The food of the grayling Thymallus thymallus (L.) of the River Lugg, Herefordshire

The examination of the stomach contents of 253 grayling from the River Lugg has provided some evidence of a possible depression of feeding activity during the summer months. The diet was varied but bottom food predominated, especially insect larvae, Crustacea and molluscs. Some surface foods were taken but plant material was rarely eaten. Substrate material, detritus and debris and even large pebbles were eaten, mainly in summer. Most seasonal variations in the diet could be related to variations in availability. Fish were not eaten but cyprinid and salmonid eggs were eaten at the appropriate season. In general, increasing amounts of larger food items were eaten by the older grayling.     

Diel pattern of first downstream post-emergence displacement in grayling, Thymallus thymallus (L., 1758)

The activity rhythm of emerging grayling, Thymallus thymallus , fry was studied under semi-natural rearing conditions, using special traps buried in the gravel. Emergence was mainly diurnal with a maximum in the first hours of daylight. Fry rested at the emergence site during the daylight and moved downstream at night, particularly during the first 3 hours of darkness. These results are compared with the known activity patterns of other salmonids.     

The distribution of perch, Perca fluviatilis L. throughout their first year of life in Llyn Tegid, North Wales

The distribution of 0+ perch, Perca fluviatilis L., in a lacustrine environment is described. Since the perch occupied many different habitats within the ecosystem throughout their first year of life a number of sampling techniques were required to sample the population. The early larvae and post larvae were planktonic and their distribution could be related to the effect of the winds. As soon as the young perch developed fins an inshore migration began. Virtually all the fish had completed this migration by the time they reached a total length of 19 mm but the majority of the population reached the shoreline before attaining this size. During June and August the 0+ perch formed large shoals around the shoreline especially in sheltered areas in water less than 3 m deep. At the end of August probably in response to falling lake temperatures the perch fry migrated into deeper water.     

Microsatellite data resolve phylogeographic patterns in European grayling, Thymallus thymallus, Salmonidae

The phylogeography of an endangered salmonid, European grayling (Thymallus thymallus), was studied based on analysis of 17 nuclear microsatellite DNA loci. In agreement with earlier mitochondrial DNA (mtDNA) studies, phylogenetic relationships of the populations suggested that northern Europe was colonized from two distinct Pleistocene refugia. Furthermore, microsatellites revealed highly supported grouping of mainland Swedish, Norwegian, Danish, German and Slovenian populations, suggesting that grayling from the northwestern and central Europe have descended from their southern conspecifics. The level of divergence between populations was substantial, even across short geographical distances. Although this was in part due to postglacial colonization patterns and contemporary barriers for gene flow, the high divergence estimates between hydrologically connected sampling locations implied efficient interpopulation reproductive isolation. Microsatellites revealed that the populations exhibited, on average, only 3.5 (+/-2.2) alleles per locus, indicating that T. thymallus has strikingly low levels of intrapopulation genetic diversity as compared with other freshwater fish species. Accordingly, as indicated by analysis of molecular variance (AMOVA), only 49.1-58.0% of the total grayling microsatellite diversity resided within populations. A latitudinal genetic diversity gradient, potentially resulting from glaciation-mediated founder events, was not evident. Alternatively, it is possible that grayling display limited dispersal behaviour/capability, leading to low long-term effective population sizes and, consequently, depauperate intrapopulation polymorphism. These findings have implications for conservation of T. thymallus. Importantly, they exemplify that microsatellites can be highly informative for intraspecific phylogeography studies dealing with substantial divergence scales.     

Structure of component parasite communities in the grayling, Thymallus thymallus L. (Salmoniformes, Thymallidae), and minnow, Phoxinus phoxinus L. (Cypriniformes, Cyprinidae), from the upper reaches of the Pechora River

A comparative analysis of parasite communities in the grayling and minnow has been performed. These communities differ in the number of constituent species and in the fact that the community of the minnow is dominated by one allogenic species, whereas that of the grayling usually has two dominants, both being autogenic species. The values of species diversity indices characterizing these communities are also different. Differences between the parasite communities of these fish species reflect the position of their hosts in the hydrobiocenosis. Species prevailing in both communities are classified as specialists, which is characteristic of parasite communities of the boreal-piedmont faunal complex. Both these communities consist of three species groups distinguished by their proportions in the total biomass, which indicates that parasitic communities are structured in a certain way and that the distribution of species in them is not random.     

Some observations on the food of the gwyniad Coregonus clupeoides pennantii Valenciennes of Llyn Tegid (Lake Bala), North Wales

The seasonal variations in the diet of adult gwyniad Coregonus clupeoides pennantii=C. lavaretus from Llyn Tegid, North Wales were studied. Stomachs were examined to determine fullness, volume and identity of contents.
A clear seasonal cycle in food intake was found. Feeding rates were low from January to April but increased during the summer (May-June) and remained at a high level until December. The period of low feeding intensity coincided with the time of spawning and the time of annulus formation of both scales and otoliths. The diet showed seasonal changes and two main periods were distinguished : December to July, when the fish fed mainly on bottom fauna, and August to November, when the diet included both bottom fauna and midwater and surface foods.
The gwyniad were shown to be opportunistic in feeding, the composition of the diet reflecting availability of food items rather than selective feeding on the part of the fish.     

Photographic identification of individual grayling, Thymallus thymallus, based on the disposition of black dots and scales

SUMMARY. The flanks of grayling are generally studded with black dots which vary in number. The number and position of these dots are well-defined for each individual and make it possible to identify each fish, in some cases, as when there are very few dots or none at all, it is necessary to make use of other features such as the general disposition of the scales.
The best method for recording these characters is by photographing each fish. When recaptured, a fish can be recognized by comparing photographs. The number and position of dots on their lines can be sorted by a computer. Ultimate confirmation is given by comparing the most likely photographs once they have been selected by the computer.     

Genetic variation of European grayling (Thymallus thymallus) populations in the Western Balkans

In order to elucidate genetic composition of European grayling (Thymallus thymallus) populations in the Western Balkans, the partial mitochondrial DNA (mtDNA) control region was sequenced and 12 microsatellite loci genotyped in 14 populations originating from tributaries of the Adriatic and Danube drainages. Eleven mtDNA haplotypes were found, one confined to the Adriatic clade, one to the Alpine group and the rest to the ‘Balkan’ grayling phylogenetic clade. Haplotypes from the Balkan clade were confined to the Danube drainage and constituted two groups: northern group with haplotypes found in the Slovenian part of the Danube drainage, and southern group, consisting from Bosnia–Herzegovina and Montenegro. Substantial genetic distance between northern and southern groups of haplotypes (0.75–1.8%) and well supported divisions within the northern group indicate very structured grayling population within the studied Danube basin that most probably did not evolve due to vicariance but rather as a consequence of multiple colonization waves that might have occurred during the Pleistocene. Furthermore, genetic distance of ~4% between Adriatic and Danube populations’ haplotypes, suggest that their separation occurred in mid-Pliocene. These findings imply a complex colonization pattern of the Western Balkans drainages. Microsatellite data also confirm high genetic diversity in Western Balkans populations of grayling (on average 7.5 alleles per microsatellite locus and H _exp 0.58). Limited stocking activities were detected based on microsatellites and mtDNA data. Regarding current knowledge of grayling phylogeography appropriate management strategies were proposed to preserve unique, autochthonous grayling populations in Western Balkan.     

Genetic assessment of spatiotemporal evolutionary relationships and stocking effects in grayling (Thymallus thymallus, Salmonidae)

Domestically reared introduced (or escaped) individuals can have detrimental genetic effects on the indigenous populations into which they are released. Consequently, numerous studies have attempted to estimate whether non-native specimens have contributed to the gene pool of wild populations. So far, the key limiting factor of such studies has been their lack of appropriate baseline genetic material. Here, microsatellite DNA analyses of historical scale samples and contemporary wild and introduced populations were used to assess spatiotemporal population structure and stocking effects among endangered Lake Saimaa (eastern Finland) grayling ( Thymallus thymallus , Salmonidae). Significant decreases in genetic differentiation were detected between wild and introduced populations since the commencement of stocking in 1986. Accordingly, up to 15% of the contemporary wild grayling were confidently identified to be of pure hatchery origin, and recent hybridization between the hatchery and indigenous individuals appeared likely. Despite these clear genetic imprints of stocking, the contemporary populations exhibited evolutionary relationships congruent with the sampling locations, and up to 73% of contemporary individuals were identified to be of pure indigenous origin. The use of historical baseline material should prove efficient for monitoring gene flow between domesticated and wild populations in other species also, e.g. salmonids, game animals and plants.     

Film and television in fishery research at Llyn Tegid (Bala Lake), Wales

A 35 mm Robot Royal camera and an electronic flash unit were used at 20–40 m depth in an attempt to identify fish shown on echo-sounder traces. No photographs were obtained. An 8 mm Eumig automatic electric-drive cine camera system was used with daylight at 2–8 m depth to test if the equipment served as a deterrent to the fish. Fish were filmed and their behaviour was unaffected by the presence of the equipment. A simple closed-circuit television system was used with daylight at 0–3 m depth. Low contrast, inherent in the particular equipment, prevented its use at greater depths. Meaningful observations of perch were possible. The use of television camera tubes sensitive to extremely low levels of daylight, and of infra-red sensitive tubes with an infra-red light source is briefly discussed. It is concluded that such systems might help to identify problems of netting technique and assist with observations of fish behaviour.     

The diet and growth of O-group flounder,Platichthys flesus (L.), in the River Dee,North Wales

Many O-group flounder, Platichthys flesus, live in the lower reaches of rivers in North West Europe; while there is extensive information on the niche that they occupy in estuarine and marine environments, little is known of their life in freshwater. The diet of O-group flounder in the Lower Welsh River Dee was studied by stomach contents analysis of diel and seasonal samples. The dominant prey were chironomid larvae and pupae, tubificid oligochaetes and cyclopoid copepods. There was little quantitative variation in diet temporally, although a weak crepuscular pattern of stomach fullness was shown. There was wide variation in length and weight in all months, but the mean values at age I were 60 mm and 2.9 g respectively.     

Enzyme activities in the blood plasma of grayling, Thymallus thymallus (Linn.), in the breeding season

Activities of alanine aminotransferase, aspartate aminotransferase, glutamate dehydrogenase and creatine kinase were determined in the blood plasma of grayling, Thymallus thymallus , in the pre-spawning, spawning and post-spawning periods. Enzyme activities increased to a maximum in the spawning period and then successively decreased, after spawning, to values close to the initial ones. Only in the case of aspartate aminotransferase did the increased activity level persist after spawning. The temporary but large increase in enzyme activity levels in the plasma of grayling appeared to be a natural and physiological phenomenon accompanying the spawning process.     

Trout in Llyn Alaw, Anglesey, North Wales. II. Growth

The annual and seasonal growth, length/weight relationship, changes in seasonal condition and specific growth rates of 17 types of trout in the newly flooded reservoir, Llyn Alaw, in Anglesey, North Wales, were investigated. Scales and length-weight data from 2076 trout caught by angling and netting during the first 4 years after impoundment were analysed to show the age, origins and growth of all fish both before and after flooding.     

Discriminating the impact of recent human mediated stock transfer from historical gene flow on genetic structure of European grayling Thymallus thymallus L.

Microsatellite markers were first used to partition individuals of European grayling Thymallus thymallus , from the Danube, Rhine and Main, and Elbe drainage systems into subpopulations and to estimate individual immigrant ancestries over the last few generations. Subsequently, the studied populations were 'purged' from recent immigrants and the proportions of evolutionary lineages within the 'purged' populations were re-estimated by applying mtDNA markers. The results confirmed a high level of admixture of the divergent mtDNA lineages ( i.e. natural secondary contact) in populations sampled at the contact zones of the drainages. In addition, a substantial amount of introgression was observed for several populations that were known to be affected by stocking of European grayling from different origins.     

Genetic differentiation of European grayling (Thymallus thymallus) populations in Serbia,based on mitochondrial and nuclear DNA analyses

Background

The structure and diversity of grayling (Thymallus thymallus) populations have been well studied in most of its native habitat; however the southernmost populations of the Balkan Peninsula remain largely unexplored. The purpose of this study was to assess the genetic diversity of Serbian grayling populations, detect the impact of stocking and provide guidelines for conservation and management.

Methods

Eighty grayling individuals were collected from four rivers (Ibar, Lim, Drina and Rzav). The mitochondrial DNA control region (CR; 595 bp of the 3''end and 74 bp of flanking tRNA) and the ATP6 gene (630 bp fragment) were sequenced for 20 individuals (five from each locality). In addition, all individuals were genotyped with 12 microsatellite loci. The diversity and structure of the populations as well as the recent and ancient population declines were studied using specialized software.

Results

We detected three new haplotypes in the mtDNA CR and four haplotypes in the ATP6 gene of which three had not been described before. Previously, one CR haplotype and two ATP6 gene haplotypes had been identified as allochthonous, originating from Slovenia. Reconstruction of phylogenetic relations placed the remaining two CR haplotypes from the River Danube drainage of Serbia into a new clade, which is related to the previously described sister Slovenian clade. These two clades form a new Balkan clade. Microsatellite marker analysis showed that all four populations are genetically distinct from each other without any sign of intra-population structure, although stocking of the most diverse population (Drina River) was confirmed by mtDNA analysis. Recent and historical population declines of Serbian grayling do not differ from those of other European populations.

Conclusions

Our study shows that (1) the Ibar, Lim and Drina Rivers grayling populations are genetically distinct from populations outside of Serbia and thus should be managed as native populations in spite of some introgression in the Drina River population and (2) the Rzav River population is not appropriate for further stocking activities since it originates from stocked Slovenian grayling. However, the Rzav River population does not represent an immediate danger to other populations because it is physically isolated from these.     

Component communities of parasites in the grayling Thymallus thymallus (L.) (Salmoniformes, Thymallidae) and the minnow Phoxinus phoxinus (L.) (Cypriniformes, Cyprinidae) from the Pechora River

Component communities of parasites of Thymallus thymallus and Phoxinus phoxinus are described. The communities differ in the number of species and in the number of dominate species, which is one in P. phoxinus and usually two in T. thymallus. In the first case the dominate species is allogenic, while in the second case dominate species are autogenic. Values of the species diversity indexes are also different for these communities. The differences between parasite communities of T. thymallus and P. phoxinus underline positions of these hosts in hydrobiocenose. Species specialists take first place in the parasite communities both of the hosts, that is characteristic for the parasite communities of the fishes from the boreal submountain faunistic complex. Parasite communities in both of the hosts consist of three groups of species discriminated by the ratio of their biomasses, that suggests forming of the groups by a coordination of the species biomasses.