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).     

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.     

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.     

Circadian-rhythmic variations of biochemical parameters in the yearlings of indigenous perch (Perca fluviatilis L.) and nonindigenous tyulka (Clupeonella cultriventris Nordmann) from the Rybinsk Reservoir (Russia)

Diurnal variations of some parameters of protein, lipid, and water metabolisms in the underyearlings of indigenous (perch, Perca fluviatilis L.) and nonindigenous (tyulka, Clupeonella cultriventris Nordmann) fish species have been analyzed. These species form the basis of feeding aggregations of young fish in the Rybinsk Reservoir pelagial. No significant daily fluctuations in the values of protein content, water, and lipids in the studied fish species were revealed. Stable interspecific differences in mean daily and hourly values of the above-mentioned components, as well as in the contents of three lipid fractions—phospholipids (PLs), free cholesterol (FC), and triacylglycerols (TAGs)—have been determined at the level of whole organism. 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 proteins, PL, and FC 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 and their similarity in young fish of different species upon adaptation to short-term changes in the environment are 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.     

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.     

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.     

Dynamics and the state of fishery resources in the Rybinsk Reservoir from 1950–2010

Data on dynamics of the main commercial fish populations in the Rybinsk Reservoir over the period of 1950–2010 have been generalized. Fishing intensity is the main factor that determines the state of fish resources. It affects not only the abundance of commercial fish but also determines changes in population characteristics, i.e., changes in age and size structure and increase in the portion of young individuals. The effect of fishing on populations of some species depends on their commercial value. Commercial fishing affects notably such species as bream Abramis brama, zander Sander lucioperca, and pike Esox lucius. Commercial fishing affects, to a lesser extent, populational characteristics of such mass fish species as roach Rutilus rutilus and blue bream Abramis ballerus whose commercial value is lower.     

Effect of environment on the adaptive abilities of fry roach Rutilus rutilus (L.) (Cyprinidae) during early ontogenesis

In recent years a considerable decrease in the abundance of predatory fishes has been observed in spawning tributaries of the Rybinsk Reservoir caused by their intensive catching. The lack of encounters with predators before the downstream migration of young fish hampers the development of necessary skills of defensive behavior in the absence of predation experience. As a result, after downstream migration, the juveniles are incapable of adapting to the predation pressure in the reservoir and are subjected to intensive elimination. The adaptive potential of the roach Rutilus rutilus L. was experimentally studied in siblings raised from the larvae to the late fry stage both in the presence and absence of a predator. It has been found that the fry that was raised under different conditions differed in their adaptive potential in new environment conditions.     

Dynamics of structural indices of populations of zander Stizostedion lucioperca (Percidae) of the Rybinsk Reservoir for 1954–2010

Data on the age and size dynamics, linear and weight growth, and feeding of zander Stizostedion lucioperca collected in the Rybinsk Reservoir in 1954–2010 were generalized. The main factors determining the numbers of zander population and causing changes in its structural indices are the intensity of fishery and feeding conditions. Beginning from the mid-1990s, commercial load considerably exceeds the adaptation possibilities of the zander population; under the impact of this factor, its numbers declined, and the age structure changed towards the domination of individuals of junior ages. Introduction of the Black-Sea sprat Clupeonella cultriventris along with of climate warming led to negative changes in the populations of prey fish, as a result of which the proportion of their own juveniles increased in the feeding of adult zander. During recent years, zander fingerlings throughout summer cannot pass to predatory feeding, which leads to a decrease in the rate of linear and weight growth of mature individuals.     

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.     

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.     

Invasion of fish with leeches (Fam. Piscicolidae) in reservoirs of the Volga river

It is shown for the first time that during 50 years of the Rybinsk reservoir's existence the abundance of parasite leeches (Piscicolidae) has increased, and the species composition has become richer. In 70 the leech Caspiobdella fadejewi (Epstein) was registered here as a mass species. This species became a real competitor to Piscicola geometra (L.) inhabiting the Volga river in all times. In early '90s the leech Acipenserobdella volgensis (Zykoff) appeared in the Rybinsk reservoir. Till 1987 this species was not found to the north from the Kuibyschev reservoir. An increase in number of fish leeches and an extension of their specific composition occurred not only in the Rybinsk reservoir but in the other reservoirs of the Volga cascade as well.     

Peculiarities of the biology of two Diaphanosoma species (Crustacea,Cladocera) in Rybinsk Reservoir

The spatial distribution, long-term dynamics of occurrence and abundance, and the peculiarities of the seasonal cycle of two cladocerans, an alien species Diaphanosoma orghidani Negrea and a native species D. brachyurum (Liévin), were studied in Rybinsk Reservoir in 2005–2011. The successful coexistence of the species for over a 7-year period was favored by the differences in their seasonal cycles, the distributional pattern in the reservoir, the predator press, and the preference of the alien species to inhabit areas of running water where the native species was not numerous. Competitive advantages of the invader under conditions of global warming are discussed.     

Ruffe (Gymnocephalus cernuus L.) (Perciformes, Percidae) helminth fauna in Rybinsk Reservoir: Recovery following a depression in abundance of the host population

This paper deals with the recovery process of ruffe helminth fauna following a catastrophic decrease in the fish population of Rybinsk Reservoir. Mass mortality was observed in ruffe from 1997 to 1999. It led to a decrease in parasite species diversity. However, two to three years later about 60% of the former parasitic species had recovered. The reasons for ruffe mass mortality in a range of waterbodies are analyzed based upon literature data. Some regularities of such epizooties in ruffe are revealed. It is suggested that epizooties are due to some unknown viral or bacterial infection, which may be facilitated by a specific combination of several factors.     

Variation of food spectra of tube-nosed goby <Emphasis Type="Italic">Proterorhinus marmoratus</Emphasis> (Perciformes,Gobiidae)—a new species in the Rybinsk Reservoir

Size-age structure and food composition of tube-nosed goby Proterorhinus marmoratus in the Rybinsk Reservoir have been studied. It was shown that food spectra changed in the process of dispersal of this species over the water body and considerably vary during the season. In the period of naturalization, feeding of the tube-nosed goby is characterized by group specialization; the object of specialization is Gmelinoides. Having dispersed over the water body and naturalized, it manifested itself as a generalist; its food composition became diverse and was determined by the seasonal dynamics of the population and biomass of food items.     

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.     

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.     

Population characteristics of yellow catfish (Peltobagrus fluvidraco) along the longitudinal profile of Three Gorges Reservoir,China

The length–frequency and age distributions, condition factor (K), gonadosomatic index (GSI) and gastrosomatic index (GaSI) of yellow catfish (Peltobagrus fluvidraco) were studied at three sites along the 500‐km longitudinal profile of Three Gorges Reservoir. Across all three sites (dam, mid‐reservoir and upper reservoir), GSI increased from April through June, with peak values observed in May and June. Mean K and GSI for fish captured near the dam were significantly higher compared to mid‐reservoir or upper‐reservoir areas. The GaSI index showed no significant variations across sites. However, the length‐frequency histogram of yellow catfish in the more riverine upper reservoir was log‐normal and skewed towards larger (total length) fish, a pattern that was significantly different from mid‐reservoir or near‐dam habitats, where fish length data were normally distributed but at a smaller length mode. Age estimations using otolith sagittae revealed that the spawning population was dominated by fish from only two age‐classes (1 and 2). This study provides novel insight into population characteristics of fish along the substantial spatial scale of Three Gorges Reservoir. Given the irregular population size‐ and age‐structure and the fact that the species is currently commercially exploited, this population is believed to be susceptible to overfishing. Restricted harvesting during peak reproductive months is recommended and suggested that additional research is needed on recruitment and harvest dynamics of this species throughout Three Gorges Reservoir. Additional research is also required to determine whether the spike in K and GSI at lentic sites is a transient product of recent impoundment or an indicator of optimal hydrologic habitat for the species.     

Dynamics of structural parameters of populations of the bream <Emphasis Type="Italic">Abramis brama</Emphasis> (Cyprinidae) in Rybinsk Reservoir in 1954–2007

The data on age, size, and sex structure of the population, on the linear and weight growth of bream Abramis brama are generalized for the period of 1954–2007 in Rybinsk Reservoir. Analysis of dynamics of these parameters demonstrated that recently a high fishing intensity is both reflected on the size of the stock but also determines the changes in structural parameters of the bream population. At present, in the exploited stock of bream, the specimens of junior ages dominate. The part of specimens older than ten years, which previously made the bulk of catches, now compose not more than 10–15%. This resulted in a rather noticeable decrease of mean age and size in catches. The previously observed sex ratio, near 1: 1, shifted towards a significant prevalence of males. The age of the first spawning and of the fish spawning for the first time decreased. These changes indicate that the fishing load surpasses adaptational potential of bream.     

Seasonal variations of functional properties of hemoglobin and ionic environment in the Freshwater fish: An example of bream, <Emphasis Type="Italic">Abramis brama</Emphasis> (Cyprinidae)

The dynamics of hemoglobin affinity to oxygen, Bohr effect value, and concentrations of sodium, potassium, calcium and magnesium were studied in the bream, Abramis brama, erythrocytes of the Rybinsk reservoir during an annual cycle. The studied parameters were most variable during the fish reproductive period. On the basis of the original studies, as well as of some published data concerning physiological–biochemical parameters, it is suggested that the state of spawning is comparable to the state of stress. The relation between the seasonal dynamics of hemoglobin functional properties and the parameters of ionic environment is revealed.