Coldwater RAS in an Arctic charr farm in Northern Norway

Use of coldwater recirculating aquaculture systems (RAS) are still very rare in Norway, and only two farms are producing Arctic charr. This project took place in one of these commercial Arctic charr farms; Villmarksfisk AS in Bardu, Northern Norway.The farm gets its make-up water from ground water that holds 5 °C year around. Temperature in the rearing water varies between 7.5 °C (“low”) to 12 °C (“high”) through the year. The biological filter in the RAS seems to work stable at both “low” and “high” temperatures, including after incidents when feeding has been stopped for a day and started on top again the day after. Such an extreme change in loading was measured as a 70% increase in TAN concentration, with only minor changes in nitrite levels recorded. The biofilter also kept the nitrite stable and low in spite of diurnal variation in TAN excretion at normal feeding regimes (every day in three periods at day-time).The farming concept is to stock the farm with wild caught juvenile fish for on-growing to market size fish (0.75–1.00 kg). A drop in growth rate during early autumn has been a main concern for the farm. This may reflect a seasonal shift in growth potential, sometimes referred to as “autumn depression”. Interestingly, there is little sign of seasonal changes in the growth of hatchery-produced fish tested in the farm. Sampling of water quality through the seasons in tanks holding fish undergoing such growth depressions indicate that TAN excretion is much higher per kg feed used in the wintertime than in the springtime. This observation corresponds with the lack of weight gain during wintertime despite that the fish is feeding. Thus, feed conversion calculations indicate that feed utilization also varies with season reaching its nadir during this period.Both challenges concerning RAS in cold water and strongly reduced growth in autumn and winter time, have been investigated from 2005 to 2007 in a project financed by the Norwegian research council and the partners in the agricultural framework agreement.     

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.     

The suitability of anadromous Arctic charr as host and vector of the monogenean Gyrodactylus salaris

Abstract –  In 2000, the Atlantic salmon ( Salmo salar L.) stock in the river Signaldalselva, North Norway was found to be infected with the monogenean Gyrodactylus salaris (Malmberg). This river system has a multispecies fish community of nine species in total. Low densities of Atlantic salmon parr were found during electrofishing in October (2003) with a prevalence of 94% and a mean abundance of 848 G. salaris. This watercourse also holds a riverine stock of anadromous Arctic charr ( Salvelinus alpinus ), which is not common in Norway. Among the parr of Arctic charr, 64% were infested with an abundance of 23 parasites per fish. The most heavily infected 0+ and 1+ juvenile Arctic charr had 469 and 534 parasites, respectively, indicating that the parasites are able to reproduce on Arctic charr in the wild. There was little variation in the rates of infestation of Arctic charr along the studied stretch of the river, even in areas with very low densities of Atlantic salmon parr. The parr of anadromous Arctic charr seem to be suitable as long-term hosts for G. salaris . Moreover, a few (22%) infested adult sea-running Arctic charr were captured after ascending the river in the autumn, which shows that large fish may also act as carriers of G. salaris . However, no parasites were recorded on potential anadromous Arctic charr before descending during early spring (April 2003 and April 2004). Thus, it is still not clear whether anadromous Arctic charr are able to disperse the parasite between watercourses. So far, it is uncertain whether G. salaris may increase the mortality rates of Arctic charr and thereby be a threat to these unusual occurring riverine anadromous Arctic charr stocks.     

Comparison of the growth performance of offspring from cultured versus wild populations of arctic charr,Salvelinus alpinus (L.), kept at three different temperatures

The effects of three different temperatures on the growth and maturation of the offspring of cultured versus wild populations of juvenile arctic charr (Salvelinus alpinus L.) were investigated. The fish (start weight 17 g) were reared for 5 months at constant temperatures of 12, 14 and 16°C under a continuous light regime (LD24:0). Growth performance was significantly influenced by both temperature and source population. The offspring from the farmed fish displayed significantly higher mean weights at all temperatures compared with the offspring from the wild fish. The results indicate that the optimal temperature for growth (T_opt) decreases with increasing fish size in the offspring of both cultivated and wild fish. Significant differences in length–weight relationship were found, with the offspring of wild fish displaying higher condition factor throughout the experiment. The results demonstrate that the offspring from multiple generation farmed population of arctic charr are better adapted to high temperatures compared with the offspring (F₁ generation) from a wild population of arctic charr, and the former are also able to maintain growth at higher temperatures. There was a significant difference in maturation between the two populations, as the offspring from cultured fish displayed significantly lower level of maturation: 0%, 4% and 2% mature compared with 24%, 40% and 42% in the offspring from wild fish at temperatures of 12, 14 and 16°C respectively. The offspring from farmed strains of arctic charr thus appear to be the most suitable population for aquaculture.     

Domestication effects on fin nipping, survival and growth in hatchery-reared arctic charr, Salvelinus alpinus (L.), in competition with wild conspecifics

When reared in captivity, first-generation hatchery-reared Arctic charr, Salvelinus alpinus (L.), from Møkkeland lake, northern Norway, differed from wild-caught conspecifics from the same source. Incidence of caudal fin damage (used as an indirect assessment of aggressive interactions) was high amongst the wild-caught charr, and there was considerable mortality amongst these fish. By contrast, hatchery-reared fish displayed little evidence of fin damage, and mortalities were low. When the charr were held in mixed groups of wild-caught and hatchery-reared fish, the hatchery-reared fish showed the most extensive caudal fin damage. Weight losses and decreases in condition were also greatest amongst the hatchery-reared charr that were exposed to competition with wild fish. The hatchery-reared charr held together with the wild fish also suffered high mortality. Thus, aggression may have been selectively directed towards hatchery-reared fish in mixed groups. Taken together, the results suggest that the energetic costs may be high for the recipients of aggression.     

Trophic interactions between introduced lake trout (Salvelinus namaycush) and native Arctic charr (S. alpinus) in a large Fennoscandian subarctic lake

Introduced fishes may have major impacts on community structure and ecosystem function due to competitive and predatory interactions with native species. For example, introduced lake trout (Salvelinus namaycush) has been shown to replace native salmonids and induce major trophic cascades in some North American lakes, but few studies have investigated trophic interactions between lake trout and closely related native Arctic charr (S. alpinus) outside the natural distribution of the former species. We used stomach content and stable isotope analyses to investigate trophic interactions between introduced lake trout and native Arctic charr in large subarctic Lake Inarijärvi in northern Finland. Both salmonids had predominantly piscivorous diets at >280 mm total length and were mainly caught from the deep profundal zone. However, lake trout had a more generalist diet and showed higher reliance on littoral prey fish than Arctic charr, whose diet consisted mainly of pelagic planktivorous coregonids. According to length at age and condition data, lake trout showed slightly faster growth but lower condition than Arctic charr. The results indicate that introduced lake trout may to some extent compete with and prey upon native Arctic charr, but currently have only a minor if any impact on native fishes and food web structure in Inarijärvi. Future monitoring is essential to observe potential changes in trophic interactions between lake trout and Arctic charr in Inarijärvi, as well as in other European lakes where the two salmonids currently coexist.     

Is the winter period a severe bottleneck of anadromous riverine Arctic charr parr?

Abstract –  Winter growth and survival of wild individually tagged juvenile Arctic charr (1+ age) from a riverine anadromous stock, were studied in a small ice-covered (∼6 months) ground water brook (temperature ∼1 °C) connected to Skibotnelva in subarctic northern Norway. The overall winter survival was estimated to be 68% from late October 2005 to early May 2006. The recaptured charr were not significantly different in initial length or weight compared with the nonrecaptured fish suggesting low size-dependent mortality. The majority (98%) of the recaptured charr showed significant increase in size, with a mean increment of 62% from their initial bodyweight and 12% of the charr parr had more than doubled their weight. The mean specific growth rate was calculated to be slightly lower (0.27) than estimated values from a growth model (∼0.35). In addition, the condition factor increased significantly during the field experiment. These results are the first individual growth data on riverine anadromous Arctic charr parr under natural winter conditions, and indicate that charr can grow relatively fast during periods with low temperature and also that ground water brooks can be good over-wintering habitat for juvenile Arctic charr. These results suggest that the winter period is perhaps a less severe bottleneck than previously recognised for the cold-adapted Arctic charr.     

Smolt characteristics of small first-time migrant, and resident Arctic charr, Salvelinus alpinus (L.), from a river system in northern Norway

Smolt characteristics were investigated in sympatric anadromous and resident Arctic charr. Salvelinus alpinus (L.), of a similar size (11-20 cm), A group of first-time migrant anadromous charr was caught while descending the Hals River and two groups of resident conspecifics were caught in Lake Storvatn. one before, and one after, the sea-run of anadromous fish had terminated. When sampled immediately after capture in fresh water the anadromous group had a higher proportion of fish visually classified as smolts. and these charr had higher gill Na⁺-K⁺ ATPase activity, higher densities of developed chloride cells in the gills, a lower condition factor, and lower plasma osmolality, than resident fish. When exposed to sea water (33%o S), only minor differences in mortality and plasma electrolyte levels were observed between anadromous and resident fish, average values of plasma osmolality and chloride concentrations being 377 mOsm and 169 mM and 387 mOsm and 174 mM, respectively. The results suggest that the first-time migrant Arctic charr had undergone some of the physiological changes that are considered typical for a parr-smolt transformation before they left fresh water. Such changes did not appear to have occurred in sympatric, resident, fish of a similar size. The parr-smolt transformation in the first-time migrants may, however, have been incomplete, because the fish did not appear to have the ability to rapidly re-establish osmo- and ionoregutatory homeostasis after direct transfer to sea water.     

Patterns of Tetracapsuloides bryosalmonae infection of three salmonid species in large,deep Norwegian lakes

Proliferative kidney disease (PKD), caused by the myxozoan endoparasite Tetracapsuloides bryosalmonae, is of serious ecological and economical concern to wild and farmed salmonids. Wild salmonid populations have declined due to PKD, primarily in rivers, in Europe and North America. Deep lakes are also important habitats for salmonids, and this work aimed to investigate parasite presence in five deep Norwegian lakes. Kidney samples from three salmonid species from deep lakes were collected and tested using real-time PCR to detect PKD parasite presence. We present the first detection of T. bryosalmonae in European whitefish in Norway for the first time, as well as the first published documentation of the parasite in kidneys of Arctic charr, brown trout and whitefish in four lakes. The observed prevalence of the parasite was higher in populations of brown trout than of Arctic charr and whitefish. The parasite was detected in farmed, but not in wild, charr in one lake. This suggests a possible link with a depth of fish habitat and fewer T. bryosalmonae-infected and PKD-affected fish. Towards a warmer climate, cold hypolimnion in deep lakes may act as a refuge for wild salmonids, while cold deep water may be used to control PKD in farmed salmonids.     

Evaluation of brook trout production in a coldwater recycle aquaculture system

Brook trout (Salvelinus fontinalis) are a commercially important coldwater species reared in Wisconsin and the Midwestern United States. Brook trout are raised by private, tribal, state, and federal fish hatchery facilities in Wisconsin. Approximately 10% of private coldwater aquaculture operations are presently raising brook trout of various strains for stocking uses and a limited amount for food markets. Growing brook trout to a larger size, if they can be reared in a shorter time span, may present a potential new sector for the aquaculture market in the Midwestern US. The present study reports hatchery production attributes, i.e., growth, survival, fin condition, feed efficiency, water chemistry requirements and general husbandry of Lake Superior strain (Nipigon) brook trout reared in a recirculating aquaculture system (RAS), operated at an average temperature of 13 °C. The recycle system at NADF reared 1379 kg of brook trout over a 10-month period from fingerling (9 g) to market size (340–454 g). The trout grew faster (0.84 g/day and 0.64 mm/day) in the RAS than fish cultured in traditional flow-through tank culture utilizing ground water at 7.6 °C (0.14 g/day and 0.35 mm/day). Final average weight of RAS fish was 260 g, while the flow-through fish averaged 65 g. Final tank densities for the RAS averaged 40.4 kg/m³ while flow-through tanks averaged 31.2 kg/m³. Throughout the project, feed conversions in the RAS ranged from 0.9 to 1.3. Water quality variables such as TAN, nitrite, DO, temperature, TSS, CO₂, ph, etc. were within safe limits for brook trout and will be discussed. It does appear from this initial research project that market size brook trout can be raised successfully in a recycle system within a similar time frame as a rainbow trout produced in a Wisconsin typical flow-through facility.     

Effects of altered photoperiod regimes during winter on growth and gonadosomatic index in Arctic charr (Salvelinus alpinus) reared in freshwater

The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming.     

Habitat use, size and age structure in sympatric brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) stocks: resistance of populations to change following harvest

Abstract– Habitat use and population dynamics in brown trout Salmo trutta and Arctic charr Salvelinus alpinus were studied in an oligotrophic lake over a period of 10 years. Previous studies showed that the species segregated by habitat during summer. While brown trout occupied the surface water down to a depth of 10 m, Arctic charr were found deeper with a maximum occurrence at depth 10–15 m. Following the removal of a large number of intermediate sized fish in 1988–89, habitat segregation between the species broke down and Arctic charr were found in upper waters, while brown trout descended to deeper waters. The following year, both species were most frequently found in surface waters at depths of 0–5 m. During the last four years, the species reestablished their original habitat segregation despite another removal experiment of intermediate-sized fish in 1992–1994. The removal of fish resulted in an increased proportion of large (≥ 25 cm) fish in both species. Furthermore, the charr stock responded by reduced abundance and increased size-at-age. The results revealed plasticity and strong resistance to harvest populations of brown trout and Arctic charr. This is probably due to internal mechanisms of intraspecific competition within each population, which result in differential mortality among size classes.     

Development and use of an Arctic charr cell line to study antiviral responses at extremely low temperatures

Arctic charr (Salvelinus alpinus) are the northernmost distributed freshwater fish and can grow at water temperatures as low as 0.2 °C. Other teleost species have impaired immune function at temperatures that Arctic charr thrive in, and thus, charr may maintain immune function at these temperatures. In this study, a fibroblastic cell line, named ACBA, derived from the bulbus arteriosus (BA) of Arctic charr was developed for use in immune studies at various temperatures. ACBA has undergone more than forty passages at 18 °C over 3 years, while showing no signs of senescence‐associated β‐galactosidase activity and producing nitric oxide. Remarkably, ACBA cells survived and maintained some mitotic activity even at 1 °C for over 3 months. At these low temperatures, ACBA also continued to produce MH class I proteins. After challenge with poly I:C, only antiviral Mx proteins were induced while MH proteins remained constant. When exposed to live viruses, ACBA was shown to permit viral infection and replication of IPNV, VHSV IVa and CSV at 14 °C. Yet at the preferred temperature of 4 °C, only VHSV IVa was shown to replicate within ACBA. This study provides evidence that Arctic charr cells can maintain immune function while also resisting infection with intracellular pathogens at low temperatures.     

The importance of egg size and egg energy density for early size patterns and performance of Arctic charr Salvelinus alpinus

The primary target of selection in most breeding programmes in aquaculture is to promote rapid growth while delaying maturation. In most cases, little is known about how such selection programmes may affect maternal provisioning of offspring and early development. Under favourable and predictable condition, which is typically the case in fish farming, females generally produce more but smaller eggs than wild females. By using a continuous range of egg size originating from females of a fourth generation of Icelandic domesticated Arctic charr Salvelinus alpinus (Linnaeus, 1758), we assessed the relative importance of maternal effects and individual egg size for energy density of individual egg and several offspring traits from fertilization until 138 days post fertilization (dpf). We found that egg size and related energy density varied more among than within females. Although egg size was not correlated with energy density (at 1 dpf) or survival (at hatching and 138 dpf), it was positively correlated with most offspring traits throughout ontogeny. We further did not find any temporal variation in the correlation with the offspring traits during ontogeny. Within clutch variation in growth, yolk sac volume and hatching time were under the influence of direct female effects (maternal or genetic effects). These results show how egg size relates to individual performance in Arctic charr and constitute a baseline for understanding how domestication may alter offspring phenotypes early in life. These findings are discussed with regard to their consequences for aquaculture of Arctic charr and salmonids in general.     

An experimental comparison of cannibalistic response in different Arctic charr (Salvelinus alpinus (L.)) stocks

Abstract– The cannibalistic response of four domesticated Arctic charr stocks were compared experimentally using a radiographic technique. Charr from Arctic Spitsbergen (80°N) consistently exhibited a much higher frequency of cannibalistic response than fish from three charr strains from mainland Norway (70°N). The results indicate that the extent of cannibalistic feeding in Arctic charr is population specific and support the hypothesis that charr from Arctic populations have stronger cannibalistic tendencies than do fish from more temperate regions.     

Effects of short‐term starvation periods on flesh quality in Arctic charr (Salvelinus alpinus) in different seasons

Possible effects of short‐term starvation on flesh quality in Arctic charr were studied in spring (March) and summer (August). Groups of juvenile Arctic charr (mean weight March 536 g ± 24; August 461 g ± 15 SEM) were starved for 1, 2 and 4 weeks (March) and 1, 2 and 3 (August). After each starvation period, the fish were slaughtered, and flesh samples collected in order to investigate quality and textural properties in the different experimental groups. Starvation had a positive effect on flesh quality giving firmer texture and lower gaping scores. Starved fish had lower cathepsin activity at slaughter, and a similar difference was seen one‐week post mortem. The results showed that the effect of starvation period was seasonally dependent. Starvation had a larger effect in summer, where a three‐week starvation resulted in firmer texture, whereas this was not seen during spring.     

Digestibility of microbial and mussel meal for Arctic charr (Salvelinus alpinus) and Eurasian perch (Perca fluviatilis)

Apparent digestibility coefficients (ADCs) for four protein‐rich alternative feed ingredients, intact baker's yeast (Saccharomyces cerevisiae), extracted baker's yeast (S. cerevisiae), zygomycetes (Rhizopus oryzae) and blue mussel (Mytilus edulis), were determined for Arctic charr (Salvelinus alpinus) and Eurasian perch (Perca fluviatilis). Diets contained 30% of test ingredients, and ADCs were compared to a reference diet containing fish meal. For Arctic charr, ADCs for dry matter (DM, 71–99%), sum of amino acids (SAA, 84–99%) and gross energy (70–99%) were significantly lower for intact S. cerevisiae than for extracted S. cerevisiae, R. oryzae and M. edulis. The ADCs for the indispensable amino acids (IAA) in Arctic charr varied between 84% and 99%. Significant differences were found in ADCs for IAA between the test ingredients for Arctic charr, with higher values for extracted S. cerevisiae and M. edulis. The ADCs in Eurasian perch varied between 83% and 95% for DM, 89% and 98% for CP, 92% and 100% for SAA, 81% and 96% for gross energy. No significant differences were found for ADCs between the test ingredients in Eurasian perch, indicating a species effect on digestibility. Furthermore, the absence of intact cell walls had a positive effect on digestibility of S. cerevisiae for Arctic charr.     

Lake-use by juvenile Atlantic salmon (Salmo salar L.) and other salmonids in northern Norway

Abstract– The utilization of lakes, and inlet and outlet streams by juvenile Atlantic salmon ( Salmo salar L.), brown trout ( Salmo trutta L.) and Arctic charr ( Salvelinus alpinus (L.), were investigated in 16 watercourses northern Norway, all known to inhabit salmon stocks. In lakes, fish were caught by small mesh size gill nets, while in rivers fish were caught electrofishing. In the shallow littoral (0-3 m depth) there were juvenile salmon in 15 of 19 investigated lakes, juvenile trout in 17 and juvenile charr in seven. Trout dominated significantly in numbers in the shallow littoral of seven lakes, while salmon and charr dominated in three lakes each. When trout and salmon were frequent in the shallow littoral, charr was usually not present in this habitat, but were found in the profundal zone in most of the lakes. Atlantic salmon parr utilized both shallow and deep lakes, and used both stones and macrophytic vegetation as shelter. The utilization of lakes by salmon parr seemed to be closely related to utilization of small inlet streams for spawning. In most inlet and outlet streams salmon dominated over trout in numbers, while charr were absent. This is the first documentation of lake-use by naturally occurring salmon parr in Scandinavia.     

Anaesthesia of Atlantic cod (Gadus morhua) — Effect of pre-anaesthetic sedation, and importance of body weight, temperature and stress

The efficacy of the anaesthetic agents benzocaine, metacaine (MS-222), metomidate and 2-phenoxyethanol was studied in Atlantic cod (Gadus morhua) with average body weights of 10 ± 4 g, 99 ± 33 g and 1022 ± 274 g at water temperatures of 8 °C and 16 °C. The agents were tested individually and as combination anaesthesia comprising pre-anaesthetic sedation with a low dosage of metomidate or 2-phenoxyethanol followed by anaesthesia with benzocaine or MS-222. All agents were administered through bath immersion with an exposure time of 5 min. The different treatments resulted in average induction and recovery times ranging from 52 ± 6 s to 182 ± 16 s and 77 ± 26 s to 659 ± 46 s respectively. Induction and recovery times varied in relation to water temperature and were generally shorter at 16 °C for all weight groups and treatments compared to 8 °C. For benzocaine and MS-222 induction and recovery times were found to increase with increasing body weight. For metomidate the recovery time increased with increasing weight whereas there were no weight related differences in induction time. No differences in either induction or recovery times associated to body weight were found for 2-phenoxyethanol. Acute stress prior to anaesthesia with MS-222 resulted in significantly shorter induction time and prolonged recovery time, as well as deeper anaesthetised fish. The dosage of MS-222 had to be reduced in order to avoid mortality in fish subjected to acute stress. Combination anaesthesia allowed a reduction of the dosages used for inducing anaesthesia and produced markedly reduced recovery times compared to agents administered individually.