Proteinases of kilka <Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> of the Rybinsk Reservoir

The effect of temperature on activity of proteinases of the stomach mucosa, intestinal mucosa, chime, and the entire body of kilka Cluperonella cultriventris is described. Significant differences are revealed in temperature characteristics (t ^o-function, Q ₁₀, and E _act) of the investigated enzymes. The temperature has a larger influence on the activity of intestinal proteinases than the activity of proteinases of the stomach, chime, and the whole kilka organism. The lowest value of E _act within the temperature range of life of this species is characteristic of chime proteinases. Hemoglobinlytic proteinases of various tissues of kilka that substantiate, at pH 3.0 and 5.0 (the action zone of cathespsins), the processes of induced autolysis contribute to efficient alimentation of other fish species. The assumption is made that a high activity level of proteinases of the digestive tract, comparable with that of other fish species of the upper Volga, enables kilka that have assimilated to the Rybinsk Reservoir to feed efficiently within the temperature range characteristic of the water-bodies of this zone.     

Circadian rhythmic changes in the lipid composition of muscles in kilka <Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Clupeidae,clupeiformes) during natural periodicity of feeding in the feeding and spawning periods in the Rybinsk Reservoir

According to data of observations in 2002–2004, differences in the pattern of diurnal fluctuations in the total content and fractional composition of lipids in muscles of mature specimens of kilka Clupeonella cultriventris from the Rybinsk Reservoir in the feeding and spawning periods were revealed. It was established that the feeding intensity in kilka considerably changes throughout 24 h in both periods of the annual cycle, while diurnal fluctuations in the fatness of muscles are distinctly manifested only in the reproductive period and have a dissimilar pattern in specimens of different sexes. In females and males, they are determined mainly by the change in the content of the fraction of reserve lipids-triacylglycerols, as a rule, by its increase in the light hours of the day, several hours after an increase in the feeding activity of fish. The pattern of diurnal fluctuations of the level of lipid fractions (phospholipids, triacylglycerols, cholesterol, and its ethers) in kilka’s muscles differs from that in the feeding period. Possible causes of the change of diurnal variations of the considered indices of lipid metabolism in kilka at an increase in the endocrine activity of its body in the reproductive period is discussed.     

Method of age determination of Ponto-Caspian kilka <Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Clupeiformes,Clupeoidei) using scales and otoliths

A method of Rybinsk Reservoir kilka Clupeonella cultriventris age determination using otolites is described. Terms of annual rings anlage on both scales and otolites are determined. A comparison of age estimates obtained through studying scales and otoliths by different operators is performed. It is shown that operators’ errors in age determination using otolites are smaller than such when the scales were used.     

Specific features of feeding in underyearlings of zander (<Emphasis Type="Italic">Sander lucioperca</Emphasis>) (Percidae) of the Rybinsk reservoir in various years

The results of the studies on feeding of zander (Sander lucioperca) underyearlings in the Rybinsk Reservoir in 2008-2010 and 2012 are presented. The study revealed that, at feeding on plankton, the assemblage of the organisms consumed by juvenile zander has not been changed compared to 1950. The underyearlings prefer to feed on large zooplankters—Daphnia longispina, Leptodora kindtii, and Bythotrephes longimanus—along with copepods. At some sampling stations, the species of macrozoobenthos were included in the young zander food. The piscine component of zander food was dominated by underyearlings of Azov-Black sea tyulka (Clupeonella cultriventris); the fries of perch (Perca fluviatilis) and cyprinids (Cyprinidae) were less important. The feeding strategy of zander underyearlings was unchanged in various years. At turning to predatory feeding, not only the ratio of sizes of predator versus prey but also the proportion of the densities of their populations plays an important role.     

Dreissenid species (Mollusca,Dreissenidae) in the Upper Volga reservoirs

The results of our long-term studies of populations of two dreissenid species (Dreisena polymorpha Pallas, 1771 and D. bugensis Andrusov, 1897) in Rybinsk and Gorkii reservoirs have been analyzed. New habitats of D. bugensis have been found in Rybinsk Reservoir.     

Interspecific differences of respiratory functions of some freshwater fish species

Hemoglobin affinity to oxygen, Bohr effect, sodium, potassium, and magnesium ion concentrations of erythrocytes in the three fish species from Rybinsk Reservoir (golden carp Carassius auratus gibelio, bream Abramis brama and pike Esox lucius) immediately after catching and during acclimation to laboratory conditions were studied. Our own and literature data on some other fish species were analyzed. The relationship between the functional features of the hemoglobin and ionic environment was found, and the changes taking place during acclimation and interspecific differences of these indices were shown.     

Molecular genetic identification and seasonal succession of toxigenic cyanobacteria in phytoplankton of the Rybinsk Reservoir (Russia)

Data on the hepato- and neurotoxigenic cyanobacteria in phytoplankton of the Rybinsk Reservoir have been obtained for the first time. Different methods for revealing toxigenic cyanobacteria (light microscopy, PCR analysis, and enzyme-linked immunosorbent assay) demonstrate the same results. Hepatotoxins microcystins and for the first time neurotoxins saxitoxins were detected in the reservoir, whereas cylindrospermopsin and anatoxin-a were not revealed. The presence of mcyE and stxA genes responsible for microcystin and saxitoxin biosynthesis in total phytoplanktonic DNA is demonstrated. The following three genera of cyanobacteria containing mcyE gene are identified: Microcystis (M. aeruginosa, M. viridis), Planktothrix (P. agardhii), and Dolichospermum (Anabaena). It is hypothesized that saxitoxin-producing cyanobacteria Dolichospermum (Anabaena) inhabit the Rybinsk Reservoir.     

Diurnal Dynamics of Activity of Peptidases at Early Ontogenesis of Bleak <Emphasis Type="Italic">Alburnus alburnus</Emphasis> (L.) from Coastal Shallows of the Rybinsk Reservoir

The diurnal dynamics of the activity of peptidases in fish larvae by the example of bleak Alburnus alburnus (L.) as the dominant species in the open and protected shallows of the Rybinsk Reservoir has been studied for the first time. Two peaks of enzyme activity in the intestinal mucosa of fish larvae are revealed: morning and night. The data on species composition and daily dynamics of number of fish larvae in the shallows of different types are presented.     

Type of rheoreaction in the early ontogenesis of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) as a factor determining its biotopic distribution

The specific features of rheoreaction in roach Rutilus rutilus (L.) larvae from open and protected shallows of the Rybinsk Reservoir have been studied. Data on length and weight of roach sampled at various habitats at B–E developmental stages are presented. It has been revealed that the type of roach larvae rheoreaction is a behavioral mechanism of their distribution over different types of habitats, not only in rivers but also in the waterbodies with slow water turnover rates—lakes and reservoirs. By the time of developmental stage E, this mechanism provides the sustainable spatial separation of juvenile fish, which in the future may lead to intrapopulation differentiation in roach.     

On the physiological-biochemical state of kilka Clupeonella cultriventris (Clupeidae, Clupeiformes) in Rybinsk Reservoir (Russia)

The results of studies into lipid total content and fractional composition in the tissue and wholebody levels in kilka (Clupeonella cultriventris) are given. The fish studied belonged to various size-age groups and were sampled in Rybinsk Reservoir during active feeding periods in 2002 and 2005. A trend was revealed of deterioration of the physiological-biochemical state in adult specimens of this invasive species. This was especially true of the modal (in terms of their proportion in population) two-year-old fish. This was evidenced by a decrease in contents of total and reserve (triacylglycerol) lipids in fish muscles during the whole study period. It is shown that, in young kilka caught in all reservoir stretches in autumn, the values of these parameters depend on the time and rate of the reservoir water level decrease during the active feeding period. Probable reasons for changes in the physiological-biochemical state in adult and young specimens in the kilka population are discussed. The discussion is in view of the recent state of the Rybinsk Reservoir ecosystem which undergoes successional modification of the pelagic zooplankton community both at the level of large taxa and of some dominant species.     

First finding of <Emphasis Type="Italic">Quistadrilus multisetosus</Emphasis> (Smith, 1900) (Oligochaeta: Tubificidae) in the Rybinsk Reservoir

Oligochaete Quistadrilus multisetosus (Smith, 1900) has been recorded in the Rybinsk Reservoir for the first time in this region. The abundance and spatial distribution of the species population in autumn 2013 are presented.     

Feeding capability of black scraper <Emphasis Type="Italic">Thamnaconus modestus</Emphasis> on giant jellyfish <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> evaluated through field observations and tank experiments

Although many fish species are known to feed on jellyfish, only a few quantitative studies on this subject have been conducted in the field or laboratory. We combined field observations and feeding experiments to quantitatively evaluate the potential feeding capability of the black scraper Thamnaconus modestus on giant jellyfish Nemopilema nomurai in a jellyfish-abundant area. Underwater observations revealed that shoals of T. modestus fed voraciously on jellyfish when the jellyfish were close to the fish’s seaweed habitat. Gut contents of field-collected T. modestus almost exclusively consisted of jellyfish. In tank trials, feeding activity of black scraper was high when light intensity was between about 1.1 lx and 50 × 10³ lx. The estimated feeding speed of T. modestus on the jellyfish in the Sea of Japan when the jellyfish bloom occurred was 10.0 ± 2.0 times fish body weight per day. The results support the prediction that T. modestus and probably other coastal medusivorous fishes have a substantial capability to eliminate jellyfish blooms. Considering that they are highly dependent on seaweed bed, protection of such habitats for these medusivores may be the most cost-efficient control method for jellyfish blooms.     

Expansion of the Range of the Black Sea Snail <Emphasis Type="Italic">Lithoglyphus naticoides</Emphasis> (C. Pfieffer, 1828) (Mollusca: Gastropoda: Lithoglyphidae) and Associated Trematode Species in the Upper Volga Basin

The Black Sea snail Lithoglyphus naticoides (C. Pfieffer, 1828) (Mollusca: Gastropoda: Lithoglyphidae) was first recorded in the Uglich Reservoir in the summer of 2013. By 2015, several new local settlements of the snail had been found in the Uglich and Rybinsk reservoirs, indicating its successful naturalization in the Upper Volga basin. Parasitological studies of L. naticoides from these habitats reveal the parthenitae of three trematode species.     

Contrasting the early life histories of sympatric Arctic gadids <Emphasis Type="Italic">Boreogadus saida</Emphasis> and <Emphasis Type="Italic">Arctogadus glacialis</Emphasis> in the Canadian Beaufort Sea

The early life stages of Boreogadus saida and Arctogadus glacialis are morphologically similar, making it difficult to assess differences in their ecological niche. The present study documented for the first time the early life stage ecology of A. glacialis, compared it to that of B. saida, and identified the factors separating the niches of the two sympatric species. The 10,565 larval gadids collected in the Beaufort Sea from April to August of 2004 and 2008 were identified to species either directly by genetics and/or otolith nucleus size, or indirectly with a redistribution procedure. Between 8.0 and 8.7 % of all gadids were assigned to A. glacialis. Larvae of A. glacialis were longer at hatch and experienced lower mortality rates than those of B. saida. The two species shared similar spatiotemporal and vertical distributions, hatching season, and growth rate. Under the ice, feeding incidence of B. saida was low (14 %) relative to A. glacialis (88 %). At lengths <15 mm, both species specialized on different prey. The diet of fish >15 mm overlapped (Schoener’s index = 0.7), with Calanus glacialis and C. hyperboreus providing >50 % of the carbon intake of both species. The higher mortality in B. saida may be explained by the smaller size at age from hatching to metamorphosis and a lower under-ice feeding incidence. The early larval stage appears to be the key period of niche divergence between the two species.     

Different feeding strategies in Antarctic scavenging amphipods and their implications for colonisation success in times of retreating glaciers

Background

Scavenger guilds are composed of a variety of species, co-existing in the same habitat and sharing the same niche in the food web. Niche partitioning among them can manifest in different feeding strategies, e.g. during carcass feeding. In the bentho-pelagic realm of the Southern Ocean, scavenging amphipods (Lysianassoidea) are ubiquitous and occupy a central role in decomposition processes. Here we address the question whether scavenging lysianassoid amphipods employ different feeding strategies during carcass feeding, and whether synergistic feeding activities may influence carcass decomposition. To this end, we compared the relatively large species Waldeckia obesa with the small species Cheirimedon femoratus, Hippomedon kergueleni, and Orchomenella rotundifrons during fish carcass feeding (Notothenia spp.). The experimental approach combined ex situ feeding experiments, behavioural observations, and scanning electron microscopic analyses of mandibles. Furthermore, we aimed to detect ecological drivers for distribution patterns of scavenging amphipods in the Antarctic coastal ecosystems of Potter Cove. In Potter Cove, the climate-driven rapid retreat of the Fourcade Glacier is causing various environmental changes including the provision of new marine habitats to colonise. While in the newly ice-free areas fish are rare, macroalgae have already colonised hard substrates. Assuming that a temporal dietary switch may increase the colonisation success of the most abundant lysianassoids C. femoratus and H. kergueleni, we aimed to determine their consumption rates (g food x g amphipods^?1 x day^?1) and preferences of macroalgae and fish.

Results

We detected two functional groups with different feeding strategies among scavenging amphipods during carcass feeding: carcass ‘opener’ and ‘squeezer’. Synergistic effects between these groups were not statistically verified under the conditions tested. C. femoratus switched its diet when fish was not available by consuming macroalgae (about 0.2 day^?1) but preferred fish by feeding up to 80% of its own mass daily. Contrary, H. kergueleni rejected macroalgae entirely and consumed fish with a maximal rate of 0.8 day^?1.

Conclusion

This study reveals functional groups in scavenging shallow-water amphipods and provides new information on coastal intraguild niche partitioning. We conclude that the dietary flexibility of C. femoratus is a potential ecological driver and central to its success in the colonisation of newly available ice-free Antarctic coastal habitats.

     

Effect of pH on the proteinase activities in the intestine mucosa,chyme, and enteral microbiota in the piscivorous fish differing in their ecological traits

The effect of pH on the activity of proteinases of intestine mucosa, chyme, and enteral microbiota was studied in three piscivorous fish species of the Rybinsk Reservoir differing in their ecological traits: pike Esox lucius, burbot Lota lota, and zander Sander lucioperca. In all fish species, studied pH of ten is optimal for the functioning of proteinases of intestine mucosa; in chyme proteinases, optimal pH values vary from six to ten. Optimal pH for functioning of proteinases of enteral microbiota is seven for zander and pike; pH of nine, for burbot. High activity of chyme and microbiota proteinases within the diapason of pH values of six to nine is a characteristic of burbot. Relative activity of proteinases of intestine mucosa in all fish species is not more than 15% of the maximal activity; that of chyme and enteral microbiota is lower than 40% in zander, close to 50% in burbot, and 80 and 50%, respectively, in pike. It is suggested that diversity of the patterns of pH-dependence of enteral microbiota proteinases relates to the specificity of microbiota in various ecological zones of the reservoir (littoral, sublittoral, and bathyal).     

Reproduction and development of <Emphasis Type="Italic">Pholis picta</Emphasis> (Perciformes: Pholidae) and <Emphasis Type="Italic">Opisthocentrus zonope</Emphasis> (Stichaeidae)

In the Peter the Great Bay (the Sea of Japan), reproduction and embryonic larval development of Pholis picta and Opisthocentrus zonope are investigated. Both species spawn in November–December at the water temperature decreasing from 7.0 to 0.2°C. Fecundity of Pholis picta is 494–1228 eggs, and of Opisthocentrus zonope—368–1360 eggs. Both species lay eggs in empty shells of Gray mussel. Parent fish permanently stay in the shell but do not actively care for the eggs. Morphological changes in the process of embryogenesis are compared between the related species. Prolarvae and larvae are described for identification, with special attention to pigmentation. The spawning behavior of adult fish and behavior of prolarvae are described.     

Feeding patterns of the black-striped pipefish <Emphasis Type="Italic">Syngnathus abaster</Emphasis> in an invaded freshwater habitat

Syngnathus abaster is an euryhaline species, which has penetrated freshwaters in Europe and its range is expanding. The goal was to investigate the feeding patterns of this species in an invaded freshwater habitat, where it first appeared at the beginning of 1990s, with implications for assessing its possible effects on invaded ecosystems. In total, 36 prey items were identified in the diet of S. abaster. The most important prey were zooplanktonic organisms, among which copepods predominated significantly. The second most important prey were cladocerans, represented by 20 species/genera. The diet composition of this species showed clear seasonal dynamics but copepods remained the predominant prey item throughout the year. Significant positive relationships between the abundance of zooplanktonic organisms in the gut contents of S. abaster and their abundance in zooplankton samples were found for copepods and Ceriodaphnia sp. S. abaster showed a significant positive electivity for copepods throughout all months. It also positively selected some large cladocerans, which probably shared the same habitat. S. abaster also consumed fish items including gobiid larvae and its own juveniles, when they were abundant in May and especially in June. The possible effect of S. abaster on native ecosystems may include the shaping of zooplanktonic communities through selective predation on copepods. This species is unlikely to be a serious food competitor for native fish inhabiting European freshwaters, the majority of which are cyprinids. Nevertheless, it can have effects on some native fish through predation on their juveniles, which might share the same habitats.     

Black-and-white snub-nosed monkey (<Emphasis Type="Italic">Rhinopithecus bieti</Emphasis>) feeding behavior in a degraded forest fragment: clues to a stressed population

Rapid global deforestation has forced many of the world’s primates to live in fragmented habitats, making the understanding of their behavioral responses to degraded and fragmented habitats a key challenge for their future protection and management. The black-and-white snub-nosed monkey (Rhinopithecus bieti) is an endangered species endemic to southwest China. The forest habitat ranges from near-continuous to fragmented. In this study, we investigated the activity budget and diet of a R. bieti population that live in an isolated and degraded habitat patch at Mt. Lasha in Yunnan Province, near the current southern limit of the species. We used our data along with data from six other sites in more-continuous habitats across its range to model factors that predict stress, including feeding effort and time feeding on lichens against potential predictive parameters. Models showed feeding effort across all sites increased with increasing altitude and latitude, and with decreasing food species diversity. There was also a strong positive relationship between feeding effort and time feeding lichens. The Mt. Lasha R. bieti population exploited a total of 36 food species, spending 80.2% of feeding time feeding on lichens, Bryoria spp. and Usnea longissima. These figures are more comparable to those living in the north than those living in the mid- and southern part of the species’ range. Given the models for feeding effort and time feeding on lichens, the unexpectedly high time spend feeding on lichens and feeding effort relative to latitude and elevation are suggestive of a stressed population at Mt. Lasha.     

Influence of magnetic field on the spatial orientation in zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) (Cyprinidae) and Roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>) (Cyprinidae)

Preferred direction of motion under influence of geomagnetic field and its modifications was registered in zebrafish (Danio rerio) raised in laboratory culture and in roach (Rutilus rutilus) from the Rybinsk Reservoir. In the geomagnetic field, specimens of zebrafish prefer two opposite directions oriented towards the north and south, while they prefer towards east and west at 90° turning of the horizontal component of geomagnetic field. The specimens of roach in the geomagnetic field prefer only the direction oriented towards east–northeast. This direction coincides with the direction along the canal where roach was sampled to the main river channel part of the Rybinsk Reservoir. At 90° rotation of the horizontal component of geomagnetic field, the direction turns to the south–southeast. The reasons for selection of certain directions in the geomagnetic field are discussed.