Collapse of the native ruffe (<Emphasis Type="Italic">Gymnocephalus cernua</Emphasis>) population in the Biesbosch lakes (the Netherlands) owing to round goby (<Emphasis Type="Italic">Neogobius melanostomus</Emphasis>) invasion

We investigated the change in benthic fish communities in three artificial lakes of the Biesbosch area in the Netherlands between two time periods: before and after the invasion of round goby (Neogobius melanostomus). Native ruffe (Gymnocephalus cernua), the dominant species in benthic gillnet and littoral beach seining catches before the invasion, almost completely disappeared in all lakes only 2 years after the invasion. We found a significant increase in 0 + perch (Perca fluviatilis) and, in some lakes, pikeperch (Sander lucioperca) abundance in gillnet catches after invasion. In the post-invasion period, the 0 + fish community was dominated by perch, and the older fish community was dominated by round goby. The species richness of 0 + fish increased in the post-invasion period owing to the invasion of gobiids. However, it did not change for older fish between periods. Our results clearly show that, owing to a similar benthic lifestyle and high niche overlap, ruffe was the only species negatively influenced by the round goby invasion. The competitive superiority of round goby over ruffe is so strong that the once-dominant species of the overall benthic fish community collapsed after only a few years of coexistence.     

Fish assemblages in deep Italian subalpine lakes: history and present status with an emphasis on non-native species

We provide a comprehensive overview of the status of fish assemblages in eight Italian subalpine lakes using multiple data sources: historical records, standardised sampling and fishery catch statistics. Thirty-four fish species were recorded, twenty of which are native, seven introduced historically and another seven introduced recently. The number of fish species in individual lakes has increased by between 25 and 65% from 1855 to the present, with the increase being higher in the larger lakes. Non-native species contributed between 4.0 and 71.5% to standardised catches by numbers and between 4.8 and 65.1% by biomass. Roach Rutilus rutilus and pumpkinseed Lepomis gibbosus dominated electrofishing and benthic catches by number, while open-water catches were dominated by the coregonids European whitefish Coregonus lavaretus and gangfish Coregonus macrophthalmus. In terms of biomass, electrofishing catches were dominated by crucian carp Carassius carassius, largemouth bass Micropterus salmoides and wels catfish Silurus glanis, benthic catches were dominated by roach, European whitefish and crucian carp, and open-water catches by coregonids. Commercial fisheries are important ecosystem services provided by subalpine lakes, with their harvests now dominated by non-native species. To deliver effective biodiversity conservation and ecosystem services provision, the prioritisation of targets and interventions of management of non-native species is needed.     

New host species and new distribution areas of <Emphasis Type="Italic">Salmincola lavaretus</Emphasis> (Copepoda: Lernaeopodidae): A parasite of coregonid fishes of Siberia

Data on the infestation of certain fish species by the parasitic copepod Salmincola lavaretus are presented for the first time. The infested fish species included Bauntovsky whitefish (Coregonus baunti), an endemic species from the Maloye and Bolshoye Kapylyushi lakes; Siberian whitefish (C. pidschian) and Siberian cisco (C. sardinella) from Bolshoye Kapylyushi Lake and Baunt Lake, which belong to the Tsypo-Tsypikan lake system (the Lena River basin, Transbaikalia); and Teletsky whitefish (C. lavaretus natio smitti) from Teletskoe Lake (the Ob River basin). Previously, S. lavaretus had been described as a parasite of Baikal omul (C. migratorius) and Baikal whitefish (C. baicalensis) from Baikal. The taxons of S. longimanus complex (S. longimanus, S. l. sibirica, S. svetlanovi, and S. lavaretus)—parasites of nasal fossae of grayling and coregonid fishes—were registered in the lakes of the Lake Baikal basin (Lake Baikal and Khovsgol Lake), the Lena River, the Yenisei and the Ob rivers (the largest rivers of the Arctic zoogeographic province), and the Kobdo River (the Western Mongolian province). It was assumed that S. longimanus complex is more widely distributed in the water bodies of the Arctic zoogeographic province of the Palearctic.     

Distribution and some biological features of skate <Emphasis Type="Italic">Bathyraja parmifera</Emphasis> (Rajidae,Rajiformes) in the northwestern part of the Sea of Japan

In the northwestern part of the Sea of Japan, skate Bathyraja parmifera in catches of the bottom trawl occurs at depths of 40 to 830 m at the near-bottom temperature of 0.4–4.9°C. Throughout the year, the skate performs migrations within the continental slope and, in the feeding period, inhabits mainly the depth range of 300 to 500 m. Maximal average density of aggregations of B. parmifera is observed in waters of northern Primorye; minimal average density is observed in Peter the Great Bay and on the Yamato Bank. In catches, skates with a length of 17–130 cm and a weight of 0.5–18.8 kg are recorded; however, fish with a length of 80–115 cm dominate. Individuals with a length of up to 40 cm feed mainly on amphipods, and larger immature and adult individuals feed on decapods, cephalopods, and fish. The value of the daily ration of B. parmifera with its growth decreases from 2.4 to 0.9% of the body weight. Specific ecological features of B. parmifera are a cause of its considerable underfishing by the bottom trawl; therefore, the total resource of this species in the considered region may be at the level of maximal estimates obtained during surveys and comprise no less than 20000 t.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 1. Gadidae (cods) family

Biological features of the three common fish species, pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, and saffron cod Eleginus gracilis (Gadidae), have been studied using a 20-year dataset (1995?2015). These species inhabit the northwestern Bering Sea in the summer–autumn period and form the schoolings in Olyutorsky-Navarin region. The size–age parameters, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, of the fish caught by different sampling gear have been analyzed. Due to the construction peculiarities and catch efficiency of the different catching gear, the largest specimens are found in the setlines and snurrevads; the fish caught by the trawls are characterized by the smallest size. The body length and body weight of pollock is greater in the pelagic trawl catches compared to the bottom trawl catches. The abundant brood of Gadidae may well be tracked on the multiyear dynamics graphs reflecting the size distribution, as well as by the decrease of biological parameters of the fish. The studied species inhabit the vast growth areas, so smaller body size of them in the coastal waters may be a result of a high ratio of the young specimens there.     

Variability of Black and Caspian Sea sprat <Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Clupeidae) growth in the contemporary range

The size and age composition of the population of Black and Caspian Sea sprat Clupeonella cultriventris, as well as the variation of the growth of fish in the reservoirs of the upper reaches of the Volga, are reported and a comparative analysis of group and individual variability of fish growth within the native (Caspian, Azov, and Black seas) and contemporary (formed due to invasion) ranges is presented. The degree of variability and the asymmetry of sprat body length distribution have been shown to increase under the conditions of large population sizes, deficit of food, and slow growth. Variability was also elevated near the borders of the range of the species, notwithstanding the abundance of food. It is shown that invasion of sea walnut comb jelly Mnemiopsis leydi into the Azov and Caspian Seas had so undermined feed base of sprat, that it is not only decreased its abundance and fecundity but also slowed growth of the fish.     

Regulation of population numbers in the <Emphasis Type="Italic">Rana arvalis</Emphasis> frog according to the results of long-term observations on the same population

An analysis of the results of long-term stationary studies (1987–1996) on a Rana arvalis population showed that the mean body length and reproductive parameters of females increased with age. Significant interannual changes in body length and egg size (but not in fecundity and reproductive effort) were also accounted for by conditions of the warm season preceding the breeding season. The dependence of egg diameter and reproductive effort on the female body length weakened with age, and only the relationship between body length and fecundity was characterized by positive allometry. The survival rate of mature females depended on the premetamorphic survival rate and, therefore, was higher in earlier generations, in which the aquatic phase proceeded under more favorable conditions. The rate of reproduction (R ₀) decreased and, therefore, further population growth slowed down only after the initial abundance of the generation had reached a relatively high level. An increase in the initial abundance of the generation exerts a strong influence on R ₀ via a decrease in the survival of premetamorphic animals and, to a lesser extent, via a decrease in the body length and fecundity of tree-and four-year-old females. Changes in the annual abundance of breeding females in R. arvalis were more abrupt and less prolonged than those in the sympatric R. temporaria population. The holding capacity of the environment for the aquatic phase of the R. arvalis life cycle was higher than that for R. temporaria. Therefore, the population abundance of R. arvalis, compared to R. temporaria, was not subject to stringent negative feedback regulation dependent on the initial number of animals.     

The ichthyofauna of coastal waters southwest of Crimea in 2003–2004

The ichthyofauna of the narrow coastal zone of southwest Crimea in 2003–2004 was represented by 79 fish species belonging to 36 families. The structure of the species composition of eggs, larvae, and adult fish in these years indicated to its restoration in comparison with the late 1980s to early 1990s. The abundance of commercial fish increased: Engraulis encrasicolus ponticus, Trachurus mediterraneus ponticus, and Mullus barbatus ponticus. The quantity of migratory fish increased: Pomatomus saltatrix and Sarda sarda. The presence in winter catches of Trachurus mediterraneus ponticus and Pomatomus saltatrix indicated favorable conditions for their wintering off South Crimea. Appearance in catches of the fish of elder age groups is evidence of the restoration of their age structure. The competitor for food Mnemiopsis leydyi still influences the food resources of the fish and, thus, their survival. If they appear in plankton simultaneously, the abundance of larvae drastically decreases. The obtained data indicate to the vulnerability of coastal biocenoses to anthropogenous impact and to the necessity of monitoring of fish resources and of their protection.     

Biological features of common fish species in Olyutorsky-Navarin region and the adjacent areas of the Bering Sea: 3. Righteye flounders (Pleuronectidae)

Biological features of the seven abundant commercial species—the Pacific halibut Hippoglossus stenolepis, the Greenland halibut Reinhardtius hippoglossoides, the Alaska plaice Pleuronectes quadrituberculatus, the northern rock sole Lepidopsetta polyxystra, the yellowfin sole Limanda aspera, the flathead sole Hippoglossoides elassodon, and the Bering flounder H. robustus (Pleuronectidae)—have been studied for a 20-year period (1995?2015). These species are present in the northwestern Bering Sea in the summer–autumn season; they form the gatherings in Olyutorsky-Navarin region. The size-weight spectra of the fish caught by different fishing gear has been analyzed, the peculiarities of the linear growth and the weight gain, as well as the spawning period and scale and the spawning conditions, have been described. The largest halibut specimens have been registered in the bottom setlines and gill nets, while flounders were in snurrevad catches; the smallest specimens have been observed in trawl catches. The abundant year-class in most of the studied species is seen well on the long-term plots of the fish size spectra and is tracked by the decrease of their biological parameters. The species that demand vast growing grounds (Pacific halibut, Alaska plaice, northern rock sole, and yellowfin sole) are characterized by a smaller average body size of the fish sampled in the coastal waters due to the prevalence of the young specimens in this area.     

Species assignment and population genetic studies of Gran Paraná pejerrey (<Emphasis Type="Italic">Odontesthes</Emphasis> sp., Atheriniformes,Atherinopsidae) from La Plata Basin in South America

Since 2013, the pelagic zone of Upper Lake Constance (ULC) has been subject to a massive invasion of the non-native three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758). Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) were used to compare weight-at-age and abundance of pelagic whitefish for years before (1997–2012) and after the invasion (2013–2015). Growth and abundance of pelagic whitefish is shown to be heavily influenced by stickleback presence. Mean autumn weight-at-age of whitefish decreased by 33.3% after the invasion took place and a significant decline in autumn CPUE in otherwise unfished cohorts of the population was also recorded. The results imply direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth and survival, and predation of eggs and larvae, hampering recruitment. These observations coincide with a sharp decline in whitefish yield. In conclusion, this study shows that the invasion of stickleback has substantially altered the pelagic fish community of ULC, with severe consequences for commercial fisheries.     

Taxonomic status and origin of some ecological forms of whitefish <Emphasis Type="Italic">Coregonus lavaretus</Emphasis> (L.) from water bodies of Siberia

Molecular genetic analysis of some ecological forms of whitefish belonging to the Coregonus lavaretus (L.) complex from different water bodies of Siberia revealed a high degree of differentiation between them. On the basis of the analysis of the mitochondrial DNA protein-coding ND1 gene, it was demonstrated that the previously described ecological forms of C. anaulorum, Yenisei River whitefish, or Issatschenko’s whitefish (C. fluviatilis), and cisco-like whitefish from Lake Baunt were good biological species. Moreover, each ecological form was represented by a number of phylogenetic lineages, one of which was species-specific. The remaining lineages were characterized by the mitochondrial DNA of another whitefish species, usually, the most common in each geographic region. The results of genetic analysis demonstrated that the formation of modern ecological forms of Siberian pidschian-like whitefish was accompanied by natural introgressive hybridization. It is suggested that most of the modern pidschian-like whitefish species originated as a result of reticulate evolution.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 4. family sculpins (Cottidae)

Based on the materials of investigations conducted for 20 years (1995?2015), the features of biology of the common fish species of the family Cottidae from the northwestern Bering Sea are studied. These species are found during summer and fall in the waters of the Olyutorsky-Navarin region. The size–age parameters of the fishes collected with different fishing gears, as well as the features of their body length and body weight dynamics, spawning time, and spawning conditions, are described. The largest exemplars of shorthorn sculpin Myoxocephalus verrucosus and staghorn sculpins, armorhead sculpin Gymnocanthus galeatus and G. detrisus, are recorded in the catches of snurrevads, while the fishes caught in trawls are characterized by smaller size. Interannual variability of the size composition of the fish is related to the abundance of certain generations or to the fishery directed to different associations of sculpins. In the coastal waters, comparatively low average body size is usual for the majority of common sculpin species (with the exception of lords, yellow Irish lord H. jordani and Gilbert’s Irish lord H. gilberti) because of the dominance of juveniles.     

Specific Features of Morphology,Ecology, and Mitochondrial DNA Polymorphism of the Whitefish (<Emphasis Type="Italic">Coregonus lavaretus</Emphasis> L.) from the Keret’ River as a New Object for Artificial Propagation

The results of a study of the specific features of morphological and genetic polymorphism of the population of the anadromous White Sea common whitefish (Coregonus lavaretus L.) from the Keret’ River are presented. As assessed by its morphological features, the whitefish population of the Keret’ is homogenous. A comparison of the Keret’ whitefish with whitefish populations of both Europe and Siberia revealed clear differences. These differences relate first and foremost to the fish locomotion and orientation in space: body depth, length and positions of fins, and interorbital width. The characteristics of skull features (craniological analysis) of the White Sea whitefish are presented for the first time. The results of an analysis of the polymorphism of the ND1 fragment of the mitochondrial DNA confirmed an earlier suggestion about the mixed origin of the Keret’ River whitefish: the descendants of three different phylogenetic lineages were revealed in the population.     

Fatty acid composition of fish species with different feeding habits from an Arctic Lake

We compared the composition and content of fatty acids (FAs) in fish with different feeding habits (sardine (least) cisco Coregonus sardinella, goggle-eyed charr (pucheglazka) form of Salvelinus alpinus complex, humpback whitefish Coregonus pidschian, broad whitefish Coregonus nasus, boganid charr Salvelinus boganidae, and northern pike Esox lucius from an Arctic Lake. Feeding habits of the studied fish (planktivore, benthivore, or piscivore) significantly affected the composition of biomarker fatty acids and the ratio of stable isotopes of carbon and nitrogen in their biomass. The hypothesis on a higher content of eicosapentaenoic and docosahexaenoic acids in the fish of higher trophic level (piscivores) when compared within the same taxonomic group (order Salmoniformes) was confirmed.     

Interannual variation of linear-weight indices,age structure,and rate of growth of chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> and factors affecting it (the Bol’shaya River basin,western Kamchatka)

The interannual variation in the size-age composition and the rate of growth of autumnal chum salmon Oncorhynchus keta in the Bol’shaya River basin (western Kamchatka) was studied. Data of biological analysis and results of back calculations of the linear growth of O. keta were analyzed for the period of 1993 to 1999. Possible reasons of interannual changes in indices such as the numerical ratio of the main age groups (3+ and 4+), average values of the length and weight of spawners, and the linear growth of O. keta are discussed. It was established that the main factor responsible for the variation of the growth and dynamics of the O. keta population in the Bol’shaya River are the numbers of the western Kamchatka pink salmon O. gorbuscha.     

No effect of round goby <Emphasis Type="Italic">Neogobius melanostomus</Emphasis> colonisation on young-of-the-year fish density or microhabitat use

The round goby Neogobius melanostomus has recently invaded several major freshwater systems in Europe and North America. Despite numerous studies predicting an impact on native fish assemblages, few have attempted to demonstrate it. In this case study, we monitored the effect of N. melanostomus colonisation on abundance and habitat utilisation of both young-of-the-year (YOY) native fish and YOY western tubenose goby Proterorhinus semilunaris in a typical, medium-sized European river. Colonisation by N. melanostomus had no apparent effect on either native fish abundance and species richness or P. semilunaris abundance. Moreover, after colonisation, both native fish and P. semilunaris occupied similar niches (i.e. microhabitats) to those occupied before colonisation. While niche use of YOY N. melanostomus and P. semilunaris overlapped significantly, YOY native fish utilised different habitats from the gobiids. We suggest that N. melanostomus did not compete for resources with YOY fish in our study area due to lack of niche overlap and/or surplus resources. As N. melanostomus rapidly dominated the fish assemblage at our site, we further suggest that utilisation of an empty niche, rather than competitive superiority, was the main factor facilitating its success.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 2. Families Macrouridae,Clupeidae, and Osmeridae

Biological features of the four common fish species, giant grenadier Albatrossia pectoralis (Macrouridae), Pacific herring Clupea pallasii (Clupeidae), Pacific rainbow smelt Osmerus mordax dentex, and Pacific capelin Mallotus villosus catervarius (Osmeridae), were studied under the 20-year dataset (1995?2015). These species inhabit the northwestern Bering Sea in the summer–autumn period and form the schoolings in the Olyutorsky-Navarin region. The size–age parameters of the fish caught by different sampling gear, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, were analyzed. The largest specimens of giant grenadier, Pacific herring, and Pacific rainbow smelt were observed in the catches performed by the bottom setline and the gill nets; the smallest fish were found in the trawl catches. The body length and body weight of Pacific herring were larger in the pelagic trawls compared to the bottom trawls; an opposite pattern was observed for the Pacific capelin. The abundant year-class in the species with short life cycle (capelin and herring) is well tracked on the longterm plots of the fish body size; this is accompanied by the decrease of their biological parameters. Herring stock covers large growing grounds; smaller body size was observed for the herring grazing in the coastal waters; young specimens dominate here.     

Variation in growth performance of Ryukyu-ayu, <Emphasis Type="Italic">Plecoglossus altivelis ryukyuensis</Emphasis>, inferred from otolith analysis

Ryukyu-ayu (Plecoglossus altivelis ryukyuensis) is an amphidromous fish species that migrates between the sea and rivers over its one-year life span. Although growth performance during the early marine stage may affect growth in the later riverine stage of this species’ life cycle, no studies have specifically examined this relationship in P. a. ryukyuensis. In the present study, we reconstructed the growth trajectories of P. a. ryukyuensis individuals collected from the Yakugachi River, Amami-Oshima Island, Japan in 2016 (n?=?47) throughout their growth period in both the sea and river by using otolith analysis. Using this, we determined the age and body size of individuals at the time of their upstream migration, as well as their growth rates during the marine and riverine stages. Results showed that body size at upstream migration significantly affected body size at the riverine stage, indicating that juveniles with larger body size in the sea had better growth performance in the river. Individuals with higher growth rates during the marine stage tended to enter the river younger and at larger body sizes than those with lower marine growth rates. Our results demonstrated the close linkage between the growth performance in the sea and in rivers of P. a. ryukyuensis. This information will contribute to better understanding variations in growth patterns of this endangered species and potentially aid in its conservation.     

Comparison of age and growth performance of diploid and tetraploid loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis> in the Yangtze River basin,China

Diploids and tetraploids of the cyprinid loach Misgurnus anguillicaudatus coexist in many natural habitats in Asia. However, little is known about the biological and ecological differences between these two ploidy forms. We examined age, body size and growth rates of fish in a mixed ploidy population of M. anguillicaudatus in the Yangtze River basin in China. The sex ratios of both diploid and tetraploid M. anguillicaudatus were highly skewed toward females, who tended to be larger than males. The age distributions of the collected specimens clearly indicated that tetraploids lived longer than diploids. For example, we found a substantial number of tetraploids that were 5+ years old, while the oldest diploids were 4+ years old. Tetraploids were also longer and heavier than diploids for both sexes. Using the empirical body size and age data, we inferred the growth patterns of these fish with the von Bertalanffy growth function. The estimated asymptotic body lengths (L _∞) indicated that tetraploids could indeed achieve larger body sizes than diploids. This difference was partially due to the increased growth rate, as demonstrated by lower growth coefficient (K) and higher growth performance index (φ’). In sum, we show that tetraploid M. anguillicaudatus exhibited significantly increased longevity and superior growth performance compared to diploids. These differences may contribute to the ecological competitiveness of tetraploid M. anguillicaudatus, thus enabling them to coexist with diploids in certain ecological settings.     

Seasonal and interannual variation of ichthyoplankton off Mauritania

Changes of the quantitative and qualitative composition of ichthyoplankton off Mauritania (21–16° N) in different seasons of 1997–2008 are analyzed. In this area, pelagic eggs and larvae of over 120 fish species belonging to 71 families are recorded. In warm periods, the fish of the tropical fauna intensively spawn off Mauritania; round sardinella Sardinella aurita, West-African horse mackerel Trachurus trecae, and jack mackerel Caranx rhonchus are dominant. In cold periods, active spawning of fish belonging to the tropical fauna is recorded, the most abundant are European pilchard Sardina pilchardus, European horse mackerel Trachurus trachurus, and Atlantic mackerel Scomber japonicus. The spawning biomass of principal commercial fish species is calculated on the basis of the quantity of eggs laid by females. Environmental factors control fluctuations of abundance and distribution of ichthyoplankton in the considered region.