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Thiamethoxam (THM) is a widely used agro-pesticide in Bangladesh, though European Union has banned this neonicotinoid insecticide due to its toxic effects on non-target organisms. A 60-day experiment was conducted to study the effect of sub-lethal concentrations of THM on gills of Banded Gourami Trichogaster fasciata. The experiment was conducted in 15 PVC tanks each containing 100L water. The 96-h LC50 value of THM was estimated as 161.06mg/L for Banded Gourami. Based on estimated 96-h LC50 value, the experiment was carried out using a control (0 mg/L of THM) and five sub-lethal concentrations (9.37, 18.75, 37.5, 75 and 150 mg/L of THM in water) with three replications. For collection of gills, fishes were sampled on day-30 and day-60 of exposure to THM. Several histopathological changes were observed in the gill tissues of treated fishes viz. clubbing and reduction of gill filaments, telangiectasis of gill lamellae, haemorrhage and damage of gill raker. Water quality parameters (e.g. DO, pH and temperature) were recorded every 15 days interval. The DO levels were found to decrease significantly with increasing THM concentrations and time of exposure, whereas no noticeable changes were observed for pH and temperature. Therefore, neonicotinoid crop insecticide like THM is capable of damaging gill tissues of an small indigenous fish Banded Gourami.

Broad-scale patterns of resource utilization and the corresponding morphological evolution is a result of an integral relationship among form and function. In addition, there is also an inherent role of the latter in determining species co-interaction and assemblage pattern that forms an integral aspect of ecological research. The present study aimed to evaluate the ecomorphological relationship among 37 fish species inhabiting the intertidal mudflats of the Indian Sundarbans by outlining the following objectives: (i) identifying and characterizing feeding guilds/groups and (ii) understanding the inter-relationship between morphometry with (a) the established feeding guild classifications and (b) observed prey taxa (that characterizes these feeding groups) for determining the role of morphometry in prey acquisition followed by (iii) the evaluation of their potential phylogenetic convergence among the species. For the first objective, two approaches for feeding guild classification were made (3-Guild and 8-Guild) for assessing the prediction accuracy of morphological characters in identifying the different guilds. While the former was based on troph values, the latter classification mode relied on the similarities in diet composition among the different fish species. For addressing the second objective, we employed two different models namely, linear discriminant (LDA) and redundancy analysis (RDA). While the LDA model tested the prediction accuracy of morphological traits in classifying the different feeding guilds, RDA was applied to model the correlation between the morphological traits and the prey categories. In the LDA model, morphological characters showed higher accuracy (78.4%) in classifying three feeding groups rather than eight feeding groups (73%). Following this, the RDA model (explaining 79.78% of constrained variance) showed gill raker intensity, protrusion length, head depth, caudal peduncle, eye diameter and inter-orbital distance to be highly associated with selection of specific prey types by species, thereby characterizing a particular feeding guild. However, generalized linear models testing for correlation between troph value and feeding groups showed substantial variation (90.35%) in the dietary index being explained by the 8-Guild classification. Hence, our study maintains the assumption that broad morphological differentiation acts as one of the underlying processes resulting in dietary variations that results in the varying modes of resource utilization by the coexisting species, thereby determining the structure of a trophic guild. Furthermore, it also suggests that in terms of prey abundance or selectivity, the 8-Guild model is much more conducive in representing the feeding habits of the species while the morphological traits reflected a relatively broader scheme of classification, (i.e., 3-Guild model) with certain traits being phylogenetically conserved within these groups.

Various biometric and geometric measures were used to discriminate between the morphologically similar river puffer, Takifugu obscurus, tiger puffer, T. rubripes, their hybrids, and their triploid hybrids. The hybrids and triploid hybrids had greater anal fin width, nostril width, and snout length than the parental species (p

Scopelogadus bispinosus has been redescribed, its species status has been restored. It has long been considered a subspecies of S. mizolepis. The species inhabits mainly the tropical and subtropical zones of the central and eastern parts of the Pacific Ocean; in the northeastern Pacific Ocean, it is found in temperate waters. A new species S. perplexus sp. n. has been described from the tropical waters of the Pacific Ocean. The new species is characterized by the presence of a large number filaments of pseudobranch (10–11), the largest of the two branchial lobes opposite the angular gill raker is relatively short; the color of the stomach surface is uniformly dark, without noticeable darkening in the back.

A new loach species (Cypriniformes: Nemacheilidae: Yunnanilini), Yunnanilus chuanheensis sp. nov. , was caught from Chuanhe in the upper reaches of the Lixianjiang River, a tributary of the Red River in Nanjian County, Yunnan Province, China. This species is a member of the traditional Y. pleurotaenia species group based on the presence of a lateral line and cephalic lateral-line canals. It can be distinguished from other species in the Y. pleurotaenia species group by the following characters: lips without papillae, anterior and posterior nostrils separated, whole body scaled, eye diameter smaller than interorbital width, outer gill raker absent on first gill arch, eye diameter greater than 18% of head length, 10–11 inner gill rakers on first gill arch, and lateral line not extending to vertical through dorsal fin insertion. To the best of our knowledge, this is the first Yunnanilus species recorded from the Red River drainage.

Species introductions provide opportunities to quantify rates and patterns of evolutionary change in response to novel environments. Alewives (Alosa pseudoharengus) are native to the East Coast of North America where they ascend coastal rivers to spawn in lakes and then return to the ocean. Some populations have become landlocked within the last 350 years and diverged phenotypically from their ancestral marine population. More recently, alewives were introduced to the Laurentian Great Lakes (~150 years ago), but these populations have not been compared to East Coast anadromous and landlocked populations. We quantified 95 years of evolution in foraging traits and overall body shape of Great Lakes alewives and compared patterns of phenotypic evolution of Great Lakes alewives to East Coast anadromous and landlocked populations. Our results suggest that gill raker spacing in Great Lakes alewives has evolved in a dynamic pattern that is consistent with responses to strong but intermittent eco‐evolutionary feedbacks with zooplankton size. Following their initial colonization of Lakes Ontario and Michigan, dense alewife populations likely depleted large‐bodied zooplankton, which drove a decrease in alewife gill raker spacing. However, the introduction of large, non‐native zooplankton to the Great Lakes in later decades resulted in an increase in gill raker spacing, and present‐day Great Lakes alewives have gill raker spacing patterns that are similar to the ancestral East Coast anadromous population. Conversely, contemporary Great Lakes alewife populations possess a gape width consistent with East Coast landlocked populations. Body shape showed remarkable parallel evolution with East Coast landlocked populations, likely due to a shared response to the loss of long‐distance movement or migrations. Our results suggest the colonization of a new environment and cessation of migration can result in rapid parallel evolution in some traits, but contingency also plays a role, and a dynamic ecosystem can also yield novel trait combinations.

The distribution and early growth of juvenile Pacific bluefin tuna (PBF) Thunnus orientalis were studied based on trawl surveys conducted around Sado Island, eastern Sea of Japan, from late August to early September in 2017 and 2018. Juvenile PBF were mainly collected in an area between the Tsushima Warm Current and land where the surface water (5-m depth) temperature ranged from 22.8 to 27.2 °C. The fork length (FL) of the fish ranged from 12 to 320 mm, and there were modes at 140–170 mm FL in the frequency distribution for both years. In 2018, there was also a mode at around 50 mm FL. Otolith microstructure analysis revealed that hatch date mainly peaked in early and mid July in both years, and in early and mid August in 2018, and corresponded with the modes of FL. In addition, differences in growth were observed between year classes, and between size classes in 2018. Total gill raker number increased with FL and was almost constant at around 100 mm FL. This study provides an update of the distribution of juvenile PBF in the Sea of Japan, which was found to be related to the Tsushima Warm Current, and indicates the importance of the eastern Sea of Japan as a nursery ground for PBF that hatch from July to August.

Dussumieria albulina (Fowler 1934), formerly regarded as a junior synonym of Dussumieria acuta Valenciennes 1847, is shown to be a valid species and is redescribed on the basis of 29 specimens, including the holotype. Although the two species resemble each other morphologically, sharing body scales with numerous longitudinal striae posteriorly, a deep body, 26 or fewer lower gill rakers on the first gill arch, and 15 or fewer branchiostegal rays, the former is distinguished by lacking parasphenoid teeth (vs. distinct conical teeth on parasphenoid in D. acuta), higher gill raker counts (total gill rakers on first gill arch 33–41 vs. 30–38), a rather slender body (20.6–24.4% SL vs. 23.4–28.2% SL in individuals of D. acuta > 75 mm SL), and melanophores scattered on the 3rd to 9th (vs. 1st to 5th) pectoral-fin rays from the uppermost ray. Analysis of the mitochondrial cytochrome oxidase I (COI) gene in both species showed them to be separated by 12% mean p-distance. A redescription of D. acuta is also provided.

Resource partitioning has an essential role in interspecific relations, especially in congener species, which share many morphological traits. In some places, small characids coexist through resource partitioning, which may reduce their interspecific competition. Astyanax species (e.g., Astyanax minor, Astyanax gymnodontus and Astyanax bifasciatus), for example, coexist in different water bodies from the Iguaçu River basin. These species have high phenotypic plasticity and many morphologic specializations that allow them to live in different habitats. Based on evidences that these species modified their feeding habits because of changes in resource availability in Iguaçu River, this study tested two hypotheses: (a) there are differences in head morphology, number of teeth and number of gill rakers among the species of Astyanax; and (b) there are differences in gill arch and gill raker morphology among the species of Astyanax, which may favour their trophic resource partitioning in Iguaçu River. The head morphological traits and quantitative morphological characters were summarized in a principal coordinates analysis (PCoA), and the analysis of similarities (ANOSIM) showed significant differences among species. Gill morphological measurements were analysed through analysis of covariance (ANCOVA), and it also showed significant differences in gill arch and gill raker morphology among species. Therefore, the analysis of ecomorphological traits related to trophic habits revealed some differences that may suggest a tendency of reducing competition for trophic resources in the Iguaçu River basin.

Mandarin fishes (Sinipercidae) are piscivores that feed solely on live fry. Unlike higher vertebrates, teleosts exhibit feeding behavior driven mainly by genetic responses, with no modification by learning from parents. Mandarin fishes could serve as excellent model organisms for studying feeding behavior. We report a long-read, chromosomal-scale genome assembly for Siniperca chuatsi and genome assemblies for Siniperca kneri, Siniperca scherzeri and Coreoperca whiteheadi. Positive selection analysis revealed rapid adaptive evolution of genes related to predatory feeding/aggression, growth, pyloric caeca and euryhalinity. Very few gill rakers are observed in mandarin fishes; analogously, we found that zebrafish deficient in edar had a gill raker loss phenotype and a more predatory habit, with reduced intake of zooplankton but increased intake of prey fish. Higher expression of bmp4, which could inhibit edar expression and gill raker development through binding of a Xvent-1 site upstream of edar, may cause predatory feeding in Siniperca., He, Li, and Lv et al. took a genomics approach to study innate feeding behavior in mandarin fish. They identify genes related to predatory feeding that underwent rapid adaptive evolution. They also functionally validate the role of bmp4-edar pathway in inducing predatory feeding in zebrafish.

To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.

International audience; 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.

A southwestern Indian Ocean (SWIO) percoid fish Serranus knysnaensis Gilchrist, 1904, was long synonymised with the comber, Serranus cabrilla (Linnaeus, 1758), from the eastern Atlantic Ocean, Mediterranean and Black Sea. However, when the species was brought out of synonymy by Heemstra & Heemstra (2004), reasons for this decision were not given. This study aims to revalidate the present taxonomic status of S. knysnaensis using morphological and molecular assessments. The two species are distinguished by the number of circumpeduncular scales (26–34 in S. knysnaensis versus 34–38 in S. cabrilla) and total gill rakers (18–22 versus 22–24). Serranus knysnaensis is also distinct from S. novemcinctus Kner, 1864, the other SWIO species of Serranus, based on total gill raker counts (18–22 versus 31–35). Genetic analysis of mitochondrial DNA barcode (COI) sequences for 17 Serranus species revealed three closely-related monophyletic clusters corresponding to S. cabrilla, S. novemcinctus and S. knysnaensis that were supported (P

Much is known about the genetic and developmental basis of mutant phenotypes in the laboratory. However, much less is known about the mechanisms that control naturally evolved phenotypes in the wild. Are specific types of genes or mutations preferred? How are developmental programs modified to generate altered phenotypes? Finally, in cases where the same phenotype has evolved in independent lineages (convergent evolution), are the same genes or mutations used?The threespine stickleback fish (Gasterosteus aculeatus) is an emerging model organism in which the approaches and tools of developmental biology, genetics, and genomics can be applied to understand evolutionary changes. Marine sticklebacks have repeatedly colonized and adapted to new freshwater environments throughout the Northern Hemisphere. Freshwater sticklebacks have evolved many changes in their skeleton relative to marine fish. For example, freshwater sticklebacks have evolved changes to their defensive armor in response to decreased predation and changes in bones used for feeding in response to differences in diet. Despite their phenotypic differences, marine and freshwater sticklebacks can be bred in the lab. Crosses between marine and freshwater sticklebacks can be used to decipher the genetic basis of their evolved phenotypic differences.In chapter 2 of this thesis, I present the results of a large quantitative genetic study of stickleback skeletal evolution. I mapped regions of the genome, known as quantitative trait loci (QTL), affecting a wide range of skeletal traits. Over 100 QTL were mapped, and a meta-analysis of their properties was performed. Using these QTL, several general questions in evolutionary genetics were addressed. First, I explored the dominance of the QTL. The dominance of a QTL is a genetic property that might affect likelihood of being used during adaptation. Surprisingly, a large proportion of skeletal QTL had an additive (intermediate) dominance. Second, I investigated the modularity of QTL. To do this, I examined serially repeating skeletal elements such as vertebrae. Most (76%) QTL that influenced such traits had specific, modular effects on just a subset of the possible domains of the phenotype. Finally, I examined whether the QTL clustered in the genome. Many large-effect skeletal QTL were clustered on chromosomes 4, 20, and 21. Inheritance of these clusters of linked adaptive alleles might allow multiple aspects of skeletal morphology to evolve rapidly and simultaneously. In summary, the large set of skeletal QTL was used to explore the genetic properties of evolved mutations. These QTL are a starting point for the identification of the molecular basis of evolved changes in the vertebrate skeleton.In chapter 3 of this thesis, I focus on one skeletal trait, gill raker number. Gill rakers are periodically patterned bones in a fish’s throat important for feeding. In response to a change in diet in freshwater populations, hundreds of freshwater stickleback populations have independently evolved a reduction in gill raker number. This phenomenon is known as gill raker reduction. I found that heritable marine/freshwater differences in gill raker number were present early in development. The gill raker number differences were due to a difference in the spacing between adjacent gill rakers. The marine/freshwater number and spacing differences were present at the earliest detectable point of gill raker specification. This result suggests that gill raker reduction is caused by an early-acting change to a lateral inhibition process controlling raker bud spacing. Next, I performed linkage mapping in F2 fish from crosses with three independently derived freshwater populations. In all three crosses, gill raker QTL mapped to chromosomes 4 and 20, suggesting a similar genetic basis. Finally, the chromosome 4 and 20 QTL affected the early spacing of gill raker buds. Collectively, these data demonstrated that parallel developmental genetic features underlie the convergent evolution of gill raker reduction in freshwater sticklebacks. These results suggest that even highly polygenic adaptive traits can have a predictable developmental genetic basis.In chapter 4 of this thesis, I present an economical method that uses next-generation sequencing to perform genome-wide genotyping of hundreds of multiplexed samples. This method was used to genotype two large marine by freshwater F2 crosses of over 350 fish each. The resulting maps significantly improved the stickleback genome assembly by making over 100 changes to the order and orientation of the scaffolds that compose the genome assembly. In the revised genome assembly, 95% of the assembly was anchored to a chromosome, compared to 87% in the original assembly. To assess linkage map quality, I mapped quantitative trait loci (QTL) controlling lateral plate number. Plate number mapped as expected to a 200 kilobase genomic region containing Ectodysplasin. In addition, plate number mapped to a chromosome 7 QTL overlapping a previously identified modifier QTL. Finally, I examined gill raker length. I found that the two freshwater populations convergently evolved shorter gill rakers relative to marine fish. I mapped eight QTL controlling gill raker length in the two crosses. However, none of the QTL were overlapping between the two crosses. Thus, the convergent evolution gill raker length reduction has a surprisingly non-parallel genetic basis.In chapter 5 of this thesis, I present additional experiments to determine the genetic basis of evolved reduction in gill raker number. Using the genotyping method developed in chapter 4, I mapped QTL controlling raker number and spacing in two large marine by freshwater F2 crosses of over 350 fish each. Overlapping QTL on chromosomes 4, 16, and 20 were found in both crosses. In addition, 14 unique modifier QTL were mapped. Together these results indicate that a combination of similar and different genetic basis underlies the convergent evolution of gill raker number. Using crosses with recombinant chromosomes, I fine-mapped the chromosome 4 and 20 QTL, substantially narrowing the interval sizes. Surprisingly, the chromosome 4 QTL in the two crosses mapped to non-overlapping regions. Therefore, even though the chromosome 4 QTL appeared to map to similar genomic regions in the two crosses, a different genetic basis was actually used. An excellent candidate gene, Fibroblast Growth Factor 20 (Fgf20) was located within one of the fine-mapped chromosome 4 QTL. I mutated the coding region of Fgf20 with a genome-editing technology called Transcription Activator-Like Effector Nucleases (TALENs). Induced loss of function mutations in Fgf20 resulted in a decrease in gill raker number. The Fgf20 mutants had a concomitant increase in gill raker spacing, similar to the evolved freshwater phenotype. Induced mutations in a second gene, Smad5, also resulted in a raker phenotype. However, Smad5 was excluded from the fine-mapped QTL intervals, so it likely does not underlie gill raker evolution. No coding changes in Fgf20 likely cause evolved gill raker reduction. These results suggest a model in which cis-regulatory mutations that affect Fgf20 expression levels or spatial patterns contribute to evolved gill raker reduction.Together, this work makes significant progress towards understanding the genetic and developmental basis of skeletal evolution in stickleback fish. The results have broad implications for understanding the process of how genetic variation contributes to adaptive evolution.

Two new species of Myxobolus Butschli, 1882 (Bivalvulida: Myxobolidae) are described from the gill of the black redhorse (Moxostoma duquesnei [Leueur][Cypriniformes: Catostomidae]) from the Little Tennessee River Basin, North Carolina, United States. Myxobolus branchiofilum n. sp. infects lumen of the lamellar arterioles and Myxobolus branchiopecten n. sp. infects the bone and cartilage at the tip of the gill rakers. They differ from all congeners by a combination of myxospore dimensions and the presence or absence of an iodinophilic vacuole in the sporoplasm, mucous envelope, intercapsular process, and sutural markings. A phylogenetic analysis of the small subunit ribosomal DNA recovered M. branchiopectin sister to Myxobolus sp. (AF378343) in a clade composed of 6 species of Myxobolus, which infect predominately cypriniform intermediate hosts. Myxobolus branchiofilum was recovered sister to Myxobolus ictiobus Rosser, Griffin, Quiniou, Alberson, Woodyard, Mischker, Greenway, Wise & Pote, 2016 in a clade composed of 8 species of Myxobolus, which predominately infect catostomid intermediate hosts. Histological sections of infected gill revealed intra-lamellar plasmodia of M. branchiofilum in the lumen of the lamellar arterioles and foci of M. branchiopecten developing in the bone and cartilage of the gill raker tip. These are the first myxozoans reported from the black redhorse. Given that these two new species are morphologically congeneric but recovered in distantly related clades, we discuss the persistent issue of myxobolid genera paraphyly/polyphyly.

Diet and morphology of Serrapinnus notomelas and Serrapinnus sp.1 were investigated across ontogeny, as a way to elucidate the key elements linked to the resource partitioning (a main driver for species coexistence). Fish sampling was conducted monthly between October 2010 and March 2012. Individuals were captured, identified, and classified into juvenile or adult. Our results show ontogenetic and interspecific differences in feeding abilities and morphological traits. Differences in body shape (relative area of the dorsal fin, length of head, height of the caudal peduncle, the aspect ratio of the pectoral and pelvic fin) favored divergent swimming performances (more maneuverability in S. notomelas and continuous swimming to Serrapinnus sp.1). We also observed divergences in trophic apparatus traits and correlations with different diets. In this context, it is highlighted that understanding the relationship between morphology and diet can assist in elucidating the processes that permeate the coexistence between sympatric species, and between ontogenetic periods. Besides, the relevant contribution of the measures of the trophic apparatus (gill raker length, the number of teeth cuspids, and intestinal coefficient) in trophic segregation seems to be a strong evidence in favor of the proposed discriminatory and predictive capacities of these traits. Resumo Dieta e morfologia de Serrapinnus notomelas e Serrapinnus sp.1 foram investigadas ao longo da ontogenia, como forma de elucidar os principais elementos ligados à partição de recursos (principal fator para a coexistência entre espécies). Foram realizadas coletas de peixes mensalmente entre outubro de 2010 e março de 2012. Os indivíduos foram capturados, identificados e classificados em juvenis ou adultos. Nossos resultados mostram diferenças ontogenéticas e interespecíficas na alimentação e características morfológicas. Diferenças na forma corporal (área da nadadeira dorsal, comprimento da cabeça, altura do pedúnculo caudal, proporção das nadadeiras peitorais e pélvicas) favoreceram desempenhos de natação divergentes (maior manobrabilidade para S. notomelas e natação contínua para Serrapinnus sp.1). Também observamos divergências nas características do aparato trófico e correlações com diferentes dietas. Nesse contexto, destaca-se que compreender a relação entre morfologia e dieta pode auxiliar na elucidação dos processos que permeiam a coexistência entre espécies simpátricas e entre períodos ontogenéticos. Além disso, a relevante contribuição das medidas do aparato trófico (número de cúspide nos dentes, rastros branquiais e coeficiente intestinal) na segregação trófica parece ser uma forte evidência a favor das propostas de capacidades discriminatórias e preditivas dessas características.

Morphological differences, including growth-related changes, were examined in three morphologically similar East Asian sea bass species,Lateolabraxjaponicus,L.maculatusandL.latus. In many cases, body measurements indicated specific patterns of growth-related proportional changes.Lateolabraxlatusdiffered from the other two species in having greater body depth, caudal peduncle depth, caudal peduncle anterior depth, snout length, and upper and lower jaw length proportions. In particular, scatter plots for caudal peduncle anterior depth relative to standard length (SL) in that species indicated complete separation from those of the other two species, being a new key character for identification. Comparisons ofL.japonicusandL.maculatusrevealed considerable proportional differences in many length-measured characters, including fin lengths (first and second dorsal, caudal and pelvic), snout length, post-orbital preopercular width (POPW) and post-orbital length. In particular, snout length (SNL) and POPW proportions of the former were greater and smaller for specimens >200 and ≤ 200 mm SL, respectively. Because the scatter plots of these proportions for the two species did not overlap each other in either size range, identification of the species was possible using a combination of the two characters. In addition, scatter plots of the POPW / SNL proportion (%) ofL.japonicusandL.maculatuswere almost completely separated throughout the entire size range examined (border level 90%), a further aid to identification. The numbers of pored lateral line scales and scales above the lateral line tended to increase and decrease with growth, respectively, inL.japonicus, whereas scales below the lateral line and gill raker numbers tended to increase with growth inL.maculatus. Because the ranges of these meristic characters may therefore vary with specimen size, they are unsuitable for use as key characters. Accordingly, a new key is proposed for the genusLateolabrax.

Betta sp. is a freshwater ornamental fish which also known as a fighting fish. One of the fundamental organs to support fishes life is respiratory organ. Fighting fish is belongs to the suborder Anabantoidei which means labyrinth fishes group. The aim of the study was to know histology of the respiratory organs of Betta sp. Histological preparations were done using paraffin method, stained with Hematoxylin-Eosin (HE). The result showed that Betta sp. has a respiratory organ common fish i.e gills and additional respiratory organ structure namely labyrinth and pseudobranch that makes Betta sp can survive in a low volume of water. The gill is consists of gill arch, gill raker, gill fillament and gill lamellae. The labyrinth is consist of connective tissue and folded ephitelium. Pseudobranch according to some literature function as an additional respiratory. Functions attributed to the pseudobranch include; regulation of oxygen to the eyes, enzyme production for use in the gas bladder, osmoregulation, and many others.

Identifying traits that underlie variation in individual performance of consumers (i.e., trait utility) can help reveal the ecological causes of population divergence and the subsequent consequences for species interactions and community structure. Here, we document a case of rapid divergence (over the past 100 generations, or ?150 years) in foraging traits and feeding efficiency between a lake and stream population pair of threespine stickleback. Building on predictions from functional trait models of fish feeding, we analyzed foraging experiments with a Bayesian path analysis and elucidated the traits explaining variation in foraging performance and the species composition of ingested prey. Despite extensive previous research on the divergence of foraging traits among populations and ecotypes of stickleback, our results provide novel experimental evidence of trait utility for jaw protrusion, gill raker length, and gill raker spacing when foraging on a natural zooplankton assemblage. Furthermore, we discuss how these traits might contribute to the differential effects of lake and stream stickleback on their prey communities, observed in both laboratory and mesocosm conditions. More generally, our results illustrate how the rapid divergence of functional foraging traits of consumers can impact the biomass, species composition, and trophic structure of prey communities.

Resource polymorphism is a widespread phenomenon in post‐glacial fishes where multiple morphotypes of a species occur sympatrically and exhibit distinct resource use. Availability of open niches and high levels of within and among species competition are thought to drive differences in morphology and may provide insights into early stages of speciation. Hovsgol grayling (Thymallus nigrescens) are endemic to Lake Hovsgol, a lake colonised by fish following the Pleistocene, and are threatened with habitat loss due to climate change and illegal harvest. Previous analysis of Hovsgol grayling diet inferred through C and N stable isotopes suggested the presence of littoral and pelagic foraging groups. We hypothesised that morphology of the two foraging groups would reflect predictions of functional morphology, indicating the presence of resource polymorphism. To test this hypothesis, we evaluated evidence from C and N stable isotopes, stomach contents, fish ages, capture location and morphology. Two foraging groups of Hovsgol grayling were identified through stomach content and C and N stable isotope analysis. Individuals with greater zooplankton consumption were more frequently captured in the pelagic zone, exhibited higher gill raker counts, larger orbit (eye) sizes, longer paired fins, narrower head width, larger maxilla and smaller size at age than the group with greater reliance on benthic invertebrate prey. These differences were generally consistent with those described in other fish species exhibiting littoral–pelagic resource polymorphism. Our study provides the first example of littoral–pelagic resource polymorphism in the salmonid subfamily Thymallinae and highlights the potential influence of competition on fish evolution.

Different branchial muscles associated with the gill arches and gill filaments in a hill-stream cyprinid fish Neolissochilus hexagonolepis have been studied. The main branchial muscles observed are the constrictors branchiales, levatores arcuum branchialium epiarcualia obliqui, epiarcualia recti, subarcualia obliqui, subarcualia recti and subarcualia transversi. In the general plan the branchial muscles of N. hexagonolepis show similarity with those of other cyprinid fishes. However, the fish bears three pairs of coracobranchiales, common to cyprinid fishes.

The silver carp, Hypophthalmichthys molitrix, is an invasive planktivorous filter feeder fish that infested the natural waterways of the upper Mississippi River basin due to its highly efficient filter feeding mechanism. The characteristic organs called gill rakers (GRs), found in many such filter feeders, facilitate the efficient filtration of food particles such as phytoplankton that are of a few microns in size. The motivation to investigate the rheology of the GR mucus stems from our desire to understand its role in aiding the filter feeding process in the silver carp. The mucus-rich fluid, in a 'thick and sticky' state may facilitate the adhesion of food particulates. The permeation and transport through the GR membrane are facilitated by the action of external shear forces that induce varying shear strain rates. Therefore, mucus rheology can provide a vital clue to the tremendous outcompeting nature of the silver carp within the pool of filter feeding fish. Based on this it was posited that GR mucus may provide an adhesive function to food particles and act as a transport vehicle to assist in the filter feeding process. The main objective of the protocol is to determine the yield stress of the mucus, attributed to the minimum shear stress required to initiate flow at which irreversible plastic deformation is first observed across a structured viscoelastic material. Accordingly, rheological properties of the GR mucus, i.e., viscosity, storage, and loss moduli, were investigated for its non-Newtonian, shear-thinning nature using a rotational rheometer. A protocol presented here is employed to analyze the rheological properties of mucus extracted from the gill rakers of a silver carp, fished at Hart Creek location of the Missouri River. The protocol aims to develop an effective strategy for rheological testing and material characterization of mucus assumed to be a structured viscoelastic material.

A new barracuda, Sphyraena stellata, is described on the basis of 41 specimens [98.0–587.0 mm standard length (SL)] collected from the Indo-Pacific. The new species can be distinguished from all congeners in having the following combination of characters: one gill raker on first gill arch; pelvic-fin insertion located slightly before vertical through first dorsal-fin origin; pored lateral-line scales 134–141 (modally 137), total lateral-line scales 139–148 (146); scales above and below lateral line 15–17 (15) and 14–16 (15), respectively; snout comparatively short, its length 13.6–15.8 (mean 14.4) % SL; upper jaw short, its posterior tip not reaching to below anterior nostril, its length 10.0–12.2 (10.8) % SL; eye small, orbit diameter and depth 4.3–7.0 (4.9) and 3.9–5.6 (4.5) % SL, respectively; anal-fin base shortish, its length 6.9–8.1 (7.5) % SL; last dorsal- and anal-fin ray lengths 4.0–5.6 (4.7) and 3.6–5.6 (4.6) % SL, respectively; anus not close to anal-fin origin, anterior and posterior margins of former to anal-fin origin 7.5–11.9 (9.9) and 5.2–8.3 (6.8) % of head length, respectively; head sensory canal pores on suborbital area simple or slightly branched, their lowermost parts not close to margin of lacrimal bone, large smooth area lacking canal pores on mid-margin of lacrimal bone; two yellow stripes on lateral surface of body (remaining as black stripes in preserved specimens); and caudal fin gray. In addition, S. helleri Jenkins, 1901 and S. novaehollandiae Günther, 1860, both being closely related to the new species, are redescribed on the basis of 4 (243.3–545.8 mm SL) and 15 (270.8–598.0 mm SL) specimens, including holotypes, respectively, with new diagnostic characters proposed for both species.

The use of a functional guild, which distills organisms into groups based on a shared role within an ecosystem, is a beneficial tool for fisheries management because it reduces data complexity, streamlines statistical analyses, and places species in an ecosystem context by defining their functional role within a community. However, few studies consider the ramification of ontogeny on guild assignments and assume species occupy a static foraging guild throughout their lives. The aim for this study was to examine the development of feeding structures and diet in four, closely related species of sciaenids (Family Sciaenidae) that forage in the water column throughout their life history (1) to determine if the structures needed to exploit microhabitat use of the water column are present at early ontogenetic stages and (2) to assess guild transitions using a hierarchical clustering approach. Significant differences were only detected in ascending process length and cb1 gill raker count among the examined sciaenids. Larimus fasciatus consumed zooplankton throughout ontogeny and possessed a shorter ascending process and a greater number of cb1 gill rakers. Cynoscion nebulosus transitioned from zooplanktivory in the larval period to piscivory as an early juvenile and possessed a longer ascending process and fewer cb1 gill rakers. Bairdiella chrysoura and C. regalis were both zooplanktivorous as early juveniles and consumed more epibenthic (benthic crustaceans and worms) prey and possessed more elongate gill rakers compared to C. nebulosus. Foraging studies that combine diet and morphological analyses are needed to place individuals into foraging guilds while capturing key life history transitions that influence foraging habits and guild assignment.

The new anchovy Stolephorus babarani n. sp. is described on the basis of 26 specimens collected from Panay Island, central Philippines. The new species closely resembles Stolephorus bataviensis Hardenberg 1933 and Stolephorus baweanensis Hardenberg 1933, all these species having a long upper jaw (posterior tip extending beyond posterior margin of preopercle), and numerous dusky spots on the suborbital area (in adults), snout and lower jaw tip. However, the new species differs from S. bataviensis by usually having the posterior tip of the depressed pelvic fin not reaching to vertical through the dorsal-fin origin (vs. extending beyond vertical through dorsal-fin origin), a shorter head (23.9–25.5% of standard length vs. 25.3–28.0%), and a greater distance between the dorsal-fin origin and pectoral-fin insertion (D–P1; 133.9–151.8% of head length vs. 109.9–136.3%). Stolephorus babarani is distinguished from S. baweanensis by having a shorter snout (3.6–3.9% of standard length vs. 3.8–4.6%). Moreover, the new species can be distinguished from S. bataviensis and S. baweanensis by higher gill raker counts on the first and second gill arches (16–18 + 21–23 and 10–13 + 18–21, respectively, vs. 14–17 + 19–22 and 9–12 + 17–20 in S. bataviensis and 14–17 + 19–22 and 9–12 + 17–21 in S. baweanensis). Stolephorus babarani is separated by 5.3% and 10.7% mean p-distances in the mitochondrial COI from S. baweanensis and S. bataviensis, respectively.

Lake-dwelling fish that form species pairs/flocks characterized by body size divergence are important model systems for speciation research. While several sources of divergent selection have been identified in these systems, their importance for driving the speciation process remains elusive. A major problem is that in retrospect, we cannot distinguish selection pressures that initiated divergence from those acting later in the process. To address this issue, we reconstructed the initial stages of speciation in European whitefish (Coregonus lavaretus) using data from 357 populations of varying age (26-10 000 years). We find that whitefish speciation is driven by a large-growing predator, the northern pike (Esox lucius). Pike initiates divergence by causing a largely plastic differentiation into benthic giants and pelagic dwarfs; ecotypes that will subsequently develop partial reproductive isolation and heritable differences in gill raker number. Using an eco-evolutionary model, we demonstrate how pike’s habitat specificity and large gape size are critical for imposing a between-habitat trade-off, causing prey to mature in a safer place or at a safer size. Thereby, we propose a novel mechanism for how predators may cause dwarf/giant speciation in lake-dwelling fish species.

The present investigation was designed to describe the surface ultrastructure of the gill system of tilapia Zilli. The gill system is formed from four gill arches and each gill arch carries a row of gill filaments on its convex border and two rows of the gill rakers on its concave border. The quadrilateral interbranchial septum has elevated part at the level of the third gill arch. By SEM observations, the gill arch was divided into three regions: rostral, middle and caudal region. The caudal region contained two characteristic structures: oval leaf-like structure and rounded-shaped structure. Each oval leaf-like structure carried two lateral rows of the triangular pointed spines separated by a median groove. All surfaces of gill arches, rakers and filaments were covered with a mosaic of the polygonal pavement cells, in addition to the opening of chloride cells and mucous cells. The gill arch and gill raker had only one appearance of taste buds named type I. Meanwhile, the filaments contained two types of different appearance of the taste buds named: type I and type II. Type I was the main common and similar to that present in gill arch and raker and characterized by its blunt end, while type II had hair-like structures that projected from the volcano-shaped depression. The gill rakers were formed from central axis surrounded by two lateral lobulated regions which carry pointed spines, taste buds and the opening of chloride cells. The surface of triangular lower pharyngeal jaw carries numerous teeth-like papillae which originated from the socket-like depression.

The distribution and feeding of the ecological morphs of whitefish is studied in Lake Imandra, the largest subarctic water body. Data on the hydrochemical and hydrobiological characteristics of the reaches of the lake, as well as on the morphological features of the whitefish branchial apparatus with low and medium gill raker number, are obtained. A relationship between feeding preferences of whitefishes and size characteristics and trophic levels of the habitats is revealed.

Ecological opportunity occurs when a resource becomes available through a decrease of interspecific competition and another species colonizes the vacant niche through phenotypic plasticity and intraspecific competition. Brook charr exhibit a resource polymorphism in some Canadian Shield lakes, where a littoral ecotype feeds mainly on zoobenthos and a pelagic ecotype feeds mostly on zooplankton. The objectives of this study were to test that (i) resource polymorphism is common in these brook charr populations, (ii) the presence creek chub and white sucker, two introduced species competing with brook charr for littoral resources, will decrease the phenotypic divergence between the two brook charr ecotypes, and (iii) the ecological release from introduced species will increase population and/or individual niche widths in brook charr. The study was based on 27 lakes and five indicators of resource use (stomach content, liver δ13C, muscle astaxanthin concentration, pyloric caecum length, and gill raker length). Our results indicate that within-lake differences in resource use by both ecotypes are common and stable through time. When facing interspecific competition, both littoral and pelagic brook charr incorporated more pelagic prey into their diet but maintained the amplitude of their differences in resource use, which contradicts our second prediction. Finally, we did not find any significant effect of introduced species on population and individual niche widths of brook charr. We suggest that the difference in feeding mode among distantly related competitors could prevent the complete exclusion of a species from a given niche and explain the lack of response to the ecological release.

The purpose of this work is to study the interaction of morphologically similar forms of pidschianlike whitefishes of the Coregonus lavaretus complex inhabiting a limited area in the riverine-lacustrine system of the Bolshoy Abakan River basin. Sequences of the 16S-ND1 fragment of the mitochondrial DNA and the first intermediate transcribed spacer ITS1 of the nuclear DNA are determined. It is shown that whitefish populations differ based on the gill raker numbers and the complex of plastic traits. Analysis of the 16S-ND1 fragment of the mtDNA revealed several divergent lineages, which is confirmed by the study of the ITS1 of the nDNA. As a result, it is shown that the riverine-lacustrine system is inhabited by two genetically divergent whitefish populations. The results of the study support the hypothesis of multiple hybridization between slightly differentiated forms/populations of whitefishes during the postglacial period. As a result of the studies carried out, the hypothesis about the origin and possible ways of migration of some phylogenetic lineages of whitefishes in the water bodies of the Yenisei River basin is proposed.

A trophic dynamic study of marine finfishes was undertaken based on stomach content analysis of twenty four species (N = 1742) collected from the nearshore coastal waters off Goa, west coast of India (15°29′07.6″ N to 15°34′44.3″ N, and 73°38′10.5″ E to 73°46′03.1″ E) during November 2010 to May 2013. This study aimed to thoroughly understand the feeding attributes of finfishes, and comprehend the possible effects of bycatch-related loss of biomass on trophic ecology. The study assessed diet preferences of the finfishes, their feeding guilds, significance of prawns as prey items, and the influence of mouth parts in prey selection. Altogether 84 prey taxa were identified from the stomach contents. Percentage Index of Relative Importance (IRI) values revealed that zooplankton (34.74), prawns (21.71), phytoplankton (19.80), and teleosts (18.62) were the major prey categories, and, among prawns, Metapenaeus dobsoni (%IRI = 19.34) was the single-most important prey item. Cluster analysis revealed three major trophic guilds namely ‘teleost feeders’ (mean Trophic Level (TrL) = 4.06 ± 0.42; mean B = 0.46 ± 0.24), ‘zooplankton feeders’ (mean TrL = 3.43 ± 0.29; mean B = 0.23 ± 0.13), and ‘prawn feeders' (mean TrL = 3.86 ± 0.25; mean B = 0.48 ± 0.32), with low diet overlap among them. Principal Component Analysis of prey categories and mouth parts of finfishes suggested that zooplanktivory is associated with gill raker density as well as number of gill arches bearing rakers, whereas gape height determined the size of large-sized prey (fish and invertebrates). The study identified M. dobsoni, mysis and teleosts as highly influential prey for predatory finfishes. The present results could be useful to resolve broader issues in fisheries management.

Divergence into discrete foraging specialist morphs living in sympatry is relatively well described in lacustrine fishes of the Salmonidae. Although piscivorous forms of Salmo trutta have been widely reported, other trophic foraging specialists are strangely rarely recorded amongst Salmo species. Microsatellite and mitochondrial genetic data segregated S. trutta collected from Loch Laidon, Scotland, into four distinct genetic groups. Three groups analysed in this study showed significant differences in body shape, stomach contents, muscle stable isotope signature, gill raker length and spacing, and habitat use. We conclude that the three genetically defined groups comprise: a generalist foraging morph, a pelagic feeding specialist morph and a profundal macrobenthos feeding morph. The features distinguishing these morphs, however, show a degree of overlap. This appears to be only the second record of invertebrate resource use partitioning associated with expression of alternative morphologies in sympatry this species and the first report of a profundal invertebrate feeding morph. Why such polymorphisms are generally rare in Salmo species remains unclear, but potential explanations are discussed.

Filter feeding fishes possess several morphological adaptations necessary to capture and concentrate small particulate matter from the water column. Filter feeding teleosts typically employ elongated and tightly packed gill rakers with secondary bony or epithelial modifications that increase filtering efficiency. The gill rakers of Hypophthalmichthys molitrix, silver carp, are anatomically distinct from and more complex than the filtering apparatus of other teleostean fishes. The silver carp filtering apparatus is composed of biserial, fused filtering plates used to capture particles ranging in size from 4 to 80 μm. Early in ontogeny, at 15-25 mm standard length (SL), silver carp gill rakers are reminiscent of other more stereotypical teleostean rakers, characterized by individual lanceolate rakers that are tightly packed along the entirety of the branchial arches. At 30 mm SL, secondary epithelial projections and concomitant dermal ossification begin to stitch together individual gill rakers. During later juvenile stages, dermal bone further modifies the individual gill rakers and creates a bony scaffold that supports the now fully fused and porous epithelium. By adulthood, the stitching of bone and complete fusion of the overlying epithelium creates rigid filtering plates with morphologically distinct faces. The inner face of the plates is organized into a net-like matrix while the outer face has a sponge-like appearance comprised of differently sized pores. Here, we present morphological data from an ontogenetic series of the filtering apparatus within silver carp. These data inform hypotheses regarding both how these gill raker plates may have evolved from a more basal condition, as well as how this novel architecture allows this species to feed on exceedingly small phytoplankton, particles that represent a greater filtering challenge to the typical anatomy of the gill rakers of fishes.