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ABSTRACT Myxobolus Bütschli, 1882 is a highly important genus of fish myxozoans, consisting of many species that cause serious diseases in ornamental cyprinid fish species in different geographic areas by infecting a wide range of organs. This study describes a new Myxobolus species infecting the gill lamellae, gill rakers and skin epidermis of goldfish (Carassius auratus) from Mohammadshahr, Iran, based on detailed morphological, histological and molecular analysis. Mature spores were small and spherical in shape, consisting of two symmetrical shell valves in frontal view, measuring 10.3 (9.8–10.9) μm in length and 10.5 (10.3–11.2) μm in width. Two equal‐sized relatively pyriform polar capsules were 5.4 (3.9–6.0) μm long and 4.5 (3.7–5.2) μm wide. The polar tubules were coiled with 4–6 turns. A comparative analysis of the morphological and molecular data confirmed that this species is distinct from other identified myxosporeans. Plasmodia in the cutaneous tissue were found in the epidermis, causing extensive hyperplasia of Malpighian cells and mild inflammatory infiltration. In the gill tissue, plasmodia affected only one side of the lamellae, leading to hyperplasia of the lamellar epithelium, edema, and lymphoplasmacytic branchitis. A novel myxozoan species, Myxobolus branchioepidermis n. sp., has been proposed. The study provides a comprehensive analysis of the morphological, histological, and molecular characteristics of this parasite, which infects the gill lamellae and epidermal layer of the skin in oranda goldfish (C. auratus). The identification of this new species adds to the growing body of research on myxozoan parasites and highlights its potential impact on ornamental fish aquaculture. [ABSTRACT FROM AUTHOR]

Key unresolved questions about particle separation mechanisms in suspensionfeeding fishes are identified and discussed, focusing on areas with the potential for substantial future discovery. The published hypotheses that are explored have broad applicability to biological filtration and bioinspired improvements in commercial and industrial crossflow microfiltration processes and microfluidics. As the first synthesis of the primary literature on the particle separation mechanisms of marine, estuarine, and freshwater suspension-feeding fishes, the goals are to enable comparisons with invertebrate suspension-feeding processes, stimulate future theoretical and empirical studies, and further the development of biomimetic physical and computational fluid dynamics models. Of the eight particle separation mechanisms in suspension-feeding fishes, six have been proposed within the past twenty years (inertial lift and shear-induced migration, reduction of effective gap size by vortices, cross-step filtration, vortical flow along outer faces of gill raker plates, ricochet filtration, and lateral displacement). The pace of discovery is anticipated to continue accelerating. Multidisciplinary collaboration and integration among biologists and engineers (including chemical, mechanical, biomedical, and filtration engineering) will result in new perspectives to identify patterns and potential unifying mechanisms across the breadth of suspension-feeding fish taxa, morphology, and function. [ABSTRACT FROM AUTHOR]

The present study was conducted to analyse the morphological and histological structure of gills in Schizothorax niger Heckel, 1838 with respect to body weight of the fish. A total of 60 fish samples were collected from landing centres around Dal Lake. The total body weight of the fish samples ranged from 63.00 g to 366.80 g with a mean value 171.49 g. A significant positive relationship was observed between body weight and gill parameters like gill arch length, total gill filament length, total gill filament number and total gill raker length (p < 0.01). However, body weight showed a non-significant weak relationship with total gill raker number (p > 0.05). Histological analysis showed that each gill arch was supported by a cartilaginous core with two rows of gill filament on the convex side and two rows of gill rakers on the concave side. Each gill filament gave rise to the secondary lamellae, which are the main sites for respiratory gaseous exchange. An epithelial lining was reported on each gill structure interspersed with large number of mucous cells. The gill rakers in S. niger were observed to be slightly pointed and narrowly spaced owing to its feeding habits. [ABSTRACT FROM AUTHOR]

Key unresolved questions about particle separation mechanisms in suspension-feeding fishes are identified and discussed, focusing on areas with the potential for substantial future discovery. The published hypotheses that are explored have broad applicability to biological filtration and bioinspired improvements in commercial and industrial crossflow microfiltration processes and microfluidics. As the first synthesis of the primary literature on the particle separation mechanisms of marine, estuarine, and freshwater suspension-feeding fishes, the goals are to enable comparisons with invertebrate suspension-feeding processes, stimulate future theoretical and empirical studies, and further the development of biomimetic physical and computational fluid dynamics models. Of the eight particle separation mechanisms in suspension-feeding fishes, six have been proposed within the past twenty years (inertial lift and shear-induced migration, reduction of effective gap size by vortices, cross-step filtration, vortical flow along outer faces of gill raker plates, ricochet filtration, and lateral displacement). The pace of discovery is anticipated to continue accelerating. Multidisciplinary collaboration and integration among biologists and engineers (including chemical, mechanical, biomedical, and filtration engineering) will result in new perspectives to identify patterns and potential unifying mechanisms across the breadth of suspension-feeding fish taxa, morphology, and function.

The Arctic cod (Boreogadus saida (Lepechin, 1774)) represents the most widespread and abundant fish in the Arctic and is a critical trophic link in its ecosystems. Like many species endemic to the region, it has lost essential habitat as the extent and thickness of sea ice have declined substantially in recent decades. Extreme warming induced by climate change continues to deteriorate polar marine environments. Thus, understanding how Arctic cod use and partition their habitat/environment is central to their conservation. We assessed Arctic cod functional morphology using traditional (including gill rakers) and geometric morphometrics and explored whether these differed among primarily depth-based habitats and age classes using multivariate techniques. While distinct ecotypes have been proposed, these were not detected in our analyses. Rather, results show similar patterns in external morphology of Arctic cod across habitats and age classes in the Beaufort Sea. However, analysis of gill rakers revealed concurrent habitat- and age-specific changes likely associated with dietary preferences. Findings indicate that although Arctic cod do not specialise in external morphological features in any habitat, important aspects of their internal feeding morphology shift as they grow, likely underpinning important distributional shifts and its critical role in transferring energy in Arctic marine ecosystems.

Aim: High repeatability among assemblages of closely related but ecologically distinct ecotypes implies predictability in evolution and assembly of communities. The conditions under which ecotype assemblages form predictably, and the reasons, have been little investigated. Here, we test whether repeatability declines as the number of ecotypes builds. Location: Postglacial lakes with a circumboreal distribution. Time Period: Data were extracted from studies published between 1982 and 2019. Major Taxa Studied: Ecotype assemblages from two Salmonid genera – Salvelinus and Coregonus. Fish in postglacial lakes commonly occur as pairs of ecotypes, typically with a pelagic and a littoral/benthic form, but in Salvelinus and Coregonus, assemblages commonly contain multiple sympatric ecotypes. Methods: We used a meta‐analysis of Salvelinus and Coregonus to empirically assess how repeatability varies across assemblages of two to seven ecotypes. We examined repeatability of use of broad niche categories as well as underlying phenotypic traits. Results: Within Coregonus, repeatability across multi‐ecotype assemblages did not break down with the addition of a third or fourth ecotype. However, in Salvelinus, repeatability was largely absent and independent of the number of ecotypes. Repeatability of trait frequency distributions was absent in both genera, yet associations between trait means and niche categories were evident, especially in Coregonus. Main Conclusions: These results show that repeatability can vary greatly between lineages; that repeatability need not break down as the number of ecotypes builds; and that high repeatability of broad niche categories may result despite marked differences in the underlying frequency distribution of trait means. These findings not only affirm the presence of repeatable ecotype assembly and early stages of divergence in postglacial fishes at a global scale, but also highlight variability among taxa and underlying phenotypic traits. [ABSTRACT FROM AUTHOR]

Pelvic spine polymorphism occurs in several species in the stickleback family (Gasterosteidae). Given the similar phenotypic polymorphisms in multiple stickleback species, we sought to determine the extent of parallelism in the ecological correlates of pelvic spine reduction. Based on a metabarcoding analysis of brook stickleback gut contents in two polymorphic populations, we found that significant diet differences were associated with pelvic spine reduction, but we found no clear or consistent trend supporting a tendency for benthic feeding in pelvic‐reduced brook sticklebacks. These results contrast with those found in threespine sticklebacks where pelvic spine reduction is often associated with a benthic diet. Hence, we found non‐parallel consequences of spine polymorphism across species. Furthermore, a difference in gill raker morphology has been frequently observed between ecomorphs with different diets in many fish species. However, we found no evidence of any difference in gill raker morphology associated with pelvic spine polymorphism in brook sticklebacks. [ABSTRACT FROM AUTHOR]

Abstract Pelvic spine polymorphism occurs in several species in the stickleback family (Gasterosteidae). Given the similar phenotypic polymorphisms in multiple stickleback species, we sought to determine the extent of parallelism in the ecological correlates of pelvic spine reduction. Based on a metabarcoding analysis of brook stickleback gut contents in two polymorphic populations, we found that significant diet differences were associated with pelvic spine reduction, but we found no clear or consistent trend supporting a tendency for benthic feeding in pelvic‐reduced brook sticklebacks. These results contrast with those found in threespine sticklebacks where pelvic spine reduction is often associated with a benthic diet. Hence, we found non‐parallel consequences of spine polymorphism across species. Furthermore, a difference in gill raker morphology has been frequently observed between ecomorphs with different diets in many fish species. However, we found no evidence of any difference in gill raker morphology associated with pelvic spine polymorphism in brook sticklebacks.

The feeding habits and habitat of different fish species influence the morphology and functions of their gill rakers. This study used gross anatomy and scanning electron microscopy to investigate the morphological features of the gill rakers in Siganus luridus, Boops boops, and Pagrus pagrus. The gill rakers appeared as medial and lateral rows in all studied fishes. Except for Pagrus pagrus, which had a unique gill rakers arrangement in which the medial row of the 4th gill arch had the most gill rakers, the longest and most gill rakers were on the 1st gill arch in all studied fishes. The gill rakers of Siganus luridus were smooth, with various spine-like shapes, such as spine-like gill rakers, which were bifid or trifid spines, or duck toe-shaped gill rakers. According to SEM of the Siganus luridus' gill rakers, the trifid end gill rakers resembled caterpillars, and the duck toe-like gill rakers had three or four finger-like spines connected by inter-spine tissue. The Boops boops had long conical gill rakers with pointed ends on the lateral sides of the 1st gill arch, and the remaining rows had short gill rakers. According to SEM of the Boops boops' gill rakers, the long gill rakers were semi-conical and only had needle-like spines on the medial surface. The short gill rakers were projected as a boat and had three different shapes based on spine distributions. Gill rakers include those with a median crest and long spine laterals, those with only lateral spines, those with usually dorsal spines, and those with long wedge-shaped spines. Pagrus pagrus' gill rakers were short, with fine-needle spines covering their tops. By SEM of the Pagrus pagrus' gill rakers, they appeared as a cylindrical elevation with spines on top. The spines were conical in shape with pointed curved or straight ends. The maximum value of the gill rakers' lengths was discovered in the lateral row of the 1st gill arch, while the minimum value was in the medial row of the 4th gill arch. As a result, this is the first study of the three fish species' gill rakers. In the studied fishes, the morphological characteristics of gill rakers demonstrated unique structural specifications in feeding behavior. [ABSTRACT FROM AUTHOR]

Members of the subfamily Heterocongrinae (Congridae) are a peculiar group of anguilliform eels that construct sandy borrows, form large colonies, and are popularly recognized as garden eels. They live with most of their bodies inside self-constructed borrows exposing their heads and trunk to feed on zooplankton, preferably copepods, that are brought passively by currents. As plankton feeders there was a suspicion that their branchial skeleton would have structures that could aid in the filtering process, such as highly developed or modified branchial rakers, which are observed in other suspension-feeding fishes, such as anchovies and sardines. Branchial rakers, however, were considered to be absent across Anguilliformes (except for Protanguilla). Nonetheless, specimens that were examined using clearing and staining and computed tomography showed, in all cases, branchial rakers associated with their gill arches. Heterocongrines have branchial rakers across their first to fourth branchial arches. These rakers are conical and apparently unossified, but further studies are necessary to attest its degree of ossification or its complete absence. Their pharyngeal tooth plates are reduced, a condition that may reflect their preference for smaller food items. Additionally, they may use crossflow filtering to feed, although detailed studies are necessary to clarify if hydrosol sieving may also aid in food capture. Furthermore, the present study proposes that the presence of branchial rakers should be better investigated in Anguilliformes with similar feeding habits as heterocongrines, considering that these structures may be more widespread within the group than previously considered. • Members of Heterocongrinae bear unossified branchial rakers in their branchial arches. • The presence of branchial rakers reflects the plankton feeding diet of heterocongrines. • Branchial rakers may have a more widespread distribution across Anguilliformes. [ABSTRACT FROM AUTHOR]

Chinese perch (Siniperca chuatsi) larvae prey on other fish species larvae at the beginning of exogenous feeding but do not eat any zooplankton in natural conditions, the mechanism behind this special feeding habit is unclear at present. This study aimed to visualize the development of gill rakers in Chinese perch larvae and observe the ingestion of larvae to different size Artemia in low salinity (5 g/L) water. Our results indicated that Chinese perch larvae demonstrated a slow development in gill rakers, larvae only had some buds from hatching to 7 days post hatching (dph), and the first and second real gill raker was observed at 9 dph and 12 dph respectively. The edar gene expression also consisted with development of gill rakers. Meanwhile, the results of ingestion showed larvae preferred to feed large size Artemia, and larvae fed the large size Artemia also had a higher npy gene expression. Compared with the larvae fed small size Artemia, the larvae which fed the large size Artemia had a higher survival rate. These data inform hypotheses development of gill rakers may influence the prey choice in Chinese perch larvae, no real gill rakers may cause the larvae can not to forage small size zooplankton at first‐feeding stage and, thus, the Chinese perch larvae form the special feeding habit. [ABSTRACT FROM AUTHOR]

The polar cod (Boreogadus saida) and the Antarctic silverfish (Pleuragramma antarctica) are pelagic fish endemic to the Arctic and Antarctica sea, respectively. Both species are abundant and play a central role as midtrophic wasp-waist species in polar ecosystems. Due to their biological and ecological characteristics (small size, complex life histories, relatively short generation cycles, movement capability, planktivorous diet, and importance as prey), the polar cod and the Antarctic silverfish are potentially good sentinels of ecosystem change. Changes in polar zooplankton communities are well documented. How changes impact ecosystems as a whole largely depend on the degree of diet specialization and feeding flexibility of midtrophic species. Here, we provide the ecomorphological characterization of polar cod and Antarctic silverfish feeding performances. A comparative functional ecology approach, based on the analysis of morpho-anatomical traits, including calculation of suction index and mechanical advantage in jaw closing, was applied to profile the feeding modes and flexibility of the two species. Ecomorphological evidence supports differences in food acquisition: the polar cod appears able to alternate particulate ram-suction feeding to a pump filter feeding, and the Antarctic silverfish results be both a particulate ram and a tow-net filter feeder. Both species exhibit opportunistic feeding strategies and appear able to switch feeding mode according to the abundance and size of the available prey, which is a clue of potential resilience to a changing environment. [ABSTRACT FROM AUTHOR]

Three‐spined sticklebacks (Gasterosteus aculeatus L.) living at the southern limit of the species distribution range could possess specific morphological and physiological traits that enable these fish to live at the threshold of their physiological capacities. Morphological analysis was carried out on samples of sticklebacks living in different saline habitats of the Camargue area (Rhone delta, northern Mediterranean coast) obtained from 1993 to 2017. Salinity acclimation capacities were also investigated using individuals from freshwater‐low salinity drainage canals and from mesohaline–euryhaline lagoons. Fish were maintained in laboratory conditions at salinity values close to those of their respective habitats: low salinity (LS, 5‰) or seawater (SW, 30‰). Fish obtained from a mesohaline brackish water lagoon (BW, 15‰) were acclimated to SW or LS. Oxygen consumption rates and branchial Na+/K+‐ATPase (NKA) activity (indicator of fish osmoregulatory capacity) were measured in these LS or SW control fish and in individuals subjected to abrupt SW or LS transfers. At all the studied locations, only the low‐plated "leiurus" morphotype showed no spatial or temporal variations in their body morphology. Gill rakers were only longer and denser in fish sampled from the LS–freshwater (FW) drainage canals. All fish presented similar physiological capacities. Oxygen consumption rates were not influenced by salinity challenge except in SW fish transferred to LS immediately and 1 h after transfer. However, and as expected, gill NKA activity was salinity dependent. Sticklebacks of the Camargue area sampled from habitats with contrasted saline conditions are homogenously euryhaline, have low oxygen consumption rates and do not appear to experience significantly greater metabolic costs when challenged with salinity. However, an observed difference in gill raker length and density is most probably related to the nutritional condition of their habitat, indicating that individuals can rapidly acclimatize to different diets. [ABSTRACT FROM AUTHOR]

In this microichthyological study the teeth and bony cores of gill rakers of three pleuronectiform species [European plaice Pleuronectes platessa Linnaeus, 1758 and European flounder Platichthys flesus trachurus (Duncer, 1892), both in the Pleuronectidae, and turbot Scophthalmus maximus (Linnaeus, 1758) in the Scophthalmidae] of the Baltic Sea are SEM imaged, described and compared for the first time. The shape and number of teeth in jaws and on pharyngeal tooth plates as well as the shape, size and number of the bony cores of gill rakers in these taxa differ. The European plaice and European flounder carry incisiform teeth anteriorly in their jaws and smoothly rounded, molariform teeth on pharyngeal tooth plates; the teeth of the plaice are more robust. The gill rakers have similar gross morphology, occurring as separate conical thornlets on gill arches. The bony cores of these thornlets (rakers) consist of vertical ribs with connective segments between them. The cores of gill rakers of the plaice and flounder reveal some differences in details. The plaice has cores with one peak, simple vertical ribs, and nodules on their lower thicker parts, while the flounder has cores with a side-branch and fine vertical ribs, which have parallel ribbing and tend to twist around the lower part of cores. The teeth of the jaws and pharyngeal tooth plates and the raker cores of the turbot are completely different from those of the plaice and flounder. In the turbot two main types of complex gill rakers are attached to the gill arches: one type has ‘sail’-shaped, high elements with one to two rows of fine conical teeth set in sockets; the other type has low tubercles with the same type of teeth. The differences among the species can be useful for studies of taxonomy and phylogeny, as well as for understanding their feeding habits.

The morphology of the orobranchial structures in fish generally reflects the feeding habits and food preferences of a species and is key in understanding the process and habits of fish feeding. This work describes the orobranchial structures of four neotropical silversides (Teleostei: Atherinopsidae): the Mexican pike silverside Chirostoma estor, the Mexican blacknose silverside Chirostoma promelas, the Argentinian silverside Odontesthes bonariensis and Patagonian pejerrey Odontesthes hatcheri, and correlates their morphological features with existing information on gut contents and feeding habits in adult fish. Results of the compared and analysed data in the present study portray an integrative view of the specialised habits of the different species. Significant morphological differences, which are related to primary feeding habits of four species, were found. C. promelas shows to be more piscivorous compared to O. hatcheri, which has main benthic habits, while O. bonariensis and C. estor have more zooplanktivorous preferences. This information provides knowledge of feeding habits and ecological interactions of these species and their prey. [ABSTRACT FROM AUTHOR]

Poeciliopsis jackschultzi sp. nov., is described based on seven specimens (17.9-26.7 mm SL) from the Río Concepción (also known as Río Magdalena), Sonora, Mexico. The new species belongs to the Leptorhaphis species group and can be distinguished from other members of this group by features of the skeleton and colouration. The new species is sympatric with P. occidentalis, a hybridogenetic all-female biotype P. monacha- occidentalis, and hybrids between P. monacha-occidentalis females and P. jackschultzi males. The distribution of P. jackschultzi is highly restricted, and the main habitat, spring-fed marshy streams and pools, is susceptible to loss and degradation in a desert environment with increasing human water demand. [ABSTRACT FROM AUTHOR]

Although sexual dimorphism is widespread in nature, its evolutionary causes often remain elusive. Here we report a case where a sex-specific conflicting functional demand related to parental care, but not to sexual selection, explains sexual dimorphism in a primarily trophic structure, the gill rakers of cichlid fishes. More specifically, we examined gill raker length in a representative set of cichlid fish species from Lake Tanganyika featuring three different parental care strategies: (i) uni-parental mouthbrooding, whereby only one parental sex incubates the eggs in the buccal cavity; (ii) bi-parental mouthbrooding, whereby both parents participate in mouthbrooding; and (iii) nest guarding without any mouthbrooding involved. As predicted from these different parental care strategies, we find sexual dimorphism in gill raker length to be present only in uni-parental mouthbrooders, but not in bi-parental mouthbrooders nor in nest guarders. Moreover, variation in the extent of sexual dimorphism among uni-parental mouthbrooders appears to be related to trophic ecology. Overall, we present a previously unrecognized scenario for the evolution of sexual dimorphism that is not related to sexual selection or initial niche divergence between sexes. Instead, sexual dimorphism in gill raker length in uni-parental mouthbrooding cichlid fish appears to be the consequence of a sex-specific functional trade-off between a trophic function present in both sexes and a reproductive function present only in the brooding sex. [ABSTRACT FROM AUTHOR]

Cladistic analysis of fishes are mostly based on osteological studies. Phylogenetic relationships within the family Characidae are poorly known in part due to the lack of anatomical studies of its members, including osteology. The present contribution aims to offer a detailed description of all bony complexes of Moenkhausia lepidura. Two remarkable morphological conditions present in the species are discussed: a bony lamella on the proximal portion of the ribs and a basal expansion of the gill rakers. A morphological survey of several species of Characidae along with available phylogenetic information of the family indicates the putative relationships of Moenkhausia lepidura with other small characids presenting bony lamella on ribs and a dark mark on the caudal fin. [ABSTRACT FROM AUTHOR]

During their evolution and speciation in the Antarctic waters, notothenioid fish occupied a variety of habitats and ecological niches. The diversification led to important variations in several morphological features related to particular aspects of their ecologies. We investigated the feeding structures and biomechanics of three phylogenetically related species (family Nototheniidae) with different ecologies: the bentho-pelagic Antarctic toothfish Dissostichus mawsoni, the pelagic Antarctic silverfish Pleuragramma antarctica, and the benthic emerald rockcod Trematomus bernacchii. The suction index (SI), the mechanical advantage in jaw closing (MA), and 14 morphological traits related to their feeding activity were analyzed. Significant differences among the species were found for all the parameters considered, supporting a high level of specialization. [ABSTRACT FROM AUTHOR]

Phenotypes reflect a complex interplay between the direct and indirect effects of multiple selective pressures; adaptive responses in individual traits may therefore be constrained by architectonic considerations and correlations with other traits. We explored whether and how three suites of neighbouring structures (respiratory, trophic and cranial) have changed over time in Rastrineobola argentea, a small pelagic cyprinid fish that is endemic to the Lake Victoria Basin in East Africa. We compared museum specimens from 1966 to modern (2010) specimens, spanning a period of almost 50 years of strong anthropogenic change in the lake, including increased frequency and extent of hypoxia and anoxia, and a dramatic restructuring of the lacustrine fish community and food-web. We found that modern R. argentea had significantly larger gills, wider heads, and shorter and more tightly packed gill rakers than their historical counterparts. Larger gill size probably represents a direct, adaptive response to more frequent bouts of hypoxia over time; the increase in head width and decrease in raker spacing may reflect correlated (and potentially maladaptive) responses to the increase in gill size. Integrative studies such as this are key to unravelling complex interactions between phenotypes and the environment. [ABSTRACT FROM AUTHOR]

Based on an almost complete impression from the base of the Pshekha Horizon (layer 2, Planorbella Beds, zone NP 21) of the North Caucasus (lower early Oligocene), we describe the basking shark Caucasochasma zherikhini gen. et sp. nov., differing from other members of family Cetorhinidae by higher number of vertebrae, weakly developed lower lobe of caudal fin, and details of the structure of gill rakers. Based on the structure of the body, it is not excluded that the described taxon was associated with the bottom to a greater degree than other species of the family (Keasius parvus and C. maximus), for which the structure of the body is known. The accumulations of plankton at the bottom could be a possible food resource for Caucasochasma. [ABSTRACT FROM AUTHOR]

Resource polymorphism, whereby ancestral trophic generalists undergo divergence into multiple specialist morphs, is common in salmonid fish populations inhabiting subarctic lakes. However, the extent to which such resource specialization into the three principal lake habitats (littoral, profundal, and pelagic) affects patterns of contaminant bioaccumulation remains largely unexplored. We assessed total mercury concentrations (THg) of European whitefish ( Coregonus lavaretus (L.)) and their invertebrate prey in relation to potential explanatory variables across 6 subarctic lakes, of which three are inhabited by polymorphic (comprised of four morphs) and three by monomorphic populations. Among invertebrate prey, the highest THg concentrations were observed in profundal benthic macroinvertebrates, followed by pelagic zooplankton, with concentrations lowest in littoral benthic macroinvertebrates in both lake types. Broadly similar patterns were apparent in whitefish in polymorphic systems, where average age-corrected THg concentrations and bioaccumulation rates were the highest in pelagic morphs, intermediate in the profundal morph, and the lowest in the littoral morph. In monomorphic systems, age-corrected THg concentrations were generally lower, and showed pronounced lake-specific variation. In the polymorphic systems, we found significant relationships between whitefish muscle tissue THg concentration and gill raker count, resource use, lipid content and maximum length, whilst no such relationships were apparent in the monomorphic systems. Across all polymorphic lakes, the major variables explaining THg in whitefish were gill raker count and age, whereas in monomorphic systems, the factors were lake-specific. Whitefish resource polymorphism across the three main lake habitats therefore appears to have profound impacts on THg concentration and bioaccumulation rate. This highlights the importance of recognizing such intraspecific diversity in both future scientific studies and mercury monitoring programs. [ABSTRACT FROM AUTHOR]

Ram suspension-feeding fishes swim with an open mouth to force water through the oral cavity and extract prey items that are too small to be pursued individually. Recent research has indicated that, rather than using a dead-end mechanical sieve, American paddlefish (Polyodon spathula) employ vortical cross-step filtration. In this filtration mechanism, vortical flow that is generated posterior to the branchial arches organizes crossflow filtration processes into a spatial structure across the gill rakers. Despite the known impact of locomotor kinematics on fluid flow around the bodies of swimming fish, the effects of locomotor kinematics on filtration mechanisms in ram suspension feeders are unknown. Potential temporal organization of filtration mechanisms in ram suspension-feeding fish has not been studied previously. We investigated the effects of locomotor kinematics associated with undulatory swimming on intraoral flow patterns and food particle transport. A mechanized model of the oral cavity was used to simulate the swimming kinematics of suspension-feeding paddlefish. We recorded fluctuations of flow speed and pressure within the model, which occurred at a frequency that corresponded with the frequency of the model's strides. Using the mechanized model in a flow tank seeded with Artemia cysts, we also showed that swimming kinematics aided the transport of this simulated food to the posterior margins of the gill slots, although the time scale of this transport is expected to vary with prey parameters such as size and concentration. Dye stream experiments revealed that, although stable vortical flow formed because of flow separation downstream of backward-facing steps in control trials, vortical flow structures in mechanized trials repeatedly formed and shed. These findings suggest strong integration between locomotor and feeding systems in ram suspension-feeding fishes. [ABSTRACT FROM AUTHOR]

Sympatric populations occur in many freshwater fish species; such populations are typically detected through morphological distinctions that are often coupled to food niche and genetic separations. In salmonids, trophic and genetically separate sympatric populations have been reported in landlocked Arctic char, whitefish and brown trout. In Arctic char and brown trout rare cases of sympatric, genetically distinct populations have been detected based on genetic data alone, with no apparent morphological differences, that is 'cryptic' structuring. It remains unknown whether such cryptic, sympatric structuring can be coupled to food niche separation. Here, we perform an extensive screening for trophic divergence of two genetically divergent, seemingly cryptic, sympatric brown trout populations documented to remain in stable sympatry over several decades in two interconnected, tiny mountain lakes in a nature reserve in central Sweden. We investigate body shape, body length, gill raker metrics, breeding status and diet (stomach content analysis and stable isotopes) in these populations. We find small significant differences for body shape, body size and breeding status, and no evidence of food niche separation between these two populations. In contrast, fish in the two lakes differed in body shape, diet, and nitrogen and carbon isotope signatures despite no genetic difference between lakes. These genetically divergent populations apparently coexist using the same food resources and showing the same adaptive plasticity to the local food niches of the two separate lakes. Such observations have not been reported previously but may be more common than recognised as genetic screenings are necessary to detect the structures. [ABSTRACT FROM AUTHOR]

Anthropogenic particles (APs), including microplastics, are ingested by a wide variety of marine organisms. Exposure of Clupeiformes (e.g. herrings, anchovies, sardines) is poorly studied despite their economic and ecological importance. This study aims to describe the morphology of the filtration apparatus of three wild-caught Clupeiformes ( Sardina pilchardus , Clupea harengus and Engraulis encrasicolus ) and to relate the results to ingested APs. Consequently, the species with the more efficient filtration apparatus will be more likely to ingest APs. We hypothesized that sardines were the most exposed species. The filtration area and particle retention threshold were determined in the three species, with sardines displaying the highest filtration area and the closest gill rakers. Sardines ingested more fibers and smaller fragments, confirming that it is the most efficient filtering species. These two results lead to the conclusion that, among the three studied, the sardine is the species most exposed to APs. [ABSTRACT FROM AUTHOR]

In this microichthyological study the teeth and bony cores of gill rakers of three pleuronectiform species [European plaice Pleuronectes platessa Linnaeus, 1758 and European flounder Platichthys flesus trachurus (Duncer, 1892), both in the Pleuronectidae, and turbot Scophthalmus maximus (Linnaeus, 1758) in the Scophthalmidae] of the Baltic Sea are SEM imaged, described and compared for the first time. The shape and number of teeth in jaws and on pharyngeal tooth plates as well as the shape, size and number of the bony cores of gill rakers in these taxa differ. The European plaice and European flounder carry incisiform teeth anteriorly in their jaws and smoothly rounded, molariform teeth on pharyngeal tooth plates; the teeth of the plaice are more robust. The gill rakers have similar gross morphology, occurring as separate conical thornlets on gill arches. The bony cores of these thornlets (rakers) consist of vertical ribs with connective segments between them. The cores of gill rakers of the plaice and flounder reveal some differences in details. The plaice has cores with one peak, simple vertical ribs, and nodules on their lower thicker parts, while the flounder has cores with a side-branch and fine vertical ribs, which have parallel ribbing and tend to twist around the lower part of cores. The teeth of the jaws and pharyngeal tooth plates and the raker cores of the turbot are completely different from those of the plaice and flounder. In the turbot two main types of complex gill rakers are attached to the gill arches: one type has 'sail'-shaped, high elements with one to two rows of fine conical teeth set in sockets; the other type has low tubercles with the same type of teeth. The differences among the species can be useful for studies of taxonomy and phylogeny, as well as for understanding their feeding habits. [ABSTRACT FROM AUTHOR]

We sought to investigate catch composition, provenance and migration patterns of an economically important coregonid, the European whitefish (EW, Coregonus lavaretus s.l.). EW displays complex life history and is heavily stocked in the Baltic Sea. By combining otolith geochemistry (Sr:Ca, Ba:Ca, 87 Sr: 86 Sr) and gill raker counts we developed an assignment framework for determining the general ecological form (anadromous or sea-spawning) and provenance (wild or stocked) of EW adults caught in the mixed stock fishery. Among the adults sampled from the Estonian coastal sea ( N = 82) 50% were stocked as fingerlings in Finland (1% were stocked as fingerlings in Estonia), and 35 and 14% were of wild anadromous and sea-spawning origin, respectively. Young-of-year individuals ( N = 55) sampled from four geographically separated rearing facilities in Finland displayed highly distinct otolith natal fingerprints, therefore demonstrating great potential for pin-pointing the provenance of adult individuals that were stocked as fingerlings. Among the adults that were stocked as fingerlings 13 different otolith natal fingerprint groups were identified, however 81% of them originated from seven distinct sources. This study underscores the prevalence of stocked individuals in the EW mixed-stock fishery, and quantitatively demonstrates the low share of wild individuals. It is suggested that current stocking practices may lack the desired effect on wild populations, and they only serve to supplement the catches. The presented results will allow to monitor the structure of EW stocks in both local and regional scale. [ABSTRACT FROM AUTHOR]

Polarized light detection has been documented in only a small number of fish species. The benefit of polarization vision for fish is not fully understood, nor is the transduction mechanism that underlies it. Past studies proposed that one possible advantage of polarization vision is that it enhances the contrast of zooplankton targets by breaking their transparency. Here, we used an optomotor apparatus to test the responses of the planktivorous Hardyhead silverside fish Atherinomorus forskalii (Atherinidae) to vertical unpolarized (intensity) and polarized gratings. We also tested and compared the spatial and temporal resolutions of A. forskalii in the intensity and polarization domains. A. forskalii responded to the polarization pattern, but only under illumination that included ultraviolet-blue (λ>380nm) wavelengths. The spatial resolution of A. forskalii was measured as a minimum separable angle of 0.57° (a 1-mm prey viewed from 100-mm distance). The temporal resolution to unpolarized vs. polarized gratings was constant, at 33 and 10Hz respectively at most of the stripe widths tested. At the smallest stripe width tested (1mm=the minimal separable angle), which correlates with the size of prey typically consumed by these fish, the temporal resolution to the polarized grating increased to 42Hz. We conclude that A. forskalii is polarization sensitive, may use polarization vision to improve detection of its planktonic prey, and that polarization may be perceived by the fish via a separate visual pathway than intensity. [ABSTRACT FROM AUTHOR]

The coexistence of species is facilitated by niche partitioning. Resource competition is a major cause of phenotypic differentiation.The major axes of differentiation in closely related species occur along the two ecological dimensions habitat and diet. Adaptive radiations typically follow these axes of variation. Some of the most important traits in the radiations of freshwater fish are body size, body shape, and a few trophic features such as mouth position, teeth type or gill rakers. In some of the most famous temperate freshwater radiations (i.e., sticklebacks, whitefish) gill rakers play a pivotal role in the adaptation to novel prey types. Cichlids are the most famous textbook examples of fast and divergent adaptive radiations. Often species differ in adaptation to alternative prey types associated to particular trophic morphologies. Pharyngeal jaw shape, oral and pharyngeal teeth and mouth position are the main traits typically studied in cichlid radiations. Gill rakers have however rarely been consider when trying to understand cichlid adaptation to the environment. Here we assess the variation of gill rakers in the cichlid assemblage inhabiting the Nicaraguan large and crater lakes. We found marked differences among species, and found interesting correlations between gill raker traits and environmental features demonstrating their role in adaptation and diversification.

Fluctuating asymmetry (FA), which can be defined as random morphologic changes on bilateral symmetry plan of paired morphometric and meristic characters in response of environmental disturbances, is an alternative tool to traditional methods of environmental health assessment that has an interesting potential to appraise the state of adaptation of a population before that acute contaminations affect the whole community or ecosystem. This study aimed to assess the occurrence of FA in three morphometric and three meristic characters of the Corocoro grunt Orthopristis ruber (Cuvier, 1830), and compare the deviations in bilateral symmetry of this reef-associated and omnivorous in Guanabara Bay (Brazil), the venue for various outdoor aquatic sports during the 2016 Olympic Games. Five indexes of FA were tested over the six characters of 66 O. ruber , which were caught during the dry and wet seasons of 2011 and at three areas Guanabara Bay of different environmental characteristics. In addition to validate the existence of FA for O. ruber , our findings revealed significant deviations in the bilateral symmetry according to the FA indexes and fish characters. Together with the FA1 index, the number of gill rakers and the number of rays of the pectoral fin provided the best methodological approach to address the levels of FA in O. ruber as a response to environmental stressors in each region. The levels of FA in O. ruber was significantly lower in the Urca region (less impacted) than for individuals caught near the Paquetá Island and Rio-Niterói Bridge sites (more degraded). Partial Redundancy Analysis also shows that the fish characters are affected in different ways by environmental stressors, but especially in response to the levels of dissolved oxygen and, secondarily, to water transparency, and that Paquetá Island is apparently less impacted than the site near the Rio-Niterói Bridge. Our results confirm the potential of FA to be used as a tool to detect environmental effects on a reef-associated fish species in a tropical polluted bay, but further studies are necessary to validate our findings for other species and ecosystems. [ABSTRACT FROM AUTHOR]

Surface ultrastructure of the gills of the angler catfish Chaca chaca was investigated to unravel the adaptive modifications associated with the feeding ecology of the fish. The fish is often found in mud or in soft substrates where they remain buried both for protection and to feed. Gill rakers present on the gill arch in most fish species are absent in this fish. The absence of gill rakers are associated with the feeding habit of the fish and is considered to facilitate the swallowing of captured prey smoothly without any hindrance. Highly corrugated surface of the gill arch and gill filaments could be associated to retain water/mucus to prevent dessicassion of the fish. Papillae like epithelial protuberances each bearing a taste bud at its summit toward the pharyngeal side of the gill arch is associated with the sorting of the food. Large number of mucous goblet cells on the gill arch epithelium are considered to secret copious mucus to lubricate the prey for easy swallowing. In C. chaca the gill septa between gill filaments are reduced. This could enhance the flexibility and permit the free movement of the gill filaments. Extensive secondary lamellae and infrequent mucous goblet cells on secondary lamellae are associated to increase the surface area to enhance efficiency of gaseous exchange. [ABSTRACT FROM AUTHOR]

Results of the morphological analysis of ecology and feeding of two sympatric forms of whitefishes (lacustrine and lacustrine-riverine) inhabiting Lake Taymyr (the Taymyr Peninsula) are presented in the article. It is revealed that these forms do not differ in the number of gill rakers on the first branchial arch and in the number of perforated scales in the lateral line, but they do differ in plastic characters, spawning periods, and area. At the age of 2-3 years they become separate in regards to feeding type. It is assumed that both forms of whitefishes inhabited Lake Taymyr simultaneously with the filling of the lake basin. Apparently the taxonomic status of the sympatric whitefishes from Lake Taymyr is broader than the term 'ecological form.' [ABSTRACT FROM AUTHOR]

The present study aimed to compare between gill rakers of some marine fishes with different feeding habits. A total of 78 specimens in 13 species belonged to 6 fish families: Sparidae (Sparus aurata, Diplodus noct, Rhapdosargus haffara and Boops boops); Family: Mugilidae (Mugil cephalus, Mugil capito and Liza aurata); Family: Siganidae (Siganus rivulatus and Siganus luridus); Family: Synodontidae (Saurida undosquamis and Synodus saurus); Family: Clupeidae (Herklotsichthys quadrimaculatus) and Family: Carangidae (Caranx sexfasciatus) were collected by irregular visits from land fish market in different localities of Egyptian Mediterranean Sea and Suez Gulf; during the period from March, 2014 to November, 2014. Results showed that, the first gill arch formed of one piece, consisting of two limbs (upper and lower limbs). The gill arch carried two rows of gill rakers on its concave border and two rows of gill filaments on its convex one. The gill rakers in the anterior row (oral row) are longer, more in number and more developed than that of the posterior row (aboral row). The gill arch in family Sparidae is bow-like shape. The anterior gill rakers on the first gill arch of most sparid species are short, conical in shape adapted to carnivorous feeding. The gill arch of fish species in Mugilidae is mostly crescent-shaped and rarely bow-shaped. The anterior gill rakers on the first gill arch are long and great in number adapted to detritus feeding. The gill arch in family Synodontidae is V shaped. The anterior gill rakers on the first gill arch appeared as clusters of small tooth patches adapted to piscivores feeding. The gill arch in family Siganidae is hook-like shape. The anterior gill rakers on the first gill arch were needle spine in shape with secondary projections adapted to herbivorous feeding. The gill arch in fish species of Clupeidae is V like shape. Gill rakers are well developed and arranged in only one row. They are numerous and elongated adapted to seizing food items in the plankton feeding. The gill arch in fish species of Carangidae is bow-like shape. Gill rakers are moderate in length and number adapted to carnivorous feeding. According to the different feeding habits, the results showed that, the highest average length of the first gill arch (mm) is recorded in carnivore and piscivore fish. The maximum averages number and the length of the anterior gill rakers are recorded in detritivore fish and plankitivore fish. The highest percentages of the anterior gill raker length /gill arch length ratio (%) are recorded in plankitivore fish and detritivore fish. Results showed that, the maximum inter raker space (μm) and the inter raker space/gill arch length (%) is recorded in carnivore fish. The maximum breadth at the raker base (μm) in the anterior row of rakers is recorded in piscivore fish. The highest breadth at the raker base/gill arch length (%) in the anterior row of rakers is recorded in carnivore, piscivore and planktivore fish. The highest posterior gill raker length (μm) and the posterior gill raker length /gill arch length ratio (%) are recorded in detritivore fish. In conclusion: The morphological characters of the gill rakers in the first gill arch were differ in species studied according to different feeding habits. So that, can be used in determine the fish family and feeding habits. [ABSTRACT FROM AUTHOR]

In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly during summer months, and S. pilchardus eggs during the winter. The marked difference between the trophic ecology of S. pilchardus in the two areas studied appears to have originated from different dietary strategies that the two populations have adopted in contrasting feeding environments. These differences are shown to profoundly affect the size and quality of prey consumed, and the effect of cannibalism on the populations. [ABSTRACT FROM AUTHOR]

Relationships between morphological traits and their ecological function frequently result in patterns that are consistently observed within taxa. Across fishes, the field of ecomorphology has identified a number of morphological traits linked to foraging tactic. Here we examined the links between morphology and diet in pumpkinseed sunfish ( Lepomis gibbosus (L., 1758)) from three temperate freshwater lakes. We focused on morphological variation in pharyngeal jaw and gill raker structures, both involved with the processing of prey after capture, in relation to diet. Using stomach contents and stable isotope analysis, we established mean resource use estimates for both populations and individual fish. Among populations and individuals within lakes, we observed that pharyngeal jaw size and gill raker spacing increased with the consumption of littoral prey (e.g., hard-shelled snails) relative to pelagic prey (e.g., zooplankton), but the morphological changes were greater for the pharyngeal jaws. Overall, the relationships that we observed between morphology and foraging tactic were consistent with patterns observed in pumpkinseed and across other fishes. Individual-level diet variation associated with morphology may result in phenotypic diversity within populations that has multiple ecological and evolutionary implications for these populations. [ABSTRACT FROM AUTHOR]

Abstract: The suspension-feeding cichlids Oreochromis aureus (blue tilapia) and Oreochromis esculentus (ngege tilapia) are able to selectively retain small food particles. The gill rakers and microbranchiospines of these species have been assumed to function as filters. However, surgical removal of these oral structures, which also removed associated mucus, did not significantly affect the total number of 11–200μm particles ingested by the fish. This result supports the hypothesis that the branchial arch surfaces themselves play an important role in crossflow filtration. Both species selectively retained microspheres greater than 50μm with gill rakers and microbranchiospines intact as well as removed, demonstrating that neither these structures nor mucus are necessary for size selectivity to occur during biological crossflow filtration. After removal of the gill rakers and microbranchiospines, O. esculentus retained significantly more microspheres 51–70μm in diameter and fewer 91–130μm microspheres compared to retention with intact structures, but the particle size selectivity of O. aureus was not affected significantly. These results support conclusions from previous computational fluid dynamics simulations indicating that particle size can have marked effects on particle trajectory and retention inside the fish oropharyngeal cavity during crossflow filtration. The substantial inter-individual variability in particle retention by suspension-feeding fish is an unexplored area of research with the potential to increase our understanding of the factors influencing particle retention during biological filtration. [Copyright &y& Elsevier]

We evaluate the usefulness of gill rakers as a post-hatch developmental marker in salmon by tracking development in undisturbed and stressed yolk-bearing salmon embryos. Native pink salmon ( Oncorhynchus gorbuscha) from Auke Creek, Juneau, Alaska and genetically stressed outbred hybrids between Auke Creek and Pillar Creek (Kodiak Island) salmon were incubated in ambient-temperature Auke Creek water. Environmentally stressed native embryos were reared in water that was 2 to 4 °C warmer than ambient. The sum of rakers on the first left and right branchial arches of natives reared at ambient temperatures averaged 23.20 (SD ± 1.64) per embryo when post-hatch sampling began. The subsequent increase in raker counts was linear and positively correlated with the accumulation of thermal units until counts reached maxima 223 days after fertilization, which coincided with the complete consumption of yolk reserves. The average maximum raker count was 39.55 (SD ± 1.76) per embryo, which is substantially fewer than the 60 rakers typically observed in adults. Neither raker development nor yolk consumption patterns were affected by hybridization. Elevated incubation temperatures accelerated raker formation and yolk consumption in native embryos, but the number of rakers associated with a given amount of yolk was the same regardless of temperature suggesting that changes in yolk consumption rate and raker development rate did not influence raker counts. These results indicate that rakers are easily observed and counted, grow in a predictable sequence, and are developmentally stable in the face of both genetic and environmental stress, thereby making them potentially reliable post-hatch developmental markers. [ABSTRACT FROM AUTHOR]

We study crossflow filtration mechanisms in suspension-feeding fishes using computational fluid dynamics to model fluid flow and food particle movement in the vicinity of the gill rakers. During industrial and biological crossflow filtration, particles are retained when they remain suspended in the mainstream flow traveling across the filter surface rather than traveling perpendicularly to the filter. Here we identify physical parameters and hydrodynamic processes that determine food particle movement and retention inside the fish oral cavity. We demonstrate how five variables affect flow patterns and particle trajectories: (1) flow speed inside the fish oral cavity, (2) incident angle of the flow approaching the filter, (3) dimensions of filter structures, (4) particle size, and (5) particle density. Our study indicates that empirical experiments are needed to quantify flow parameters inside the oral cavity, and morphological research is needed to quantify dimensions of the filter apparatus such as gill rakers, the gaps between rakers, and downstream barriers. Ecological studies on suspension-feeding fishes are also needed to quantify food particle size and density, as these variables can affect particle retention due to hydrodynamic processes during crossflow filtration. [ABSTRACT FROM AUTHOR]

Introduced pumpkinseed in Iberian reservoirs display marked external morphological differentiation along two simultaneous dimensions of flow and trophic structure. We assessed the degree of internal morphological differentiation using gill rakers, pharyngeal jaws and the levator posterior muscle among pumpkinseeds occupying four different habitats and determined whether prey consumption accounted for any discernible differences in feeding structures among ecomorphs. Results showed significant differentiation by habitat based on pharyngeal muscle and jaw dimensions in all study reservoirs, with pelagic pumpkinseeds having smaller jaws than littoral pumpkinseeds in four of the five reservoirs. Gill rakers, however, differentiated morphs in only three of the five reservoirs, corresponding to differences in zooplankton consumption among pelagic and littoral individuals in those reservoirs. Based on all internal morphological traits, greater divergence was seen along the littoral-pelagic trophic axis in the lacustrine zones of reservoirs compared to the fluvial zone. Overall differences noted in internal morphology are likely the result of phenotypic plasticity; the ability of this species to readily adapt to changing physical environments may explain the success of the pumpkinseed in its introduced range. [ABSTRACT FROM AUTHOR]

1. The adaptive radiation of fishes into benthic (littoral) and pelagic (lentic) morphs in post-glacial lakes has become an important model system for speciation. Although these systems are well studied, there is little evidence of the existence of morphs that have diverged to utilize resources in the remaining principal lake habitat, the profundal zone. 2. Here, we tested phenotype-environment correlations of three whitefish ( Coregonus lavaretus) morphs that have radiated into littoral, pelagic and profundal niches in northern Scandinavian lakes. We hypothesized that morphs in such trimorphic systems would have a morphology adapted to one of the principal lake habitats (littoral, pelagic or profundal niches). Most whitefish populations in the study area are formed by a single (monomorphic) whitefish morph, and we further hypothesized that these populations should display intermediate morphotypes and niche utilization. We used a combination of traditional (stomach content, habitat use, gill raker counts) and more recently developed (stable isotopes, geometric morphometrics) techniques to evaluate phenotype-environment correlations in two lakes with trimorphic and two lakes with monomorphic whitefish. 3. Distinct phenotype-environment correlations were evident for each principal niche in whitefish morphs inhabiting trimorphic lakes. Monomorphic whitefish exploited multiple habitats, had intermediate morphology, displayed increased variance in gillraker-counts, and relied significantly on zooplankton, most likely due to relaxed resource competition. 4. We suggest that the ecological processes acting in the trimorphic lakes are similar to each other, and are driving the adaptive evolution of whitefish morphs, possibly leading to the formation of new species. [ABSTRACT FROM AUTHOR]

Abstract: The surface ultrastructure of the gill arches and the gill rakers of an herbivorous fish, Cirrhinus mrigala was investigated by scanning electron microscopy. These structures show significant adaptive modifications associated with the food and feeding ecology of the fish. Closely lying short gill rakers and narrow inter-raker channels on the gill arches are associated to filter and retain food particles. Prominent epithelial protuberances on the gill rakers and the gill arches enable the taste buds, located at their summit, to project well above the surface of the epithelium. This could increase the efficiency of the taste buds in selective sorting of palatable food. Surface specializations of the postlingual organ are recognized adaptive modifications for selecting, trapping or holding food particles. Prominent molariform teeth born on the lower pharyngeal jaw, and the chewing pad opposite it, are associated to work together as an efficient pharyngeal mill. Mucous goblet cells are considered to elaborate mucus secretions to trap, glue and lubricate food particles for their smooth transport for swallowing. [Copyright &y& Elsevier]

Abstract. If natural communities are assembled according to deterministic rules, coexisting species will represent a nonrandom subset of the potential species pool. We tested for signatures of assembly rules in the distribution of species' traits in Pacific rockfish (Sehastes spp.) assemblages. We used morphology, dietary niche (estimated with stable nitrogen isotopes), and distribution data to identify traits that relate to local-scale resource use (the α-niche) and to environmental gradients (the β-niche). We showed that gill raker morphology was related to trophic position (an α-niche axis), while relative eye size was associated with depth habitat (a β-niche axis). We therefore hypothesized that, within assemblages of coexisting rockfish species, the gill raker trait would be overdispersed (evenly spaced) due to limiting similarity, while relative eye size would be clustered due to environmental filtering. We examined the evolutionary relatedness of coexisting species to ask whether phylogenetic community structure and trait distributions gave similar indications about the roles of assembly processes. We tested the trait distributions and phylogenetic structure of 30 published rockfish assemblages against a null model of random community assembly. As predicted, the gill raker trait tended to be more evenly spaced than expected by chance, as did overall body size, while relative eye size was more clustered than expected. Phylogenetic community structure appeared to reflect historical dispersal and speciation and did not provide consistent support for assembly rules. Our results indicate that rockfish community assembly is nonrandom with regard to species' traits and show how distinguishing traits related to the α- and β-niches and incorporating functional morphology can provide for powerful tests of assembly rules. [ABSTRACT FROM AUTHOR]

Studies of adaptive divergence have traditionally focused on the ecological causes of trait diversification, while the ecological consequences of phenotypic divergence remain relatively unexplored. Divergence in predator foraging traits, in particular, has the potential to impact the structure and dynamics of ecological communities. To examine the effects of predator trait divergence on prey communities, we exposed zooplankton communities in lake mesocosms to predation from either anadromous or landlocked (freshwater resident) alewives, which have undergone recent and rapid phenotypic differentiation in foraging traits (gape width, gill raker spacing, and prey size-selectivity). Anadromous alewives, which exploit large prey items, significantly reduced the mean body size, total biomass, species richness, and diversity of crustacean zooplankton relative to landlocked alewives, which exploit smaller prey. The zooplankton responses observed in this experiment are consistent with patterns observed in lakes. This study provides direct evidence that phenotypic divergence in predators, even in its early stages, can play a critical role in determining prey community structure. [ABSTRACT FROM AUTHOR]

Morphometric and genetic variation were examined in parental Carassius auratus gibelio and Carassius carassius individuals, and their natural hybrids. Of meristic traits, only the number of gill rakers clearly distinguished hybrids (39·4 ± 1·4) from parental C. a. gibelio (48·3 ± 0·7) and C. carassius (28·6 ± 1·1). MtDNA sequences showed that the hybrids were descendants of female C. a. gibelio. Microsatellite analysis confirmed the presence in hybrids of variants typical of C. a. gibelio and C. carassius. [ABSTRACT FROM AUTHOR]

Alewife, Alosa pseudoharengus, populations occur in two discrete life-history variants, an anadromous form and a landlocked (freshwater resident) form. Landlocked populations display a consistent pattern of life-history divergence from anadromous populations, including earlier age at maturity, smaller adult body size, and reduced fecundity. In Connecticut (USA), dams constructed on coastal streams separate anadromous spawning runs from lake-resident landlocked populations. Here, we used sequence data from the mtDNA control region and allele frequency data from five microsatellite loci to ask whether coastal Connecticut landlocked alewife populations are independently evolved from anadromous populations or whether they share a common freshwater ancestor. We then used microsatellite data to estimate the timing of the divergence between anadromous and landlocked populations. Finally, we examined anadromous and landlocked populations for divergence in foraging morphology and used divergence time estimates to calculate the rate of evolution for foraging traits. Our results indicate that landlocked populations have evolved multiple times independently. Tests of population divergence and estimates of gene flow show that landlocked populations are genetically isolated, whereas anadromous populations exchange genes. These results support a ‘phylogenetic raceme’ model of landlocked alewife divergence, with anadromous populations forming an ancestral core from which landlocked populations independently diverged. Divergence time estimates suggest that landlocked populations diverged from a common anadromous ancestor no longer than 5000 years ago and perhaps as recently as 300 years ago, depending on the microsatellite mutation rate assumed. Examination of foraging traits reveals landlocked populations to have significantly narrower gapes and smaller gill raker spacings than anadromous populations, suggesting that they are adapted to foraging on smaller prey items. Estimates of evolutionary rates (in haldanes) indicate rapid evolution of foraging traits, possibly in response to changes in available resources. [ABSTRACT FROM AUTHOR]