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ABSTRACT Adaptive radiation is considered to be a major source of biodiversity in charrs of the genus Salvelinus. These fishes demonstrate numerous examples of diversification in postglacial lakes and rivers resulting in the emergence of different ecomorphs, including piscivorous. Usually, the number of fish feeders does not exceed two, suggesting the existence of ecological and/or internal factors that prevent further diversification. Under these circumstances, rare instances of increases in the number of piscivorous morphs are of particular interest. Here, we present a comprehensive study of the piscivorous charr assemblage in Lake Kronotskoe, residence of the most diverse species flock of Salvelinus fishes. To unravel the diversity and ecological relationships of piscivorous charrs, we analysed their morphology and microsatellite DNA polymorphism, distribution within the lake, trophic preferences and parasite load, as well as trace element accumulation, stable isotope and free fatty acid ratios. We revealed that, apart from a few strictly benthivorous morphs, the lake is inhabited by four closely related but morphologically and genetically distinct morphs that exhibit a range of piscivorous specialisation: from opportunistic secondary predation to ultra‐specialised primary piscivory. They effectively exploit the spatiotemporal structure of the ecosystem and experience diversifying selection due to niche discordance. Each piscivorous morph develops specific phenotypic, ecological and life history traits that allow it to terminate weakly overlapping branches of the trophic chain and share the energy flows of the lake ecosystem. Our data suggest that Lake Kronotskoe facilitates high level of ecological opportunity that favours niche expansion and allows the piscivorous lineage to simultaneously realise the archetypical modes of ecological diversification available to fishes in cold‐water freshwaters. [ABSTRACT FROM AUTHOR]

Climate-related shifts in hatch timing could mean that age-0 largemouth bass Micropterus salmoides in north temperate lakes reach larger sizes and experience higher survival, which may contribute to increased prevalence of this species in many lakes. However, information on age-0 largemouth bass life history is lacking for these lakes. We estimated hatch dates, daily growth rates (DGR), and length-based probability of piscivory of age-0 largemouth bass in Wisconsin lakes to: (1) provide baseline data on early life history; (2) compare hatch timing between years with different spring temperature regimes, and (3) project how shifts in hatch timing might influence total length (TL) distributions of age-0 bass if mean DGR remained constant. Most age-0 largemouth bass (>90%) collected from ten Wisconsin lakes (N = 746) hatched between 23 May and 24 June during 2012 and 2013 and did not switch to piscivory during their first summer. Prevalence of positive correlations (16 of 24 lake-year pairings) between TL in and age indicates hatch timing may influence TLs attained by age-0 largemouth bass in August in some lake-years. Mean daily water temperatures in May 2012 were 3.1 °C warmer than in May 2013 for the five of the six lakes where hatch dates were estimated in both years. On average, earliest and median hatch dates for age-0 largemouth bass in these six lakes were 10–11 d earlier in 2012 than in 2013 and hatch duration was approximately 8 d longer in 2012. Despite differences in hatch timing, mean DGR was relatively consistent (range = 0.61–0.74 mm/d) between lakes and years. Simple simulations suggest that earlier hatch dates could result in more age-0 largemouth bass reaching TLs associated with piscivory and overwinter survival by the end of their first summer if growth rates did not change, which could translate to higher recruitment.

The development of diverse capture mechanisms during foraging allows predators to select their preys and succeed in their capture, with the least energy expenditure possible. In this context, we seek to understand how prey selection mechanisms exhibited by freshwater fish piscivores relate to their foraging mode. The study was carried out in the floodplain of the Upper Paraná River, where fish were captured from March 2006 to June 2013. The fish were identified and measured, their stomachs were removed, and the stomach contents were analysed. Quantile regressions were used to evaluate possible effects and relationships between the sizes of piscivores and their prey. A significant positive effect on the predator–prey size relationship was observed, indicating an increased size of consumed prey with increased size of piscivore, mainly for Acestrorhynchus lacustris, Hoplerythrinus unitaeniatus, Hoplias intermedius, Hoplias mbigua, Hoplias sp. 2, Pseudoplatystoma corruscans, Rhaphiodon vulpinus and Salminus brasiliensis. Ambush predators were more likely to consume slow‐moderate and fast prey, while pursue predators only consume fast prey. Several mechanisms can influence a piscivore's foraging behaviour, and body size is an important factor for both the piscivore and its prey. From the prey's point of view, the way they swim and the complexity of the habitat are important characteristics to ensure their survival. For piscivores, the foraging mode will influence the type of prey consumed, depending on the prey's swimming mode. [ABSTRACT FROM AUTHOR]

The introduction and spread of alien fish species pose a major threat to native communities and ecosystem functioning in freshwaters. Black bullhead is one of the most successful invaders in European waters with several detrimental effects on native biota and ecosystems. In this study, we used stable isotope analysis to compare the body size and season-dependent diet, trophic position, isotopic niche size, and niche overlap of the invasive black bullhead with two native fish species (roach and European perch) in Lake Balaton, Hungary. We found that black bullhead could be characterized by invertivore-piscivorous feeding habit with a high rate of fish consumption. The rate of fish predation by invasive black bullhead increased with body size, while no seasonal differences were observed in fish consumption. Contrary to our hypothesis, little evidence of actual feeding competition was found between black bullhead and native fishes. Our results suggest that the studied species assimilate distinct energy resources in different proportions leading to a substantial amount of niche partitioning among them. We conclude that black bullhead may represent a threat for native, small-sized fishes primarily through predation and recommend urgent management actions (e.g. selective removal of the species) to minimize its adverse impacts on native communities. [ABSTRACT FROM AUTHOR]

Climate change has myriad impacts on ecosystems, but the mechanisms by which it affects individual species can be difficult to pinpoint. One strategy to discover such mechanisms is to identify a specific ecological factor related to survival or reproduction and determine how that factor is affected by climate. Here we used Landsat imagery to calculate water clarity for 127 lakes in northern Wisconsin from 1995 to 2021 and thus investigate the effect of clarity on the body condition of an aquatic visual predator, the common loon (Gavia immer). In addition, we examined rainfall and temperature as potential predictors of water clarity. Body mass tracked July water clarity strongly in loon chicks, which grow chiefly in that month, but weakly in adult males and females. Long‐term mean water clarity was negatively related to chick mass but positively related to adult male mass, suggesting that loons foraging in generally clear lakes enjoy good foraging conditions in the long run but might be sensitive to perturbations in clarity during chick‐rearing. Finally, chick mass was positively related to the density of docks, perhaps because angling removes large fishes and thus boosts the abundance of the small fishes on which chicks depend. Water clarity itself declined strongly from 1995 to 2021, was negatively related to July rainfall, and was positively related to July air temperature. Our findings identified both long‐term and short‐term water clarity as strong predictors of loon foraging efficiency, and suggest that climate change, through water clarity, impacts freshwater ecosystems profoundly. Moreover, our results identified the recent decrease in water clarity as a likely cause of population decline in common loons. [ABSTRACT FROM AUTHOR]

The threatened fishing cat (Prionailurus viverrinus) is an elusive and medium-sized cat that is adapted to mangroves, swamps, wetlands and riverine habitats. A close look at the literature indicates that fishing cats are piscivorous; however, this is based on very few studies. Understanding the patterns of resource utilisation by species is crucial for assessing their role in ecosystems and in ensuring their conservation. Therefore, our study presents insights into fishing cat feeding patterns from mangroves of the Godavari delta, Andhra Pradesh, India. We collected 303 putative fishing cat scats and conducted diet analysis using 120 genetically identified scats. Our analysis revealed that fish was the most important prey for fishing cats in the study area (61.6% in frequency of occurrence), followed by crabs (30%) and rodents (28.3%). The prey composition did not vary significantly between the three seasons but there were differences between the survey years. The niche breadth also varied across the three seasons, with lowest niche breadth estimated in summers (0.36) with highest contribution of fish in the diet and highest in winters (0.75) probably due to increased contribution of other prey items along with fish. Our results suggest that long-term conservation and survival of the fishing cats depends on fish populations, which are the main prey of the species and thus recommend the need to protect the fish populations in the Godavari delta and the surrounding riverine habitats. Given the importance of fish to the diet of the fishing cat, the health of waterways throughout their distribution must be one of the focal strategies of conservation action. [ABSTRACT FROM AUTHOR]

Predation is a crucial ecosystem function, transferring nutrients and shaping the abundance and diversity of animals within communities. On coral reefs, fish-fish predation (i.e., piscivory) is arguably one of the best known ecosystem functions, yet is also one of the least well quantified. Recent work has suggested that the prey capture performance of piscivorous fishes may differ when feeding on actively swimming vs. cryptobenthic fish prey. However, the extent of this difference remains unquantified. Our goal, therefore, was to conduct performance-based experiments comparing piscivorous fishes feeding on two different fish prey types, namely, actively swimming vs. cryptobenthic prey (i.e., prey sitting on the benthos). While predators were able to immediately detect actively swimming prey, when feeding on cryptobenthic prey, predators were generally unable to detect the prey until it moved. Both focal predators, the grabber Pseudochromis fuscus and the engulfer Pterois volitans were less successful at capturing cryptobenthic prey (mean 28% probability of capture), compared to actively swimming prey (85%). Overall, our study demonstrates the heterogeneous nature of fish predation on coral reefs, and the challenges of feeding on different prey functional groups. [ABSTRACT FROM AUTHOR]

Arctic char (Salvelinus alpinus) is a top predator and the most widespread fish in Arctic lakes. The presence of Arctic char affects the predator–prey dynamics of the key species in the food webs in these lakes. This study sought to elucidate the effects of habitat (littoral, pelagic, or profundal) and lake morphometry on the trophic position of this char in the food web. Using stomach content and stable isotope analyses, we investigated the effect of fish length, habitat, and time (individual survey years: 2008, 2013, 2018, and 2019) on the dietary niches of landlocked Arctic char populations during summer in two west Greenland lakes: Badesø (area 0.8 km2, mean depth 9.2 m) and Langesø (area 0.3 km2, mean depth 5.0 m). The small char (<20 cm fork length) in Badesø generally foraged less littoral macroinvertebrates than those from Langesø. The large chars were mainly piscivorous in both lakes. In Badesø, there was a shift from relying on littoral to pelagic invertebrates by the small char from 2008–2013 to 2018–2019. The proportionally larger size of the littoral habitat in the smaller Langesø led to an increased reliance on littoral-derived macroinvertebrates in the diet of the small char, more so than in the larger Badesø, where the predominant reliance was on pelagic sources. [ABSTRACT FROM AUTHOR]

We report feeding behaviour, dates of peak reproduction, and sexual size dimorphism of the fishing bat, Noctilio leporinus, in the Gulf of Mexico. For the first time we document the size of cheek pouches in N. leporinus and fish species consumed in the water bodies of southern Mexico and analyse differences in wing morphology and biomechanical flight descriptors between the sexes. We found sexual dimorphism in size for most of the external measurements but not in wing characters. This species can consume prey up to a third of its size. We confirmed the presence of N. leporinus in localities in Tabasco, Mexico 60 years after the first report. [ABSTRACT FROM AUTHOR]

Mass spawning in fish culture often brings about a marked variance in family size, which can cause a reduction in effective population sizes in seed production for stock enhancement. This study reports an example of combined pedigree information and gene expression phenotypes to understand differential family survival mechanisms in early stages of Pacific bluefin tuna, Thunnus orientalis, in a mass culture tank. Initially, parentage was determined using the partial mitochondrial DNA control region sequence and 11 microsatellite loci at 1, 10, 15, and 40 days post-hatch (DPH). A dramatic proportional change in the families was observed at around 15 DPH; therefore, transcriptome analysis was conducted for the 15 DPH larvae using a previously developed oligonucleotide microarray. This analysis successfully addressed the family-specific gene expression phenotypes with 5739 differentially expressed genes and highlighted the importance of expression levels of gastric-function-related genes at the developmental stage for subsequent survival. This strategy demonstrated herein can be broadly applicable to species of interest in aquaculture to comprehend the molecular mechanism of parental effects on offspring survival, which will contribute to the optimization of breeding technologies.

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Evaluations of resource use among native piscivores in natural lakes have consistently documented significant partitioning that supports coexistence. Partitioning may be less prominent in reservoirs where water‐level fluctuations can compress habitat and trophic diversity, but studies are lacking. Stable isotopes and bioenergetic models were used to quantify trophic interactions within a native piscivore assemblage inhabiting a temperate irrigation reservoir and explore implications for coexistence with a focus on threatened bull trout (Salvelinus confluentus). As hypothesised, adult bull trout exhibited the greatest degree of trophic specialisation by consuming mostly coldwater pelagic forage fish, which were consumed seasonally by the more abundant burbot (Lota lota) and northern pikeminnow (Ptychocheilus oregonensis). Numerous trophic niche overlap probabilities exceeded 70%, were as high as 93% and greatest between bull trout and burbot. Bioenergetics simulations demonstrated the high seasonal consumption capacity of burbot relative to northern pikeminnow. As a result, threefold to fourfold fewer burbot were required to consume the annual productivity of coldwater prey important for bull trout, particularly in the absence of small‐bodied mesothermic or eurythermal fish as a buffer. Collectively, our analysis elucidated relatively strong trophic niche overlap among similarly sized piscivores, the importance of maintaining a diverse forage fish community for promoting coexistence and the greatest potential for competitive interactions between adult bull trout and burbot if key prey were limited or less diverse. More studies in regulated systems are needed to test for consistent patterns and identify mechanisms that limit or promote coexistence amid growing human‐induced environmental change and demands on freshwater. [ABSTRACT FROM AUTHOR]

Predation on anadromous salmon can have important consequences for both predators and prey. Salmon provide large seasonal pulses of energy and nutrients via carcasses, eggs and juveniles to many freshwater consumers, and conversely, predation can represent a significant source of mortality for juvenile salmon. Recent declines of Chinook salmon (Oncorhynchus tshawytscha) populations in Alaska have raised concern that predation might inhibit their recovery. Here, we quantify patterns of predation by freshwater fishes on juvenile salmon across seasons, habitats, predator sizes and streamflow levels in the Arctic‐Yukon‐Kuskokwim region of Alaska. We analysed piscivore stomach contents and identified prey using DNA sequence "barcoding." In coastal rivers, juvenile pink (O. gorbuscha) and chum (O. keta) salmon contributed heavily to Arctic grayling (Thymallus arcticus) and Dolly Varden char (Salvelinus malma) diets, coho salmon (O. kisutch) prey were rare, and Chinook salmon were not detected. In interior rivers, Arctic grayling, burbot (Lota lota) and northern pike (Esox lucius) consumed small numbers of Chinook salmon. Predation on Chinook salmon was documented disproportionately in sloughs during a summer of exceptionally high streamflow. Dietary and distributional patterns suggested northern pike and burbot may exclude salmon from sloughs in low‐gradient river reaches that would otherwise provide suitable rearing habitat. The data also provided tentative support for the hypothesis that high streamflow induces juvenile Chinook salmon to move from mainstem habitats into sloughs, where they face an increased risk of mortality. Incorporating predation risk into climate adaptation, fisheries management and habitat restoration decisions may help to facilitate Chinook salmon recovery. [ABSTRACT FROM AUTHOR]

The feeding ecology of juvenile Pacific bluefin tuna (PBF) Thunnus orientalis in the Sea of Japan was examined to better understand the survival process before fishery recruitment. Stomach content analysis showed that the main prey items were fish, especially Japanese anchovy Engraulis japonicus, cephalopods, mainly small squid Enoploteuthis chunii, and copepods. In addition, although both fish prey and cephalopods were important for large juveniles (100-300-mm fork length, FL), the stomach contents of small juveniles (40-99 mm FL) mainly included fish prey. The strong possibility of cannibalism was also suggested, although its contribution to total food consumption was limited. The size of fish prey increased significantly with the FL of PBF. Nitrogen isotope ratios (i.e. δ15N) also increased with increasing FL (12-227 mm), suggesting that the trophic level increases rapidly during the juvenile stage because of the active feeding on fish by PBF. Such feeding habits, especially feeding on fish, would be essential to achieve a high growth rate and would therefore be associated with the survival of juvenile PBF before recruitment in the Sea of Japan. In addition, PBF exhibited a decrease in stomach fullness during the night-time, and their estimated gastric evacuation rate was 0.36 h-1. [ABSTRACT FROM AUTHOR]

The carnivorous largemouth bass Micropterus salmoides has been introduced to many regions and poses a threat to native aquatic organisms due to predation, resulting in a significant decrease in biodiversity. Under conditions of prey scarcity, the largemouth bass is thought to consume smaller conspecifics. However, little is known about this species’ dietary reliance on intraspecific predation and its impact on the population structure. We investigated the length–frequency distribution of largemouth bass and estimated their reliance on intraspecific predation using stable carbon and nitrogen isotopes in an agricultural pond with no available prey fish. Almost all individual largemouth bass were collected via the pond drainage system. Within the largemouth bass population, the dominant length class was composed of fish measuring 100–160 mm standard length (SL), whereas few individuals measuring < 100 mm SL (first-year juveniles) were collected. The results from a Stable Isotope Analysis in R mixing model indicated that all four length classes (105–146, 165–180, 216–246, and 300–337 mm SL) of largemouth bass fed mainly on juvenile conspecifics and on red swamp crayfish (Procambarus clarkii). First-year juveniles could have been predated by other individuals of various sizes. The dominant 100–160 mm SL length class may have experienced a weak predation pressure when they were in the first-year juvenile class. Consequently, the largemouth bass population was unbalanced, with few first-year juveniles (< 100 mm SL) and dominance of a 100–160 mm SL length class.

Abstract Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times. Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios. We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants. Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

Hatchery propagation techniques, such as pellet- rearing, can result in altered feeding behaviour. Walleye Sander vitreus (Mitchill) is a commonly propagated sportfish, yet little is known regarding its ability to switch to live prey post- stocking. The objectives were to evaluate temporal changes in diet composition and condition as well as evaluate the relationship between total length and presence of different prey consumed by stocked walleye fry and fingerlings. Fingerling walleye had higher average proportions of empty stomachs and benthic invertebrates but less fish that stocked walleye fry. The presence of zooplankton, benthic invertebrates or fish was not related to walleye length. Walleye condition was similar between cohorts and did not change over days post- stocking. Percent similarity index values between cohorts were variable (0.0 to 67.9%). It was concluded that stocked walleye fingerlings consume lower quality prey items than stocked fry counterparts at least up to 49- day post- stocking, which may have implications for post- stocking survival. [ABSTRACT FROM AUTHOR]

Cisco Coregonus artedi was once an important native fish in Lake Ontario; however, after multiple population crashes, the cisco stock has yet to recover to historic abundances. Rehabilitation of cisco in Lake Ontario is a fish community management objective, but the extent to which recent non-native species and pelagic food web changes have influenced cisco is not well understood. We described cisco diets in contemporary Lake Ontario following the addition and spread of non-native zooplankton species. We collected 618 cisco and processed 178 for full diet analysis in eastern Lake Ontario using mid-water trawls and bottom-set gill nets from 2016 to 2020. We found that Lake Ontario cisco were mostly zooplanktivorous, and non-native zooplankton dominated their diet during July and September. Cisco smaller than 300 mm had a more diverse diet including both native and non-native zooplankton, while cisco larger than 300 mm fed almost exclusively on non-native predatory cladocerans Bythotrephes longimanus and Cercopagis pengoi (98.9% consumed prey dry mass). We also found fish eggs, presumed to be of coregonine origin in 75% of non-empty December-collected cisco diets, suggesting eggs subsidize cisco diets when available. Juvenile round goby Neogobius melanostomus , alewife Alosa pseudoharengus and rainbow smelt Osmerus mordax were found in 2% of all analyzed non-empty stomachs. Lake Ontario cisco diet appears to be more similar to zooplanktivorous Lake Superior cisco than Lake Michigan where piscivory is prevalent. Lake Ontario cisco diets reflected zooplankton community changes indicating that non-native predatory cladocerans are now an important energy source supporting this native species. [ABSTRACT FROM AUTHOR]

The ontogenetic diet shift to piscivory can be energetically beneficial for fish growth and allows larger, more energetically profitable prey to be consumed. A shift to piscivory may be easier for longer individuals within a cohort due to larger gape size, and an early shift is likely advantageous, potentially leading to increased growth rates and survival. Such length-dependent ontogenetic diet shifts may explain the intracohort variability in length that is common for age-0 walleye (Sander vitreus). The objectives of this study were to describe seasonal intracohort variability in length, identify the timing of the shift to piscivory and determine if the onset of piscivory was length-dependent in age-0 walleye. Walleye initially fed on zooplankton, but shifted to piscivory during July of 2010 and June of 2011. The onset of piscivory in age-0 walleye was associated with length-dependent differences during both years, in which longer individuals within the cohort became piscivorous earlier than shorter individuals within the same cohort. Intracohort variability in length was detected and increased postontogenetic diet shift. Age-0 walleye that experience a growth advantage could benefit from increased survival and feeding opportunities.

In Arizona, USA, Double-crested Cormorants (Nannopterum auritum) primarily overwinter, whereas Neotropic Cormorants (N. brasilianum) are common residents year round. Concern exists that both species are increasing in numbers and may have a negative impact on fish populations. We collected data during January 2017–April 2019 to characterize cormorant numbers seasonally, describe their foraging patterns, and evaluate environmental factors associated with cormorant numbers at community fishing waters. With more than 100 trained volunteers, we surveyed water bodies across the state simultaneously once each quarter of the year during January 2017–March 2018. We also visited 36 community fishing waters and other locations to document cormorant foraging activities and to explore potential associations between environmental factors and the maximum number of cormorants counted at each site. We collected stomach contents from lethally sampled cormorants to examine size and species of consumed fish. Our seasonal counts showed the greatest cormorant numbers during the winter and spring, with larger concentrations in metropolitan areas and fewer birds at higher elevations. At community fishing waters, cormorants fed primarily on fish ≤12 cm long, though they did consume larger sport fish in reservoirs and along the Colorado River. At community fishing waters, cormorant numbers were positively associated with the number of artificial structures in/near the water’s edge and with the number of large trees within 200 meters of the water. To reduce cormorant numbers and their anticipated impacts, we recommend stocking larger, stout-bodied fish and removing woody vegetation close to shorelines while adding fully submerged structures to provide security cover for fish from cormorants. This study is unique and important in that it addresses cormorant populations located in the southwestern USA, an area that has not historically been viewed as waterbird habitat, and it presents an unbiased evaluation of cormorant foraging activities in desert areas manipulated by water. It also offers reasonable, non-lethal actions to reducing potential cormorant impacts on aquatic resources.

Every animal dies. In nature, mortality usually occurs due to predation by other animals. One of the fundamental consequences of mortality is the transfer of energy and nutrients from one organism (prey) to another (predator). On coral reefs, these key interactions and processes, that are essential for ecosystem functioning, are primarily mediated by fishes; up to 53% of fishes on coral reefs can be regarded as piscivorous.To date, piscivory on coral reefs has been primarily studied with regard to the species piscivores feed on, and how piscivores control populations. Consequently, understanding prey selectivity by piscivorous fishes has been a major goal. However, prey functional traits may also be important in understanding these 'energy transactions', especially in complex ecosystems such as coral reefs.Our goal, therefore, was to quantify—at a community level—functional traits of prey that have been shown to influence predator–prey interactions. We found that, on average, deep‐bodied, social fishes occupy higher positions in the water column, whereas solitary species are usually elongate and more closely associated with the benthos. On closer examination, we found that solitary species have a size‐dependent relationship, with substratum associations shifting to water column associations, at approximately 50 mm body length.Our results reveal three distinct prey functional groups: cryptobenthic substratum dwellers, solitary epibenthics and social fishes. These groups display significant differences in their morphologies and behaviours. Furthermore, based on a meta‐analysis of published mortality rates of small‐bodied (<100 mm TL) reef fishes, we show that the three groups display different mortality rates, possibly due to differential exposure to, and potential to be captured by, different predator types.Although fishes are widely available on coral reefs, they may not be equally available as prey to all piscivore types. Prey are not simply victims; they are capable of influencing potential predation through functional traits. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Phytosaurs are a group of large, semi‐aquatic archosaurian reptiles from the Middle–Late Triassic. They have often been interpreted as carnivorous or piscivorous due to their large size, morphological similarity to extant crocodilians and preservation in fluvial, lacustrine and coastal deposits. However, these dietary hypotheses are difficult to test, meaning that phytosaur ecologies and their roles in Triassic food webs remain incompletely constrained. Here, we apply dental microwear textural analysis to the three‐dimensional sub‐micrometre scale tooth surface textures that form during food consumption to provide the first quantitative dietary constraints for five species of phytosaur. We furthermore explore the impacts of tooth position and cranial robustness on phytosaur microwear textures. We find subtle systematic texture differences between teeth from different positions along phytosaur tooth rows, which we interpret to be the result of different loading pressures experienced during food consumption, rather than functional partitioning of food processing along tooth rows. We find rougher microwear textures in morphologically robust taxa. This may be the result of seizing and processing larger prey items compared to those captured by gracile taxa, rather than dietary differences per se. We reveal relatively low dietary diversity between our study phytosaurs and that individual species show a lack of dietary specialization. Species are predominantly carnivorous and/or piscivorous, with two taxa exhibiting slight preferences for 'harder' invertebrates. Our results provide strong evidence for higher degrees of ecological convergence between phytosaurs and extant crocodilians than previously appreciated, furthering our understanding of the functioning and evolution of Triassic ecosystems. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, the composition of the diet and the feeding activity of Electrophorus varii were evaluated. The influence of ontogeny and seasonality in these feeding parameters was also examined. Fish were collected in the Curiaú River Basin, Amazon, Brazil, from March 2005 to February 2006, during the rainy (January-June) and dry (July-December) seasons. Diet composition was characterized based on the analysis of stomach contents and feeding dynamics was assessed based on the Stomach Fullness Index (IR) calculated using stomach weight. Stomach content and RI data were grouped into four-cm size classes (40-80, 80-120, 120-160, and 160-200) and two seasonal periods (rainy and dry). The influence of ontogeny and seasonality in the diet was investigated through PERMANOVA, and in the food dynamics through ANOVA. The analysis of stomach contents revealed that fish were the most consumed preys by electric eels, especially Callichthyidae and Cichlidae. Diet composition and RI values of electric eels were not influenced by ontogeny and seasonality. Electric eels are fish predators, regardless of size class and seasonal period.

Many modern groups of marine fishes first appear in the fossil record during the early Palaeogene (66–40 Ma), including iconic predatory lineages of spiny-rayed fishes that appear to have originated in response to ecological roles left empty after the Cretaceous/Palaeogene extinction. The hypothesis of extinction-mediated ecological release likewise predicts that other fish groups have adopted novel predatory ecologies. Here, we report remarkable trophic innovation in early Palaeogene clupeiforms (herrings and allies), a group whose modern representatives are generally small-bodied planktivores. Two forms, the early Eocene (Ypresian) †Clupeopsis from Belgium and a new genus from the middle Eocene (Lutetian) of Pakistan, bear conspicuous features indicative of predatory ecology, including large size, long gapes and caniniform dentition. Most remarkable is the presence of a single, massive vomerine fang offset from the midline in both. Numerous features of the neurocranium, suspensorium and branchial skeleton place these taxa on the engraulid (anchovy) stem as the earliest known representatives of the clade. The identification of large-bodied, piscivorous anchovies contributes to an emerging picture of a phylogenetically diverse guild of predatory ray-finned fishes in early Palaeogene marine settings, which include completely extinct lineages alongside members of modern marine groups and taxa that are today restricted to freshwater or deep-sea environments.

The carnivorous largemouth bass Micropterus salmoides has been introduced to many regions and poses a threat to native aquatic organisms due to predation, resulting in a significant decrease in biodiversity. Under conditions of prey scarcity, the largemouth bass is thought to consume smaller conspecifics. However, little is known about this species' dietary reliance on intraspecific predation and its impact on the population structure. We investigated the length–frequency distribution of largemouth bass and estimated their reliance on intraspecific predation using stable carbon and nitrogen isotopes in an agricultural pond with no available prey fish. Almost all individual largemouth bass were collected via the pond drainage system. Within the largemouth bass population, the dominant length class was composed of fish measuring 100–160 mm standard length (SL), whereas few individuals measuring < 100 mm SL (first-year juveniles) were collected. The results from a Stable Isotope Analysis in R mixing model indicated that all four length classes (105–146, 165–180, 216–246, and 300–337 mm SL) of largemouth bass fed mainly on juvenile conspecifics and on red swamp crayfish (Procambarus clarkii). First-year juveniles could have been predated by other individuals of various sizes. The dominant 100–160 mm SL length class may have experienced a weak predation pressure when they were in the first-year juvenile class. Consequently, the largemouth bass population was unbalanced, with few first-year juveniles (< 100 mm SL) and dominance of a 100–160 mm SL length class. [ABSTRACT FROM AUTHOR]

We studied the postnatal development of the skull of Noctilio leporinus, examining the relationship between ectocranial elements, including shape changes and sutures closure and fusion. Most shape changes and structure development were observed at subadults and adults; zygomatic arch, sagittal crest, occipital process and mandibular processes developed noticeably up to the adult stage. Cranial sutures closure and fusion sequences of N. leporinus agree with that of hystricomorph rodents, artiodactyls, primates, sirenians and carnivores, beginning with the cranial vault followed by the basicranium, supporting a conserved pattern for mammalia. Detailed comparisons exhibit a complete cranial sutures fusion reached earlier at Desmodus rotundus regarding N. leporinus and Pteropus sp., and an early fusion for the sutura coronalis plus late fusion for the sutura sagittalis at N. leporinus regarding Desmodus rotundus. The drastic shape changes of cranial elements, as well as sutures closure and fusion in N. leporinus at subadults and adults, seem to be closely related to the acquisition of morphological specializations during stages of development when the fisher bat begins to feed independently. [ABSTRACT FROM AUTHOR]

Andrea Soares Araújo3 In this study, the composition of the diet and the feeding activity of Electrophorus varii were evaluated. The influence of ontogeny and seasonality in these feeding parameters was also examined. Fish were collected in the Curiaú River Basin, Amazon, Brazil, from March 2005 to February 2006, during the rainy (January- June) and dry (July-December) seasons. Diet composition was characterized based on the analysis of stomach contents and feeding dynamics was assessed based on the Stomach Fullness Index (IR) calculated using stomach weight. Stomach content and RI data were grouped into four-cm size classes (40-80, 80-120, 120-160, and 160-200) and two seasonal periods (rainy and dry). The influence of ontogeny and seasonality in the diet was investigated through PERMANOVA, and in the food dynamics through ANOVA. The analysis of stomach contents revealed that fish were the most consumed preys by electric eels, especially Callichthyidae and Cichlidae. Diet composition and RI values of electric eels were not influenced by ontogeny and seasonality. Electric eels are fish predators, regardless of size class and seasonal period. [ABSTRACT FROM AUTHOR]

Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift. [ABSTRACT FROM AUTHOR]

Innovations may provide access to new resources but often result in significant trade-offs. Pharyngognathy is a classic pharyngeal jaw innovation in which the left and right lower pharyngeal jaw (LPJ) bones are united into a single structure, producing a strong bite but reduced gape. Throughout cichlids, pharyngeal suturing occurs along the entire medial border between LPJ bones, except in peacock bass (Cichla), where these bones are connected by ligaments only in their anterior region. We show that this limited attachment permits the jaw bones to spread apart and we link this feature to an increase in pharyngeal gape that is comparable to non-pharyngognathous species. The capacity of the LPJ bones to spread apart is strongest in juveniles and is mostly lost during development. Juvenile Cichla exhibit size-specific pharyngeal gape similar to non-pharyngognathous percomorphs; however, adults exhibit pharyngeal gape on par with other predatory cichlids. Relaxation of pharyngeal suturing offsets a major deleterious consequence of pharyngognathy by reducing gape limitation and we propose this may accelerate the ontogenetic transition to piscivory. Partial reversal of the classic cichlid pharyngeal jaw innovation highlights the functional trade-offs that often accompany innovations and may be a major cause of variation in their macroevolutionary consequences. [ABSTRACT FROM AUTHOR]

Individual variability in dispersal strategies, where some individuals disperse and others remain resident, is a common phenomenon across many species. Despite its important ecological consequences, the mechanisms and individual consequences of dispersal remain poorly understood. Here, riverine Northern pike (Esox lucius) juveniles (age 0+ (young‐of‐the‐year) and 1+ years) were used to investigate the influence of body size and trophic position (at capture) on the dispersal from off‐channel natal habitats and the subsequent consequences for body sizes, specific growth rate and trophic position (at recapture). Individuals that dispersed into the river ("dispersers") were not significantly different in body size than those remaining on nursery grounds ("stayers"). For trophic position, 0+ dispersers were of significantly lower trophic position than stayers, but with this not apparent in the 1+ fish. Following dispersal into the river, the dispersers grew significantly faster than stayers and, on recapture, were significantly larger, but with no significant differences in their final trophic positions. Early dispersal into the river was, therefore, not associated with early dietary shifts to piscivory and the attainment of larger body sizes of individuals whilst in their natal habitats, contrary to prediction. These results suggest that despite an increasing risk of mortality for individuals dispersing early from natal areas, there are long‐term benefits via elevated growth rates and, potentially, higher fitness. Such early dispersal behaviour could be driven by early competitive displacement. [ABSTRACT FROM AUTHOR]

THE ASSOCIATION between Dalmatian Pelicans Pelecanus crispus and Great Cormorants Phalacrocorax carbo was studied at three Greek sites, Megali Prespa, Kerkini and Karla. At Prespa, the two species seemed to use each other mutually: pelicans benefited from fish that tried to escape from the cormorants by swimming towards the surface while cormorants used the pelicans as a cue to the presence of fish shoals. When a pelican flew towards a cormorant, other cormorants immediately flew there and dived instantly. The association usually was very brief, lasting only a mean of 114 seconds. Pelicans mostly foraged singly or in small groups (mean 3.2 individuals) and often there were also few cormorants (median 6). Kleptoparasitism was recorded at all three sites, but at Kerkini and Karla, pelicans associated with the huge fishing flocks of cormorants and predominantly kleptoparasitized them. Around 20% of attacks were successful. Thirty-one attacks were very violent with the pelican holding the cormorant until it dropped its fish. [ABSTRACT FROM AUTHOR]

Most studies of Lake Michigan lake trout (Salvelinus namaycush) have focused on adults, with scant attention to juveniles (<400 mm). We explored the spatial distribution and diet of juvenile lake trout using U.S. Geological Survey September bottom trawl data (2015–2022) and stomach content information opportunistically collected since 2012 by various agencies using multiple gear types. Most juvenile lake trout in the September bottom trawl survey were caught at 37–64 m bottom depths. Length frequency data from the bottom trawl survey identified three size classes likely associated with wild juvenile lake trout age: < 85 mm (∼age-0), 85–170 mm (∼age-1) and > 170 mm (∼age-2+). Largest catches of wild lake trout < 170 mm occurred along a northeastern transect (near Frankfort, Michigan), whereas most > 170 mm were collected along southern transects. Mysis diluviana was the dominant prey for juvenile lake trout < 170 mm, and > 250 mm were primarily piscivorous, while 170–250 mm appeared to be a transitional period of switching from Mysis to fish. Species composition of prey fishes consumed by lake trout varied spatially and we found evidence of seasonal and annual diet variation within Grand Traverse Bay. Diporeia , once an important component of juvenile lake trout diet, appears to no longer be consumed by juvenile lake trout in Lake Michigan to any measurable degree. Continued research on the ecology of juvenile lake trout may provide insight into the effects of a changing ecosystem on juvenile lake trout diet and growth, thereby contributing to the effort to rehabilitate the Lake Michigan lake trout population. [ABSTRACT FROM AUTHOR]

Along the north and central coast of Rio de Janeiro State (22025’S–23000’S), southeastern Brazil, the Guiana Dolphin Sotalia guianensis forages on neritic prey, mainly fish. From the analysis of the dolphin’s stomach contents and the identification of partially digested prey, it was verified that the most frequent prey species were young specimens of Trichiurus lepturus. Comparing our results with previous studies on the feeding habits of Guiana Dolphin in the same region, we noticed the maintenance of its feeding preferences during more than two decades, indicating little or no change in the use of prey by this top predator.

The ontogenetic diet shift to piscivory can be energetically beneficial for fish growth and allows larger, more energetically profitable prey to be consumed. A shift to piscivory may be easier for longer individuals within a cohort due to larger gape size, and an early shift is likely advantageous, potentially leading to increased growth rates and survival. Such length-dependent ontogenetic diet shifts may explain the intracohort variability in length that is common for age-0 walleye (Sander vitreus). The objectives of this study were to describe seasonal intracohort variability in length, identify the timing of the shift to piscivory and determine if the onset of piscivory was length-dependent in age-0 walleye. Walleye initially fed on zooplankton, but shifted to piscivory during July of 2010 and June of 2011. The onset of piscivory in age-0 walleye was associated with length-dependent differences during both years, in which longer individuals within the cohort became piscivorous earlier than shorter individuals within the same cohort. Intracohort variability in length was detected and increased postontogenetic diet shift. Age-0 walleye that experience a growth advantage could benefit from increased survival and feeding opportunities. [ABSTRACT FROM AUTHOR]

The early foraging ecology of alligator gar (Atractosteus spatula) is poorly documented, with little information available on young‐of‐year food habits or ontogenetic diet shifts. We conducted laboratory experiments to quantify prey selection and foraging behaviours of larval and early juvenile alligator gar (16–80 mm TL) simultaneously offered zooplankton, chironomid larvae and one of three densities of fish prey. The smallest size groups of alligator gar consumed zooplankton almost exclusively, but with increasing size, selection for zooplankton declined and selection for fish prey increased. At higher densities of fish prey, alligator gar exhibited lower selection for zooplankton and positively selected for fish at smaller sizes. Ingestion efficiencies for chironomids were considerably lower than for zooplankton or fish prey, resulting in low rates of consumption and negative selection for chironomids by all size groups of alligator gar. Fish prey elicited a different foraging response from alligator gar than zooplankton or chironomids, as alligator gar pursued and struck at fish over longer distances than for other prey types. With increasing size, alligator gar used a wider vertical range of the water column for foraging, changed their strike tactics and exhibited decreased handling times for zooplankton and fish. These observations indicate that alligator gar undergo several functional and behavioural changes during early ontogeny that facilitate a rapid transition to piscivory, but fish prey density strongly affects prey consumption patterns and the size at which alligator gar transition to piscivory. [ABSTRACT FROM AUTHOR]

In this study we assessed, for the first time, grazing by Serrasalmus brandtii outside its natural range. We observed higher grazing proportions in samples from sites where S. brandtii is the dominant species in relation to sites where it is recorded as present and sites where it is absent. S. brandtii grazed preferentially on caudal fins in relation to all other fins alone or combined. It also preferred to mutilate fins instead of flesh. Larger fish had a higher probability of being mutilated and had a higher number of mutilated fins than smaller fish, which is expected as large fish represent a larger resource to their consumers. S. brandtii avoided mutilating conspecifics and, as its abundance increased, so did the number of species being preferentially grazed. White piranhas were introduced in the Jequitinhonha River basin and increased the incidence of mutilation on netted fishes. This species preferentially grazed on caudal fins from large fishes, without, in most cases, killing its prey. Interestingly, white piranhas avoided cannibalism, and, as its abundance increased, so did the number of species being preferentially grazed. [ABSTRACT FROM AUTHOR]

Food web structure and dynamics depend on relationships between body sizes of predators and their prey. Species‐based and community‐wide estimates of preferred and realized predator–prey mass ratios (PPMR) are required inputs to size‐based size spectrum models of marine communities, food webs, and ecosystems. Here, we clarify differences between PPMR definitions in different size spectrum models, in particular differences between PPMR measurements weighting prey abundance in individual predators by biomass (rbio) and numbers (rnum). We argue that the former weighting generates PPMR as usually conceptualized in equilibrium (static) size spectrum models while the latter usually applies to dynamic models. We use diet information from 170,689 individuals of 34 species of fish in Alaskan marine ecosystems to calculate both PPMR metrics. Using hierarchical models, we examine how explained variance in these metrics changed with predator body size, predator taxonomic resolution, and spatial resolution. In the hierarchical analysis, variance in both metrics emerged primarily at the species level and substantially less variance was associated with other (higher) taxonomic levels or with spatial resolution. This suggests that changes in species composition are the main drivers of community‐wide mean PPMR. At all levels of analysis, relationships between weighted mean rbio or weighted mean rnum and predator mass tended to be dome‐shaped. Weighted mean rnum values, for species and community‐wide, were approximately an order of magnitude higher than weighted mean rbio, reflecting the consistent numeric dominance of small prey in predator diets. As well as increasing understanding of the drivers of variation in PPMR and providing estimates of PPMR in the north Pacific Ocean, our results demonstrate that that rbio or rnum, as well as their corresponding weighted means for any defined group of predators, are not directly substitutable. When developing equilibrium size‐based models based on bulk energy flux or comparing PPMR estimates derived from the relationship between body mass and trophic level with those based on diet analysis, weighted mean rbio is a more appropriate measure of PPMR. When calibrating preference PPMR in dynamic size spectrum models then weighted mean rnum will be a more appropriate measure of PPMR. Predator‐to‐prey body mass ratios (PPMRs) are key parameters in size spectrum models, but are conceptualized differently depending on the type of model. We clarify the definitions which differ according to whether individual prey are weighted numerically or by biomass. Using diet data from 170,689 individual fish predators, we show that that the two metrics are not substitutable and evaluate how variance in PPMR metrics emerge across taxonomic levels and spatial scales. [ABSTRACT FROM AUTHOR]

Large and long‐lived piscivorous brown trout, Salmo trutta, colloquially known as ferox trout, have been described from a number of oligotrophic lakes in Britain and Ireland. The "ferox" life history strategy is associated with accelerated growth following an ontogenetic switch to piscivory and extended longevity (up to 23 years in the UK). Thus, ferox trout often reach much larger sizes and older ages than sympatric lacustrine invertebrate‐feeding trout. Conventional models suggest that S. trutta adopting this life history strategy grow slowly before a size threshold is reached, after which, this gape‐limited predator undergoes a diet switch to a highly nutritional prey source (fish) resulting in a measurable growth acceleration. This conventional model of ferox trout growth was tested by comparing growth trajectories and age structures of ferox trout and sympatric invertebrate‐feeding trout in multiple lake systems in Scotland. In two of the three lakes examined, fish displaying alternative life history strategies, but living in sympatry, exhibited distinctly different growth trajectories. In the third lake, a similar pattern of growth was observed between trophic groups. Piscivorous trout were significantly older than sympatric invertebrate‐feeding trout at all sites, but ultimate body size was greater in only two of three sites. This study demonstrates that there are multiple ontogenetic growth pathways to achieving piscivory in S. trutta and that the adoption of a piscivorous diet may be a factor contributing to the extension of lifespan. [ABSTRACT FROM AUTHOR]

Disruption of ecosystems by human activities has caused worldwide extinction threats, which has prompted conservationists to implement captive breeding programmes that aid the recovery of imperilled species. Understanding factors that limit the survival of hatchery‐spawned fishes after stocking is critical to future conservation efforts using captive populations.As the size at which juvenile piscivorous fishes shift to consuming other fish can influence their survival, the transition to piscivory by hatchery‐spawned Ptychocheilus lucius Girard, 1856 (Colorado pikeminnow) was investigated after stocking the San Juan River in New Mexico, Colorado, and Utah, USA. The stable isotope 15N was used to track ontogenetic changes in the trophic position of individuals stocked at age 0, with the expectation that they would become fully piscivorous by age 2. By sampling the isotopic signatures of Colorado pikeminnow across multiple years, the ability of river discharge and densities of fish prey to explain interannual variation in trophic position was also explored.Annual variation in river flow and the densities of fish prey had little predictive power in explaining variation in δ15N of age‐1 or age‐2 Colorado pikeminnow. After assessing the isotopic signatures of potential prey, a Bayesian isotopic mixing model suggested that invertebrates comprised nearly 25% of the diet of of both age‐1 and age‐2 individuals. The relationship between Colorado pikeminnow size and δ15N within stocked cohorts indicated that juveniles slowly transitioned to consuming fish prey as they grew, rather than abruptly switching, as indicated from a limited number of dietary studies using wild fish.Together, these results suggest that Colorado pikeminnow stocked into the San Juan River slowly transition to consuming fish prey. If this pattern leads to poor survival and recruitment, the effectiveness of this management action for conservation could be compromised. [ABSTRACT FROM AUTHOR]

Cannibalism is an intra-specific predation often resulting in massive mortality in intensive cultured fish species. In piscivorous species, the onset of predation is inevitable. This study explored the link between predation abilities and the onset of cannibalism in pikeperch larvae, a top predator species, with a potential for the European inland aquaculture. Cannibals and non-cannibals, aged between 17 and 34 days-post-hatching, were tested to compare their predatory behavior using zebrafish and pikeperch larvae as prey. Each tested fish was confronted with three other fish (pikeperch or zebrafish) (n = 204 tests) in an arena (20 × 7 × 4 cm with 2 cm of water height, 280 mL) and their behavior was recorded for 20 min. The normal predatory behavioral sequence (orientation, approach, attack and capture) was much more efficient in cannibals (calculated as the ratio of number of captures on the number of attacks) than in non-cannibals in both the predation (0.31 ± 0.28 vs. 0.05 ± 0.15; p adjust < 0.0001) and the cannibalism (0.21 ± 0.29 vs. 0.02 ± 0.08; p adjust = 0.0006) tests. The shift to a piscivorous diet involved a modification of the attack tactic, replacing a "S-shape" by an attack without "S-shape" but with a tail propulsion. This second tactic developed earlier in cannibals whereas non-cannibals are only able to perform the "S-shape" attack used during the first days of life. Cannibalism was linked to the onset of an efficient piscivory behavior. • Cannibalism is an intra-specific predation resulting in massive mortality in fish. • Pikeperch is a predatory freshwater fish with precocious onset of piscivory. • Predatory behavioral sequence is more efficient in cannibals than in non-cannibals. • The shift to piscivory involved a change from a S-shape to an attack without S-shape. • Cannibalism is linked to the onset of an efficient piscivory behavior. [ABSTRACT FROM AUTHOR]

ABSTRACT Habitat complexity influences species diversity and regulates trophic interactions, mostly by increasing resource partitioning within habitats and providing refuge for prey. The influence of habitat complexity on more than two trophic levels is not well understood, mainly because behavioral modifications of prey and predator may influence the outcome of trophic interactions. Thus, we conducted a two-factor experiment with a three-level trophic chain: a piscivorous fish [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], an invertivorous fish (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) and an aquatic macroinvertebrate (Chironomidae larvae). We measured prey consumption in low, intermediate and high habitat complexity, provided by submerged macrophyte densities, in the presence and the absence of the piscivore, intending to test the hypothesis that higher habitat complexities decrease predators foraging success in different trophic levels. We calculated the percentage of consumed prey in all treatment combinations. There was no significant effect of habitat complexity on prey consumption for neither the piscivorous nor the invertivorous fish, but a positive correlation was found between the percentages of consumed prey by both the piscivore and the invertivore. Observed modifications in the foraging behavior of the piscivore may have resulted in similar prey consumptions in low and high macrophyte densities. Moreover, more active M. forestii could have suffered a higher predation pressure by H. unitaeniatus, resulting in the positive correlation found. We conclude that behavior patterns in different habitat complexities possibly influenced predation rates in the three experimental trophic levels.

Fish-eating in bats evolved independently in Myotis vivesi (Vespertillionidae) and Noctilio leporinus (Noctilionidae). We compared cranial morphological characters and bite force between these species to test the existence of evolutionary parallelism in piscivory. We collected cranial distances of M. vivesi, two related insectivorous bats (M. velifer and M. keaysi), two facultatively piscivorous bats (M. daubentonii and M. capaccinii), and N. leporinus. We analyzed morphometric data applying multivariate methods to test for differences among the six species. We also measured bite force in M. vivesi and evaluated if this value was well predicted by its cranial size. Both piscivorous species were morphologically different from the facultatively piscivorous and insectivorous species, and skull size had a significant contribution to this difference. However, we did not find morphological and functional similarities that could be interpreted as parallelisms between M. vivesi and N. leporinus. These two piscivorous species differed significantly in cranial measurements and in bite force. Bite force measured for M. vivesi was well predicted by skull size. Piscivory in M. vivesi might be associated to the existence of a vertically displaced temporal muscle and an increase in gape angle that allows a moderate bite force to process food. [ABSTRACT FROM AUTHOR]

Abstract Atlantic bluefin tuna (Thunnus thynnus) larvae show strong piscivorous feeding behavior at the very early larval stage and this enables them to grow at high rates. We conducted a laboratory experiment in which Atlantic bluefin tuna larvae were offered larval prey for the first time at different ages to simulate the early onset of piscivory at three treatments: yolk-sac larvae (YSL), delayed onset of piscivory (DYSL) and a solely planktivorous diet (Rotifers). The otolith microstructure was then used to compare the larval size distribution at the onset of the experiment with the estimated previous size-at-age of the survivors at the end of the experiment by back-calculation. Within a cohort, our results show size-selective mortality of the largest larvae independent of the differences in the timing of onset of piscivory and differences in growth patterns. The results also corroborate the rapid response of Atlantic bluefin tuna to piscivory in terms of growth reflected in the otolith increment widths. Being bigger did not infer a survival advantage and mortality rates did not decline with increasing larval size. Smaller size at a given age could under certain conditions and stages of development confer a survival advantage of individual members of a larval cohort when suitable small-sized prey is available. Highlights • This study examines size-selective mortality at the transition from a piscivorous diet, using laboratory experiments on Atlantic bluefin tuna larvae • Otolith microstructure was used to compare the size distribution at the onset of the experiment with the estimated previous size-at-age of the survivors at the end of the experiment • Results show mortality of the initially largest larvae at the end of the experiment, regardless of the timing of piscivorous transition [ABSTRACT FROM AUTHOR]

There is increasing evidence that phenotypic variation can strongly impact community structure and ecosystem functions. Alewife Alosa pseudoharengus is a planktivorous fish species that strongly impact lake ecosystems. It has previously been demonstrated that phenotypic variation related to differences in life history among landlocked and anadromous alewife populations alters the strength of interactions with other species, potentially modifying its role in the community. The migration between freshwater and marine ecosystems by anadromous alewife creates seasonal differences in alewife densities, which causes lake zooplankton communities to alternate between large‐body size and higher densities in the spring, and small‐body size and low densities in the summer and fall. In lakes with resident (landlocked) alewife, predation from alewife modifies the zooplankton community to having low zooplankton densities and mainly small‐bodied zooplankton year‐round. The strong effects of phenotypic variation in alewife on zooplankton may be important for coexisting species that rely on zooplankton as a resource. Here we use estimates of growth, and direct diet and stable isotope analyses to ask if the presence‐ and phenotypic variation of alewife alters the ontogenetic trajectory of young‐of‐the‐year (YOY) largemouth bass Micropterus salmoides, which depend on zooplankton in the early life stages. We found that both the presence‐ and phenotypic variation of alewife affects growth, trophic position, and diet of largemouth bass. YOY largemouth bass from lakes without alewife grew faster, switched to piscivory earlier, and reached higher trophic positions than in alewife lakes. In lakes with landlocked alewife largemouth bass grew slower and obtained a lower trophic position than those in lakes with anadromous alewife. These divergences can be explained by the strong effects of alewife on zooplankton community structure. Our results demonstrate how the strong effects of phenotypic variation can propagate through natural food webs to influence important life history transitions in other species. [ABSTRACT FROM AUTHOR]

Abstract: A few of the >1300 bat species recognised worldwide are known to consume fish to various extents. However, empirical information about how and how much different bat species capture and consume fish is limited and is probably distorted due to the biases introduced by occasional observations. In this review, we aim to synthesise the knowledge so far generated on fishing bats, in order to 1) assess the incidence of fishing in different bat species; 2) discuss the evolutionary framework and origins of fishing behaviour; and 3) identify the ecological challenges of fishing and review the state of knowledge about kinetic, morphological, sensory, behavioural, and physiological adaptations related to fishing. Fishing bats can be clustered into three groups based on the incidence of fish consumption. Noctilio leporinus is the only species in which fishing is widespread (occurring in most populations) and common (occurring most of the time and carried out by many individuals). Myotis vivesi, Myotis pilosus, and Myotis capaccinii comprise the second group, characterised by exhibiting regular fishing behaviour that is restricted to a limited number of populations. Noctilio albiventris, Myotis daubentonii, and Myotis macropus are classified in a third group, because although the occasional presence of fish traces in faeces has been reported, regular fishing behaviour in the wild has not been confirmed. Fishing was developed independently multiple times in different bat lineages, probably under different selective pressures and ecological scenarios. Nevertheless, all fishing species face similar challenges in terms of detecting, capturing, handling, and metabolising fish, which require specific kinetic, morphological, sensory, behavioural, and physiological adaptations. Both basic information about fishing behaviour in different species and specific knowledge of the biological adaptation are still missing. Thus, in this review we identify gaps in the knowledge and suggest experimental approaches to overcome them. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to analyse the trophic ecology of speckled peacock bass Cichla temensis inhabiting two tributaries of the middle Negro River, the Aracá River and the Demeni River. Using an analysis of stomach contents and stable isotope composition (δ15N, δ13C) of scales, we describe the diet and evaluate the trophic position of subadult and adult individuals. We then test whether diet shifts and trophic positions occurred among successive size classes and among sample locations. The stomach content analysis confirmed the piscivorous feeding habit of the species and showed that the speckled peacock bass preyed on a variety species belonging to different trophic guilds. The length of the ingested prey increased with the size of the speckled peacock bass. Diet composition and trophic position were not different among size classes. δ13C values yielded significant shifts among the size classes: larger individuals displayed higher δ13C values than smaller individuals. Trophic position varied between locations, with lowest values observed in fish from the Aracá River. This study demonstrated that diet of C. temensis may vary according to the size of the fish, even at the subadult or adult stages, and according to the river/locality, even within a same basin. We then suggest that further studies take into account local availability of food resources to better explore C. temensis diet and tropic ecology. [ABSTRACT FROM AUTHOR]

Abstract: Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions. [ABSTRACT FROM AUTHOR]