Tolerance of parr of Arctic charr, Salvelinus alpinus, to reduced dissolved oxygen concentrations

One year old pan Item Windermere (north west England) tolerated lower incipient lethal levels of oxygen [18 20 mg 1 ¹: 15 17% air saturation value (ASV)] at lower (5, 10°C) than at higher (15, 20°C) an elimation temperatures (2·2 2·4 mg 1 ¹ 22 25% ASV). Values were not significantly different for two races of charr in the lake and are amongst the lowest recorded for salmenid species.     

Racial differences in eggs and juveniles of Windermere charr, Salvelinus alpinus

At least four races of charr occur in Windermere, the largest natural lake in England: north basin and south basin autumn spawners, north basin and south basin spring spawners. This study examines racial differences between eggs and juveniles, and relates juvenile size and survival to egg size. There were no major differences between races for egg incubation times and the percentage of eggs hatching successfully, the latter being high (mean values 76–96%) with a negligible proportion of abnormal alevins (<0.8%). Although there were no significant differences in the lengths of the female parents, both eggs and alevins were significantly larger for the autumn spawners than the spring spawners. Size differences in alevins, especially live weight, were positively related to egg size but not female parent size. Mean percentage survival for juveniles attaining the independent feeding stage was higher for the progeny of autumn spawners (32%) than spring spawners (3%). Racial differences in the egg and alevin stages therefore appear to have a significant effect on subsequent survival, and could be ultimately responsible for the relatively small proportion of spring spawners (only 4–6%) in the Windermere population of charr.     

Lake enrichment and the status of Windermere charr, Salvelinus alpinus (L.)

All English populations of Arctic charr, Salvelinus alpinus (L.), are found in the Lake District (northwest England). There are at least four races of charr in Windermere, the largest lake in England; the North and South basins of the lake each contain two distinct races that spawn in autumn and spring respectively. The spring spawners in both basins probably represent less than 15% of the total population in the lake.
Changes in the population density of charr in the lake are described briefly and examined in relation to the trophic status of the lake. Other factors that could possibly affect the charr population are reviewed, especially the influence of climate change.     

How fish-helminth associations arise: an example from Arctic charr in Loch Rannoch

Three sympatric morphs of Arctic charr Salvelinus alpinus occur in Loch Rannoch, Scotland, and are identified by their differing head morphology and diet. These are small-headed benthic, large-headed benthic and pelagic morphs. Six species of endoparasitic helminth were found in the fish, but the morphs had different patterns of infection. Overall infections in pelagic charr were heavier than in large-headed benthics, which were in turn heavier than in small-headed benthics, even though benthic charr live longer than pelagics. Pelagic fish had high prevalences and intensities of pseudophyllidean tapeworms, the intermediate hosts of which are copepods. The prevalence and intensity of metacercariae of Diplostomum sp. (the intermediate hosts of which are snails) were high in the benthic morphs. The results are discussed in terms of the effects of ecological factors on transmission of helminth parasites to their hosts and the evolution of host-parasite associations.     

Growth backcalculations based on otoliths incorporating an age effect: adding an interaction term

An extension, including an age × length interaction, was developed for a recent model incorporating the age effect in the backcalculation of growth in length from otoliths. The interaction was demonstrated using empirical data from Arctic charr Salvelinus alpinus .     

Growth and Dietary Niche in Salvelinus Alpinus and Salvelinus Fontinalis as Revealed by Stable Isotope Analysis

Arctic charr, Salvelinus alpinus, and brook charr, Salvelinus fontinalis, inhabiting three lakes in the de la Trinité River and adjacent watershed, north shore, Gulf of St. Lawrence, were sampled in 1998. Arctic charr growth differed among lakes with the smallest fish coming from the largest lake. Arctic charr weight–length equation exponents were almost identical at all sample sites. Brook charr growth was also similar in all lakes. July stomach samples from Arctic charr consisted almost entirely of cladocerans in the largest lake, less so in the intermediate sized lake and were mostly aquatic insects in the smallest lake. Brook charr stomach contents were more varied and included fish. Carbon, nitrogen and sulphur stable isotope analyses (SIA) were used to provide a spatially and temporally integrated image of charr diets. SIA corroborated observed among-lake differences and similarities in species diets and suggested lake morphometry may influence measured results. The ¹⁵N signature in brook charr muscle increased with fork-length, as a result of a shift towards piscivory with size. The ¹⁵N signature in Arctic charr muscle tissue showed a significant negative correlation with fork-length in two of the studied lakes that appears related to dietary niche shifts. Results demonstrate the ability of SIA to detect dietary shifts otherwise unobservable from standard gut content analysis.     

Parasites of freshwater resident and anadromous Arctic charr (Salvelinus alpinus) in Greenland

Twenty-one metazoan parasite species were found in Arctic charr at three coastal sites in west Greenland, including Neascus sp. and the nematode Pseudoterranova decipiens , new records for Arctic charr. Twelve species are new records for Arctic charr in Greenland. The quantitative composition of the parasite communities varied, but the freshwater species ( Diphyllobothrium ditremwn, Eubothriutn salvelini, Proteocephalus longicollis, Crepidostotnutn farianis ) were usually numerically dominant, even in anadromous fish. The absence from Greenland of Mysidacea, Amphipoda, Ephemeroptera and Odonata excludes parasites requiring such organisms as intermediate hosts, including the cestode Cyathocephalus truncatus , nematodes of the genus Cystidicola , and freshwater acanthocephalans.     

A hermaphroditic Arctic charr from Loch Rannoch, Scotland

An individual Arctic charr from Loch Rannoch was found to contain a gonad the anterior portion of which consisted of ovarian tissue. This is an extremely rare condition in salmonid fish and in this instance is possibly the result of environmental contamination.     

Population structure, ecological segregation and reproduction in non-anadromous Arctic charr, Salvelinus alpinus (L), in four unexploited lakes in the Canadian high Arctic

Land-locked populations of Arctic charr in four lakes on Northern Ellesmere Island (80° N) were found to consist of two distinct sizes: 'dwarf' and 'normal' charr. Both groups attained sexual maturity but differed in appearance and habitat. The smaller fish, occupying the more marginal habitats, retained their parr-markings; the larger group had the general characteristics of smolts, being more silvery and without parr-marks. In their juvenile stages, the charr destined to attain the larger group were indistinguishable from members of the smaller group. Although fish in the larger group were capable of cannibalism, this was rarely observed. In general, the fish in the larger group were older than the smaller ones but great variation in size at a given age resulted in certain age classes containing representatives of both groups. The population structure varied considerably between lakes; a high proportion of 'normal' charr correlated well with a high growth rate in the first few years of development. It is postulated that the two groups live in dynamic equilibrium where the advantages of progenesis (retention of juvenile characters by adults) in the smaller type are traded against the larger proportion of the energy resources available to the larger type. The concept of heterochrony in an ecological setting is introduced.     

Infection of Salmincola edwardsii (Copepoda: Lernaeopodidae) in an age-structured population of Arctic charr—a long-term study

The parasite-host relationships between Salmincola edwardsii (Copepoda: Lernaeopodidae) and Arctic charr Salvelinus alpinus were studied in lake Takvatn, northern Norway, over an 8-year period. The infection levels were modest, with an overall prevalence of 16·1% and an abundance of 0·5 parasites fish⁻¹. Most of the infected fish (54·1%) had only one parasite attached, whilst only 4·3% had more than 10. In general, parasite infection increased with increasing age, and hence size of the fish. The increase was modest up to age 7, whereafter a steep increment in parasite burdens occurred. Within each age class there was little effect of either fish size, gender, maturation or choice of macrohabitat upon parasite abundance. There was also little year-to-year variation in infection of the different age classes, indicating a high degree of stability of the parasite-host interactions in this system. The infection levels exhibited seasonal changes, being lowest in early summer and highest during winter. The infection rates seemed to be related to seasonal and ontogenetic habitat shifts of the charr.     

Social rank and brain levels of monoamines and monoamine metabolites in Arctic charr,Salvelinus alpinus (L.)

Summary Dominance hierarchy was determined in 5 groups of juvenile Arctic charr (Salvelinus alpinus), each group consisting of 4 fish. Telencephalon and brain stem (remaining parts of the brain) were analyzed with regard to their content of monoamines and monoamine metabolites. No significant differences were observed in the concentrations of norepinephrine (NE), dopamine (DA), or serotonin (5-hydroxytryptamine, 5-HT) between fish with different social rank. However, the concentration of 5-hydroxyindoleacetic acid (5-HIAA), the principle metabolite of 5-HT, was significantly higher in subordinate fish, and a significant inverse linear correlation was found between 5-HIAA concentration and social rank (as measured by dominance index) in the brain stem. In the telencephalon the dominant fish had a significantly higher level of homovanillic acid (HVA), a major DA metabolite. These findings indicate a greater serotonergic activity, possibly associated with increased stress, as well as a lower dopaminergic activity, possibly associated with reduced aggression, in subordinate charr. The differences between dominant and subordinate fish could either be caused by social interactions or reflect innate individual differences in monoamine utilization, predisposing individuals for dominant or subordinate positions in the dominance hierarchy.Abbreviations DA dopamine - DI dominance index - NE norepinephrine - 5-HT serotonin (5-hydroxytryptamine) - 5-HIAA 5-hydroxyindoleacetic acid - 5-HTOH 5-hydroxytryptophol - HVA homovanillic acid     

Changes in brain serotonergic activity during hierarchic behavior in Arctic charr (Salvelinus alpinus L.) are socially induced

Summary The experiment was performed in two phases. During the first phase (phase 1) the dominance hierarchy was determined in 4 groups of Arctic charr (Salvelinus alpinus L.), each group consisting of 4 fish. Phase 2 was started by rearranging phase 1 fish into 4 new groups. Group 1 consisted of previously dominant fish and groups 2, 3 and 4 of fish that previously held rank 2, 3 and 4, respectively. After phase 2 telencephalon and brain stem were analyzed with regard to their contents of serotonin (5-hydroxytryptamine, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), the principle metabolite of 5-HT. No correlation was found between the social rank (measured as dominance index) during phase 1 and the brain serotonergic activity (measured as the ratio 5-HIAA/5-HT) determined after phase 2. However, most important, the 5-HIAA/5-HT ratio was significantly correlated with the last experienced social rank, i.e. that acquired during phase 2. These results shows that the difference in brain serotonergic activity between dominant and subordinate fish develops through social interactions. Further, we found that previous subordinate experience inhibited aggressive behavior, an effect which, in the light of available information on stress and 5-HT, could be related to the increase in brain serotonergic activity. We hypothesize that stress induces an increased serotonergic activity which in turn inhibits the neuronal circuitry which mediates aggressive behavior.Abbreviations 5-HT serotonin (5-hydroxytryptamine) - 5-HIAA 5-hydroxyindoleacetic acid     

Smolting characters in anadromous and resident Arctic charr, Salvelinus alpinus (L.)

Morphological differences, haematocrit value and chloride cells were examined in downstream migrating Arctic charr, Salvelinus alpinus (L.) from the Hals River, North Norway, and resident charr from Lake Storvann. Fish were classified as visual parr, silvery parr or smolt based on the degree of silvering and the Occurrence of lateral parr marks. On average, 47% of downstream migrating Arctic charr were classified as visual molts, but only 14% of the resident charr. Charr longer than 20 cm fork length were mainly classified as visual molts. Morphometrical analyses of body size and shape revealed that most of the variations could be explained in terms of variations in fork length. Length adjusted ratios of post-anal distances were significantly higher in migrating charr than in resident charr. The number of developed chloride cells, the cell nucleus diameter in the basin of secondary gill lamellae and blood haematocrit values were significantly higher among downstream migrating charr than in resident charr. However, morphological differences between anadromous and resident Arctic charr were not necessarily synchronized with the development of chloride cells.