was conducted in two areas of the Zaporizhzhia Reservoir – in the Samara Bay and the lower part of the reservoir near the Viyskove village. The material was collected during research fish surveys in the summer-autumn period of 2024. The object of the study were age-3+ pikeperch and perch. The number of fishes used in the study was 20 specimens of each species. Hematological and histological studies were carried out according to generally accepted methods. The concentration of heavy metals in water samples was determined on a C115-M1 atomic absorption spectrophotometer in mg/L. Findings. According to the content of Cd, Mn, Cu, and Zn in both studied areas of the Zaporizhzhia Reservoir, there was an excess of the MPC for water bodies used for fishery purposes. The difference between the cytometric parameters of fish from different areas of the Zaporizhzhia Reservoir was mostly insignificant (р≥0.05), except for the width of the pikeperch nucleus and the area of ​​the perch erythrocyte nucleus, which were significantly larger in the fish of the Samara Bay (р≤0.05). The results of the study indicate the dependence of changes in the formed elements of the blood on the physiological state of the fish and on their environment. Among the studied fish of the lower part of the reservoir, the largest count of erythrocytes with pathological changes was observed in pikeperch, it was 1.32 times higher than in perch. Among fish of the Samara Bay, the highest count of pathologies in blood cells was also noted for pikeperch and was 1.17 times higher compared to that of perch. The results of these studies indicate an unfavorable ecological condition in both areas of the Zaporizhzhia Reservoir. The histological studies of the fish liver showed a number of pathological phenomena were revealed. The most common pathology of the liver cells of the studied fish from both areas of the reservoir was necrosis in pikeperch from the Samara Bay. Fish in the lower part of the reservoir had significantly fewer pathologies. Histological analysis of pikeperch and perch gills showed a high degree of pathological changes. The majority of pathologies were detected in pikeperch from the Samara Bay, which may indicate an average degree of pollution of the water by heavy metals and oil products. Based on these data, the histo-morphometric parameters of percid tissues can be used in the future to assess the ecological state of the water and the level of human impact of the Zaporizhzhia Reservoir, as well as be used as an additional indicator during the comprehensive assessment of the impact of anthropogenic factors on hydroecosystems. Originality. For the first time, a study of the morphological and histological characteristics of the gills, liver, and blood of percids (pikeperch and perch) from different areas of the Zaporizhzhia Reservoir was conducted. Practical Value. Histo-morphometric parameters of percid tissues can be used in the future to assess the ecological state of water and the level of human impact of the Zaporizhzhia Reservoir, as well as be used as an additional indicator during the comprehensive assessment of the impact of anthropogenic factors on hydroecosystems.

New types of aerial robots (NTARs) have found extensive applications in the military, civilian contexts, scientific research, disaster management, and various other domains. Compared with traditional aerial robots, NTARs exhibit a broader range of morphological diversity, locomotion capabilities, and enhanced operational capacities. Therefore, this study defines aerial robots with the four characteristics of morphability, biomimicry, multi-modal locomotion, and manipulator attachment as NTARs. Subsequently, this paper discusses the latest research progress in the materials and manufacturing technology, actuation technology, and perception and control technology of NTARs. Thereafter, the research status of NTAR systems is summarized, focusing on the frontier development and application cases of flapping-wing micro-air vehicles, perching aerial robots, amphibious robots, and operational aerial robots. Finally, the main challenges presented by NTARs in terms of energy, materials, and perception are analyzed, and the future development trends of NTARs are summarized in terms of size and endurance, mechatronics, and complex scenarios, providing a reference direction for the follow-up exploration of NTARs.

The research carried out on the ichthyoparasitofauna of fish from the Percidae family (perch - Perca fluviatilis, walleye - Sander lucioperca, bream - Gymnocephalus cernuus), taken from the ten dam lakes on the course of the Preajba Valley river, lakes that are part of the Preajba-Făcăi Lake Complex site revealed the following aspects: 6 species of parasites were identified: 1 trematode (Clinostomum complanatum), 2 cestodes (Diphyllobothrium latum, Triaenophorus nodulosus), 1 nematode (Eusstrongylides excisus) and 2 crustaceans (Lernaea cyprinacea, Argulus foliaceus), in two of the three host species studied. Most species of parasites (6) were identified in Perca fluviatilis (perch): Clinostomum complanatum, Diphyllobothrium latum, Triaenophorus nodulosus, Eustrongylides excisus, Lernaea cyprinacea, Argulus foliaceus in Sander lucioperca (saddle), 1 parasite (Eustrongylides excisus) and Gymnocephalus cernuus (ghibort) in which no parasites were identified. The clinical signs of the disease were highlighted in the case of lerneosis and argulosis in perch by the presence of hemorhagic wounds and obvious ulcerations, as well as parasites. [ABSTRACT FROM AUTHOR]

Seeking out appropriate habitat or food resources is one of the key reasons why animals move. Despite the benefits of movement, some individuals in a population remain resident or express alternative movement phenotypes. Movement, however, is energetically costly and can result in resources being diverted away from growth and reproduction. The presence of multiple movement phenotypes within populations suggests that each can have commensurate levels of performance depending on the underlying environmental conditions.Here we explore the context‐dependent costs and benefits of upstream and downstream juvenile dispersal in a large river system. We expect that if the energetic costs of moving (upstream against a current or downstream with a current) exceed any benefits to growth, then residents (who do not move) will have faster growth. Alternatively, movement costs may be offset if individuals move to more favourable environments, resulting in dispersers benefiting with faster growth.We used biological information naturally archived in the otoliths of a potamodromous fish, golden perch Macquaria ambigua, to quantify how movement phenotypes affect growth across individuals exposed to spatiotemporally varying environmental conditions.We found that juvenile growth differed considerably among dispersal phenotypes (resident, upstream, downstream, stocked): in general, surviving wild‐spawned downstream and upstream dispersers and hatchery‐stocked fish all grew faster than individuals that remained resident within their natal reach. Further, juvenile growth was sensitive to local environmental conditions and had carryover effects from an individual's natal‐year. Juvenile growth of all dispersal phenotypes was higher in years with below average natal‐year summer discharge (when fish are ~2–3 months old), likely because of increased concentrations of food resources. In contrast, the effects of natal‐year spring discharge (around the time individuals were spawned) were dependent on dispersal direction, with positive effects for downstream dispersers and upstream dispersers, and negative effects for resident individuals.Our results suggest that an individual's growth can benefit from early‐life movement, although the magnitude of this effect depends on local environmental conditions and the direction travelled. Our study reinforces the importance of heterogeneous and connected riverscapes that foster a diversity of individual growth responses. [ABSTRACT FROM AUTHOR]

Variations in the size and shape of the eye have been observed in many species of fish. As eye size is positively related to visual acuity, larger eyes should favour foraging and detection of predators.However, few studies have examined the variation in eye morphology in relation to the complexity of lake conditions, including environmental perturbation and spatial variation in predation and competition. Such tests are especially important as the degrading of the visual climate is expected due to climate change, where browning, turbidity and variations in structural complexity should set different demands for visual acuity of foraging fish under predation risk.In this study, we tested the variation of the eye size among 667 individuals of an aquatic predator perch, Perca fluviatilis, from littoral and pelagic habitats of 14 lakes. We used Secchi depth to assess the effects of the visual climate of our lake systems, as fish foraging is highly related to visual conditions, and studied eye size variation in relation to the contribution of the pelagic resources to an individual's diet and the risk of predation.Secchi depth, the pelagic contribution to the diet and the percentage of piscivores had significant effects on eye size.These variable outcomes suggest that the lake environment in terms of visual climate, predation landscape and diet are major factors of eye size variation in this generalist predator. As many fish species trade off foraging against predation risk, future studies will show whether the complexity of intra‐ and interspecific interactions contribute to the variation in eye size in freshwater fish. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Anadromous fishes play important roles in nutrient dynamics for freshwater ecosystems; however, the trophic pathways have been less documented for iteroparous species like river herring (Alosa pseudoharengus and A. aestivalis) compared to semelparous species like Pacific salmon (Oncorhynchus spp.). Given recent increases in restoration activities to improve connectivity, an understanding of how anadromous river herring influence the morphology, physiology, and life history of predatory fishes can help predict restoration responses. We aimed to quantify the trophic influence of juvenile anadromous river herring on predatory white perch (Morone americana) and yellow perch (Perca flavescens) using a combination of stable isotopes, growth rates, and condition indices. We sampled six lakes in coastal Massachusetts—three lakes with anadromous river herring and three similar lakes without river herring. Bayesian mixing models of δ13C and δ15N indicated white perch consumed juvenile river herring in higher proportions (69–75%) compared to co-occurring prey fishes (11–16%). Lakes with juvenile river herring contained perch with significantly higher condition values, higher immature growth rates (age 1 and 2), lower mature growth rates (> age 3), significantly smaller mature lengths, and lower mortality rates compared to perch in lakes without river herring. These divergent life history traits of perch in response to consumption of juvenile river herring are consistent with observations in other predatory fishes. Direct links between river herring and predator condition, growth, and life history trajectories suggest broad influences on ecosystem structure across trophic levels through physiological, morphometric, and life history modifications. [ABSTRACT FROM AUTHOR]

Purpose. The aim of the study was to investigate morphological and histological features of the gills, liver and blood of percids – pikeperch (Sander lucioperca Linnaeus, 1758) and perch (Perca fluviatilis Linnaeus, 1758) from different areas of the Zaporizhzhia Reservoir. Methodology. The study was conducted in two areas of the Zaporizhzhia Reservoir – in the Samara Bay and the lower part of the reservoir near the Viyskove village. The material was collected during research fish surveys in the summer-autumn period of 2024. The object of the study were age-3+ pikeperch and perch. The number of fishes used in the study was 20 specimens of each species. Hematological and histological studies were carried out according to generally accepted methods. The concentration of heavy metals in water samples was determined on a C115-M1 atomic absorption spectrophotometer in mg/L. Findings. According to the content of Cd, Mn, Cu, and Zn in both studied areas of the Zaporizhzhia Reservoir, there was an excess of the MPC for water bodies used for fishery purposes. The difference between the cytometric parameters of fish from different areas of the Zaporizhzhia Reservoir was mostly insignificant (р≥0.05), except for the width of the pikeperch nucleus and the area of the perch erythrocyte nucleus, which were significantly larger in the fish of the Samara Bay (р≤0.05). The results of the study indicate the dependence of changes in the formed elements of the blood on the physiological state of the fish and on their environment. Among the studied fish of the lower part of the reservoir, the largest count of erythrocytes with pathological changes was observed in pikeperch, it was 1.32 times higher than in perch. Among fish of the Samara Bay, the highest count of pathologies in blood cells was also noted for pikeperch and was 1.17 times higher compared to that of perch. The results of these studies indicate an unfavorable ecological condition in both areas of the Zaporizhzhia Reservoir. The histological studies of the fish liver showed a number of pathological phenomena were revealed. The most common pathology of the liver cells of the studied fish from both areas of the reservoir was necrosis in pikeperch from the Samara Bay. Fish in the lower part of the reservoir had significantly fewer pathologies. Histological analysis of pikeperch and perch gills showed a high degree of pathological changes. The majority of pathologies were detected in pikeperch from the Samara Bay, which may indicate an average degree of pollution of the water by heavy metals and oil products. Based on these data, the histo-morphometric parameters of percid tissues can be used in the future to assess the ecological state of the water and the level of human impact of the Zaporizhzhia Reservoir, as well as be used as an additional indicator during the comprehensive assessment of the impact of anthropogenic factors on hydroecosystems. Originality. For the first time, a study of the morphological and histological characteristics of the gills, liver, and blood of percids (pikeperch and perch) from different areas of the Zaporizhzhia Reservoir was conducted. Practical Value. Histo-morphometric parameters of percid tissues can be used in the future to assess the ecological state of water and the level of human impact of the Zaporizhzhia Reservoir, as well as be used as an additional indicator during the comprehensive assessment of the impact of anthropogenic factors on hydroecosystems. [ABSTRACT FROM AUTHOR]

The results of our preliminary studies indicated that the diets of predatory fishes can be bioindicators of faunistic changes in ecosystems and indirectly of changes taking place in aquatic environments in the Pomeranian Bay. We examined the diet composition of top predators Gadus morhua, Sander lucioperca, Perca fluviatilis, and the mesopredator Neogobius melanostomus. The diet composition of the perch, pikeperch, and round goby in the Pomeranian Bay was analyzed for the first time. Our findings indicated that perch, an euryphagous species, is the best potential bioindicator because it is present in the area studied most of the year and has a low to moderate feeding index (FI). Baltic cod, also an euryphagous species, could be a good bioindicator in the areas where it is abundant and occurs frequently, but not in the Pomeranian Bay, where it is caught mainly in the fall. Round goby, which is present in the area studied and had a low FI, is a stenophagous species that preys mainly on benthic species, while pikeperch had a very high FI and the least number of prey species in its diet. The results of trophic interaction analysis among the predators analyzed and their non-native/invasive prey are also provided. [ABSTRACT FROM AUTHOR]

The ability of fish to sustain environmental perturbations during fragile early‐life stages can be of vital importance for populations and species facing rapid global environmental change. One of the potential challenges for aquatic organisms, including teleost fish, is rising concentration of dissolved organic carbon (DOC) in freshwater environments, known as brownification, which causes a cascade of changes including a decreased visibility and pH. Conversely, humic substances are increasingly recognised for their potential antimicrobial and immunostimulant properties. The questions remain whether exposure to humic waters high in DOC during the development causes significant perturbation, and to what extent genetic and parental factors may maintain optimal development in such a possibly challenging environment.To address these questions, we generated pure and hybrid (inter‐population) crosses of Eurasian perch (Perca fluviatilis) originating from clear‐water and humic lakes. Fertilised eggs from each cross were exposed to natural humic and clear‐water lake water. Intra‐chorionic space diameter (embryo diameter) and hatching success were recorded.Perch embryos successfully developed even in a small volume of water (5 mL) and majority hatched (70%) by 13 day post‐fertilisation. Embryo diameter was influenced by the interaction between cross type and treatment where embryos with maternal clear‐water origin were smaller than embryos of humic water origin in both clear‐water and humic water treatments. The probability of hatching was not related to female size, but rather to embryo diameter at the eyed stage and the interaction between cross type and treatment, resulting in pure clear‐water crosses hatching earlier and at higher numbers.Our study shows that effects of humic water are not uniformally negative in perch and discloses population‐dependent responses to humic water exposure during development. Our experimental design also illustrates the utility of multi‐well plates for conducting complex high‐throughput experiments beyond traditional model species and opens new possibilities for testing perch genotype–environment associations in early‐life traits.Taken together, results of this study add to the growing evidence that humic substances may have complex effects on fish during early life, motivating further investigations on their role in shaping natural phenotypes and potential use in the applied sector. [ABSTRACT FROM AUTHOR]

Whether foraging sunbird pollinators hover or perch, the type of perch used, and the direction of flower probing are generally thought to be determined by matching shapes of decurved bird bills and curved flower tubes, as well as inflorescence architecture. However, few studies have objectively quantified aspects of sunbird foraging behaviour to test predictions based on adaptive trait matching. I investigated sunbird foraging in a population of Pelargonium fulgidum, a species with slightly upcurved flowers borne on upward-oriented peduncles, which grows along the west coast of South Africa. Long-range photographs revealed that Cinyris chalybeus, a sunbird species with a slightly decurved bill, hovers or perches during foraging, and uses both the inflorescence and alternative vegetation structures as perch. Contrary to previous suggestions, both male and female sunbirds probe flowers from either of two alternative directions (sternotribic versus nototribic) in more or less equal proportions, and frequently display flexibility in both foraging behaviour and flower probing direction. Predominant or complete sternotribic and nototribic flower probing were explained by hovering versus use of an inflorescence perch respectively, whereas use of an alternative perch resulted in similar proportions of each mode of flower probing. The number of flowers per visited inflorescence and number and proportion of probed flowers did not vary with foraging behaviour or flower probing direction. Although certain foraging behaviours resulted in predictable flower probing directions, variation in foraging behaviour and the presence of many alternative perches provided by vegetation surrounding P. fulgidum plants resulted in variability in flower probing direction that appears not to affect foraging efficiency. Relatively weak reciprocal curvature of flower tube and sunbird bill, resulting in easy access to nectar from multiple feeding directions, likely facilitates flexible foraging. This study shows that environmental context may facilitate more complex foraging behaviour than that predicted by adaptive trait matching. [ABSTRACT FROM AUTHOR]

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The presence of microplastics (MP) in the organs of five fish species caught in the freshwater reservoirs of northern Poland was evaluated. Gills, liver, and digestive tracts of several commercial fish species such as common perch, silver Prussian carp, roach, and rainbow trout were tested to assess MP uptake due to their high population size as well as they play significant role as biomonitors. Since the mentioned species are gladly consumed they can be considered as a source of MP for humans. MP items were identified in all fish species. The highest contribution of MP was observed in predatory fish such as rainbow trout and perch. None of the correlations between MP abundance and fish body size. The number of items per individual fish ranged from 1 to 12, with an average of 1.78. Among the investigated MP shapes two types were found: fibers (56 %) and particles (44 %). MP were observed in different organs, such as the gills (50 %), liver (11 %), and digestive tract (39 %). The most dominant color observed was blue (58 %). The dominant size range was 1–5 mm (42 %), and 0.1–0.5 mm (42 %) respectively. The FT-IR characterization revealed the presence of polymers predominantly containing polyethylene, polypropylene, polyacrylic acid, cellophane, and polystyrene. [ABSTRACT FROM AUTHOR]

As one of the world's most regulated river basins, the semi-arid Murray–Darling Basin (MDB) in south-eastern Australia is considered at high ecological risk, with substantial declines in native fish populations already identified and climate change threats looming. This places great importance on the collection and use of data to document population trends over large spatial extents, inform management decisions, and provide baselines from which change can be measured. We used two medium-term data sets (10 MDB basin-wide fish surveys from 2004–2022) covering the 23 catchments and 68 sub-catchments of the MDB to investigate trends in the distribution of common riverine species at the entire basin scale. Fifteen native species were analysed for changes in their contemporary range, and whilst short-term changes were identified, all species showed no significant continuous trend over the study period. We further analysed the native species extent relative to their historic records, with bony herring and golden perch occurring in 78% and 68% of their historic river kilometres, respectively, whereas southern pygmy perch, northern river blackfish, silver perch, mountain galaxias, and freshwater catfish were all estimated to occur in less than 10% of their historic extent. Six established non-native species were also analysed and were very consistent in extent over the years, suggesting that they are near the available limits of expansion of their invasion. We provide effect sizes for the spatial extent index which can be used as baselines for future studies, especially those aiming to monitor changes in the spatial extent and population status of native species, or changes in the spatial extent of new or existing non-native species. [ABSTRACT FROM AUTHOR]

Growth is one of the most direct and common ways fish respond to climate change, as fish growth is intimately linked to the temperature of the environment. Observational studies on the effect of shifts in temperature on fish growth are scarce for freshwater fish, and particularly lacking for lake populations. Here, changes in growth rate of bream (Abramis brama), perch (Perca fluviatilis), pikeperch (Sander lucioperca), and roach (Rutilus rutilus) over three decades were studied and compared with changes in temperature in the two largest lakes of western Europe: Lake IJsselmeer and Lake Markermeer in the Netherlands. In the autumnal survey catches of bream, perch, and roach, the mean length of YOY increased significantly between 1992 and 2021 in both lakes, but for YOY pikeperch, no temporal changes were found. In a length‐stratified dataset of age groups of bream, roach, and perch, the relationship between length and age differed significantly between time periods. In the more recent time periods, indications for higher growth rates across multiple ages were found. Temperature during the growth season increased in the same decades and showed significant correlations with the YOY mean length, for bream, perch, and roach in both lakes, and for pikeperch in Lake Markermeer. These results point toward consistent temperature‐induced increases in growth over the age groups for bream, roach, and perch. These increases were found despite the simultaneous process of de‐eutrophication in this water system and its potential negative effect on food production. For pikeperch, it is hypothesized that the absence of temporal increase in YOY growth rate is related to its necessary switch to piscivory and subsequent food limitation; the lower thermal range of its main prey smelt, Osmerus eperlanus, is hypothesized to have inhibited food availability for YOY pikeperch and its opportunity to achieve higher growth rates. [ABSTRACT FROM AUTHOR]

Two forms of gigantism are differentiated in fish, Brobdingnagian and Goliathan gigantism, the former applying to populations whose individuals are all larger than is typical for the taxon, the latter to single individuals within a population. While Brobdingnagian gigantism is largely explained by various ecological and evolutionary rules, Goliathan gigantism is not. A mechanistic hypothesis is proposed which explains Goliathan gigantism in terms of the reduction of oxygen requirements of individual fish via moving to cooler temperatures and/or acquiring larger, more energy‐dense prey, which enable them to get bigger, and, in the process, sometimes generate bimodal size distributions that may qualify as gradual forms between Goliathan and Brobdingnagian gigantism. This mechanism, which relies on the manner in which their gill surface area grows, is more likely to operate in fish that can get big in the first place than in fish that remain small. [ABSTRACT FROM AUTHOR]

The loss of biodiversity and biotic homogenization are on the rise in ecosystems around the world as a result of species invasions, habitat degradation, and the effects of climate change. In the Sacramento–San Joaquin Delta, nonnative species make up the majority of the fish community, and declines in native species have been well documented; however, little is known about whether these trends have resulted in biotic homogenization. In this study, we used data from a long-term beach seine survey to analyze regional beta diversity trends of nearshore fish assemblages in the Delta from 1995 to 2019. Overall, we found no evidence of regional biotic homogenization occurring over the study period. Regional beta diversity increased moderately over time and was significantly influenced by the high interannual variability of freshwater inflow. These beta diversity patterns were driven by the non-native Mississippi Silverside that has proliferated in the system in recent years, but also by a handful of native fish species such as the Sacramento Sucker, Tule Perch, and Splittail. Overall, our results offer a contrast to other highly invaded ecosystems around the world and suggest that despite the near extinction of some native fish species, there remain pockets of suitable habitat in the Delta that may play a key role in the conservation of remnant native fish diversity. [ABSTRACT FROM AUTHOR]

Fish meat is recommended for consumption as a source of protein, essential unsaturated fatty acids, and fat-soluble vitamins, unfortunately it can also be a source of dangerous contaminants. The aim of the study was to assessment the level of Zn, Cu and Pb in water and bottom sediments collected in summer and autumn from the Koronowo Reservoir and the Wierzchucińskie Duże Lake and in the tissues of perch (Perca fluviatilis L.) and rudd (Scardinius erythrophtalmus L.) for health risk assessment of potential consumers. Metals accumulated in the tissues in the following order: meat, liver and gills: Zn > Cu > Pb. Of the four factors taken into account, such as: type of tissue, fish species, catching season and place of catching, the first one determined the degree of metal accumulation to the greatest extent. The high level of Pb in muscle tissue was determined by the content of this metal in tissue collected from rudd from Wierzchucińskie Duże Lake in the summer (0.383 mg kg−1 ww). The bioconcentration factor (BCF) of Pb, Zn and Cu in all tissues of analysed fish was much higher from water than from sediments. The highest value of metal pollution index (MPI) in the meat (1.42), liver (12.97), and gills (8.49) was calculated for summer-caught fish. The research indicated that consumption of 100 g of fish meat could meet daily requirement for Zn up to 26.3 % and for Cu in 16.4 %. The potential risk of Pb consumption according to RDA is as much as 2.4 %.

Wound healing incurs various challenges, making it an important topic in medicine. Short-chain peptides from fish protein hydrolysates possess wound healing properties that may represent a solution. In this study, perch hydrolysates were produced from perch side steams using a designed commercial complex enzyme via a proprietary pressure extraction technique. The average molecular weight of the perch peptides was 1289 kDa, and 62.60% of the peptides had a low molecular weight (≤1 kDa). Similarly to the beneficial amino acid sequence FPSIVGRP, FPSLVRGP accounted for 6.21% abundance may have a potential antihypertensive effect. The concentrations of collagen composition and branched-chain amino acids were 1183 and 1122 mg/100 g, respectively. In a fibroblast model, active perch peptides accelerated wound healing mainly by increasing the secretion of procollagen I, fibronectin, and hyaluronan. In an SD rat model established to mimic human wounds, orally administered perch hydrolysates with a molecular weight below 2.3 kDa accelerated wound healing, which mainly resulted from collagen-forming amino acids, branched-chain amino acids, and matrikine. Collectively, the residue of perch extract can be upcycled via a hydrolysis technique to produce not only bioactive sequences but also short-chain peptides. Considering the therapeutic potential to promote wound healing, such by-products are of great value and may be developed as dietary nutraceuticals.

Day and nighttime autumn fish abundance and biomass were studied in the pelagic and littoral zones of Lake Sauka in Latvia. Both pelagic methods (hydroacoustics and trawling) revealed significantly higher fish abundance and biomass during the day than at night, especially in deeper zones (below 3 m). Roach (Rutilus rutilus) and Eurasian perch (Perca fluviatilis) dominated the trawl catches during the day, while roach and ruffe dominated at night. Fish smaller than 14 cm strongly dominated in both the trawl catches and hydroacoustic observations. Our hydroacoustic sampling found inhomogeneous pelagic distributions of fish aggregated in big shoals during the day. In the littoral zone, which was sampled by beach seining, both the abundance and biomass were significantly higher at night than during the day. Roach, bleak, and European perch usually dominated in beach seine catches during the day and at night. The daytime pelagic biomass found by hydroacoustics was 62 kg/ha and it decreased to approximately 11 kg/ha at night. The littoral biomass found by beach seining was diurnally opposite, 4 kg/ha during the day and 37 kg/ha at night. It is obvious that diurnal horizontal migrations between pelagic and littoral zones, and shoaling behavior during the daytime are common patterns in the shallow Lake Sauka during the autumn. The study of the spatial distribution of fish is extremely important for the establishment of an appropriate monitoring plan for the purposes of the Water Framework Directive with regard to the morphometry of the lake, the geographical location, and the sampling period of the year. This study also shows that the combination of completely non‐invasive hydroacoustic and other methods that are invasive (trawls, beach seines) but not as destructive as gillnets, which are normally used for scientific fish monitoring in Europe, could be a future way forward for fish monitoring. [ABSTRACT FROM AUTHOR]

We conducted an acoustic telemetry study of native golden perch (Macquaria ambigua) to examine movement behaviour in areas affected by methane seeps and hypoxia in the intermittent Condamine River, Murray‐Darling Basin (MDB), Australia.Fish were collected during periods of no flow and hypoxia (dissolved oxygen [DO] <1 mg/L). Despite these conditions, 38 of 43 fish tagged with acoustic transmitters were detected for >3 months post‐tagging in the study reach and 27 fish were being detected after 14 months. During periods of elevated river flow and relatively high DO, 30 fish moved away from their original tagging locations, with three undertaking movements (>7 km) outside the study reach and not returning.Generalised additive mixed models showed a significant increase in the probability of movement as soon as flow commenced and when water temperatures exceeded 19°C. As flows receded, most fish that had moved exhibited accurate homing behaviour to their original tagging location.The patterns of movement and site fidelity exhibited by golden perch correspond with previous studies of the species in intermittent rivers not affected by methane seeps and severe hypoxia, suggesting that the methane seeps and hypoxia did not inhibit fish movement nor render the affected habitats unsuitable for habitation.Golden perch can survive and remain active in water with much lower DO (<1 mg/L) than previously described for large‐bodied native fishes in the MDB. However, fish condition in the study reach was slightly lower than other regions of the MDB, providing preliminary evidence that fish residing in habitats affected by chronic hypoxia and methane seepage may experience sub‐lethal stress.Our results demonstrate the importance of field‐based data on the behavioural and physiological responses of fish to chronic hypoxia and methane exposure to guide appropriate management responses. [ABSTRACT FROM AUTHOR]

Aim: Biotic interchanges between Africa, India, and Eurasia are central to explaining the present‐day distribution and diversity of freshwater organisms across these landmasses. Synbranchiformes is a diverse and species‐rich clade of freshwater acanthomorph fishes found on all southern continents except Antarctica, and include eel‐ and perch‐like, air‐breathing and non‐air‐breathing fishes. Lacking a comprehensive and resolved phylogeny of the entire clade, contemporary interpretations of synbranchiform biogeography invoke scenarios as disparate as Gondwanan vicariance and pan‐global rafting to explain their modern‐day distribution. Here, we study their biogeographic history of continental dispersal events and test whether these are associated with increases in lineage diversification. Location: Asia, India, Africa freshwater habitats. Taxon: Synbranchiformes (gouramis, snakeheads, swamp eels, and relatives). Methods: We used nearly 1000 ultra‐conserved elements (UCEs) and Sanger‐sequenced genes to infer a phylogeny with representatives of all major synbranchiform lineages and nearly two‐thirds of its known species diversity. Incorporating fossil calibrations, we inferred a time‐calibrated phylogeny to which we apply Bayesian methods of ancestral area reconstruction and test for diversification rate shifts. Results: Analyses of UCE data provide a resolved phylogeny for major synbranchiform lineages. Divergence times support a most recent common ancestor of the entire clade approximately 79.2 million years ago. We infer significant increases in lineage diversification in both the spiny eels (Mastacembelidae) and the genus Betta (Osphronemidae). Main Conclusions: Our results reject the hypothesis of Gondwanan vicariance explaining synbranchiform biogeography. Instead, our analyses reconstruct a southeast Asian origin of the entire clade and independent dispersal events to other continents by snakeheads, anabantids, and spiny eels, with no signal of elevated lineage diversification occurring after these invasions. Higher lineage diversification rates in spiny eels pre‐date their arrival to Africa, while the high diversification rates observed in Betta were initiated prior to the flooding of insular Sundaland in southeast Asia. [ABSTRACT FROM AUTHOR]

Non-neoplastic thyroid hyperplasia is common in terrestrial animals, secondary to nutritional imbalances or other goitrogenic compounds. Thyroid hyperplasia is relatively common in teleost fish; however, malignant thyroid neoplasia is rarely reported. We diagnosed cases of thyroid neoplasia in a population of jade perch (Scortum barcoo). The 3,000 affected fish had grossly apparent, bilateral pharyngeal swellings. Histologic examination confirmed proliferative thyroid lesions ranging from hyperplasia to well-differentiated follicular cell carcinoma. In addition, the younger population of animals on the farm also had bacterial septicemia and mild Dactylogyrus sp. gill infections. Feed analysis revealed a severe deficiency of iodine and vitamin C in the homemade fish diet used on the farm. The concentrations of other minerals, such as zinc, were also on the lower end of the recommended requirements for freshwater fish. The farm was using surface water in its recirculating aquaculture system. We recommended a switch to a commercial aquaculture diet, as well as to use well water rather than surface water to avoid any contaminants, and to treat the younger fish with an antibiotic for bacterial septicemia. Our case provides evidence of progression from nutritional-associated thyroid hyperplasia to neoplasia in farmed teleost fish. [ABSTRACT FROM AUTHOR]

Widespread persistent contaminants are a global environmental problem. In the Baltic Sea, wildlife contamination was first noticed in the 1960s, prompting the Swedish Environmental Protection Agency to establish a comprehensive Swedish National Monitoring Programme for Contaminants in Marine Biota (MCoM) in 1978 run by the Swedish Museum of Natural History. Eight species have been analysed, four fish species (Atlantic herring, Atlantic cod, European perch, viviparous eelpout), one bivalve species (blue mussel), and egg from three bird species (common guillemot, common tern, Eurasian oystercatcher). Here, we present a dataset containing MCoM data from its start until 2021. It includes 36 sets of time-series, each analysed for more than 100 contaminants. The longest time-series is for common guillemot and starts in 1968. We describe the structure of MCoM including historic changes to the number of stations, sample treatment, analytical methods, instruments, and laboratories. The MCoM data is available at the Bolin Centre repository and on GitHub through our R package mcomDb. The latter will be updated yearly with new MCoM records. [ABSTRACT FROM AUTHOR]

The St. Lawrence River is an important North American waterway that is subject to anthropogenic pressures including intensive urbanization, and agricultural development. Pesticides are widely used for agricultural activities in fields surrounding the yellow perch (Perca flavescens) habitat in Lake St. Pierre (Quebec, Canada), a fluvial lake of the river where the perch population has collapsed. Clothianidin and chlorantraniliprole were two of the most detected insecticides in surface waters near perch spawning areas. The objectives of the present study were to evaluate the transcriptional and biochemical effects of these two pesticides on juvenile yellow perch exposed for 28d to environmental doses of each compound alone and in a mixture under laboratory/aquaria conditions. Hepatic mRNA-sequencing revealed an effect of chlorantraniliprole alone (37 genes) and combined with clothianidin (251 genes), but no effects of clothianidin alone were observed in perch. Dysregulated genes were mostly related to circadian rhythms and to Ca2+ signaling, the latter effect has been previously associated with chlorantraniliprole mode of action in insects. Moreover, chronic exposure to clothianidin increased the activity of acetylcholinesterase in the brain of exposed fish, suggesting a potential non-target effect of this insecticide. Further analyses of three clock genes by qRT-PCR suggested that part of the observed effects of chlorantraniliprole on the circadian gene regulation of juvenile perch could be the result of time-of-day of sacrifice. These results provide insight into biological effects of insecticides in juvenile perch and highlight the importance of considering the circadian rhythm in experimental design and results analyses. [ABSTRACT FROM AUTHOR]

It is well established that non‐native fish can become invasive and outcompete and displace native fish populations. However, little research has explored the potential benefits that non‐native fish may provide to native fish populations. To address this information gap, we examined how the availability of non‐native perch (Perca fluviatilis) as prey could benefit populations of the endemic longfin eel (Anguilla dieffenbachii) and the native shortfin eel (Anguilla australis) in two neighbouring open‐water wetlands in the Rakatu‐Redcliff wetland complex in the Southland region of Aotearoa New Zealand. The Redcliff wetland fish community comprised native fish only, while the Rakatu wetland comprised native fish and non‐native perch. We compared the size, condition, population density, population size structure and diet of eels in these wetlands. While eels were not necessarily larger or better conditioned in Rakatu wetland, their population density was three times higher than the Redcliff wetland, with young‐of‐the‐year perch comprising ca. 40% of their diet. Furthermore, juvenile eel density was four times lower in Redcliff wetland, suggesting that cannibalism may occur at this site to support the existing eel population. Based on our findings, we suggest that freshwater managers consider the predator–prey dynamics of both native and non‐native fish before removing non‐native species, to avoid unintended negative consequences for native predatory fish species. [ABSTRACT FROM AUTHOR]

The phenomenon of sexual dimorphism in climbing perch, which shows that female fish grow faster than males, underlies the development of mono-sex culture. Female mono-sex culture is more applicable for farmers by crossing neo-male fish with normal females. The timing of sexual differentiation in climbing perch is still unknown. It is very useful in sex reversal procedures to produce neo-male climbing perch. This study revealed the time and status of climbing perch sexual differentiation. Ten samples of climbing perch from the spawning of five pairs of parents were taken from the nursery pond at 10–29 days post-hatching (dph). Samples were prepared through a histology preparation procedure. Observations of the structure and characteristics of the gonads were carried out using a light microscope and analyzed histologically. The results indicated that gonad samples aged 10, 11, 12, 13, 15, and 16 dph showed primordial germ cells surrounded by somatic tissue forming genital ridges and mitotic division. Meanwhile, the gonads begin to differentiate as ovaries found at 18 dph with the presence of oogonia and ovarian cavities. Gonads aged 20–21 dph increasingly showed single oogonia cells (size 20–37.5 µm), germ cell cysts, genital ridges, oocytes undergoing the vitellogenesis process, perinucleolar oocytes, and the formation of the ovarian cavity. Sex differentiation of climbing perch was predicted from 18–21 dph. This conclusion underlies that the sex reversal procedure in climbing perch must be carried out before 18 dph. [ABSTRACT FROM AUTHOR]

Understanding the impact of anthropogenic threats, such as light pollution, on biodiversity is necessary to establish effective guidelines to protect diminishing wildlife. In this study, we examined the effect of artificial light at night (ALAN) on the roosting behaviour of Chimney Swifts Chaetura pelagica, a highly threatened migratory bird species that lives commensally with humans, where it often breeds and roosts in artificial structures such as chimneys. Although Chimney Swifts are known to use time of sunset in combination with temperature, wind and season to coordinate roost entry, we predicted that high ALAN exposure would override these natural cues and lead to a delayed entry compared with sites with less light pollution. To test this, we examined the effects of ALAN on the start and end times of entry to 21 roosting sites located along a light pollution gradient in New Jersey and the New York Metropolitan area. We found that ALAN was a significant predictor of roosting entry time, with birds entering later in sites with more light pollution. While Chimney Swifts initiated roosting earlier in the summer months compared with the autumn, this effect was absent in areas with high light pollution. These findings highlight the need to determine the causes and consequences of light pollution effects. [ABSTRACT FROM AUTHOR]

We have studied the regularities that determine the preservation and/or change in statistically significant differences when switching from comparing the average values of plastic traits of juvenile fish to comparing the average values of their indices. An algorithm for evaluating the factors determining the variability of plastic traits and their indices in allometry has been proposed. We identified and parametrized three cases of variability: (a) statistically significant differences are absent between the values of plastic traits and their indices, (b) significant differences disappear when switching from comparing features to comparing their indices, and (c) significant differences in both cases remain. Case (b) is associated with different initial length of juveniles and different hatching time; case (c) is determined by different growth rates in the compared groups. The approach was tested on the selection of fingerlings of the Perca fluviatilus L. perch from two water bodies of the Staritsky district of Tver oblast. [ABSTRACT FROM AUTHOR]

We investigated 14 antibiotic residues in 8 marketed freshwater fish species from southeast China and estimated the associated health risks to local consumers. The antibiotic residues were determined by UPLC-MS/MS. Our findings revealed widespread distribution of quinolones (QNs), tetracyclines (TCs), and chloramphenicols (CAPs) in the freshwater fish. Notably, the average concentrations of enrofloxacin and ciprofloxacin reached levels as high as 62.5 μg/kg wet weight (ww) and 11.7 μg/kg ww, respectively, and detection frequencies were 68.7% for enrofloxacin and 31.6% for ciprofloxacin. Additionally, we detected chloramphenicol, a prohibited antibiotic, in samples with a detection frequency of 0.76%. Among the fish species, the mean concentration of total antibiotic residues was highest in bluntnose black bream (263.3 μg/kg), followed by English perch (52.4 μg/kg), crucian carp (46.3 μg/kg), black carp (28.6 μg/kg), yellowcheek carp (21.0 μg/kg), grass carp (15.3 μg/kg), bighead carp (3.78 μg/kg), and mandarin fish (3.69 μg/kg). We estimated the daily intake values of these antibiotic residues which were lower than the acceptable daily intake values and hazard indexes were much less than 1. It indicates that there is very low direct health risk to consumers. Despite that, investigation on the chronic impact, such as antibiotic-resistant bacteria, gut microbiota disruption, and allergic reactions, is urgently needed. [ABSTRACT FROM AUTHOR]

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]

One of the negative impacts of non-native invasive species on trophic interactions in an invaded ecosystem occurs via increased interspecific competition for food resources between the invader and local species of the same food niche. In freshwaters, there are usually several fish species that feed on similar food resources. Ponto-Caspian gobies are amongst the most successful and widespread invaders colonising European waterways. They have a wide food niche and an opportunistic feeding strategy, with a focus on benthic invertebrates and piscivory occurring occasionally mainly in the case of large individuals. Competition with native percids for food resources is predicted on the basis of high dietary overlap. However, studies published so far provide no unequivocal answer. In order to resolve this question, we conducted a comparative taxonomic analysis of gut content, with an emphasis on chironomids and amphipods, of the invasive monkey goby (Neogobius fluviatilis), racer goby (Babka gymnotrachelus) and the native Eurasian perch (Perca fluviatilis) occurring sympatrically in a large lowland European river, the Bug River in Poland. We found that each species forages in slightly different habitats, as indicated by the different composition of prey species in the gut content. This suggests feeding niche partitioning between the studied species facilitating their co-existence and reduction or avoidance of competition for food resources. Resource partitioning regarding prey types and foraging habitats is a mechanism for permitting the co-existence of closely-related alien gobies with similar food preferences in the invaded waters and co-occurrence with local species. This mechanism can contribute to their invasion success, as observed in European waters during the recent decades. We also demonstrate that precise prey identification to the lowest possible taxon is crucial to reveal the dietary overlap between co-occurring fish species and to predict the impact of alien invaders on native species through interspecific competition, as well as to recommend such an approach in studies upon fish foraging strategies. [ABSTRACT FROM AUTHOR]

The present work is the first comprehensive study of fungus‐like stramenopilous organisms (Oomycota) diversity in Lithuanian fish farms aimed at proper identification of saprolegniasis pathogens, which is important for water quality control, monitoring infection levels and choosing more effective treatments for this disease in aquaculture. Pathogenic to fish, Saprolegnia and other potentially pathogenic water moulds were isolated from adult fish, their eggs, fry and from water samples. All detected isolates were examined morphologically and confirmed by sequence‐based molecular methods. A total of eight species belonging to the genera Saprolegnia, Achlya, Newbya and Pythium were identified. Four species (S. parasitica, S. ferax, S. australis and S. diclina) were found to be the main causative agents of saprolegniasis in Lithuania. S. parasitica and S. ferax dominated both in hatcheries and open fishponds, accounting for 66.2% of all isolates. S. parasitica was isolated from all farmed salmonid fish species as well as from the skin of Cyprinus carpio, Carassius carassius and Perca fluviatilis. S. australis was isolated from water and once from the skin of Oncorhynchus mykiss, and S. diclina was detected only once on the skin of Salmo salar fish. In addition, Achlya ambisexualis, Saprolegnia anisospora and Newbia oligocantha isolated during this study are noted as a possible source of saprolegniasis. The results of this study are relevant for assessing the risk of potential outbreaks of saprolegniasis or other saprolegnia‐like infection in Lithuanian freshwater aquaculture. [ABSTRACT FROM AUTHOR]

A helminthological survey of three fish species (Perca fluviatilis, Stizostedion lucioperca and Esox lucius) from the lower section of the Dniprovske Reservoir (also known as Zaporizhzhia) revealed the presence of the dioctophymatid nematode Eustrongylides excisus (third stage larvae). The study was conducted in 2020 and 2021. It was found that the total prevalence of infection was more than 40%. The nematode was found in the liver, abdomen and muscles. Significant tissue lesions were observed in some fish specimens. They were visually accompanied by mechanical damage, oedema and inflammation. The intensity of infection in P. fluviatilis and S. lucioperca was 14.18 ± 0.81 and 12.69 ± 0.73, respectively. In turn, the intensity of infection in E. lucius had the lowest value 2.40 ± 0.41. The abdomen and muscles of P. fluviatilis and S. lucioperca were affected more than the liver. No statistically significant differences were found between the intensity of infection of the abdomen and muscles in P. fluviatilis. Furthermore, the musculature of S. lucioperca was more heavily infected than the abdomen. In E. lucius, nematodes were found only in the abdominal cavity. [ABSTRACT FROM AUTHOR]

Simple Summary: Basic information on the ecology and behaviour of many aquatic insects is lacking because of the absence of studies. Here, we investigated whether demographic aspects such as survival, sex ratio, and population size are different between sexes and individuals of different ages of Teinopodagrion oscillans, a damselfly species endemic to the Andean region, living in a protected area. We also recorded the behaviour of this species and the area frequented by the adults near the water. Survival, recapture, and lifespan (14.1 ± 0.59 days) were similar for both sexes and all age groups. Mature males were larger, while the distance from the water where animals perched was similar for all individuals. Weather variations affected the demography of this population in a significant way. Individuals perch on any available support (≤0.1–12 m high) and show high fidelity to their perch site, with mature males making short flights from the perch to intercept other individuals and to hunt prey. The tandem position was formed on macrophytes, and females lay eggs by submersion of their abdomen. Our results provide crucial information for short- and long-term conservation decisions of the biodiversity in ecosystems of the Andean region. The demography and behaviour of Teinopodagrion oscillans was studied in a protected area in the Andean region of Colombia. Adult damselflies were individually marked, and using their recapture histories, we estimated survival, longevity, sex ratio, and population size using Cormack-Jolly-Seber models. Other aspects of their behaviour were recorded. Survival, recapture, and lifespan (14.1 ± 0.59 days) were similar for both sexes and all age groups. Mature males were larger, and the distance from the water was similar for all individuals. The most supported model was the time-dependent model for survival and recapture. This suggests that weather variations affect the demography of this population in a significant way. Individuals exhibited high fidelity to their site perch, perching with open wings near water on a variety of perches. Mature males make short flights from the perch to intercept conspecific and interspecific males and to hunt prey. The tandem position was formed on macrophytes, and then the pair flew away. Oviposition lasted for 11.23 min on average, with the females ovipositing by abdomen submersion. Our results offer insights into the demographic characteristics and behaviour of this species, providing crucial information for the short- and long-term, from the demography of one species to the conservation of ecosystems of the Andean region. [ABSTRACT FROM AUTHOR]

The size and shape variability of three bones of river perch from two adjacent reservoirs in the upper reaches of the Techa River (the Southern Urals, Russia), the Techa storage reservoir cascade of liquid radioactive technogenic wastes (contaminated for over 50 years), and Lake Irtyash (control) has been studied using geometric morphometrics methods. Perch bones in adjacent populations differ in shape; however, they are similar in growth rates. The range of sex variability of the bone shape is on average 5.4 times less than the intergroup differences of the perch population. With age, the frontal bone growth rates slow down, the praeoperculum growth rates do not change, and the cleithrum increases. Sexual dimorphism in bone sizes of older fish and a low level of sex differences in the shape of the frontal bone and praeoperculum in the Techa cascade population has been revealed. These data characterize a high degree of phenotypic plasticity of the perch and adaptive restructuring of its morphogenesis associated with the local environment of technogenic reservoirs. [ABSTRACT FROM AUTHOR]

Integrated multi-trophic aquaculture (IMTA) is a solution to biomitigate waste by rearing species from different trophic levels. In European freshwater fishponds, common carp is often produced along with secondary fish species. Developing recycling IMTA systems requires better understanding of the complexity of trophic interactions between fish. Analyses of fatty acid and stable isotopes of carbon and nitrogen are suitable tools for determining food preferences of fish species. Three IMTA systems, including carp, roach, rudd and perch, were investigated in ponds: a semi-intensive (SI) pond in which fish were fed pellets; a semi-intensive pond in which fish were fed pellets, coupled with a lagoon planted with macrophytes (SIC); and an extensive (E) pond in which fish were not fed pellets. In the SI and SIC ponds, fatty acid profiles of carp, roach and rudd were closed to those of pellets. The δ13C and δ15N values of fish confirmed that they mainly fed on pellets, but the diet of roach and rudd also contained natural food sources. In the E ponds, fatty acid profiles of carp, roach and rudd slightly differed but their δ13C and δ15N values were similar. Mixing model indicated that fish from E ponds mainly fed on zooplankton. Regardless of the IMTA systems, fatty acid and stable isotope analyses indicated that juveniles consumed mainly large zooplankton. In the three systems, the FA profile of perch was closed to that of juvenile fish. Mixing model estimated that perch supplemented their diet with large zooplankton and crayfish. In the SI and SIC ponds, the distribution of commercial pellets drove the trophic interactions among fish. In the E ponds, fish had significant feeding overlap due to the limited resources available. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the impact of three aquaculture production systems on the biodiversity and productivity of aquatic invertebrates. We compared two conventional fishpond designs (extensive and semi-intensive) with a new design combining a semi-intensive carp polyculture fishpond with a planted lagoon, called coupled semi-intensive design. All fishponds were stocked with the same proportions of common carp, roach, and Eurasian perch. Fish density was double in coupled semi-intensive and semi-intensive ponds compared to extensive ponds for which no formulated feed was provided. Benthic macroinvertebrates were sampled in May and September. Zooplankton was sampled monthly from May to November. For benthic macroinvertebrates, community taxonomic richness, biomass, production, and mean individual dry mass were higher in lagoons than in the coupled semi-intensive, semi-intensive and extensive fishponds. Zooplankton production was highest in extensive fishponds and lowest in coupled semi-intensive ponds. Zooplankton production peaked in summer and was lower than benthic macroinvertebrates production in May and September. Asellus aquaticus, whose production was higher in September than May, was the dominant macroinvertebrate in lagoons, but was almost absent from all fishponds. Bosmina longirostris, the most productive plankton taxon, especially in extensive fishponds, reached peak production in July and August. Our study highlighted the functional role of a shallow, fishless, planted lagoon linked to the fishpond for biodiversity and production of benthic macroinvertebrates and zooplankton. [ABSTRACT FROM AUTHOR]

In recent decades many lake fish populations have faced complex pressures particularly due to climate warming and eutrophication. In Lake Pyhäjärvi, southwest Finland, profound changes have occurred in the commercial winter fisheries targeting the coregonids vendace, Coregonus albula, and whitefish, Coregonus lavaretus. The responses of vendace have been examined earlier, and here the detailed analyses are extended to the whitefish. In the 1970s and 1980s, the coregonid fishery was sustainable, but in 1991–1998, intense exploitation led to recruitment overfishing of vendace. Despite temporarily improved growth and recruitment of whitefish during vendace decline, whitefish population biomass declined throughout the study period, while perch (Perca fluviatilis), roach (Rutilus rutilus) and ruffe (Gymnocephalus cernuus) increased and vendace and smelt (Osmerus eperlanus) maintained their abundance. As many other northern lakes, Pyhäjärvi seems to be changing from coregonid to perch dominance due to climate warming and eutrophication. Whitefish decline was associated with decreases in fecundity, winter survival of embryos, and larval density. The spawning stock was kept small by intensive fishery. The decline of the relative fecundity was likely due to food competition with vendace and especially the perch and roach populations that increased with eutrophication and more frequent hot summers. The winter survival of whitefish embryos decreased when the introduced signal crayfish (Pacifastacus leniusculus) increased. Despite decreasing fishing effort in the 2000s the larval numbers continued to decline. In the prevailing circumstances in Pyhäjärvi, whitefish will with high probability remain as a minor and still declining species of the fish assemblage. The long-term decline of the whitefish (Coregonus lavaretus) population in the boreal lake Pyhäjärvi, southwest Finland is described. Whitefish decline was associated with decreases in fecundity, winter survival of embryos, and larval density. The spawning stock was kept small by intensive fishery. [ABSTRACT FROM AUTHOR]

The trophic niche of aquatic generalist predators is influenced by ontogeny, habitat characteristics, availability and type of prey, and competitive interactions. Many interrelated lake characteristics influence the availability of prey and may thereby impact foraging niches and the trajectory of ontogenetic niche shifts. Our work uses Eurasian perch (Perca fluviatilis) as a model species to examine the correlation of multiple lake and fish community characteristics with the size‐dependency of perch populations' realised trophic niche. We used carbon and nitrogen stable isotopes to correlate the changes in perch trophic position across a gradient of total lengths in seven gravel pit lakes that differed in lake morphology, habitat heterogeneity, productivity, structural complexity, and fish community composition. Perch populations in lakes with more shallow‐water habitat reached a higher trophic position at smaller sizes than perch in deeper lakes. However, the changes in trophic position with increasing size were less pronounced compared to perch from deeper lakes. Large individuals from the latter perch populations ultimately achieved higher mean trophic positions compared to fish from shallow lakes. Perch in lakes with more shallow‐water habitat may, therefore, achieve lower rates of piscivory because of higher relative availability of macroinvertebrates or greater competition with zooplanktivores. Our results suggest that large, piscivorous perch are more likely to develop in deeper lakes, and that these changes in perch trophic position across ontogeny are more strongly related to the depth of lakes than to the type of structured habitat in the littoral zone. [ABSTRACT FROM AUTHOR]

In an experimental assessment of the stamina of fish the perch was shown to be almost twice as strong as the roach in terms of swimming power. In the early stages, interspecific differences are weakly expressed, but, with an increase in body size and weight, differentiation increases significantly. The rapid growth rate of burst swimming speed of the perch provides the ability to feed on more mobile objects. With age, the diet of fish is diverged to a large extent, roach feeding mainly on sedentary animals and plant food compared to perch almost completely switching to feeding on fish and benthic invertebrates. This allows for the potential competitive tensions in the cohabiting species to be reduced. [ABSTRACT FROM AUTHOR]

Long-chain polyunsaturated fatty acids (PUFA) are critical for reproduction and thermal adaptation. Year-round variability in the expression of fads2 (fatty acid desaturase 2) in the liver of European perch (Perca fluviatilis) in a boreal lake was tested in relation to individual variation in size, sex, and maturity, together with stable isotopes values as well as fatty acids (FA) content in different tissues and prey items. ARA and DHA primary production was restricted to the summer months, however, perch required larger amounts of these PUFA during winter, as their ARA and DHA muscle content was higher compared to summer. The expression of fads2 in perch liver increased during winter and was higher in mature females. Mature females stored DHA in their gonads already in late summer and autumn, long before the upcoming spring spawning period in May. Lower δ13CDHA values in the gonads in September suggest that these females actively synthesized DHA as part of this reproductive investment. Lower δ13CARA values in the liver of all individuals during winter suggest that perch were synthesizing essential FA to help cope with over-wintering conditions. Perch seem able to modulate its biosynthesis of physiologically required PUFA in situations of stress (fasting or cold temperatures) or in situations of high energetic demand (gonadal development). Biosynthesis of physiologically required PUFA may be an important part of survival and reproduction in aquatic food webs with long cold periods. [ABSTRACT FROM AUTHOR]