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.     

Density‐dependent diel activity in stream‐dwelling Arctic charr Salvelinus alpinus

Intraspecific competition plays a significant role in shaping how animals use and share habitats in space and time. However, the way individuals may modify their diel activity in response to increased competition has received limited attention. We used juvenile (age 1+) Arctic charr Salvelinus alpinus to test the prediction that individuals at high population density are more active and distribute their foraging activity over a greater portion of the 24‐h cycle than individuals at low population density. Individually tagged fish were stocked in seminatural stream enclosures at low (2 fish/m²) and high (6 fish/m²) density. During each of two 2‐week experimental rounds, activity of all fish within each enclosure was recorded every 3 h over seven 24‐h cycles. At high density, fish were more active and distributed their activity over a greater portion of the 24‐h cycle, with increased activity particularly at crepuscular times. Fluctuations in ecological conditions (e.g., water temperature and light intensity) also affected activity. Fish at high density grew as fast as fish at low density. This study demonstrates that individuals exhibit a degree of behavioral flexibility in their response to changes in ecological conditions and suggests that intraspecific competition can cause animals to modify temporal aspects of their activity to gain access to resources and maintain growth.     

Allometric trajectories of body and head morphology in three sympatric Arctic charr (Salvelinus alpinus (L.)) morphs

A study of body and head development in three sympatric reproductively isolated Arctic charr (Salvelinus alpinus (L.)) morphs from a subarctic lake (Skogsfjordvatn, northern Norway) revealed allometric trajectories that resulted in morphological differences. The three morphs were ecologically assigned to a littoral omnivore, a profundal benthivore and a profundal piscivore, and this was confirmed by genetic analyses (microsatellites). Principal component analysis was used to identify the variables responsible for most of the morphological variation of the body and head shape. The littoral omnivore and the profundal piscivore morph had convergent allometric trajectories for the most important head shape variables, developing bigger mouths and relatively smaller eyes with increasing head size. The two profundal morphs shared common trajectories for the variables explaining most of the body and head shape variation, namely head size relative to body size, placement of the dorsal and pelvic fins, eye size and mouth size. In contrast, the littoral omnivore and the profundal benthivore morphs were not on common allometric trajectories for any of the examined variables. The findings suggest that different selective pressures could have been working on traits related to their trophic niche such as habitat and diet utilization of the three morphs, with the two profundal morphs experiencing almost identical environmental conditions.     

The lipid composition of two species of serrasalmid fish in relation to dietary polyunsaturated fatty acids

The lipid composition of two species of Serrasalmid fish with different natural feeding habits were compared in relation to the polyunsaturated fatty acids (PUFA) supplied in their diets. Mylossoma aureum , a herbivorous piranha, was maintained on oatmeal flakes in which : 2(n-6) and : 3(n-3) were the only PUFA and accounted for 40–8 and 1.2%, respectively of dietary fatty acids. Serrasalmus nattereri , the carnivorous red piranha, was fed mosquito larvae containing .0-33.4% of their total fatty acids as : 2(n-6)+18 : 3(n-3) and 4.9-8.5% as 20 : 4(n-6)+20 : 5(n-3). The two species had similar lipid class compositions in liver, brain, viscera and carcass, except that lipids from M. aureum were generally richer in triacylglycerols. In both species, visceral and carcass lipid contained high levels of triacylglycerols whose principal PUFA was : 2(n-6). In M. aureum the major PUFA in liver total lipid and triacylglycerols was : 2(n-6) whilst the major PUFA in liver phospholipids were : 4(n-6) and : 5(n-6), with : 6(n-3) being a minor component. The level of : 6(n-3) in ethanolamine glycerophospholipids was significantly greater in brain than liver of M. aureum. Although absent from dietary lipid, : 6(n-3) was the major PUFA in phosphatidylcholine and ethanolamine glycerophospholipids from both the liver and brain of S, nattereri . In both species, the ratio of (n-6)/(n-3)PUFA was consistently lower in tissue lipids than in dietary lipids. The results are consistent with (i) the herbivorous M. aureum converting dietary C18 PUFA to their C20 and C22 homologues, (ii) the carnivorous S, nattereri forming : 6(n-3) from either 18:3(n-3) or 20: 5(n-3) and (iii) both species selectively desaturating and elongating (n-3) rather than (n-6) PUFA.     

Anaesthetization of Arctic charr Salvelinus alpinus (L.) with tricaine methanesulphonate or 2-phenoxyethanol for immediate blood sampling

Anaesthetization of Arctic charr Salvelinus alpinus with tricaine methanesulphonate or 2-phenoxyethanol did not alter plasma protein, glucose, free amino acid, non-esterified fatty acid, ion or osmolality levels, suggesting that their use allows for the normal determination of these plasma variables.     

Lipid‐rich zooplankton subsidise the winter diet of benthivorous Arctic charr (Salvelinus alpinus) in a subarctic lake

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Metabolic effects of intravenous LCT or MCT/LCT lipid emulsions in preterm infants

Most lipid emulsions for parenteral feeding of premature infants are based on long-chain triacylglycerols (LCTs), but inclusion of medium-chain triacylglycerols (MCTs) might provide a more readily oxidizable energy source. The influence of these emulsions on fatty acid composition and metabolism was studied in 12 premature neonates, who were randomly assigned to an LCT emulsion (control) or an emulsion with a mixture of MCT and LCT (1:1). On study day 7, all infants received [13C]linoleic (LA) and [13C]alpha-linolenic acid (ALA) tracers orally. Plasma phospholipid (PL) and triacylglycerol (TG) fatty acid composition and 13C enrichments of plasma PL fatty acids were determined on day 8. After 8 days of lipid infusion, plasma TGs in the MCT/LCT group had higher contents of C8:0 (0.50 +/- 0.60% vs. 0.10 +/- 0.12%; means +/- SD) and C10:0 (0.66 +/- 0.51% vs. 0.15 +/- 0.17%) than controls. LA content of plasma PLs was slightly lower in the MCT/LCT group (16.47 +/- 1.16% vs. 18.57 +/- 2.09%), whereas long-chain polyunsaturated derivatives (LC-PUFAs) of LA and ALA tended to be higher. The tracer distributions between precursors and products (LC-PUFAs) were not significantly different between groups. Both lipid emulsions achieve similar plasma essential fatty acid (EFA) contents and similar proportional conversion of EFAs to LC-PUFAs. The MCT/LCT emulsion seems to protect EFAs and LC-PUFAs from beta-oxidation.     

Mitochondrial DNA diversity among four sympatric morphs of Arctic charr, Salvelinus alpinus L., from Thingvallavatn, Iceland

Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were examined in progeny of four sympatric morphs of Arctic charr ( Salvelinus alpinus L.) from Thingvallavatn, Iceland. The mtDNA analysis with 46 hexanucleotide restriction enzymes indicates that the Thingvallavatn morphs are very closely related. Sequence divergence was less than 0.2% between any of the five clones detected. Although not significant, the topology of the mtDNA UPGMA dendogram was similar to that from a previous allozyme survey. Icelandic Arctic charr show greater affinity to charr from the British Isles than those from North America supporting their current taxonomic distinction.     

Phenotypic variation in growth trajectories in the Arctic charr Salvelinus alpinus

Animals with determinate growth have shown little variation in individual growth patterns, but similar analyses for animals with indeterminate growth have been lacking. We analysed the amount of phenotypic variation in growth patterns across ages among individuals of a hatchery-based population of Arctic charr, Salvelinus alpinus, Salmonidae, using the infinite-dimensional model and including the effects of group size structure. There was little phenotypic variation in growth trajectories: individuals that were small (in relation to the mean) early in life were among the smallest 2.5 years later. If the genetic variation reflects phenotypic variation, not much evolutionary change can be expected. Our results show that there are ecological conditions that determine the strong covariation of size across ages, most likely size-related dominance behaviour, which can mask the true variation of growth patterns. Thus, social interactions can have strong evolutionary effects on traits not directly involved in the behavioural interactions.     

Behaviour,physiology and carotenoid pigmentation in Arctic charr Salvelinus alpinus

The behaviour during an exploration task and the response to a confinement stress of Arctic charr Salvelinus alpinus were evaluated. Behaviour of individuals during 90 min of exploration was classified into high and low activity. High‐activity individuals had higher plasma cortisol levels following stress compared to low‐activity individuals. This indicates that high‐ and low‐activity individuals correspond to reactive and proactive stress‐coping styles. Further, a pigmentation analysis showed that high‐activity individuals had a higher number of carotenoid spots cm^?2 than low‐activity individuals. Thus, carotenoid pigmentation, as melanin pigmentation in other salmonids, could be linked to stress‐coping style in S. alpinus.     

Do northern riverine anadromous Arctic charr Salvelinus alpinus and sea trout Salmo trutta overwinter in estuarine and marine waters?

By use of acoustic telemetry, the present study showed that both riverine anadromous brown trout (sea trout) Salmo trutta and Arctic charr Salvelinus alpinus in a north Norwegian river descended the river within the first 4 months after spawning in late September and spent long parts of the remaining winter period in the estuary and also possibly partly in salt water. This contradicts the general assumption, based on studies of lake‐dwelling populations, that both species, and in particular S. alpinus, overwinter and spend 9–11 months in fresh water at northern latitudes and the rest of the year in salt water.     

Temperature effect on the immune defense functions of Arctic charr Salvelinus alpinus

The Arctic charr Salvelinus alpinus is an endangered fish species in Finland, and thus farming is carried out mainly for stocking purposes. Farmed charr are susceptible to infection with atypical Aeromonas salmonicida (aAS). Losses of valuable brood stock will severely reduce the genetic diversity of stocked charr. No commercial vaccines are available to prevent aAS infection, and vaccines against furunculosis (caused by typical A. salmonicida, tAS) do not protect the charr against aAS infection. The effects of a metabolizable oil-adjuvanted, bivalent vaccine (containing killed aAS and A. salmonicida salmonicida bacteria) on the immune system of 1 yr old hatchery-reared charr originating from Lake Inari in Northern Finland were examined. Fish vaccination in Finland generally takes place either from October to November or from February to April, when the water temperature is low (1 to 3degrees C). The water temperature starts to increase in mid-May. Therefore, we also investigated whether post-vaccination (p.v.) temperature had an influence on the immune system of this cold-water fish species. The fish were immunized intraperitoneally at 2.9 degrees C at the end of April. After 52 d, during which the water temperature increased from 2.9 to 10.0 degrees C, the charr were exposed to 1 of 3 test temperatures: 10.3, 14.1 or 18.1 degrees C. Prior to vaccination, and 49, 75 and 103 d p.v., several immune parameters were measured in both unvaccinated and vaccinated charr. Vaccination induced a significant anti-aAS-specific antibody response, and increased plasma lysozyme activity at all p.v. temperatures. The haemolytic activity of the complement system was unaffected either by vaccination or p.v. temperatures. There was a slight positive correlation between p.v. temperature and lysozyme activity of the charr. The significant increase in lysozyme activity took place in vaccinated charr in the first 49 d p.v. as water temperatures increased from 2.9 to 10 degrees C. Furthermore, the highest activity of lysozyme in the plasma was observed 49 d p.v. Our results indicate that a rise in water temperature above 10 degrees C does not significantly enhance the vaccination response of charr. This could be one reason why farmed Arctic charr, which are well adapted to a cold climate, are highly susceptible to aAS infection in the summer.     

Dietary manipulation with high marine fish oil intake of fatty acid composition and arachidonic acid metabolism in rat cerebral microvessels

Male weanling Wistar rats were maintained on one of two semisynthetic diets, differing only in the type of oil used: (i) 10% by weight marine fish oil (MFO group) containing 20% eicosapentaenoic acid (EPA) and 17% docosahexaenoic acid (DHA), or (ii) 10% by weight sunflower oil (SFO group). The control group was kept on standard diet for 4 weeks. Blood-free microvessels were isolated from brain cortex by a rapid micromethod, and their fatty acid composition was determined by gas chromatography. It was found that the proportion of n-3 fatty acids (including EPA and DHA) increased significantly in the microvessels of the MFO group, accompanied by a decrease of the n-6 fatty acid series. The changes in fatty acid composition of endothelial cells were not significant in the SFO group in comparison to the control. The amounts of lipoxygenase and cyclooxygenase metabolites were determined. Dietary fish oil decreased the percentage of total products of arachidonate by 50%, while the SFO diet had no effect on it. The amount of lipoxygenase products in the MFO group decreased significantly from 16931±3131 dpm to 6399±357 dpm/300 mg wet weight of brain. Significantly less PGF-1, PGF-2 and 12-hydroxyhepta-decatrienoic acid (HHT) were found in the capillaries of MFO treated animals, in comparison to the SFO group. The ratios of vasoconstrictor and vasodilator metabolites of arachidonate cascade were not modifed by the diets. Our results suggest that fish oil diet reduces the arachidonate cascade in cerebral microvessels. This effect may explain for the efficiency of n-3 fatty acids in vascular diseases.     

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.     

Seasonal changes in sea-water tolerance of Arctic charr (Salvelinus alpinus)

Summary Groups of Arctic charr,Salvelinus alpinus, which had been acclimated to water with a salinity of 7 g·l^–1 and natural temperature and photoperiod, were exposed to water with different salinities and temperatures in June, September and February. At a salinity of 15 g·l^–1, plasma osmolality, plasma Na⁺, Cl^–, Mg²⁺ concentrations and the activity of gill Na-K-ATPase were stable, irrespective of temperature and season. In June, the charr were able to regulate blood plasma ionic levels within narrow limits when exposed to a salinity of 34 g·l^–1 (sea water) and a temperature of 8°C. The hypo-osmoregulatory capacity was less, but sufficient if the temperature was only 1°C during the seawater exposure. At the start of the experiment, the gill Na-K-ATPase activity was significantly higher in June than corresponding enzyme activities in September and February. Furthermore, an increase in gill Na-K-ATPase activity during the seawater exposure (8°C) was seen in June. Irrespective of ambient temperature and salinity, no fish died during the June experiments. In September and February, exposure to sea water produced marked increases in plasma osmolality and plasma ion concentrations. There were no changes in gill Na-K-ATPase activity. Consequently, the fish became dehydrated and were moribund after a short period of seawater exposure. Highest mortality was recorded when charr were exposed to winter sea conditions (34 g·l^–1 and 1°C) in February. The results indicate that an increase in daylength induce a hypo-osmoregulatory capacity in the Arctic charr during summer. In fall and winter, however, reduced daylength are accompanied by poor hypo-osmoregulatory capacity. This leads to high mortality as a result of increased electrolyte levels and dehydration.     

No evidence for an indirect benefit from female mate preference in Arctic charr Salvelinus alpinus,but female ornamentation decreases offspring viability

Female mate choice is considered an important evolutionary agent, but there has been an ongoing debate over the fitness consequences it produces, especially in species that have a resource‐free mating system. We examined a potential fitness benefit resulting from the pre‐spawning mate preference in Arctic charr Salvelinus alpinus, a salmonid fish with no parental care. The females were first allowed to discriminate behaviourally between two males presented to them in a free choice test. We then tested with controlled fertilizations whether the females would accrue indirect genetic benefits for their offspring, as measured by embryonic viability, if they had mated with the male they preferred. Both parental identities influenced offspring survivorship, but the females did not consistently prefer the male which gave her the higher reproductive success. Neither was the degree of male red breeding coloration associated with female preference or the observable genetic quality. In contrast, there was a negative relationship between female coloration and her offspring survivorship, suggesting a significant trade‐off in resource investment between sexual ornamentation and reproduction. To conclude, the potential indirect fitness consequences arising from females' pre‐spawning mate preference seem to be negligible in early stages of development of Arctic charr. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 602–611.     

Summer seawater tolerance of small-sized Arctic charr, Salvelinus alpinus, on Svalbard

Migrating Arctic charr (Salvelinus alpinus) parr (118 ± 34.4 mm) were caught close to the rivermouth of the Dieset river on Spitsbergen (79°10′N), Svalbard. When subjected to a seawater tolerance test (34 ppt at 6°C) their blood plasma osmolality and sodium and magnesium concentrations increased significantly. After 90 h of exposure, average plasma osmolality was 410 (±54.1) mOsmol. Corresponding sodium and magnesium concentrations were 207 (±35.9) mmol l⁻¹ and 2.7 (±1.36) mmol l⁻¹, respectively. Survival at this time was only 12.5%. When smaller fish (96 ± 26.6 mm) were exposed to seawater, mortality was 100% within 72 h. We conclude that small-sized Svalbard charr may survive only short periods in seawater. Therefore, the lack of adequate hypoosmoregulatory capacity limits their access to marine food resources. Received: 29 December 1997 / Accepted: 12 April 1998     

Cannibalism and protective behavior of eggs in Arctic charr (Salvelinus alpinus)

From video recordings of spawning events, we quantified protective and cannibalistic behavior of Arctic charr occurring immediately after spawning. The number of fish cannibalizing on stray eggs was examined regarding (a) whether more than one male shed milt during the spawning event, that is, whether sperm competition occurred, (b) whether the sperm competition included few or many males, that is, the intensity of sperm competition, and (c) the density of fish at the spawning site. Response behavior toward egg cannibalism was also examined among females and dominant males in order to determine any parental investment toward protecting the eggs after spawning. Cannibalistic behavior was seen in almost 50% of the spawnings, and the multiple spawning events showed the highest numbers of fish cannibalizing on eggs. Both the number of males releasing milt and the number of fish approaching the spawning site were positively correlated with egg cannibalism. Sperm competition was, however, not a prerequisite for egg cannibalism. Although we also observed partial filial cannibalism, protective behavior of eggs was seen both among dominant males and females, suggesting that charr actually conduct parental care.     

Seawater tolerance in first-time migrants of anadromous Arctic charr (Salvelinus alpinus)

Anadromous juvenile Arctic charr (Salvelinus alpinus) were caught in the Sila River (66°21'N, 13°10'E, Nordland County, Norway) by use of a fish trap during their migration towards the sea in May/June. The absence of tags (not captured before) and examination of otoliths from sacrificed fish revealed that none of the experimental charr had previously encountered seawater. During 4 days of exposure to seawater, only minor changes in blood plasma osmolality, and blood plasma concentrations of Na⁺, Cl^- and Mg²⁺ were detected. An increase in Na⁺-K⁺-ATPase activity was measured during the exposure period. These results verified that first-time migrants exhibit hypoosmoregulatory capacity similar to that of smoltified Atlantic salmon (Salmo salar). Accordingly, the Arctic charr first-time migratory behaviour, including late descent and a possible stay within an estuary, cannot be taken as evidence of a poorly developed seawater tolerance.