Diets of deepwater oreos (Oreosomatidae) and orange roughy Hoplostethus atlanticus

The diets of black oreo Allocyttus niger, smooth oreo Pseudocyttus maculatus, spiky oreo Neocyttus rhomboidalis and orange roughy Hoplostethus atlanticus were determined from examination of contents of 240, 311, 76 and 415 non‐empty stomachs, from fishes sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand. Hoplostethus atlanticus had an opportunistic predatory strategy with a broad diet dominated by prawns and mesopelagic teleosts, but with substantial components of mysids and cephalopods. Pseudocyttus maculatus was strongly specialized on gelatinous zooplankton (jellyfish and salps). Allocyttus niger consumed mainly salps and hyperiid amphipods, and to a lesser extent fishes, prawns, mysids and copepods. Neocyttus rhomboidalis primarily consumed salps, along with mysids, euphausiids and fishes. Only P. maculatus did not exhibit significant ontogenetic variation in diet. The diets were also influenced by year and bottom depth. Differences in the distributions and diets of the four species probably reduce conflicts in resource use.     

The morphology and chemistry of the scales of the orange roughy and the smooth and spiky oreo dories

Proton and deuteron microprobes were used to establish the two-, and three-dimensional patterns of calcium, fluorine, carbon and oxygen variation in the scales of the orange roughy (Hoplostethus atlanticus) smooth oreo dory (Pseudocyttus maculatus) and spiky oreo dory (Neocyttus rhomboidalis).     

Size-biased predation by the gila topminnow poeciliopsis occidentalis (Baird and Girard)

The objective of this study is to document under both field and laboratory conditions the phenomenon of size-biased feeding by the Gila topminnow, Poeciliopsis occidentalis, and to shed light on the mechanisms responsible for this process. Adult female Gila topminnows feed in Monkey Spring, Santa Cruz County, Arizona, on a variety of food items, but Hyalella azteca is an important element of its invertebrate diet. The size of the amphipods ingested by female topminnows is a function of the size of the fish, with larger fish taking larger prey. There is also a strong preference for topminnows to select large amphipods from within the size limits imposed by the width of the mouth.The correlation between fish size and prey size was also seen in the laboratory, utilizing Daphnia similis and food pellets as prey. The tendency to select large prey from a range of available sizes was prominent with both Daphnia and pellets. The feeding period in the laboratory is characterized by two distinct phases. During the first phase, feeding is rapid and nonselective. As the feeding progresses, the rate of feeding drops dramatically and selectivity increases.More complex laboratory feeding experiments gave equivocal results. When fish were presented pellets of two sizes at different densities and at different ratios of small to large, size biased feeding was not clearly evident. Both predator and prey densities, agonistic behavior, and reaction distance should be explored more thoroughly as next steps in attempts to mimic feeding behavior in nature.Extracted from a Ph. D. thesis written by the junior author     

Food habits of small fishes in a common reed <Emphasis Type="Italic">Phragmites australis</Emphasis> belt in Lake Shinji,Shimane, Japan

To clarify the feeding habits of reed fishes, the gut contents of 13 fish species collected in a Phragmites australis belt in Lake Shinji were examined. Six species showed ontogenetic and/or seasonal changes in food use patterns. Smaller individuals generally preyed on small planktonic items (e.g., calanoid and cyclopoid copepods) or small crustaceans (gammaridean amphipods), subsequently changing to other prey items (e.g., mysids and filamentous algae) with growth. The most important dietary items for the reed fish assemblage comprised planktonic copepods, gammaridean amphipods and mysids. However, the relative importance of these changed seasonally, gammaridean amphipods being the most important in autumn and winter, and planktonic copepods and mysids the most important in spring and in summer. Cluster analysis based on dietary overlaps showed that the reed fish assemblage comprised five feeding guilds (planktonic-copepod, mysid, gammaridean-amphipod, filamentous-algae, and detritus feeders). Of these, the three former guilds were the most abundantly represented, whereas detritivores were represented by a single species.     

Feeding habits of <Emphasis Type="Italic">Bathydraco marri</Emphasis> (Pisces,Notothenioidei, Bathydraconidae) from the Ross Sea,Antarctica

In comparison with other bathydraconids, all species of the genus Bathydraco are poorly known from an ecological perspective. The diet of juvenile Bathydraco marri Norman, 1938 was studied for the first time in specimens collected in the southwestern Ross Sea during summer 1998. Fish were collected in a single otter trawl catch at 330–340 m depth. The stomach content analysis showed that this species fed exclusively on crustaceans. Overall, 20 prey taxa were identified to genus or species level. Mysids, amphipods and copepods were the most important prey in decreasing order of importance. Other prey, such as Euphausia superba, isopods and tanaids were eaten occasionally and in very small amounts. A multivariate analysis was applied to feeding data to assess ontogenetic or sex-related changes in diet. No difference was detected between sexes, whereas diet of small and large fish differed in some degree. An ontogenetic shift from small and pelagic crustaceans such as copepods to benthic–benthopelagic prey such as amphipods and mysids was observed. Relating present results with published data on physiological characteristics of B. marri, it was possible to infer their feeding behaviour and mode of life. Like other bathydraconids, this species appeared to be an inactive and sluggish fish, which relied on more or less motile benthic or epibenthic prey adopting a “sit and wait” feeding strategy. On the other hand, smaller fish seem to be more active, feeding also on pelagic prey such as copepods that can be seasonally abundant, thus reducing the intraspecific competition for food.     

Seasonal variation of gelatinous plankton consumption by fish in the South-western Atlantic Ocean: a question of strategy*

Gelatinous plankton is an important food resource for several species of fishes in the Southwestern Atlantic Ocean. Some fish depend heavily on these organisms and are specialized to feed on ctenophores, salps and medusae, while others only consume gelatinous plankton occasionally. We hypothesize that consumption of gelatinous plankton by fishes represents an alternative food resource when primary prey are not available during cold periods in the study area. To determine seasonal variations of gelatinous plankton consumption by fishes, data samples were grouped into cold and warm periods. A total of 64,567 stomachs belonging to 106 species of fish were analysed, of which 32,943 (51%) contained food items. Of those containing food items, 2719 (8.2%), from 38 fish species, contained gelatinous items. Fourteen species ingested gelatinous in warm period, nine in cold period, and 15 in both periods. The proportion of stomachs with gelatinous was significantly greater during the cold period. Ctenophores were the most predominant prey in both periods, followed by salps and medusae. Consumption of ctenophores, salps and medusae was unevenly distributed within the area during the different periods. Classification methods (group average sorting utilizing Bray–Curtis similarity measures based on log (X + 1) identified eight areas of consumption. SIMPER (similarity percentages) analyses revealed that nine fish species contributed most to gelatinous plankton consumption. The seasonal and spatial variation of gelatinous consumption by fish would be related to the availability of food in each period. Strategies of gelatinous consumption, including survival, feeding opportunities and prey specialization, are discussed.     

Food habits of fishes in azostera marina bed at aburatsubo, central japan

To clarify the feeding habits of seagrass fishes, the gut contents of 31 fish species collected in aZostera marina bed at Aburatsubo central Japan, were examined. Ontogenetic changes in food preference were recognized in 12 species. In general, juveniles of the latter preyed mainly on small crustaceans (e.g., gammaridean amphipods) or planktonic animals (e.g., calanoid and cyclopoid copepods), subsequently changing to other prey items (e.g., hard-shelled animals) with growth. Cluster analysis based on dietary overlaps showed that the seagrass fish assemblage comprised seven feeding guilds (small-crustacean, planktonic-animal, large-crustacean, polychaete, fish, hard-shelled mollusc and detritus feeders). Of these, small-crustacean feeders and planktonic-animal feeders were the most abundantly represented, including juveniles of several species, which, when adult, transferred to other feeding guilds. On the other hand detritivores were represented by a single species.     

Seasonal dynamics of growth and feeding of big-headed sculpin <Emphasis Type="Italic">Batrachocottus baicalensis</Emphasis> (Cottidae) in the Cape Berezovyi area (southern Baikal)

The seasonal features of the growth and feeding of one of the mass fish species of the littoral zone of Lake Baikal, big-headed sculpin Batrachocottus baicalensis, are investigated in the study area near the Cape Berezovyi (southern Baikal). It is found that the greatest increase of the linear parameters of the individuals of all age classes occurs in autumn, in the middle of the feeding period. Twenty-nine food objects, i.e., invertebrates and fishes, have been noted in the feeding spectrum of big-headed sculpin. It is found that the amphipods comprise the basic food year round. The transition of big-headed sculpin to predominant consumption of fish food is noted in the reproduction periods of other sculpins in the shallows. In general, the seasonal changing in species composition and food object ratio in the food are due to the fish life cycles, migrations of amphipods of different species, and, to a lesser extent, changing numbers of different groups of zoobenthos.     

Distribution of antarctic zooplankton around Elephant Island during the austral summers of 1988, 1989, and 1990

Year to year variation and vertical distributions of epipelagic Zooplankton around Elephant Island and King George Island were examined with samples collected with bongo nets and a 1 m² MOCNESS during the austral summers (Jan–Feb.) of 1988, 1989 and 1990. Copepods were the major components of epipelagic Zooplankton (in numbers) with dominance of Metridia gerlachei (1988 and 1989) and small calanoids and cyclopoids (1990). Euphausiids and salps were the next most abundant groups. The percent composition of euphausiids decreased from 1988 to 1990 while that of salps increased. The abundance of salps exceeded euphausiids and major taxa of copepods in 1990. Local patches of polychaetes and amphipods were also found. Statistically significant annual variations with increased numbers in 1990 were found by analyses of variance in total abundance, abundances of copepods, salps, chaetognaths and amphipods, but abundances of euphausiids, polychaetes and fishes showed no significant annual variations. When the study area was divided geographically, horizontal variability in abundance within each year showed no significance in total abundance, abundances of copepods, euphausiids, amphipods and fishes, but significance in salps, polychaetes and chaetognaths. Results of site clustering based on covariances of abundances of eleven major taxa were well matched, though not perfect, with the distribution of surface water temperatures which could be used as a tracer of source water masses suggesting that spatial variation was related to hydrodynamic conditions. Factor analyses showed that annual and spatial variations in abundance were mainly caused by only two taxa, Metridia gerlachei and salps (mostly Salpa thompsoni). These two taxa were responsible for about 60% and 30% of total variance, respectively, and were useful indicators of the interannual variation. That is, 1988 and 1989 were the years of M. gerlachei, and 1990 was the year of salps. From vertically stratified MOCNESS samples, it was shown that the major taxa in this study area were active vertical migrators. While most samples obtained by relatively shallow tows (uppermost 100 m depth) were composed of exclusively one or two taxa, those from relatively deep tows (down to 200 m) showed various patterns of vertical stratification suggesting that the patterns of vertical migration were species specific. Species specific ontogenetic vertical migration associated with elevated habitat temperatures also seemed to be responsible for the annual variation in zooplankton distribution in the upper water column.     

Feeding of the stone sculpin Paracottus knerii (Cottidae) in the littoral of southern Baikal

The food spectrum and seasonal dynamics of feeding of the stone sculpin Paracottus knerii in the littoral of southern Baikal is investigated. Altogether, 29 species of invertebrates are recorded. All year round, the bulk of food, similarly to other areas of the lake, consisted of amphipods; other groups of zoobenthos were represented insignificantly. The significance of particular amphipod species in the food of fish depended on their ecological and morphofunctional traits. The seasonal changes in the species composition and the ratio of food items in the food depended on life cycles of fish and on the migrations of zoobenthic organisms.     

Feeding ecology of dominant groundfish in the northern Bering Sea

We investigated current diets of the six most abundant benthic fish in the northern Bering Sea. Our objective was to explore feeding strategies and potential competition with other top predators as ecosystem changes occur in the northern Bering Sea ecosystem. Our approach used stomach content data collected from field sampling during spring 2006 and 2007. Calanoid copepods and ampeliscid amphipods were important prey of Arctic cod (Boreogadus saida) but in different proportions depending upon fish size, feeding location, and local environmental conditions. Snailfish (Liparidae) occupied a broad niche and fed on a variety of benthic amphipods. Arctic alligatorfish (Ulcina olrikii) and Arctic staghorn sculpin (Gymnocanthus tricuspis) consumed ampeliscid amphipods predominantly. Shorthorn sculpin (Myoxocephalus scorpius) had a less-diverse diet, with snow crab (Chionoecetes opilio) most important by weight. Finally, all Bering flounder (Hippoglossoides robustus) sampled had empty stomachs. Our results indicate that ampeliscid amphipods, which have high biomass in the central region of the northern Bering Sea, are the most important prey for the dominant groundfish in the Chirikov Basin. Generally, all dominant benthic fish in the northern Bering Sea had narrow feeding niches, except snailfish. High diet overlap was found among many of the fish species, including Arctic cod and snailfish, snailfish and Arctic alligatorfish, and Arctic alligatorfish and Arctic staghorn sculpin. These findings are consistent with a relatively short food chain for benthic fish that are for the most part specialized feeders with narrow preferences for food and may be affected by changes in benthic prey distributions.     

Diet and trophic niche of Macrourus spp. (Gadiformes, Macrouridae) in the Ross Sea region of the Southern Ocean

Both Macrourus caml and M. whitsoni are probably abundant and widespread in the Ross Sea region at depths between approximately 500 and 2100 m. We present the analysis of stomach contents (including regurgitated stomach contents) from an undifferentiated mixture of 33 specimens of these species (henceforth Macrourus spp.) in the Ross Sea region of the Southern Ocean. Samples of stomach contents were obtained from the Ross Sea slope (between about 71° and 73° S) and on the Scott Island and seamount chain. Overall, amphipods were the dominant prey found in Macrourus spp. stomachs with an index of relative importance (IRI) of 43%. About half the amphipods were Eurythenes gryllus and about half could not be identified. Based on stable isotope results, unidentified amphipods were probably herbivorous rather than carnivorous. Other important prey were copepods (especially for fish with total length less than 30 cm), krill (mainly Euphausia superba for larger fish) and fishes (Pleuragramma antarcticum and Gymnoscopelus opisthopterus). Minor prey found in stomachs included isopods, mysids, salps and polychaetes, with rocks and fragments of coral, echinoderm and shell also found. Stomach contents data provide evidence of both pelagic and benthic feeding. Carbon and nitrogen stable-isotope analysis of 161 Macrourus spp. muscle tissue samples from the Ross Sea slope, Admiralty and Scott seamounts and two parts of the Pacific-Antarctic fracture zone (near 65° S) are presented. Nitrogen isotope results (??¹⁵N = 10.6 ± 1.0??, mean ± SD) were generally consistent with stomach contents. Carbon isotope results (??¹³C = ?24.7 ± 0.8??) were consistent with Southern Ocean residence but higher than phytoplankton values (?29.9 ± 1.2??). We found that Macrourus spp. in the Ross Sea region have a trophic level of 3.8 ± 0.3, placing them well below the top of the food chain. Trophic level of Macrourus spp. was significantly affected by location and by size of fish (especially for fish less than 30 cm), whereas sex, fatness and bottom depth were not significant.     

Feeding habits and trophic levels of Mediterranean fish

The estimation of fractional trophic levels(TROPHs) is essential for the management offisheries resources as well as for quantifyingthe ecosystem effects of fishing. We gatheredall available information concerning thefeeding habits of 332 fish stocks, belonging to146 species, 59 families and 21 orders,throughout the Mediterranean Sea, and estimatedtheir TROPH values. The latter ranged from 2.0to 4.5 and the following functional trophicgroups were identified: (a) pure herbivores (TROPH = 2.0–2.1, mean = 2.02, SD = 0.03),which were very rare and represented by Siganus luridus, Siganus rivulatus andSarpa salpa, all of which feed on red,brown, green and blue-green algae; (b)omnivores with a preference for vegetablematerial (2.1 < TROPH < 2.9, mean = 2.5,SD = 0.12), but feeding on other prey, such assponges, hydrozoans, anthozoans, polychaetes,ostracods, isopods, amphipods and copepods. This type of omnivore was very rare among thecases reviewed; (c) omnivores with a preferencefor animal material (2.9 < TROPH < 3.7,mean = 3.4, SD = 0.19) feeding on a wide variety ofprey (e.g., algae, foraminifera, brachyurans,balanoids, ascidians, amphipods,appendicularians, annelids, isopods,gastropods, cnidarians, ophiurids, polychaetes,cladocerans, mysids, euphausids, fish larvae,cephalopods). They were the most numerous andwere mainly represented by species of thefamilies Blenniidae, Bothidae, Centracanthidae,Gobiidae, Labridae, Lotidae, Macrouridae,Mullidae, Ophidiidae, Soleidae, Triglidaeand Engraulidae; and (d) carnivores witha preference for large decapods, cephalopodsand fish (3.7 < TROPH < 4.5). They werethe next most abundant group among the casesreviewed. They were mainly represented byspecies of the families Dalatiidae, Lophiidae,Scombridae, Scyliorhinidae, Synodontidae,Torpedinidae, Merlucciidae, Xiphiidae andZeidae. This group was divided into twosubgroups: one exhibiting a preference fordecapods and fish (3.7 < TROPH < 4.0,mean = 3.85, SD = 0.09) and another one exhibitinga preference for fish and cephalopods (4.0 相似文献   

Preliminary estimates of the age and growth of immature smooth oreo Pseudocyttus maculatus Gilchrist 1906 (Oreosomatidae) in the Falkland Islands region of the South Atlantic

Sectioned otoliths were used to estimate the age of 29 specimens of the smooth oreo (Pseudocyttus maculatus Gilchrist 1906) from the Falkland Islands region of the South Atlantic. This represents the first ageing study of this species in this region of the world. All specimens were immature (sub-adults), the largest having a maximum total length of 347 mm. Growth increments were observed in sectioned otoliths and assumed to be annual in periodicity. The maximum age estimate of individuals in this study was 20 years and the form of somatic growth was similar to previous research on this species from Australian waters. The otolith microstructure consisted of an inner, mostly opaque zone with wide increments followed by an outer, mostly translucent zone with narrower increments. It is suggested that these zones correspond to the two growth phases in the life history of this species, namely the pelagic juvenile phase (opaque zone) and the demersal sub-adult/adult phase (translucent zone). Received: 27 May 1997 / Accepted: 31 October 1997     

Fish feeding guilds in shallow rocky and soft bottom areas on the Swedish west coast

Multivariate analyses of the diet relationships within fish assemblages resulted in the recognition of five major feeding guilds in shallow (0-9 m) rocky- and soft-bottom habitats on the Swedish west coast. The two habitats had similar guilds that could be broadly described as piscivores, decapod feeders, copepod feeders and amphipod and mollusc feeders. The last guild on the rocky bottom was more strictly one of amphipod feeders, whereas the last guild on soft bottoms consisted of infauna feeders (mainly polychaetes and bivalves). A comparison of the diet of the entire fish assemblages showed that amphipods and gastropods were more prevalent as prey taxa on rocky bottoms, whereas bivalves and teleosts were more common on soft bottoms. A large proportion (12 out of 27 species) of the fish species investigated was found in both habitats. These fish species generally seemed to rely on the same major prey groups in the two habitats, but also included prey taxa characteristic for the habitat in which they resided. Sea trout Salmo trutta , mackerel Scombrus scombrus , saithe Pollachius virens , whiting Merlangius merlangus and cod Gadus morhua were found to be the major piscivores in both the investigated habitats. Herring Clupea harengus and members of the family gobiidae were the most prevalent prey species for piscivores within the rocky- as well as the soft-bottom fish assemblage. A comparison of feeding modes suggested that the fish assemblage on rocky bottoms predominantly (60% of the food items) relied on food found in vegetation. On soft bottoms, the average distribution of food categories among fish species was 44% benthic, 35% pelagic and 21% vegetation-associated food items.     

Influence of morphology and amphibious life-style on the feeding ecology of the mudskipper Periophthalmus argentilineatus

The potential feeding advantages that are offered to the barred mudskipper Periophthalmus argentilineatus by its amphibious life-style were investigated. To this end the feeding ecology of these fish, the position they occupy in the mangrove food web and the importance of different morphological factors for their diet were studied. Analysis of gut contents showed that the major component of the barred mudskipper diet changes during growth from small crustaceans ( e.g. copepods and amphipods) to polychaetes to mangrove crabs. This dietary shift was found to be facilitated through enlargement of the mouth, as well as elongation of the gut. The use of stable isotope analysis revealed that barred mudskippers had a similar trophic position as other zoobenthivore fish species, but that their diet did not appear to be affected by competition for food with other zoobenthivores. The amphibious habits of the barred mudskipper provide specific advantages to its feeding ecology, such as access to an abundant food source of mangrove crabs, which are mostly inaccessible for other fish species.     

Invasive Ponto-Caspian Amphipods and Fish Increase the Distribution Range of the Acanthocephalan Pomphorhynchus tereticollis in the River Rhine

Non-indigenous species that become invasive are one of the main drivers of biodiversity loss worldwide. In various freshwater systems in Europe, populations of native amphipods and fish are progressively displaced by highly adaptive non-indigenous species that can perform explosive range extensions. A total of 40 Ponto-Caspian round gobies Neogobius melanostomus from the Rhine River near Düsseldorf, North Rhine-Westphalia, Germany, were examined for metazoan parasites and feeding ecology. Three metazoan parasite species were found: two Nematoda and one Acanthocephala. The two Nematoda, Raphidascaris acus and Paracuaria adunca, had a low prevalence of 2.5%. The Acanthocephala, Pomphorhynchus tereticollis, was the predominant parasite species, reaching a level of 90.0% prevalence in the larval stage, correlated with fish size. In addition, four invasive amphipod species, Corophium curvispinum (435 specimens), Dikerogammarus villosus (5,454), Echinogammarus trichiatus (2,695) and Orchestia cavimana (1,448) were trapped at the sampling site. Only D. villosus was infected with P. tereticollis at a prevalence of 0.04%. The invasive goby N. melanostomus mainly preys on these non-indigenous amphipods, and may have replaced native amphipods in the transmission of P. tereticollis into the vertebrate paratenic host. This study gives insight into a potential parasite-host system that consists mainly of invasive species, such as the Ponto-Caspian fish and amphipods in the Rhine. We discuss prospective distribution and migration pathways of non-indigenous vertebrate (round goby) and invertebrates (amphipods) under special consideration of parasite dispersal.     

The biology of the panga, Pterogymnus laniarius (Teleostei: Sparidae), on the Agulhas Bank, South Africa

Aspects of the biology of the panga, Pterogymnus laniarius, a commercially important endemic southern African, demersal sparid fish species, are described from material collected monthly between February 1994 and July 1995 on the Agulhas Bank, South Africa. Growth studies based on sectioned sagittal otoliths revealed that the panga is relatively slow growing with ages of 16 years being recorded. Growth was best described by the von Bertalanffy growth model as L_t = 379.4 (1-e^{–0.13(t+1.78)}). Estimates of total mortality, natural and fishing mortality were estimated at 0.36 year^–1 0.28 year^–1 and 0.08 year^–1, respectively. Detailed histological examination revealed that panga are late gonochorists, males and females maturing after a non-functional intersexual interval. Females mature at approximately 200 mm fork length or 4 years of age. Reproductive activity occurs throughout the year, peaking slightly in winter when small pelagic eggs are spawned. Gametogenesis was found to be similar to that of other sparid fishes and marine teleosts in general. The panga feeds predominantly on crustaceans with a distinct ontogenetic shift in feeding habits. Juvenile fish feed predominantly in the water column on mysids after which they move to the benthos with subadult fish feeding on ophiuroids and amphipods. Adult fish remain on or near the benthos, feeding predominantly on crabs with polychaetes, ophiuroids and fishes also present in the diet in smaller quantities. Several aspects of the panga's biology such as it's late gonochoristic reproductive style, protracted spawning season, maturation before recruitment and the ability to utilise large areas of the Agulhas Bank by feeding on soft substratum prey are thought to enable this species to sustain a higher fishing pressure than other sympatric sparid species. The panga's longevity, slow growth and high natural mortality rate mitigates against these factors and needs to be considered in the development of a management strategy.     

Associations between gelatinous zooplankton and hyperiid amphipods (Crustacea: Peracarida) in the Gulf of California

Hyperiid amphipods are pelagic crustaceans that live associated with gelatinous zooplankton including medusae, ctenophores, siphonophores, and salps. Standard plankton sampling disrupts natural associations, so the most reliable way to determine an association is through direct observation of the organisms in their environment. The planktonic fauna of the Gulf of California dwelling between 10 and 3000 m was surveyed using SCUBA diving and a remotely operated submersible (ROV) during March 2003. Here we report our observations on a total of 14 symbiotic associations found between the hyperiid amphipods and various taxa of gelatinous zooplankton. We found parental care behavior in a group of amphipods (Oxycephalidae) in which this phenomenon has not been previously reported. For two hyperiid species, Euthamneus rostratus and Vibilia australis, we present the first information on their symbiotic relations. Additional hosts were discovered for other well-known and widely distributed hyperiid species (i.e. Brachyscelus crusculum, Hyperoche medusarum). Photographic evidence of some of these interactions is included in this contribution. This is the first survey of these relationships in the Gulf of California, and many aspects of the ecology and biology of these symbioses remain to be studied.     

Seasonal changes in feeding and relative condition factors of Arctic grayling (<Emphasis Type="Italic">Thymallus arcticus</Emphasis>) in a stretch of the middle reaches of the Yenisei River

The seasonal dynamics of feeding spectra and diet of Arctic graying in a stretch of the middle reaches of the Yenisei River (from the dam of the Krasnoyarsk HPP to the mouth of the Kan River) was studied in 2009–2013. Its connection with the food-supply state and fish growth has been traced. It has been shown that the intensity of fish feeding is relatively stable throughout the year, despite significant fluctuations in zoobenthos biomass. The contribution of groups dominating in diet (amphipods and larvae of caddisflies) changes depending on the month. Amphipods prevail in the diet of fish during the period from June to October and caddisflies prevail in the winter and spring months. Among caddisflies, selective feeding on a small species, Apatania crymophila, has been revealed. The change of the primary diet component during the summer period corresponds to a sharp increase in the coefficients of relative condition factors with a peak in August–September. It has been assumed that changes in the ratio of weight and linear sizes of fish are associated not only with an increase in the water temperature, but also with the grayling switching to the consumption of amphipods with a higher nutrition value.