Exercise,agonistic behaviour and food acquisition in Arctic charr,Salvelinus alpinus

Synopsis Although swimming is energetically costly, a number of studies on salmonid species have demonstrated increased growth rates in fishes forced to swim for prolonged periods at moderate speeds (typically 1–2 body lengths per sec). This suggests that additional energetic costs of swimming are more than met by alternative compensatory gains. The mechanisms underlying such effects are not fully understood. In this paper, we describe an experiment designed to examine one possible mechanism, namely a swimming-induced inhibition of aggression, with consequent beneficial effects on growth. The study used Arctic charr,Salvelinus alpinus, a species for which a positive relationship between exercise and growth has been clearly established. Using direct behavioural observations on small groups, we demonstrate that individuals displaying high levels of aggressive behaviour are able to monopolise access to food and that enforced swimming at a moderate speed (1 body length per sec) reduces the incidence of aggression although not the degree of monopolisation of food shown by aggressive individuals. These results suggest that the enhanced growth rates accompanying enforced swimming may reflect lower energetic costs of reduced aggressive activity rather than improved access to food by subordinates.     

Ascorbic acid status in high-mountain charr,Salvelinus alpinus,in relation to the reproductive cycle

Synopsis Concentrations of total and dehydroascorbic acids and of glutathione were determined in tissues of male and female Arctic charr at different stages of the reproductive cycle. In fish inhabiting an Alpine lake (2344 m above sea level) the ascorbic acid concentrations were significantly higher in the ovary (344 g g^–1 in August) than in the testis (62.6 g g^–1). The ascorbate concentration was significantly higher in liver and kidney of males than in females in the period prior to spawning. This suggests that there was an intensive investment of body ascorbate reserves in the ovary and the results indicated that females deposited approximately 10 times the amount of vitamin C in ovaries than males deposited in testes. However, the endogenous stores cannot account for all ascorbate deposited in ovaries and the remainder must come from food consumed in summer. Since the resident charr of the high-mountain lake had the ascorbate concentration in ovary by one order of magnitude higher than in cultured salmonids it is plausible to speculate that the change in ascorbic acid metabolism reflects the adaptation to the harsh environmental conditions.     

Segregation in spawning and early life history among polymorphic Arctic charr, Salvelinus alpinus, in Thingvallavatn, Iceland

The relationships among time of spawning, incubation temperature, timing of first feeding and early growth were examined in four sympatric morphs of Arctic charr in Thingvallavatn, Iceland. Large benthivorous charr spawn in July-August at sites with cold ground-water flow. Planktivorous and piscivorous charr spawn in September-November and are not confined to ground-water sites. The spawning of small benthivorous charr overlaps with that of other morphs. Progeny of large benthivorous charr start feeding 2-3 months earlier than the progeny of autumn spawners. This results in differential size distribution and growth rates of young in the spring.     

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.     

Experimental evidence of cannibalism and prey specialization in Arctic charr,Salvelinus alpinus

Synopsis Use of a radiographic technique enabled the study of prey selection and individual specialization in Arctic charr, Salvelinus alpinus, fed with small charr and dry pellets under laboratory conditions. Both naive and experienced fish (mean weight 475 g, mean length 34.9 cm), selected the smallest individuals when offered juvenile charr (6–16 cm) as prey. The selected prey were, on average, 22% of the predator length. Cannibalism appeared to involve individual specialization, since when groups of large charr were given the opportunity to feed on juveniles one day every two weeks, the same individuals were cannibalistic throughout the sampling period of two months. When large charr were presented with alternate cycles of different food types consisting of dry pellets and fish prey, the charr exhibited a strong and consistent feeding specialization with three distinct groups being recognised: cannibals, pellet eaters and non-feeding fish.     

Genetic differentiation among local populations and morphotypes of Arctic charr, Salvelinus alpinus

The systematica of coexisting morphotypes of Arctic charr, Salvelinus alpinus , has been a matter of dispute ever since the days of Linnaeus. Widespread allelic variation at an esterase locus has led some investigators to propose that the morphotypes reflect a complex of at least three sibling species. We tested this hypothesis by examining 42 electrophoretically detectable loci in natural and transplanted charr populations from 15 localities in S Norway. The absolute values of Nei's genetic distance between morphotypes and populations are small (typically in the order of 0.001), and morphotype changes may occur without accompanying changes in frequencies of esterase alleles. Differentiation among localities explains far more of the total gene diversity than differences between morphotypes in the four cases of naturally occurring sympatric morphotypes examined. The data are consistent with an intraspecific population structuring based on locality, and the multiple species hypothesis is rejected.     

The effect of stocking density on the behaviour of Arctic charr (Salvelinus alpinus L.)

Recent studies have demonstrated that Arctic charr ( Salvelinus alpinus ) exhibit higher growth rates when held at high stocking densities. It has been argued that these increased growth rates are a result of decreased social interactions at the increased densities. The current study was designed to test this hypothesis by examining: (1) the frequency of agonistic interactions, (2) the proportion of time spent swimming and (3) growth rates among groups of young of the year Arctic charr held at different stocking densities. It was found that charr reared at higher densities exhibited significantly higher mean weights and lengths than those at the lower densities. The behavioural observations revealed that charr initiated significantly fewer agonistic interactions and spent a significantly greater amount of time shoaling at high densities than charr held at the medium or low densities. It is argued that these behavioural responses may serve to lower energy expenditures, resulting in the increased growth rates.     

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.     

Seawater acclimation of diploid and triploid brook charr (Salvelinus fontinalis), diploid Arctic charr (Salvelinus alpinus), and their diploid and triploid hybrids

Seawater acclimation of diploid (FF) and triploid (F2F) brook charr Salvelinus fontinalis , diploid (AA) Arctic charr Salvelinus alpinus , and diploid (FA) and triploid (F2A) hybrids between female brook charr and male Arctic charr was investigated. Triploidization of brook charr and the hybrid did not have any effect on the acclimation. Seawater acclimation of the hybrid was achieved during the experimental period and was comparable to that observed in brook charr. Acclimation could not be ascertained in Arctic charr since the level of cortisol, a stress indicator, was still high at the end of the experiment. No relationship between either length or condition factors and plasma osmolality was observed. Elevated plasma cortisol concentrations in Arctic charr and in diploid or triploid hybrids, both in fresh water and sea water, indicate more favourable rearing conditions for brook charr.     

Salinity tolerance of freshwater acclimated, small-sized Arctic charr, Salvelinus alpinus from northern Labrador

Arctic charr, Salvelinus alpinus , less than 150 mm in size were frequently captured at sea in northern Labrador in areas where salinities of 30‰ or higher had been recorded. These captures were inconsistent with many earlier reports for other areas that indicated Arctic charr less than 150 mm in size were not found at sea. A series of salinity challenge tests was carried out in the field, using wild Ikarut River charr, and in the laboratory, using cultured Fraser River charr, to understand more about the potential fate of these small fish. The results of challenge tests with small Arctic charr (< 120 mm) indicated that at intermediate salinities (10–20‰), these fish can readily survive. In laboratory tests with salinities at 30‰, survival was size dependent and would suggest that in natural situations, small charr would require periodic access to fresh or brackish water to stay alive. The influence of water temperature on salinity tolerance may be important when fish are exposed to temperatures that are below 0° C.     

Microprobe analyses of anadromous Arctic charr, Salvelinus alpinus, otoliths to infer life history migration events

Otoliths of Arctic charr, Salvelinus alpinus, from north Labrador were examined to gather life history information pertinent to anadromous migrations. Wavelength dispersive electron microprobe measurements confirm the presence of strontium in otolith tissue. Trace element analyses of charr otoliths imply that otolith strontium/calcium concentration ratios are related to external environmental factors with salinity having a great influence. Otoliths clearly record habitat shifts consistent with migration across major salinity boundaries. Most charr first migrate to sea following at least 2 years in freshwater. Generally, when anadromy begins, it continues annually. Robust relationships in otolith chemistry, combined with macrostructure patterns in field-captured specimens, provide time-series data describing individual migrational histories. Validation studies are still required in order to couple information contained within daily increments with chemical analyses to infer additional temporal events in diadromous migrations. Received: 6 November 1996 / Accepted: 18 May 1997     

Mitochondrial DNA analysis of Scottish populations of Arctic charr, Salvelinus alpinus (L.)

Mitochondrial DNA analysis of a total of 82 individuals from seven Scottish populations of Arctic charr ( Salvelinus alpinus L.) using restriction fragment length polymorphism and direct nucleotide sequencing of the cytochrome b gene revealed little variation within or between populations. One of 19 restriction enzymes showed a polymorphism that was present in three of the seven populations. Only one nucleotide substitution was detected in a 288 base pair segment of the cytochrome b gene examined in 26 fish. Approximately 4% of the mitochondrial genome was surveyed with these complementary procedures.     

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.     

Genetic analysis of four sympatric morphs of Arctic charr,Salvelinus alpinus,from Thingvallavatn,Iceland

Synopsis The degree of genetic differentiation among four morphs of Arctic charr (small benthivorous, large benthivorous, piscivorous, and planktivorous) from Thingvallavatn, Iceland, was determined electrophoretically. Five of 36 enzyme loci were found to be polymorphic (Est2, Gpi3, Ldh4, Mdh4, 5 and Pgm2). However, only Est2 and Mdh4,5 showed enough variability to permit statistical analysis of divergence among morphs. All four morphs are very closely related; the values of Nei's (D) range from 0.00004 to 0.00126. These morphs are conspecific and do not represent different evolutionary lineages. There is significant genetic differentiation between the small benthivorous charr and the other three morphs. The relative relatedness of morphs based on gene frequency data is only partially concordant with that based on morphology and ecological specialization. The biological significance of this result is unclear because of the limited number of polymorphic loci upon which the genetic analysis is based and the high degree of relatedness among morphs.     

Effects of food quality on maturation rate in Arctic charr, Salvelinus alpinus (L.)

The effects of food quality on maturation rate were followed in progeny from wild Arctic charr, caught in Lake Fattjaure, northern Sweden. The fish were reared at five different food quality levels. In the first summer, the fry were given feed of three qualities: diluted with cellulose in three proportions (0, 15 and 25%). During the second winter the impact of changed food quality level was studied by transferring half the fish from the high (control) to the low food quality level and vice versa.
Maturation rate was lower in males reared at the high and improved food quality levels than in males reared at the medium, low and reduced food quality levels. The maturation rate in females was similar at all levels, though the rate tended to increase at the reduced food quality level.
Fish reared at the high and medium levels had similar growth rates, whereas fish at the low food quality level experienced slower growth. Reduced food quality did not arrest the growth offish, whereas improved food quality enhanced their growth.     

Effect of feeding frequency on food intake and growth of Arctic charr, Salvelinus alpinus L.

Social interactions and dominance hierarchy effects are important factors governing rates of growth of Arctic charr, Salvelinus alpinus L. The effects of hierarchy were increased as access to food became more restricted, i.e. feeding frequency was reduced, but these effects could not be attributed to direct competition for food since fish were fed to satiation at each feeding period. The results suggest that, whilst some fish on the restricted feeding regime were able to maintain good rates of growth, feeding by the majority of the fish was inhibited by the presence of larger individuals. Due to the importance of these hierarchy effects it was not possible to demonstrate physiological adaptations in fish allowed infrequent access to food.     

The cultural importance and international recognition of the Arctic charr Salvelinus alpinus populations of Windermere,UK

The Arctic charr Salvelinus alpinus populations of Windermere, England’s largest natural lake in the Lake District of north-west England, have been studied since the 1940s. However, the species’ cultural importance has a much longer history and these populations have been fished since 1223. As early as 1660, Arctic charr were exploited in a high-profile commercial net fishery and greatly enjoyed by locals and in a ‘potted’ form by wealthier members of UK society. However, overfishing led to substantially decreased catches and commercial netting was stopped in 1921. Local fishing for Arctic charr persists to the present as a small recreational plumb-line fishery using artificial lures. These fishing activities and resulting catches have long held great cultural interest for the local community and visiting national and international tourists. The cultural importance of the Arctic charr populations of Windermere has recently been the subject of national media interest that culminated in a 2017 documentary film highlighting environmental issues facing the Arctic charr and also celebrating the role of this iconic species in the cultural life of Windermere. In addition, international recognition of the Arctic charr populations of Windermere also contributed to the Lake District becoming a UNESCO World Heritage Site in 2017.

     

Reproduction and development in the dwarf form of Arctic charr Salvelinus alpinus from Lake Davatchan, Transbaikalia

Biological characteristics in the deepwater dwarf form of Arctic charr Salvelinus alpinus from Lake Davatchan, Transbaikalia, are described. In nine from fifteen attempts of artificial insemination of eggs from a female by sperm from a male, developing eggs are obtained. Embryonic and larval development is described at the initial temperature 1.6–3.6°C and subsequent (from early gastrulation to the transition of larvae to exogenous feeding) average temperature 4.4 and 8.6°C. To take into account the data obtained previously (Pavlov et al., 1990, 1993b), the comparison of early ontogeny is conducted between the dwarf and small forms of charr from Lake Davatchan and the charr from Lake Leprindokan (two lakes are separated by the ridge 8 km in width). A substantial similarity in early ontogeny between the dwarf and small forms of charr from Lake Davatchan suggests that genes controlling development of the embryos and prelarvae until the transition of the young to exogenous feeding have not been subjected to natural selection determining a considerable differentiation between two forms and their reproductive isolation. Published in Voprosy Ikhtiologii, 2008, Vol. 48, No. 1, pp. 102–119. The article was translated by the author.     

The Relationship between Egg Size and the Rate of Early Development in Arctic charr, Salvelinus alpinus

Previous studies have found no consistent relationship between egg size and the rate of development in fish. This is surprising since there are several hypothesis as to why such a relationship should exist. By using eggs from Arctic charr, Salvelinus alpinus, we examined several developmental features repeatedly on live individuals. In all measured parameters except date of hatching, embryos from smaller eggs were found to develop faster. Time of hatching has often been used as a principal measurement for rate of development in fish, but our results suggest that this should be discontinued, since it is poorly correlated with the rates of development of other early life history features.     

Influence of body weight and temperature on growth rates of Arctic charr, Salvelinus alpinus (L.)

When reared for a period of 6 months at a temperature of 10°C Arctic charr, Salvelinus alpinus , increased in weight from 18 g to approximately 135 g. Specific growth rates decreased as the fish increased in size and the relationship between size and growth rate could be described by the equation:
where G _w is specific growth rate and W is fish weight in grams. Temperature effects upon growth were examined using previously published data. Below the optimum growth temperature, the growth rate of a fish of given size could be predicted using the equation:
where T is the rearing temperature.
Rates of growth of Arctic charr were as high as those reported for other salmonid species reared under similar conditions. Preliminary results suggested that growth rates of charr may be lower in salt water than in fresh water.