Dominance hierarchy formation in Arctic charr Salvelinus alpinus (L.): nutrient digestibility of subordinate and dominant fish

Arctic charr Salvelinus alpinus (L.) were individually tagged and maintained in circular tanks for 102 days in order to allow the development of dominance hierarchies. At the end of the trial period, the charr were anaesthetized in benzocaine and identified as dominant, beta (β) and subordinate according to a set of established criteria including size, coloration and bite marks. The gut contents were then collected and analysed for apparent digestibility coefficient of nutrients using the chromic oxide method. Subordinate fish had significantly lower specific growth rates and apparent nutrient digestibility coefficients of both dry matter and lipid compared with dominant fish. Although specific growth rate was significantly lower in the β fish compared with dominant charr, this did not influence the apparent digestibility coefficient of nutrients to any major extent.     

The potential of Arctic charr, Salvelinus alpinus (L.), for mariculture

There would appear to be considerable potential for Arctic charr, Salvelinus alpinus (L.), to be cultured in marine conditions in countries where coastal winter salinity is below oceanic, and temperatures remain above freezing. Sea lochs on the west coast of Scotland represent one such environment where freshwater run-off leads to depressed salinities (20-30 practical salinity units) and the North Atlantic Drift leads to winter sea water temperatures typically around 6-8^oC.     

Lipid nutrition in Arctic charr, Salvelinus alpinus (L.): a mini review

Abstract. Several investigations have used Cr₂O₃ (chromic oxide) as an indigestible marker in digestibility studies. However, in this review the effect of chromic oxide on dietary lipid during passage through the digestive tract, and the gastrointestinal microflora in long-term nutrition studies in Arctic charr, Salvelinus alpinus (L.), are discussed. Based on these results it is suggested that the use of chromic oxide may lead to erroneous results. Furthermore, this paper focuses on the effect of dietary linoleic add (18:2 n–6), acetate and salinity on lipid and individual fatty acid digestibilities in Arctic charr.
No full studies have been carried out regarding the essential fatty acid requirement (EFA) of Arctic charr. Available data indicate that (n–3) polyunsaturated fatty acids (PUFAs) are the prime EFA, as in most other salmonids. Furthermore, quantitative EFAn requirements may be higher than the 1% dietary level described for other salmonids. Feeding (n–3) PUFAs at 1% lead to high contents of (n–9) PUFAs in the polar lipids, presently recognized as'indicators'of EFA deficiency. Moreover, this review focuses on elongation and desaturation of short-chain EFA to their C₂₀ C ₂₂ counterparts, and the feedback inhibition of this ability.     

Dietary methionine requirement of juvenile Arctic charr Salvelinus alpinus (L.)

The dietary methionine requirement of juvenile Arctic charr Salvelinus alpinus (L.) was assessed by feeding diets supplemented with graded levels of DL-methionine (9, 12, 15, 18, 21, and 24 g kg⁻¹dietary protein) for 16 weeks at 12°C. All diets contained 400 g kg⁻¹ protein, 170 g kg⁻¹ lipid, 66 g kg⁻¹ ash and an estimated 17.5 MJ digestible energy (DE) kg⁻¹. When live-weight gain was examined using quadratic regression, the estimate of methionine requirement for optimal growth was 17.6 g kg⁻¹ of dietary protein (DP) or 7 g kg⁻¹ of the diet. Requirements estimated on the basis of carcass protein and energy gains were 18.8 and 17.9 g kg⁻¹ DP, respectively. Plasma methionine concentrations and ocular focal length variability measurements did not provide a sensitive measure of requirement, because each responded in a linear fashion to increasing dietary methionine levels. Based on the prevalence of cataracts, the methionine level required to prevent lens pathology (26.7 g kg⁻¹ DP) appears to be higher than that required for maximum growth.     

Effect of sorting on size-frequency distributions and growth of Arctic charr,Salvelinus alpinus L.

Arctic charr, Salvelinus alpinus, were reared in either unsorted groups or in groups that had been sorted into ‘small’ and ‘large’ fish. At the start of the experiment the size-frequency distributions of unsorted and pooled ‘small’ and ‘large’ fish were similar, but after 5 months' rearing distributions were markedly different. There was evidence that growth of ‘small’ fish improved in the absence of larger conspecifics, but size-sorting also led to reduced growth of some large fish, with the consequence that size-sorting did not lead to overall increases in biomass gain and rates of production.     

Trophic polymorphism among Arctic charr Salvelinus alpinus L., from Loch Ericht, Scotland

Abstract— This article examines the morphology and ecology of Arctic charr Salvelinus alpinus in Loch Ericht, Scotland, Gill netting revealed that two forms of charr existed within the loch, a pale form and a colored form. Multivariate analysis of nine size-corrected morphometric measurements of the head region revealed that pale and colored charr differed significantly in the size and shape of the head characteristics and that both groups were easily discriminated on the basis of these characteristics. Stomach contents showed that the colored form fed predominantly on zooplankton and the pale form mainly consumed benthic macro-invertebrates, with larger pale individuals consuming other fish. On the basis of diet and morphology, the terms planktivorous and piscivorous were adopted for the two forms respectively. Length at age also distinguished the two groups, with piscivorous charr being smaller than colored charr up to age 8+ then surpassing the maximum length attained by planktivorous charr at ages of 9+ and above. The results are discussed in relation to other instances of sympatric morphs of Arctic charr.     

Muscle carotenoid concentrations in sexually maturing and immature Arctic charr, Salvelinus alpinus (L.)

Muscle carotenoid concentrations were measured in immature and maturing 2+ Arctic charr, Salvelinus alpinus (L.), sampled from April until ovulation started in November. In immature fish, muscle carotenoid concentration increased steadily and had reached about 10 mg kg^?1 by the end of the experiment. In mature fish of both sexes, pigment concentrations decreased during the autumn and muscle carotenoid concentrations were significantly lower than in the immature fish during the latter stages of the trial. No significant difference in muscle pigmentation was observed between sexes. Carotenoid concentrations were lowest in the cranial region of the fillet, but decreased in all parts of the fillet when the charr became mature. In females, the decrease seemed to be most marked in the caudal region. At the termination of the experiment, fillets accounted for about one-half of the carotenoid content in mature fish of both sexes. High concentrations of pigment were recorded in the skin and fins of mature males. In mature female charr, pigment was almost equally distributed among skin, fins and ovaries     

Influence of sea ranching on hatchery-reared anadromous Arctic charr, Salvelinus alpinus (L.)

Anadromous Arctic charr, Salvelinus alpinus (L.), from the River Halselva in Finnmark, northern Norway, were used as broodstock for the production of smolts. During the smolting period the fish were either shielded from normal working routines, subjected to normal work routines, or exposed to excessive work routines (stress) within the hatchery. None of the handling routines affected the gill-Na-K-ATPase activity, or the hypoosmoregulatory capacity of the charr. Compared with normal handling, neither stress nor shielding caused any significant difference in the migratory behaviour of the charr, in the duration of the sea residence, or in homing success. However, the stressed group did show a lymphocytopenia at end of the rearing period.     

The status of Arctic charr Salvelinus alpinus in Britain and Ireland

Abstract –  The Arctic charr occurs in lakes across Britain and Ireland and was previously described here as 15 separate species. Most authorities now agree that all these stocks belong to a single polymorphic species complex Salvelinus alpinus (L.). This fish is given little protection in British and Irish law and there has been a steady loss of natural populations in recent years in all the countries concerned. A few new stocks have been created either intentionally or accidentally. In Scotland, only a small proportion of the 258 recorded natural populations has been studied and at least 12 of these are now extinct. There are at least four introduced populations originating from native Scottish stocks, but the fate of stocks introduced from Canada for aquaculture is uncertain. In England, there are eight extant populations in Cumbria and four others extinct. The status of introduced stocks in England is uncertain but there is probably one population surviving in Yorkshire. In Wales, eight lakes with resident Arctic charr populations have been recorded, three of these populations are natural, one is extinct and four have been introduced. In Ireland, of the 74 known populations, approximately 30% are extinct. There is no evidence to indicate that introduced stocks (some of them from Iceland) in a small number of lakes have survived there. A range of factors is involved in the extinction of populations and these include pollution, eutrophication, acidification, afforestation, engineering, exploitation, aquaculture, introductions and climate change. Much research remains to be done and unique stocks of this valuable species will continue to be lost unless positive action is taken through local conservation management backed by appropriate national legislation.     

The influence of dietary astaxanthin and temperature on flesh colour in Arctic charr Salvelinus alpinus L.

Arctic charr Salvelinus alpinus L. averaging 150 g were fed six diets containing from 0 to 192 mg astaxanthin per kilogram dry diet al two temperatures (8 C and 12 C), After reaching an average weight of 320 g (102 days at 12 C and 126 days at 8 C), the fish were killed for evaluation of flesh pigmentation using instrumental colour measurement. There was a positive relationship between dietary astaxanthin and muscle redness up to a dietary concentration of around 70 mg kg^-1, where a plateau in pigmentation was reached. Tail sections were more intensely pigmented compared with the neck and dorsal regions. Within each temperature regime, flesh coloration was positively correlated to specific growth rate. Fish maintained at 8 C had significantly higher pigmentation compared to those grown at 12 C.     

Littoral spawning habitats of three southern Arctic charr (Salvelinus alpinus L.) populations

Abstract Arctic charr populations in southern latitudes are nonmigratory, with all life‐stages limited to freshwater lakes and in‐ or out‐flowing tributaries. Although many of these populations are reported to also spawn in lake littorals, little is known about the physical characteristics of putative spawning grounds. A total of 23 discrete spawning sites within three Irish lakes were located by fyke netting of spawning adults and snorkelling in littoral habitats. Spawning sites were found to be long, narrow strips running parallel to the shore at a maximum depth of 124 cm. Spawning sites were limited to areas of coarse mineral substrate with an adequate (c. 8 cm) depth of clean interstitial spaces. In individual lakes, combined areas of spawning sites made up 0.4–0.7% of available littoral. Egg densities varied considerably between sites (33–900·eggs m^?2) and were significantly correlated with gradient and width of spawning sites. No evidence of redd digging was found. The shallow, localised and restricted nature of spawning grounds makes such populations vulnerable to anthropogenically induced postoviposition changes in surface water level, eutrophication processes such as increased lake sedimentation and elevated nutrient status.     

Survival, growth, sexual maturation and reproduction of brook charr, Salvelinus fontinalis (Mitchill), Arctic charr, Salvelinus alpinus L., and their hybrids

Survival of hybrids (FA, AF) between brook charr, Salvelinus fontinalis (Mitchill), (FF) and Arctic charr, Salvelinus alpinus L., (AA) were compared at three fish farms. Survival of hybrids and Arctic charr was impaired in warm water. In cold water, brook charr and hybrids showed similar survival percentages until the spawning period. Each spawning period was followed by an increase of mortality, but to a much higher degree in brook charr. Growth was studied in the best (cold water) fish farm. During the first 2 years of rearing, brook charr had the highest relative weight. The weight of the two hybrids approached that of brook charr in the third year because of the drastic decrease of growth rate in brook charr after the spawning period. No differences between genotypes of either females or males could be detected in the eviscerated weights, the dressing percentages, or the gonado-somatic indexes. The two hybrids matured sexually, but their sperm quality was inferior to that of the pure species. Crosses between the 4-year-old breeders from the F1 population (FF, FA, AF and AA) were achieved. Survival from the eyed stage to 6 weeks post-hatching was significantly lower in F2 progeny than in back-crosses or pure species crosses. Even though the survival following spawning periods and the total biomass produced were better in hybrids than in brook charr raised in cold water, we believe the farming of this hybrid should not be carried out. The full development of sexually mature hybrids does not resolve problems linked with precocious sexual maturation in brook charr farming carried out in eastern Canada.     

Phenotypic and genetic parameters of body and compositional traits in Arctic charr, Salvelinus alpinus (L.)

Abstract. Phenotypic and genetic parameters of body and compositional traits were estimated for a population consisting of 327 two-year-old Arctic charr, Salvelinus alpinus (L.), from 21 full-sib groups. Heritability estimates for body traits, such as fork length, gutted weight, condition factor and visceral weight, were all of intermediate magnitude (0·24–0·45). Heritabilities for carcass component traits, e.g. fat, protein, dry matter and astaxanthin contents, were low to medium (0·0–0·28). Genetic and phenotypic correlations were high between astaxanthin content and body traits, whereas they were medium to low between astaxanthin content and carcass compositional traits such as fat, dry matter and protein contents. The genetic variation in fat and dry matter contents was closely associated with variation in body weight. Selection for higher body weight at 2 years will probably lead to small, but positive, correlated changes in fat content. Our findings suggest that it should be possible to select for higher astaxanthin content in Artic charr to improve their flesh coloration.     

Muscle colour development in Arctic charr, Salvelinus alpinus (L.), monitored by fibre-optics and electrical impedance

Farmed Arctic charr, Salvelinus alpinus (L.), (n = 2 70) with a wide range of carotenoid muscle pigmentation were produced by feeding astaxanthin at different levels (0-120 mg kg^?1 feed). Steaks were scored subjectively for pigment concentration (dark = high score). Internal reflectance spectra were measured with a relatively non-destructive 1-mm-diameter fibre-optic probe. Colour scores were only moderately correlated with reflectance (R = 0.66 and P< 0.01, using data at 500, 610 and 520 nm) because the small-diameter probe had a short light-path through the tissue and was highly responsive to scattering. However, in fish without astaxanthin in their diet, this sensitivity to microstructural causes of scattering revealed that fibre-optic reflectance increased (P < 0.01) with age from 400 nm (r = 0.68) to 440 nm (r = 0.40), and from 530 nm (r = 0.30) to 700 nm (r = 0.56). In agreement with these results, colour scores decreased with age (r = -0.52; P < 0.001; n = 85), as did electrical resistance 24 h post-mortem (r = -0.42 at 120 Hz, r = -0.39 at 1 kHz and r = -0.54 at 10 kHz; P < 0.001). Resistance was correlated with colour score (r = 0.40 and P < 0.001 for resistance at 10 kHz) and with fibre-optic reflectance (R = 0.42 and P < 0.01 for resistance at 120 Hz and 1 kHz versus reflectance from 420 to 680 nm). Thus, without astaxanthin in the diet, muscle colour and tissue integrity at 24 h deteriorated with the age of the fish.     

Summer habitat use and feeding of juvenile Arctic charr,Salvelinus alpinus,in the Canadian High Arctic

Abstract – Owing to limited knowledge of the habitat use and diet of juvenile Arctic charr from the High Arctic, particularly young‐of‐the‐year (YOY), we assembled data obtained from samples taken in and around Lake Hazen, Nunavut, Canada, to assess juvenile habitat use and feeding. Juvenile charr demonstrated a preference for stream environments, particularly those fed by warm upstream ponds. Charr occupying both stream and nearshore lake habitats were found to feed similarly, with chironomids occurring most frequently in diets. Some older stream‐dwelling charr preyed on smaller, younger Arctic charr. Preferred stream occupancy is likely mediated by physical barriers created mainly by water velocity, and by distance from the lake, lake‐ice dynamics, low water depth, and turbidity. Water velocities resulted in stream habitat segregation by size, with YOY mainly found in low‐velocity pools and back eddies adjacent to stream banks, but not in water velocities >0.1 m·s^?1. Greatest charr densities in streams were found in small, shallow, slow‐flowing side channels, which are highly susceptible to drought. Under predicted climate change scenarios, streams fed by small ponds will be susceptible to intermittent flow conditions, which could result in increased competition among juvenile charr for the remaining stream habitats. In addition, glacier‐fed streams are likely to experience increased flow conditions that will exacerbate physical barriers created by water velocity and further reduce the availability of preferred stream habitat.     

The influence of temperature on the apparent nutrient and fatty acid digestibility of Arctic charr, Salvelinus alpinus L.

To study the influence of temperature on the nutrient and fatty acid digestibility of salmonid fish, Arctic charr, Salvelinus alpinus L., were fed dry pelleted diets at 10 and 0.6 °C for 81 days. The diets had a carbohydrate/lipid content of 23.7/13% and 6.4/ 27% and a constant protein content of around 50%. At the end of feeding period, gut contents were collected from the mid- and hind-gut regions, and analysed for the apparent digestibility coefficient (ADC) of nutrients using chromic oxide as digestibility marker. Fish maintained at 0.6 °C had a lower ADC of protein, carbohydrate, lipid and dry matter compared to those maintained at 10 °C. This shows that increased gastrointestinal holding time following low temperature adaptation does not fully compensate for lowered digestive/absorptive metabolism. Feeding high carbohydrate diets had no significant influence on nutrient utilization at 10 °C, but appeared to reduce the ADC of most macronutrients at 0.6 °C. The ADC of the individual fatty acids increased with decreasing chain length and increased with unsaturation. Maintaining the fish at 0.6 °C significantly reduced the ADC of saturated fatty acids, while the monounsaturated fatty acids, and in particular, the polyunsaturated fatty acids were hardly influenced by environmental temperature. It is suggested that the reason may be a shift in digestive lipase specificity caused by changes in the substrate state or lowered solubilization of saturated fatty acids in bile micelles, which thus reduces the uptake into the enterocyte.