Comparative analysis of diurnal variations of the lipid composition in perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis> L.) and tyulka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> Nordmann) from the Rybinsk Reservoir pelagial

Diurnal variations of the total content and fractional composition of lipids in the organisms of underyearlings of indigenous (perch) and nonindigenous (tyulka) species have been analyzed. These fish species form the basis of feeding aggregations of young fish in the Rybinsk Reservoir pelagial. Stable interspecific differences in mean daily and hourly values of the content of total lipids and in the level of three fractions-phospholipids (PLs), cholesterol (CS), and triacylglycerols (TAGs)—have been determined. It is shown that the level of adipose reserves and the content of TAG in the tyulka are higher than in perch, while the contents of PL and CS are lower. Diurnal variations of the level of each of the three fractions in both fish species are similar, but the ranges of variations are wider in tyulka than in perch. Possible mechanisms for the regulation of lipid metabolism (including the participation of neuroendocrinal centers) and their similarity in young fish of different species upon adaptation to short-term changes in the environment have been discussed. It is suggested that the modern state of the zooplankton community in the Rybinsk Reservoir pelagial negatively affects the feeding of perch underyearlings and parameters of lipid metabolism in their organisms.     

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.     

On the diurnal rhythm and feeding electivity in kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis>) in Rybinsk Reservoir

Diurnal rhythms, feeding electivity, and feeding resources were studied for the new for Rybinsk Reservoir fish species, kilka (Clupeonella cultriventris). It is revealed that, in Rybinsk Reservoir, kilka actively feeds during day time. Selective feeding is a characteristic of this fish. Yearlings prefer small Cyclopoida and their young specimens dominating in zooplankton. Two-year-old fish actively select innumerous but large crustaceans of genera Heterocope, Bythotrephes, Leptodora, and Cyclops. Possible factors determining selection of food items by kilka are discussed. These factors are as follows: zooplankters’ biomasses, the extent of plankters’ aggregations, body size, and visibility of some prey species for kilka (as determined by movement pattern, transparency and cuticle color, presence of eggs, or large eye).     

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.     

The role of kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Nordmann)) in the diet of predatory fish of the Rybinsk reservoir

Data on predator fish feeding in the Rybinsk reservoir in the first years (2000–2003) of Ponto-Caspian kilka expansion are given. It is shown that the kilka’s penetration into the Rybinsk reservoir caused changes in the feeding spectra of predator fish. Kilka became one of the main objects of predator feeding throughout the whole year. In the open water period, it is consumed by pikeperch Stizostedion lucioperca (Linnaeus) and Volga pikeperch Stizostedion volgense (Gmelin) in the pelagial and by pike Esox lucius Linnaeus and perch Perca fluviatilis Linnaeus in the sublittoral and shallow bays. In winter it is mostly eaten by burbot Lota lota (Linnaeus) and pikeperch.     

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.     

Infection of mollusks and fish by the trematode Apophallus muehlingi (Jagerskiold, 1898) and its interrelations with intermediate hosts

In the Rybinsk Reservoir (Upper Volga basin), a sharp decrease in the occurrence of Apophallus muehlingi (Jagerskiold) parthenites was found in the population of the Ponto-Caspian snail Lithoglyphus naticoides Pfeiffer in 2009–2010. In the muscles of cyprinid underyearlings (ide Leuciscus idus (L.) and dace Leuciscus leuciscus (L.)), interspecific differences in protein content were revealed following their infection by metacercariae in the experimental environment. The helminth infection caused an increase in glycogen content in both fish species. A reduction of motor activity induced by muscle damage might be the main reason for the observed changes in biochemical characteristics.     

Underyearlings of dreissenid mussels (Dreissenidae,Bivalvia) in the phytophylic communities in the mouth area of the Rybinsk Reservoir tributary

The data on the abundance and biomass of dreissenid underyearlings in macrophyte stands in different zones of the mouth part of a small tributary of Rybinsk Reservoir are presented. The highest density and biomass of underyearlings are recorded in the transient zone of the reservoir and the river mouth cross section. It is shown that the number of dreissenid underyearlings inhabiting the mouth area has not changed considerably in the years with unfavorable meteorological conditions.     

Fish population density in Rybinsk Reservoir pelagic area

The density of individual species and the total density of pelagic fishes at stations in the Rybinsk Reservoir was evaluated in 1991, 1994, 2006, and 2007. A reliable difference was found to exist between the total fish density in pelagic areas in the 1990s and the 2000s. The density of many species (smelt, zander, perch, and zope) showed considerable variations in both abundance and biomass.     

Interannual Variability of Morphological Characters in Roach Rutilus rutilus (Cyprinidae) Underyealings of Coastal Habitats in of the Rybinsk Reservoir off Borok Settlement (Yaroslavl Oblast)

Journal of Ichthyology - Interannual variability in the underyearlings of roach Rutils rutilus, sampled in different years at the same point of the Rybinsk Reservoir was revealed. The variability...     

Formation and development of the Black Sea-Caspian kilka Clupeonella cultriventris (Clupeidae) in the Rybinsk reservoir

We studied the state and development of the population of the Black Sea-Caspian kilka Clupeonella cultriventris in the Rybinsk reservoir from 1994 to 2010. The population dynamics, the rate of growth of the kilka, as well as its food relationships with other fish species of the pelagial community, were analyzed. It was found that the period of exponential increase in the numbers was replaced by the period of interannual fluctuations. With the development of the population, tendencies for a decrease in the rate of growth of the kilka and aggravation of its food relationships with other species are revealed, which is determined by changes in the structure of pelagic aggregations of fish. One of the most significant environmental factors determining dynamics of the numbers and state of the kilka population in the northernmost part of its modern range is water temperature.     

Effect of pH on the activity of proteinases in intestinal mucosa,chyme, and microbiota of fish from the Cuciurgan reservoir

Proteolytic activities of the intestinal mucosa, chyme, and enteral microbiota have been studied in a wide range of pH values in five fish species from the Cuciurgan reservoir (Moldova). Differences in pH dependence of the intestinal proteinase activity of fish are determined by their feeding type. The maximum activity of proteinases is found in the pumpkinseed Lepomis gibbosus. The minimum activity of proteinases has been demonstrated by the zander Zander lucioperca. The pH optimum of the mucosa and chyme in all fish species (except for the European perch Perca fluviatilis) is 10. The pH optimum of the intestinal microflora varies from 6.0 (in the common carp Cyprinus carpio) to 10 (in the crucian carp Carassius carassius), whereas that in the perch from the Cuciurgan and Rybinsk reservoirs is 7. The majority of fish species, mostly Zander lucioperca and Lepomis gibbosus, are characterized by high proteniase activity of the microbiota, in the pH ranging from 6 to 9. It is assumed that proteinases in the enteral microbiota of fish are able to make up for the relatively low activity of those synthesized by their digestive system in the range of low pH values.     

Feeding of grey gurnard Eutrigla gurnardus (Triglidae) in the area of the Rockall Seamount

Specific features of feeding of grey gurnard Eutrigla gurnardus depending on vertical distribution and habitat conditions in the area of the Rockall Seamount in 2000 were considered. The intensity of feeding of grey gurnard from April to September decreased by several times. The main food of this species in spring are euphausiids and that in autumn are fish. Males feed slightly more intensively than females. The intensity of feeding, distribution, and behavior of grey gurnard in different seasons and at different depths near bottom and in the pelagial noticeably differ and depend on the composition of distribution and numbers of dominant food items (euphausiids, sand eel Ammodytes marinus, fish juveniles).     

On the problem of ecological groups formation in European perch Perca fluviatilis populations

Simulation model of the intraseasonal growth dynamics of young-of-the-year European perch Perca fluviatilis has been developed and studied. The model has been constructed based on the principles of bioenergetics and covers all the main physiological utilization processes of energy that come with food, including somatic growth, expenses on metabolism, and partial loss of energy with egestion and excretion. It is assumed that there are two space-separated biotopes called “inshore” and “pelagial” with different feeding conditions. Fish move from inshore to pelagial as the amount of food in the inshore biotope gets lower, provided that the actual ration is reduced down to the predetermined threshold level. It is demonstrated that the combined distribution of fish specimens belonging to one generation according to weight by the end of their growth period mainly depends on the intensity of exchange process between the biotopes. The ratio between the abundance values of young fish localized in different biotopes is determined by the threshold ration level, which motivates fish to move, as well as the duration of spawning, and, accordingly, length of hatching period.     

Biological and ecological characteristics of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) at different depths in the pelagial of the Irminger Sea

Results of comparative analysis of several ecological and biological indices of Sebastes mentella from the northern Atlantic (the Irminger Sea, Reykjanes Ridge) inhabiting different depths, 0–500 and 501–1000 m, are provided. A considerable similarity in the rates of linear and weight growth, sexual maturation, composition of parasitofauna, the degree of invasion by parasites of most species, specific features of invasion by copepod Sphyrion lumpi, as well as the pattern of pigment formations on the skin of S. mentella from two studied layers, testify to the absence of isolated groups of this species in the pelagial of the Irminger Sea. It was established that the formation of perch aggregations at a depth larger than 500 m takes place due to a partial redistribution from the upper layer of individuals aged 5 to 18 years and a complete departure to large depths of perch individuals older than 18 years. A conclusion was made that it is incorrect to use as a criterion for the intraspecies differentiation of the perch the insignificant differences in the occurrence of pigment formations on the skin that are the result of age changes in fish and an obvious pathology of this phenomenon. A decrease in the occurrence of melanin inclusions in the muscular tissue of fish at a depth larger than 500 m is also related to age changes and the change in the diet of the perch. Vertical variation, in particular biological parameters in pelagic aggregations, was determined by specific features of biology, ecology, and the life cycle of the species. In establishing measures of control of the international fishery in the pelagial of the Irminger Sea, it is necessary to proceed from the unity of aggregations of S. mentella throughout the vertical of their distribution.     

Density of the Fish Population in River Channel Parts of the Ivankovo Reservoir in 2012–2015

The density of some species and total density of fishes have been estimated in river channel parts of the Ivankovo Reservoir in 2012–2015. The significant differences in the total abundance of fishes in 2012–2013 and 2014–2015 have been revealed. The increase in the number of tyulka (Clupeonella cultriventris (Nordmann, 1840)) in the Black and Azov seas in 2014–2015 was determined by their periodic fluctuations typical for any species with a short life cycle. Changes in the abundance of bream and silver bream in the reservoir pelagial relate to their vertical redistribution under the effect of environment factors.     

Role of the daily food ration of perch fry (Perca fluvialis) in infestation with Bunodera luciopercae (Trematoda, Allocreadiidae)

The list of intermediate hosts of Bunodera luciopercae is given. In Lake Syamozero they are represented by crustaceans Heterocope, Ophryoxus. Data on their role in the ration of juvenile perch are given. Diurnal dynamics of the ratio between infected and noninfected plankton in feeding and the process of the formation of fish infection have been studied.     

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.     

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.     

Mensurative approach to examine potential interactions between age-0 yellow perch (Perca flavescens) and bluegill (Lepomis macrochirus)

Bluegill (Lepomis macrochirus) and yellow perch (Perca flavescens) populations are often sympatric in the Great Plains region of the U.S.A. and portions of Canada; however, very little attention has been given to potential interactions between these species for available resources, especially during the early life stages. Relationships between age-0 bluegill and yellow perch growth and relative abundance were explored across multiple lakes and years within the Nebraska Sandhill region, USA. In addition, four habitat patch types (open water, Phragmites spp., Typha spp., Scirpus spp.) were sampled for age-0 bluegill and yellow perch, and food habits were examined for each species during August, September, and October of 2009 in one of these lakes. Age-0 yellow perch growth was negatively related to age-0 bluegill relative abundance across a spatiotemporal scale. Age-0 bluegill and yellow perch exhibited similar habitat use (moderate–high overlap), but generally consumed different important and dominant prey taxa (bluegill consumed both macroinvertebrates—56?% and zooplankton—44?%, while yellow perch consumed more zooplankton—66?%), which resulted in low overall diet overlap between species. Previous research indicates that age-0 yellow perch diet ontogeny often results in feeding predominately on macroinvertebrates and positively selecting them (and avoiding zooplankton prey) at sizes observed in our study. Therefore, yellow perch growth rates may be compromised by the presence of bluegill because of the need to consume less energetically profitable prey items such as zooplankton.