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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.

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.

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.

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.

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.

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.

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.

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 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.

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.

Ten species of Carangoides from the Red Sea are reviewed. Imposter Trevally, Carangoides talamparoides Bleeker, is reported from the Red Sea for the first time on the basis of four small specimens and three adults trawled off Jizan, southern Saudi Arabia. Previously known from the Gulf of Oman east to Guam, its distribution range is extended to the Red Sea. Carangoides talamparoides superficially resembles C. malabaricus and may be easily confused, but it differs generally in lower gill raker counts, 25–31 (vs. 32–38), longer snout, the length 10.0–13.6% fork length in adults (vs. snout shorter, 8.5–10.8% fork length in adults); and premaxilla with slightly concave anterodorsal margin laterally (vs. premaxilla with distinctly concave margin laterally); greenish yellow blotch dorsoposteriorly on orbit membrane (vs. no blotch on orbit membrane); and white tongue (vs. tongue mainly dark). Description is provided for Red Sea specimens of Carangoides talamparoides and brief accounts for nine other Red Sea congeners. A key and table are also provided to help distinguish Red Sea Carangoides species, and a molecular phylogenetic analysis of the COI barcoding region is presented for all available Red Sea species and other Indo-Pacific species of the genus Carangoides.

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.

Planktivorous silver carp and bighead carp (collectively, the bigheaded carps) have been stocked worldwide and their invasion has caused severe impacts on many freshwater ecosystems. Exploiting the chance provided by the specific hybrid bigheaded carp stock in Lake Balaton (Hungary) covering the entire morphological range between the two species (including gill raker morphology), we implemented a comprehensive study (1) to reveal the feeding habits of hybrid bigheaded carps living in a mesotrophic, lacustrine habitat and (2) to assess how biotic and abiotic environmental factors and gill raker morphology affect diet composition. We found that all bigheaded carps utilized primarily zooplankton and neglected the scarce and inefficiently digestible phytoplankton, irrespective of gill raker morphology. Moreover, we observed strikingly high levels of inorganic debris consumption, but the proportion of inorganic matter in the guts was not associated directly with the concentration of suspended inorganic particles. Variance in the diet composition of bigheaded carps was related mostly to environmental factors, including the wind-induced resuspension of inorganic particles and seasonally variable availability of food resources. In conclusion, the effects of abiotic environmental factors and available food resources could overwhelm the effect of gill raker morphology in shaping the feeding habits of bigheaded carps.

We examined spatial variability in meristic and morphological characteristics of the branchial basket of sardine Sardinops sagax collected from four geographical regions around the southern African coast, namely Namibia and the South African west, south and east coasts. Our analysis tested the hypothesis of three putative sardine stocks off South Africa, one in each of the three geographical regions. We therefore collected fish data from Namibia to compare with South Africa, because sardine from the two countries are considered to be separate stocks. Morphometric measurements (gill arch length and gill raker spacing) and meristic data (number of gill rakers) were collected from the left side of the first gill arch from a total of 377 sardine, approximately equally divided between the regions. A multivariate general linear model with caudal length as covariate was used to assess differences among fish from the four regions and significant differences were observed, although not always consistently across a...

A variety of parameters associated with breathing and feeding of silver carp were measured in response to declines in dissolved oxygen (DO) levels when the fish were fed microalgae Padorina morum (PM group) and Chlorella ellipsoidea (CE group), respectively, to explore the relationship between breathing and feeding while filtering microalgae particles at different DO levels. The results indicated that (i) respiratory frequency (fR) of the fish in CE group were higher significantly than those in PM group at DO levels of 0.98–7.49 mg/L (P

Hybridization can influence a range of characteristics and outcomes for an organism; however, relatively little is known about evolutionary consequences on nutritional performance. Information on hybrid nutritional performance would provide an understanding of how hybrids interact with their environment and insights into mechanisms affecting survival. Our goal was to test for relationships between hybridization and nutritional performance in invasive bigheaded carps (Hypophthalmichthys nobilis), silver carp (Hypophthalmichthys molitrix), and their hybrids in the Marseilles reach of the Illinois River, Illinois, USA. Silver carp showed better nutritional performance relative to bighead carp. Early generation bighead and silver carp hybrid groups were intermediate to both parental lines, thereby, reducing their nutritional performance, and advanced generation bighead and silver carp groups were nutritionally more similar to their respective parental species. Differences in gill raker morphology and feeding ...

18 pages, 5 figures, 4 tables, In spite of shrinking populations, the Allis shad (Alosa alosa Linnaeus, 1758) is a species of commercial importance in Europe. On the Iberian Peninsula, especially in the international Minho River, it also represents an important cultural heritage. From the mid-twentieth century on, a marked decrease in the number of spawners occurred in that river, following the reduction of available habitat due to dam construction. We investigated the biology and ecology of the Minho River’s Allis shad population, considering: spawners age structure and migration behaviour, reproductive biology, hybridization with Twaite shad (Alosa fallax Lacepède, 1803), juvenile growth, habitats and diet, as well as parasites. Results suggest that males migrated 1 year earlier than females and earlier in the season. Females’ gonadosomatic index increased with time and was higher within the spawning area. According to gill raker numbers, the level of hybridization is higher in juveniles than in adult samples (17 and 3.6 % respectively). To the best of our knowledge, we present the first report of the parasite Anisakis pegreffii in Allis shad, as well as other mouth and visceral cavity parasites. We also reported the first molecular confirmation of the parasite Rhadinorhynchus pristis to this species. Our results will be useful for future management and conservation of the studied population, which is one of the last stable European shad populations., This study was funded by a PhD grant from the FCT (Portuguese Foundation for Science and Technology) supporting Micaela Mota (SFRH/BD/44892/2008). The research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE-Operational Competitiveness Programme and national funds through FCT-Foundation for Science and Technology, under the project ‘‘PEst-C/MAR/LA0015/2013’’.

Resource polymorphism may play an important role in the process of speciation. The Arctic char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south-western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise FST were detected among all lakes (range from 0.05 to 0.28, all P

SUMMARY 1. Ecological experiments showing large effects are predicted to drive contemporary trait changes resulting from evolution and phenotypic plasticity. However, few classic ecological experiments conducted in the wild have been investigated for evidence of contemporary trait change. 2. We examined a classic experiment in trophic ecology, the introduction of alewife (Alosa pseudoharengus) to Crystal Lake, Connecticut, U.S.A. (Brooks & Dodson, 1965), for the presence of contemporary trait change. 3. Alewife were introduced to Crystal Lake, an inland lake isolated from the coastal ocean, from an anadromous (migratory sea-run) source population. We utilised museum specimens collected soon after introduction and modern samples to measure changes in gill-raker morphology for the Crystal Lake alewife population since its introduction. We compared the gill-rakers of the Crystal Lake population to those of other nearby anadromous and landlocked (freshwater resident) alewife populations. 4. At introduction, the Crystal Lake population showed gill-raker spacing (GRS) similar to that of anadromous populations. Following introduction, we found evidence for a rapid decrease in GRS, an important trait for size-selective prey capture in fishes. This decrease occurred alongside a dramatic decline in zooplankton size, shown by Brooks and Dodson (1965) to be caused by the onset of alewife predation. After 45 years of isolation in freshwater, the Crystal Lake population showed GRS typical of landlocked populations. 5. Brooks and Dodson’s study is a classic example of the strong effects predators can have on prey communities. Our study shows that such community effects of predators may feed back to shape predator trophic morphology. The rate of trait change observed for the Crystal Lake alewife population is comparable to rates observed from evolutionary experiments conducted explicitly to examine trait changes over contemporary time scales. 6. We conclude that strong ecological effects of introduced populations may be important drivers of contemporary trait change. We propose that classic ecological experiments represent underutilised resources for examining interactions between contemporary trait change and ecological effects in the wild.

Summary Studies of trophic divergence in fishes and other organisms emphasise resource availability as a driving factor, but usually in terms of alternate resources within particular resource-limited systems. In contrast, the role of overall ecosystem productivity in shaping trophic diversity among systems has received less attention. Divergence along productivity gradients may be relevant because aquatic systems span a range of productivities, humans are accelerating the natural process of eutrophication, and productivity controls community and ecosystem processes that govern the availability and costs/benefits of alternative resources. Here, we study whether populations of white perch (Morone americana) differ in traits related to trophic divergence and how such variation might be predicted by landscape patterns of lake productivity. White perch populations differed in their body dimensions, fin lengths and gill raker structures. Each of these traits showed significant and often strong (r2 up to 0.91) correlations with lake Secchi depth and other metrics of lake productivity, such that white perch from more eutrophic systems tended to be larger, have more gibbous bodies, longer fins, more subterminal mouths and gill rakers with greater spacing. Isotopic 15N was correlated with phenotypic divergence, and fish from eutrophic systems exhibited a trophic shift at smaller sizes. Our results suggest that productivity has surprising ability to predict trait variation at the landscape scale. The fact that a number of the study populations were established in the last century and that some lakes became eutrophic in that period, suggests fish trophic traits can respond quickly to lake conditions.

Phenotypic variation in populations of fishes that inhabit postglacial lakes is often associated with trophic specialisations. A common sympatric foraging divergence seen in Arctic charr is into either plankton or littoral-zoobenthos feeding specialisms. In this study, we report a sympatric polymorphic Arctic charr population which is not centred on this divergence but instead manifests as a plankton (pelagic)—profundal zoobenthos foraging specialisms. The head shape of profundal fish was round and robust, the body thick set and pectoral fins long and wide. In contrast, the head of pelagic fish was pointed and slender, the body fusiform in shape and with short, narrow pectoral fins. There was no difference between profundal and pelagic fish in gill raker number. Body lipid content was significantly higher in pelagic fish as were the number or Diphyllobothrium cysts. The carbon isotope ratio was more heavily depleted in profundal fish. There was no dietary overlap in the prey items recovered from stomach contents of profundal and pelagic fish. We suggest the proximate driver behind the sympatric divergence was the successful exploitation of the profundal zone. The consequences of this have led to the development of adaptations in morphology and behaviour to support and maintain this divergence.

Northern freshwater fi shes, particularly members of the genus Coregonus, have been used as a model for studying microevolution due to their well known colonization history coupled with parallel patterns of phenotypic differentiation. We assessed and described the phenotypic diversity among ciscoes in the Yellowknife Bay region of Great Slave Lake using 1) traditional taxonomic methods for cisco species and 2) contemporary linear and geometric morphometric methods. Four morphs were identifi ed using a qualitative visual assessment of gross morphology and/or location of capture in comparison to published taxonomy for the genus Coregonus. The morphs identifi ed were assigned the following colloquial names: A) 'adfl uvial', B) 'lacustrine', C) 'shortjaw', and D) 'least'. Univariate analyses on taxonomic measures indicated that cisco varied in terms of age, number of lateral line scales, number of anal fi n rays, middle gill raker length, and lower gill arch length. By contrast, fi ve morphs were identifi ed using cluster analysis of linear and geometric morphometric data combined with age and gill raker number. The additional phenotypic cluster entailed a splitting of large and small lacustrine morphs into two groups. Multivariate analyses indicated a strong relationship between body shape and gill raker number, eye size, age and mouth morphology. These results suggested that the segregation among morphs was based on differential usage of trophic and/or habitat resources as well as life history variation such as age at maturity. Our results indicated that the level of phenotypic diversity was greater than previously documented for Great Slave Lake and that this diversity was similar to that reported for ciscoes in the Laurentian Great Lakes.

Summary Understanding the trophic ecology of closely-related species is important for providing insight on inter-specific competition and resource partitioning. Although catostomids often dominate fish assemblages in lotic systems, little research has been conducted on their ecology. This study was developed to provide information on the trophic ecology of catostomids in several Iowa rivers. Food habits, diet overlap, and gill raker morphology were examined for highfin carpsucker Carpiodes velifer, quillback C. cyprinus, river carpsucker C. carpio, golden redhorse Moxostoma erythrurum, shorthead redhorse M. macrolepidotum, silver redhorse M. anisurum, and northern hogsucker Hypentelium nigricans sampled from four Iowa rivers (2009). Diet overlap among all species was calculated with Morista’s index (C). Food habit niche width was quantified with Levin’s index (B) and similarity in gill raker morphology was compared with analysis of covariance. Values from Morista’s index suggested significant overlap in the diets of highfin carpsucker and river carpsucker (C = 0.81), quillback and river carpsucker (C = 0.66), and shorthead redhorse and silver redhorse (C = 0.67). Levin’s index indicated that golden redhorse (B = 0.32), quillback (B = 0.53), and river carpsucker (B = 0.41) had the most generalized feeding strategies as their food niche widths were substantially wider than the other species. Gill raker length and spacing were positively correlated with the standard length of the fish for all species (gill raker length: r2 = 0.67–0.88, P ≤ 0.01; gill raker spacing: r2 = 0.63–0.73, P ≤ 0.01). Slopes of regression of gill raker length and spacing to standard lengths were significantly (P ≤ 0.05) different among species, indicating that rates of change in gill raker morphology with body length varied among species. Differences in gill raker morphology likely allow catostomids to partition resources and reduce competitive interactions.

Asian carps are classified as either bighead carp Hypophthalmichthys nobilis or silver carp H. molitrix by multiple presumptively diagnostic morphological characteristics; however, hybrids pose a dilemma. Fish sharing the morphological characteristics of both species were observed in an Illinois River backwater (Calhoun County, Illinois) approximately 5 mi (8 km) upriver from the confluence with the Mississippi River as well as in two locations in Pool 26 of the Mississippi River (Madison County, Illinois). Biopsied tissues from individuals exhibiting mixed morphological features were analyzed at four diagnostic allozyme loci (ADH-1*, sMDH-A*, CK-A*, and sSOD-1*) via starch gel electrophoresis. This comparison revealed a high percentage of hybridization (22.5%) from an indiscriminate sample of 120 fish. Moreover, an unexpected percentage (12.5%) of individuals identified in the wild as either parental bighead carp or silver carp by gill raker morphology were genetically identified as hybrids. Fin...

The presence of two morphotypes of Arctic charr Salvelinus alpinus was confirmed via morphological variation and otolith strontium (Sr) within three open-lake systems of southern Baffin Island, Nunavut, Canada: Qinngu (LH001), Iqalugaarjuit Lake (PG082) and Qasigiat (PG015). Analysis of otolith Sr indicates that a component of each S. alpinus population within lakes LH001 and PG082 is migratory (large-maturing S. alpinus), whereas another component is lake-resident (small-maturing S. alpinus). Alternatively, small and large maturing S. alpinus may both inhabit tidal habitats during their lifetime in lake PG015. Three morphological characters were identified by principal factor analysis (PFA) as characters that were different between maturity groups for all lakes studied: eye diameter, pectoral fin length and pelvic fin length. As well, upper jaw length (LH001 and PG082) and fork depth (PG015) were identified in PFA as traits that differed between morphs. Univariate tests of morphological characters identified by PFA demonstrated maturity group differences with the exception of eye diameter in Lake PG015 and upper jaw length and pelvic fin length in lake LH001. No difference was found in the MANOVA test of upper and lower gill raker number between small-maturing and undeveloped fish within all lakes studied. Clear morphological variation observed between small-maturing and undeveloped fish in all three lakes of the study suggests ecological niche separation between morphotypes. This is the first documented case of lake-resident S. alpinus use of the tidal habitat in the presence of a migratory large-maturing morphotype.

Four Special Areas of Conservation (SACs) have been designated in the Republic of Ireland for Twaite shad, Alosa fallax (Lacepede), based on recent historical information on spawning activity—the estuarine reaches of the Rivers Munster Blackwater, Suir, Barrow–Nore and Slaney. The spawning status of some of these populations is considered to have declined substantially in recent years, and no known spawning areas of Allis shad, Alosa alosa (L.), are known for Ireland. Data are presented confirming the presence of both Allis shad and Twaite shad in all four SACs. The majority of the material has come as by-catch from estuarine commercial salmon netsmen. Angling is the principal source of material from the R. Barrow. Examination of scale and gonad material of Allis shad indicates some degree of readiness for spawning as well as spawning having taken place. Gonadosomatic index (GSI) data from the R. Barrow for Twaite shad in the May spawning period (2000–2002) had mean GSIs of 13.7–15% with maxima in the range of 21–28%. GSI values of 18% and 22% have been recorded in the July period for individual Allis shad from the upper estuaries of the R. Slaney and R. Suir, respectively, with both fish displaying gonad maturity stage V or VI (after Pina, 2000). Low GSI values have been recorded from other Allis shad in the June–July period displaying gonad condition varying from stage III (immature) to stage VIII (spent). These findings point to a possibility that Allis shad do engage in spawning activity, whether mono-specifically or with Twaite shad. The possibility of the latter is supported by gill raker count data presented. These show clearly defined value ranges for Twaite and for Allis as well as a series of fish with intermediate counts. The apparently low population levels of Twaite shad within the SACs identify a need to examine what measures might be undertaken to ensure the favourable conservation status of this species.

The morphology of pumpkinseed Lepomis gibbosus populations from five Catalonian waterbodies (north-eastern Spain) that vary in hydromorphometry was examined and compared to a native North American reference site that contained two morphological variants of this species. Populations exhibited significant differences in fin location, body depth and caudal peduncle length, which are known to have functional significance in the hydrodynamics of swimming and hence the foraging mode. Differences were also noted in internal morphological traits functionally related to prey selection. Pumpkinseed populations that fed extensively on zooplankton showed narrow gill raker spacing, and mollusc-feeding populations had longer and wider pharyngeal bones. Discriminant function analysis (DFA) provided significant separation of all populations on the basis of both external and internal morphology, with the main axis of separation being geographical rather than environmental. The secondary DFA axis, however, did separate populations that fed primarily on zooplankton from those that were primarily benthic invertebrate feeders. In this regard, a population that occupied an Iberian steep-sided reservoir with an unstable littoral zone showed similar morphological adaptations to the limnetic morphological variant native in North America, supporting previous studies showing that fish morphology is strongly affected by prey type and feeding mode. The results suggest that pumpkinseeds are able to adapt, morphologically, to the types of habitats and prey present in Catalonian waterbodies, and this may partially explain why they are so successful in areas where they have been introduced.

A reputedly 'unique' Irish form of Arctic char, characterised by its long and numerous gill rakers and referred to as Salvelinus fimbriatus (Regan, The Annals and Magazine of Natural History 2 (1908) 225), has long been known to inhabit Coomasaharn Lough in the south-west of Ireland. However, this species description was based on a single specimen and, in the intervening period, little research on the unusual gill attributes of the char population has been published. In 2000, the char population of the lake was surveyed by gill netting. The morphometrics of the head region and the gill raker attributes of this population of Irish char were compared with two other Irish char populations. The results of this analysis highlighted the specialised morphology of the Coomasaharn char in an Irish context and demonstrated the planktivorous nature of the Coomasaharn char.

The widespread Neotropical cheirodontine Odontostilbe fugitiva is reviewed, and three new species of the genus are described from the Amazon basin. A neotype is designated for O. fugitiva, from the mouth of the río Mazán, upper río Amazonas basin, Peru. Three nominal species are herein considered as synonyms of O. fugitiva: O. madeirae, O. drepanon, and O. caquetae. The three new species are respectively O. ecuadorensis from the río Napo basin, O. nareuda from the rio Madeira basin, and O. parecis from the rio Guaporé basin (rio Madeira basin). Among other diagnostic characters, gill rakers are especially informative in distinguishing species. Description of gill raker denticulation is provided for the first time for species of the Cheirodontinae. Secondary sexually dimorphic characters are described for all species. O queirodontíneo neotropical Odontostilbe fugitiva, de ampla distribuição, é revisado e três espécies novas são descritas para o gênero na bacia Amazônica. Um neótipo é designado para O. fugitiva, da boca do rio Mazán, alto rio Amazonas, Peru. Três espécies nominais são consideradas sinônimas de O. fugitiva: O. madeirae, O. drepanon e O. caquetae. As três espécies novas são, respectivamente, O. ecuadorensis da bacia do rio Napo, O. nareuda da bacia do rio Madeira e O. parecis da bacia do rio Guaporé (bacia do rio Madeira). Entre outros caracteres diagnósticos, os rastros branquiais são especialmente informativos para distinguir as espécies. Uma descrição da denticulação dos rastros branquiais é apresentada pela primeira vez para espécies de Cheirodontinae. Caracteres de dimorfismo sexual secundário são descritos para todas as espécies.

Feeding habits and gill raker morphology were examined for the three major planktivorous pelagic fishes, Japanese anchovy Engraulis japonicus, Pacific round herring Etrumeus teres and Japanese jack mackerel Trachurus japonicus, off the northern and western coasts of Kyushu, in the north-eastern part of the East China Sea in the summer months of 2001. Using fishes in the same size range (80-140 mm, standard length), the stomach contents of the three fish species were compared. The diet of the Japanese anchovy mainly consisted of Oncaeidae copepods, while the diets of the Pacific round herring and Japanese jack mackerel were dominated by calanoid copepods at all stations. Comparisons between prey size in the stomach, zooplankton size in the water and gill raker morphology suggested that the stomach contents of the three species were characterized mainly by the difference in the feeding behaviour between Japanese anchovy (filter-feeding) and the other two species (particulate-feeding), rather than by the difference in the morphology of feeding apparatus only. It was concluded that behavioural adaptations in the feeding of these pelagic fishes brought about trophic partitioning to some degree in this pelagic ecosystem in summer. Although the diets of these three species overlapped to some extent, there was still little likelihood of competition between the Japanese anchovy and the other two species. The potential for competition between the Pacific round herring and the Japanese jack mackerel is discussed.

Rainbow trout Oncorhynchus mykiss are one of the most widely stocked salmonids worldwide, often based on the assumption that they will effectively utilize abundant invertebrate food resources. We evaluated the potential for feeding morphology to affect prey selection by rainbow trout using a combination of laboratory feeding experiments and field observations in Flaming Gorge Reservoir, Utah–Wyoming. For rainbow trout collected from the reservoir, inter–gill raker spacing averaged 1.09 mm and there was low variation among fish overall (SD = 0.28). Ninety-seven percent of all zooplankton observed in the diets of rainbow trout collected in the reservoir were larger than the interraker spacing, while only 29% of the zooplankton found in the environment were larger than the interraker spacing. Over the size range of rainbow trout evaluated here (200–475 mm), interraker spacing increased moderately with increasing fish length; however, the size of zooplankton found in the diet did not increase with in...

We assess morphological diversity of species of the Cynoscion group in the Gulf of Guayaquil (GOG) using traditional morphometric methods. Five species from the GOG assemblage (C. albus, C. analis, C. phoxocephalus, C. squamipinnis, and Isopisthus remifer) are compared to four species from a relatively well-studied assemblage in the western Atlantic (C. arenarius, C. nebulosus, C. nothus, and C. regalis). The two regional species assemblages broadly overlap in morphology, but sympatric species segregate relatively well within each assemblage. The GOG species segregate primarily along the major axis of shape variation in the study, which is associated with variation in the anal, second dorsal, and caudal fins. The western Atlantic species segregate primarily along the second major axis of shape variation, which is most strongly associated with variation in gill raker length, and less strongly with pectoral fin length, eye diameter, and length of the third dorsal spine. Patterns of morphological divergence among the western Atlantic species support the hypothesis that morphological divergence is associated with ecological divergence. Comparisons across assemblages indicate that morphological divergence among species in the GOG is substantial. Consequently, Cynoscion species in the GOG may be highly divergent in ecological habits, which would have important management implications, but further ecological research is needed. This study provides a first glimpse into the major patterns of morphological diversification in the Cynoscion group.

The location of the holotype of Rhombus cocosensis Bleeker (presently known as Engyprosopon cocosensis) has been listed as unknown. The alleged holotype was found recently in Leiden (RMNH) and examined confirming it as the holotype. It has palmate gill rakers, a type of gill raker limited, within the Bothidae, to the genus Asterorhombus. Thus, Asterorhombus cocosensis is a nominal species of that genus. “Engyprosopon cocosensis” of has no palmate gill rakers and was an obvious misidentification made without examing the holotype. There is no junior synonym for this fish. The purpose of this paper is to name the species and redescribe it.

Infection patterns of trophically transmitted helminth parasites were compared with feeding ecology in two sympatric whitefish Coregonus lavaretus morphs from two lake systems in northern Norway. In both lakes, the pelagic morph was an obligate zooplanktivore, while the benthic morph utilized both the benthivore and zooplanktivore trophic niches. The differences in niche utilization between the two morphs were associated with differences in trophic morphology (gill raker numbers), suggesting that they were genetically dissimilar and reproductively isolated. The benthic morph had the highest number of helminth species, probably because they exhibited a broader niche width compared to the pelagic morph. In both lakes, the species composition and intensities of helminths reflected the trophic diversification of the whitefish ecotypes with respect to different habitat choice (benthic v. pelagic) and dietary specialization (benthivore v. zooplanktivore feeding strategies within the benthic whitefish morph). Zooplanktivorous fish from both morphs acquired parasites mainly from pelagic copepods and in almost equal quantities. The benthivore feeders within the benthic morph had the highest proportion of parasites with transmission stages from benthic organisms. Host feeding behaviour seemed to be a major determinant of the helminth community structure, and helminths appeared to be useful indicators of long-term trophic specialization of whitefish ecotypes.

Background. The ability to distinguish between stocks in mixed fisheries is a prerequisite for a sustainable fisheries management. In the Gulf of Bothnia the relative contribution of endangered river-spawning and sea-spawning whitefish, Coregonus lavaretus (Linnaeus, 1758), to fisheries catches are currently not well known. This also applies to the southern Åland Islands, a major feeding ground for river-spawning whitefish from northern rivers. River- and sea-spawning whitefish are mixed while away from the breeding grounds and off the spawning season, and cannot be distinguished based on external features. Materials and methods. Analysis on gill raker numbers of river-spawning (n = 480) and sea-spawning (n = 456) whitefish from twelve locations at the Finnish west coast and the Åland Islands was performed. In whitefish sampled from feeding grounds at the Åland Islands the strontium concentration was analysed in otoliths from fish (n = 20) with low (27) and high (30) number of gill rakers. Results. A marked difference in the mean gill raker number of the river- and sea-spawning whitefish stocks was observed. The weighted mean of gill rakers of whitefish caught at spawning locations showed that the number of gill rakers of fish from rivers and the sea were 29.9 ± 2.14 (n = 480) and 26.7 ± 2.21 (n = 456), respectively. The difference between the two groups was highly significant (t = 22.50, df = 934, P < 0.0001). The means differed by 3.20 (2.92–3.48, 95% CL) indicating the groups are well separated. In whitefish sampled at feeding grounds at the Åland Islands, otolith strontium concentration was higher (t = 2.09, df = 18, P = 0.04) in fish having 27 gill rakers (3.86 ± 0.30 mg · g–1, n = 10), compared to those having 30 gill rakers (3.54 ± 0.35 mg · g–1, n = 10). Otolith strontium analysis thereby supported the utility of gill raker counting data for estimating the proportion of river- and sea-spawning whitefish in mixed populations. As expected, the gill raker counting method successfully indicated temporal alterations in the proportions of river- and sea-spawning whitefish on feeding grounds. Conclusion. Gill raker counting is an easy, fast, and inexpensive method that can be used to estimate the spatiotemporal occurrence and migratory patterns of river- and sea-spawning whitefish at the southern feeding grounds in the Gulf of Bothnia, and thereby aid in a sustainable management of whitefish stocks.

In northern Transbaikalia, independently evolving landlocked populations of Arctic charr are found in mountain lakes. To assess the diversity of charr in this region, speciation modes involved in the evolution of charr forms, and the role of trophic polymorphism in their divergence, we studied the morphology and feeding of dwarf, small, and large forms of Arctic charr from a number of Transbaikalian lakes. Meristic data on charr from five lakes support the earlier conclusion that the three forms do not represent separate lineages but have independently diverged in sympatry in each of the lakes. In 10 lakes, the dwarf form showed varying degrees of differentiation from normal (small and large) charr in meristic characters (up to morphologically distinct and presumably reproductively isolated groupings), which is viewed as various levels of sympatric divergence. Indexes of gill raker length in fish from 20 lakes vary among populations of both dwarf and normal charr, with forms having short and long rakers being sympatric in some of these lakes. However, the index can be used only for comparing charr of different forms up to about 32 cm fork length (FL) because it is strongly negatively correlated with size in larger fish. The study of charr diets in 21 lakes indicates that large charr are piscivorous whereas dwarf and small charr feed on a wide range of invertebrates, partitioning these resources in different ways. Planktivores, including very specialized ones, and non-planktivores (benthic feeders, insectivores) can be identified within the small and dwarf forms. The proportion of plankton in the diets of dwarf and small charr is positively correlated with the number and length of gill rakers while the proportion of benthos is negatively correlated. Allopatric planktivorous and non-planktivorous small charr differ in body proportions; parallel emergence of such morphotypes in different parts of the range is a characteristic feature of the Salvelinus alpinus complex.

A variety of morphological, behavioral, physiological, and biochemical characteristics are used to identify and classify fishes. In practice though, it is more common to use morphometric measurements (i.e., body length, body depth, head length, eye diameter, jaw length) and meristics (i.e., fin ray, scale, teeth, gill raker, and lateral line pore counts). These morphometric measurements are usually presented as a proportion of either standard or total length. Unfortunately, in early works, it was often vague as to how lengths were taken. In addition, a protocol of how to measure standard length has never been standardized; consequently, several different definitions and interpretations exist. If a standardized protocol was implemented this could make comparisons of new measurements with older ones more difficult if the specimens are damaged, in a fragile state of preservation, or no longer exist. Standard length as a measurement has been in use for over a century, only the name is modern. This study reviews the chronological development of the concept of standard length and provides suggestions as to how ichthyologists should proceed into the next century.

Gill raker counts were made on the first gill arch from the larval to adult stages of the California sardine Sardinops caeruleus. A model relating gill raker number (N R ) to fish length (L S ) was developed and can be described by N R = 152 (1 - e -0.014(LS-11.4) .

We used gill raker measurements of kokanee salmon and zooplankton body dimensions to assess how gill raker structure and prey retention probabilities change with fish age. Cumulative proportion of filtering area between gill rakers and retention probabilities for smaller zooplankton decreased with increasing age of kokanee. Assuming strict filter feeding, only the largest of zooplankters would be retained by age-3 kokanee.

– Generalist fish species often exhibit two or more recognizable morphotypes specialized to exploit a particular habitat and niche. Divergent benthic and pelagic morphs of sunfish of the North American sunfish genus Lepomis have been found in some populations. The proximate cause of this phenomenon is not known. It could be differential survival and habitat segregation among different morphs produced by different genotypes within a species or it could be a phenotypically plastic response to environmental influences such as diet. I tested the hypothesis that variation in feeding morphology (body shape, gill raker and pharyngeal jaw morphology) in the orangespotted sunfish, Lepomis humilis occurs in response to diet. Fish were collected as young-of-the-year and were reared in individual aquaria and fed three differing arthropod diets. According to a multivariate analysis of covariance on principal components derived from body truss, gill raker and pharyngeal jaw measurements, diet significantly affected morphology. Fish that fed on a diet of mealworms developed a significantly more blunt snout based on a least squares means estimation of component values.

The genetic and environmental basis for polymorphism in gill raker number and length in sympatric anadromous and nonanadromous morphs of sockeye salmon, Oncorhynchus nerka, was investigated. Analysis of 30 full sib families involving pure types and reciprocal hybrids revealed that the variation was partitioned significantly among families within cross types and among cross types in both traits. As in the wild, kokanee displayed more gill rakers than sockeye; reciprocal hybrids displayed intermediate counts. Gill raker length also varied markedly among cross types, with pure sockeye displaying 19% longer gill rakers than comparable sized kokanee. This difference was in the opposite direction predicted, given the common positive association between gill raker number and length in sympatric morphs of the same species in fishes. Gill raker number and length were generally not correlated within cross types, suggesting independent divergence of the traits. The results are discussed in relation to genetic and trophic divergence of the morphs and to factors selecting for differentiation in the two gill raker traits.

We measured morphometric and meristic parameters of gill rakers from the first gill arch of 36 adult lake herring (Coregonus artedi) from Lake Superior that ranged in length from 283–504 mm. These data, coupled with the mean of the smallest two body dimensions (length, width, or breadth) of various zooplankton prey, allowed us to calculate retention probabilities for zooplankton taxa that are common in Lake Superior. The mean of the smallest two body dimensions was positively correlated with body length for cladocerans and copepods. The large cladoceran, Daphnia g. mendotae, is estimated to be retained at a greater probability (74%) than smaller cladocerans (18%-38%). The same is true for the large copepod, Limnocalanus macrurus (60%), when compared to smaller copepods (6–38%). Copepods have a lower probability of being retained than cladocerans of similar length. Lake herring gill rakers and total filtering area are also positively correlated with fish total length. These data provide further ev...

This paper describes patterns of developmental asymmetry in a limnetic-benthic stickleback species pair from Paxton Lake, British Columbia. Three gill raker characters and one armor character were compared among full-sib parental crosses and their hybrids (F1, F2 and backcrosses). All crosses displayed asymmetry, but no differences in mean or fluctuating asymmetry were detected among laboratory-reared crosses. When wild-caught limnetics and benthics were included in the analyses significant differences in FA among groups were detected in gill raker length and plate number. The effect appears to be solely due to wild-caught benthics, though the reasons for their greater asymmetry are unknown. The patterns in laboratory-reared crosses suggest that asymmetry is unlikely to promote reproductive isolation between the parental species.

Food selection and growth of young snakehead Channa striatus were studied in the laboratory and in a field trial. In the laboratory, first-feeding snakehead larvae of 6–7 mm total length (TL) with a mouth opening of 0.55 mm selected for Artemia nauplii, and against formulated feed. Fish began feeding on formulated feed at 12mm TL when their mouth width reached 1.0mm. In both laboratory and field trials, snakehead diets changed as fish size increased. For fish 15–20 mm TL, cladocerans and copepods were 96.5% of their diet. With fish 30–40 mm TL, zooplankton consumption was greatly reduced while benthic organism consumption increased. Fish 45–50 mm TL fed exclusively on benthic invertebrates. Diet shift from zoo-plankton to benthic invertebrates was not due to reduced zoo-plankton availability, but was instead related to changes in gill raker structure. Low density of benthic invertebrates in the field trial caused reduced fish growth rates when fish switched diets from zooplankton to benthos. Our results indicate that snake-head can take Artemia nauplii as a larval starter food, then accept formulated feed at ≥12 mm TL. Zooplankton can serve as food for snakehead < 40 mm, but formulated feed should be provided for larger fish which are unable to catch zoo-plankton.

The menhadens Brevoortia gunteri and B. patronus are sympatric and morphologically similar. The two species are planktophagous and exhibited significant (P < 0·0001) food resource partitioning, with phytoplankton predominating in B. patronus stomachs and zooplankton in B. gunteri. The branchial apparatus of both species is of the typical alosine form. Brevoortia patronus has significantly more branchiospinules per mm (x=19·47) and significantly longer gill rakers (x=13·35 mm) than B. gunteri (x=14·11, x=12·01 mm respectively). B. patronus is characterized by a gill raker system forming a fine-meshed filter capable of retaining smaller food items. The results support the hypothesis that food resource partitioning is related to different morphological features of the branchial apparatus.

Four new species of the genus Diaphus are described. Three of these are in the subgeneric group with a suborbital luminous organ and are members of the D. fulgens species group with a raised AOa1 photophore. D. impostor sp. nov. from the Indo‐West Pacific is most similar to D. aliciae, differing in lower gill raker count and smaller size. D. wisneri sp. nov. from north of Hawaii and south Pacific lacks a luminous scale at the PLO and has a lower gill raker count than similar species. D. kora sp. nov. from north‐east of New Zealand has a large luminous scale at the PLO, and a longer Vn and lower gill raker counts than similar species. D. kapalae sp. nov. from the south‐western Pacific is most similar to D. splendidus and D. antonbruuni, from which it differs by the presence of an Ant, higher gill raker counts, and position of the VLO photophore.

Significant morphological differences were found between orange roughy, Hoplostethus atlanticus, caught in 1993 on the Puysegur Bank and those caught on the Lord Howe Rise, New Zealand. A total of 17 separate body measurements and counts were taken from each fish. Treating the sexes separately, significant differences were found between sites when linear relations between eight particular body measures and standard length were compared. The eight measures indicating differences in shape were head length, snout length, orbit diameter, maxilla width, premaxilla length, caudal peduncle, gill raker count, and anal fin count. Discriminant functions were used to compare sites and sexes, and these permitted a >90% success rate in distinguishing fish from the two sites. A discriminant function could not be found which successfully separated two separate tows made on the Puysegur Bank, indicating that phenotypic differences do not vary as much within a site as they do between sites. All analyses made suggested that fish from the two different areas had different body shapes. Morphological differences, such as those found in the current investigation, could only arise if the fish populations from the two areas were relatively discrete. There may be some movement of fish between areas, quite possibly enough to bring about relative genetic homogeneity, but clearly there is insufficient to prevent the two populations from differing phenotypically. These differences suggest that morphometric analysis may be a useful tool for distinguishing New Zealand orange roughy stocks.

The analysis was aimed at identifying the characteristics of hybrids of Atlantic salmon, Salmo salar L., and sea trout, Salmo trutta L. Nineteen metric characters and 11 meristic characters of reciprocal hybrids of these species aged 0+ and 1+ which were released into and grew in natural watercourses were analyzed. At ages 0+ and 1+, both of the hybrids were similar to trout in head length, minimum body depth, and dorsal fin height. Both hybrids were similar to salmon at the age of 0+ in the length of the caudal fin indentation (fork length as the % of total length) and at age 1+ in upper jaw length (% of head length). Hybrid metric characters were also either intermediate or exceeded the parental species (length of pectoral fins at age 1+). Analysis indicates that metric characters are difficult to use to identify hybrids. Among the meristic characters, low gill raker and pyloric caeca counts can be used to identify hybrids.