The initial feeding of Arctic charr (Salvelinus alpinus) alevins at different temperatures and under different feeding regimes

Alevins of Arctic charr (Salvelinus alpinus) were raised at four temperatures (3°, 6°, 8° and 12°C) and at each temperature food was presented at three different points in development, viz. early in the yolk-sac period, at two-thirds yolk utilization and at yolk exhaustion. Growth and survival were studied. Initial feeding occurred at or shortly after swim-up at all temperatures, and temperature did not affect the developmental stage at which feeding began. Alevins to which food had been presented earliest grew more rapidly after feeding commenced at all temperatures except 3°C. Exogenous feeding enhanced growth, the alevins receiving food at yolk exhaustion having the lowest growth rate up to that point. Mortality was very low except at 12°C, which was a supra-optimal temperature for the rearing of charr alevins from the point of view of both growth and survival.     

Comparative growth study of wild- and hatchery-produced Arctic charr (Salvelinus alpinus L.) in a coldwater recirculation system

The growth performance of Arctic charr of wild (W) and hatchery (H) origin was compared in a commercial coldwater recirculation system (Villmarksfisk, Bardu, 68°N, 19°E, Norway). The initial individual body mass was 115 g and similar between groups. The rearing temperature was 9.2 °C and the fish were held under continuous light (24:0 L:D). At the end of the experiment (day 240), the average body mass of the H fish was 451 g compared to 231 g in the W fish. The accumulated mortality of wild Arctic charr was about 40%; 10 times higher than the mortality of hatchery-produced Arctic charr (4%). The difference in growth performance and survival rate impose a great disadvantage of using this wild caught fish as compared to commercially available hatchery-produced Arctic charr in coldwater recirculation system. However, further improvements in the production chain (catching, live transport, quarantine, size grading, etc.) may still make production of wild caught Arctic charr profitable, especially as it demands a higher price in niche markets.     

Growth of Arctic charr (Salvelinus alpinus L.) under conditions of constant light and temperature

Arctic charr, Salvelinus alpinus, display distinct cycles of food intake, growth and conversion when reared in the laboratory under constant conditions (continuous light; temperature 10°C). Growth rates peaked in December–January and June–July and it is suggested that charr may have an endogenous growth rhythm with a 6-month cycle.     

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.     

Impact of a new artificial shelter on Arctic charr (Salvelinus alpinus, L.) behaviour and culture performance during the endogenous feeding period

Shelter is of major importance in many species of fish both in the wild and in aquaculture. Sheltering behaviour of Arctic charr has been poorly studied in aquaculture. A new type of shelter made of PVC agricultural drain cut in half was tested on culture performance and behaviour during the endogenous feeding period. This device offered grooves where alevins could position themselves and lie in a vertical position. A first experiment compared fish with and without shelter in incubator compartments. All fish were measured at 122, 158, and 190 days post fertilization (dpf) and observed at 126, 139 and 157 dpf. Fish provided with shelter showed better growth performances, lower mortality and started first exogenous feeding about six days later compared to fish without shelter. These effects from shelter provision were also associated with much less mobility in fish provided with shelter. At 126 dpf, all fish provided with shelter were immobile while other fish displayed horizontal stationary body movement (86%) or swam against the water current (7%). At 157 dpf, 85% of fish without shelter were immobile compared to 95% in fish provided with shelter. Both categories displayed stationary body movements. In most cases, there was one single fish per groove and a stable average value of 2.4 grooves was maintained between two successive fish throughout the study. The second experiment was a preference test where the fish were placed in similar compartments but occupied by a half shelter. We found that 61% of the fish were located under the shelter at 122 dpf while at 157 dpf, 58% were on the shelter and 42% out of the shelter. The present results revealed Arctic charr behavioural characteristics in the presence of a new type of artificial shelter at very early stages of development. This shelter enables the fish to stabilize in a vertical position without producing any movement and to choose by itself its favorite location throughout development. This device could be used to improve Arctic charr growth, performance and fish welfare during the endogenous feeding period.     

Carotenoid pigmentation in relation to feed intake, growth and social interactions in Arctic charr, Salvelinus alpinus (L.), from two anadromous strains

Feed intake, growth and carotenoid pigmentation in 1 + Arctic charr, Salvelinus alpinus (L.), of the Hammerfest and Svalbard strains were studied in fish reared in either separate or mixed groups for 11 weeks.
Hammerfest charr grew faster than charr from the Svalbard strain at the group level. The slower overall growth in the Svalbard strain was accompanied by greater variability in feed intake and growth rates than observed amongst the fish of the Hammerfest strain. The higher incidence of bite marks amongst the Svalbard chart suggested that aggressive encounters were more frequent amongst fish of this strain. No significant differences were observed in muscle carotenoid concentration. There was, however, a highly significant positive correlation between muscle carotenoid concentration and weight gain for individual fish of both strains, irrespective of whether the fish were reared separately or in mixed groups. Estimates of muscle carotenoid retention varied from 78 to 96 mg g⁻¹, but there were no differences between strains or between fish reared in single or mixed-strain groups.
There were no differences in muscle carotenoid composition between strains or between fish reared in separate or mixed groups. Astaxanthin and idoxanthin, a metabolite of astaxanthin, were present in approximately equal proportions, and made up about 99% of the muscle carotenoid content.
The results of this study suggest that flesh pigmentation and its variability may be profoundly influenced by the level of social interactions, mediated through effects on feed intake and growth. These effects may mask genetic variations in the capacity to deposit carotenoids.     

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.     

Effect of rearing density on the early growth and variation in growth of juvenile Arctic charr, Salvelinus alpinus (L.)

Abstract. Arctic charr, Salvelinus alpinus (L.), from the same full-sib family were reared under two different densities for 97days at 10°C. In one treatment density was adjusted every 2 weeks by means of a tank enclosure to a density of 50kg/m³. In the other treatment the density was allowed to increase as fish biomass increased to 50kg/m³. Density had no significant effect on the variation observed in individual fish weights over the course of the growth trial. Density had a significant effect on the relationship between fish weight and specific growth rate. The increasing density treatment had an overall higher mean specific growth rate of 0·1%/day.     

Feed intake and growth of Arctic charr, Salvelinus alpinus (L.), fed diets supplemented with oxytetracycline and squid extract

This study examined the long-term effects of a potential feeding deterrent, oxytetracycline (OTC), and a putative feeding stimulant, squid extract, on feed intake, growth and dry matter (DM) digestibility in Arctic charr, Salvelinus alpinus (L.). Fish were fed one of four diets for 9 weeks: 1. commercial feed formulation (basic); 2. BM (basic plus 20 g kg⁻¹ OTC); 3. BMS (BM plus 10 g kg⁻¹ squid extract); 4. BS (basic plus 10 g kg⁻¹ squid extract). The feed intake of Arctic charr was not reduced by the addition of OTC to the basic feed, and addition of squid extract to the medicated feed did not enhance feed consumption. DM digestibility and growth tended to be reduced in groups of fish fed diets supplemented with the antibiotic (BM and BMS). This suggests that OTC may have interfered with nutrient digestion and absorption. OTC does not seem to be a feeding deterrent for Arctic charr, possibly indicating that the charr is a rather unselective feeder. Because the medicated feeds were readily accepted, there may be little to be gained by addition of feeding stimulants to these types of feeds for charr.     

Influence of feeding frequency on growth and size dispersion in Arctic charr Salvelinus alpinus (L.)

Abstract Dominance hierarchy formation in groups of fish is thought to be a major reason for the development of size heterogeneity. The objective of the current experiment was to examine the influence of different feeding frequencies on growth and changes in size distribution in groups of Arctic charr Salvelinus alpinus (L.). The fish were fed equivalent excess rations continuously for 24 h a day, for 2 h twice a day (early morning and evening), for 2 h once a day in the morning or for 2 h once every other day also in the morning. Growth was measured by individual weighing of fish four times during the 130‐day experiment. Coefficient of variation in size within rearing groups was used to assess size dispersion and the possible development of hierarchies within the groups. Feeding frequency did not influence variation in size within groups, and there were no signs of hierarchy formation.     

Screening for organic acids in fish tissues with special reference to the distribution of taurine inRutilus rutilus L.

A liquid chromatographic method for rapid profiling of some organic acids and other compounds of physiological interest in fish tissues is presented. The method provides the detection of -ketoglutaric, malic and pyruvic acid and is optimized for the quantitation of citric, phosphoric, succinic, lactic and fumaric acids, as well as glucose and especially taurine. These substances were separated in a single analytical run on a cation exchange column with dilute sulfuric acid as the elutant. The effluent was monitored by a refractive index or an UV detector at 208 nm wavelength. Resolution was satisfactory. No further treatment was found to be necessary when samples were deproteinized with perchloric acid. Taurine (2-aminoethansulfonic acid), not previously described in the roach (Rutilus rutilus L.), occurs in considerable amounts in red and white muscle and heart tissue. However, it is also present in all other tissues.     

A review of recent developments in Tilapia culture,with special reference to fish farming in the heated effluents of power stations

Preliminary studies suggest that Tilapia species are suitable for culture in the heated effluents of power stations. Growth and reproduction may be normal or near normal in saline conditions, and Tilapia are able to tolerate low oxygen levels and moderately low temperatures (6–12°C). Population control techniques and food requirements are described and discussed. Although Tilapia may have a secondary role as sport fish or in clearing excessive plant growth in power stations, their main value would seem to be as food fishes.     

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.     

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.     

Microflora of Arctic charr, Salvelinus alpinus (L.): gastrointestinal microflora of free-living fish and effect of diet and salinity on intestinal microflora

Abstract. The adherent aerobic bacterial flora present in the gastrointestinal tract and faeces of free-living Arctic charr, Salvelinus alpinus (L.), from Lake Takvatn, Northern Norway, were identified both qualitatively and quantitatively. Approximately 10⁵ bacteria g⁻¹ were found in both the small and large intestines. The predominant bacterial species were identified as Aeromonas , Enterobacteriaceae, Micrococcus and Lactobacillus. Other microorganisms isolated included Acinetobacter, Cytophaga, Flavobacterium, Moraxella, Pseudomonas, Vibrio , Coryneforms and Streptococcus. The intestinal microflora of free-living fish was dominated by Aeromonas and Lactobacillus , but the intestinal bacterial flora of wild fish transferred to hatchery was affected by feeding them either a capelin roe diet or a commercial feed in fresh and sea water. Approximately 55% of the bacterial flora in intestinal contents from fish fed the capelin roe diet was Enterobacteriaceae when the fish were held in fresh and sea water. However, when the wild-caught charr were fed a commercial diet in fresh water, Aeromonas and Pseudomonas dominated in faeces, while Vibrio and Pseudomonas were predominant in the diet group held in sea water.     

Survival and growth of turbot larvae Scophthalmus maximus L. Reared on different food organisms with special regard to long-chain polyunsaturated fatty acids

Turbot larvae reared on rotifers (Brachionus plicatilis) and Artemia (San Francisco brand) nauplii (A) were compared with those fed on different copepod (Eurytemora affinis) stages (B). In one trial, growth and survival of larvae from hatching to day 21, their fatty acid pattern and that of their food organisms were examined. At the age of 21 days larvae of group A measured 11·1 ± 1·6 mm total length (TL) compared with 14·8 ± 1·1 mm TL for group B. From day 3 to 8 survival was 29% (A) and 38% (B). Long-chain polyunsaturated fatty acid composition of turbots resembled that of their corresponding diets. Artemia and Artemia fed larvae were lacking 22 : 6 n-3 fatty acid.In a further study, survival of larvae from day 11 to 21 fed on Artemia nauplii (C) or copepods (D) was found to be greater with the latter diet (73 versus 93%) whereas growth during this experiment was similar in both groups. Before the start of this trial they had been reared on a mixture of copepod nauplii and Brachionus. No influence on weaning success was observed. 22 : 6 n-3 fatty acid is seen to be essential for turbot larvae: elongations of fatty acids by the larvae were not found.     

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.     

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.