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Abstract The reproductive performance of farmed Arctic charr exhibits substantial individual variation. The causes behind this variation have not yet been properly explained, despite the species relatively long history in aquaculture. The aim of the present study was to provide better understanding of the issue by evaluating parent and gamete traits in relation to fertility and offspring viability under routine hatchery conditions. Are losses mainly due to failed fertilisation or mortality? Are maternal or paternal factor more predominant? The study covered sex hormone status of the broodstock, egg traits (egg size and wateriness of egg batches), milt traits (volume, density, and sperm motility characteristics), and symmetry of early cell division. We found that the majority of offspring loss occurred as embryo mortality, although a significant additional loss could be assigned fertilisation failure. Fertilisation and mortality rates were not inter-correlated. Neither of the evaluated egg traits, egg size and wateriness of newly stripped egg batches, proved to be useful indicators of egg quality. With regard to sperm traits, milt density as well as several computer assisted sperm analysis (CASA) parameters, i.e. swimming speed (VAP, VSL, and VCL) and beat cross frequency (BCF), were correlated with reproductive performance and could potentially be used as quality indicators for Arctic charr. Together, male 17,20β-P levels and BCF explained 69.5% of the between male variation in proportion of successfully eyed eggs. The results support previous indications that post-ovulatory aging of oocytes is contributing to the impairment of reproductive performance in farmed Arctic charr. In addition, a significant paternal factor to this impairment has been exposed. However, the cause and mechanism involved are still far from clear. Highlights • Broodstock and gamete traits were evaluated together with fertility and embryo viability under routine hatchery conditions. • Embryo mortality, rather than failed fertilisation, was the main cause for egg loss in the studied Arctic charr broodstock. • Besides post-ovulatory aging of oocytes, paternal fertility issues, which needs to be investigated further, were revealed. [ABSTRACT FROM AUTHOR]

The Swedish breeding program for Arctic charr ( Salvelinus alpinus L.) has been running for 30 years and includes seven selected generations. In this study, we evaluated the differences in growth between the first generation of selected Arctic charr and the present generation. We demonstrate that not only has growth been improved through selective breeding but also that a change in the seasonal growth capacity has occurred. Selection has induced a high winter growth capacity, but the largest weight gain between generations was seen during summer. As a result of selective breeding, the production time to reach a slaughter weight of 600–700 g has been reduced by 10 months since the start of the breeding program in 1985, and improvements in the final weight have been of the magnitude of 11% per generation. To be able to keep up with the faster growth and altered seasonality of this strain, feeding management needs to be adapted. In this study, a model based on the theoretical energy need of the Arctic charr is presented, which makes it possible to make such adaptions in feeding management. [ABSTRACT FROM AUTHOR]

Limited knowledge exists about the residing microbiome in gamete-related samples in fish. A potential effect between the seminal microbiome composition and sperm quality traits has been previously suggested in humans and livestock. Using a metabarcoding approach, we aimed to gain insights into the structure of the residing prokaryotes and microbial eukaryotes in ovarian fluid (n = 10) and milt (n = 84) from farmed Arctic charr - a species with highly variable reproductive success in captivity. In addition, sperm quality traits were recorded on the sampled males to investigate potential associations with the residing seminal microbiome. Higher microbial diversity was found in the ovarian fluid compared to the milt habitat. Even though the residing microbiome showed distinct differences between the two habitats, substantial overlap was observed, with >70% of the milt core microbiome being found in the ovarian fluid habitat. Statistically significant associations were found between the Shannon diversity index and sperm motility-related traits. Additionally, a fungal operational taxonomic unit (OTU) potentially belonging to the Leotiomycetes class was associated with sperm concentration and motility. Overall, our study documents the microbiome structure of gamete-related samples from Arctic charr. Even though some associations were obtained between sperm quality parameters and either microbiome diversity or with a fungal OTU, follow-up studies on a larger scale with more tank replicates are needed to confirm the robustness and causality of these relationships. • First report of the residing microbiome structure in gamete-related samples on fish • Associations were found between the Shannon diversity index and sperm motility-related traits. • A fungal operational taxonomic unit was associated with sperm concentration and motility. [ABSTRACT FROM AUTHOR]

Traditional sources of protein in fish feed for salmonids, such as fishmeal, face sustainability problems. Therefore, ingredients not attractive for human consumption are increasingly being considered for the development of future feeds. However, it is uncertain how this alternative range of ingredients will affect fish growth, quality and consumer opinion. In this experimental study, we tested a new fish feed on Arctic charr, containing a protein mixture from the Baltic Sea and yeast, all ingredients unattractive for human consumption. This feed comprised of sprat ( Sprattus sprattus ) and herring ( Clupea harengus ), blue mussels ( Mytilus edulis ) and baker's yeast ( Saccharomyces cerevisiae ), in a ratio of three parts to the whole. Fish fed with this feed grew 11.5% less than the control group. The digestibility and microscopy analysis of the faeces suggested a lower digestibility of the test feed, presumably caused by the fish's inability to utilize the nutrients from the yeast cells. Consumers' perceptions of the final product were evaluated through a sensory evaluation, indicating no differences in scores of fillet quality between the two treatments. Potential implications of these results are discussed in context of feed composition, quality and other factors including species biology and season, which are relevant topics in the discussions on feed sustainability. Statement of relevance Evaluating a feed mix unattractive for human consumption. [ABSTRACT FROM AUTHOR]

Two lab-based trials quantified the effect of a range of continuous light (LL) treatments overwinter on the somatic growth and incidence of sexual maturation in the fall age 2 of individually identified under-yearling Arctic charr (Labrador strain) at constant 10 °C. Controls were maintained under simulated natural photoperiod (LDN; Latitude 45°N). In trial 1 ( n = 120/trt, mean 54 g initial body weight), LL starting the 1st day of either October, November, December, January or February (all returned to LDN on April l) resulted in a step-wise reduction in maturity of 43, 55, 59, 67 73% compared with 77% in the control (sexes pooled). In trial 2 ( n = 90/trt, mean 24 g initial body weight), LL starting either August 13 or October 1 and ending April 1 reduced maturity to < 10%, compared to 33% (LL Dec1-Apr1) and 50% in the LDN controls. LL starting October 1 and ending either February 1, April 1 or June 1 were equally effective, resulting in < 15% maturity. The importance of returning from LL to LDN in spring to reduce maturity was demonstrated by the LL constant (Oct–Oct) treatment which resulted in relatively high maturity, 31%. The reduction of maturity rate was independent of both somatic growth and condition factor during winter in all treatment groups. Among fish that matured, the timing of completion of sexual maturation was affected by both the LL start and end date. [ABSTRACT FROM AUTHOR]

The effects of dietary lipid oxidation on fish are diverse and contradictory. In this study, herring oil was oxidized to five different levels (peroxide values (POV): 20.44, 182.97, 56.12, 33.27 and 0.00 meq kg − 1 ) and used to formulate five experimental diets. Juvenile Arctic charr ( Salvelinus alpinus , mean body mass ± SD: 2.41 ± 0.11 g) were reared on the five diets for 67 days. In another experiment, juvenile Nile tilapia ( Oreochromis niloticus ) (1.71 ± 0.40 g) were reared on three diets formulated with oxidized oils having POV of 19.55, 447.27 and 32.72 respectively, for 90 days. Growth responses were monitored in quadruplicate groups of 60 individuals of Arctic charr and 100 for Nile tilapia, respectively. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were only studied in Arctic charr. At the end of the study, the Arctic charr group reared on a diet with oils in the primary oxidation state had significantly lower body mass and specific growth rate, but higher hepatosomatic index compared to the rest of the groups. The activities of CAT and GPx increased with dietary lipid oxidation while that of SOD remained fairly stable. In Nile tilapia, both final body mass and condition factor were significantly lower in the group fed fresh oil than in the groups fed oxidized oils. Fillet lipid content decreased with lipid oxidation while ash and protein did not differ amongst tilapia groups. The results suggest that Arctic charr are more susceptible to lipid oxidation than are Nile tilapia. These differences may be the result of species differences in tolerance to oxidized lipids, variable lipid intake or access to vitamin E/tocopherol in feed. Statement of Relevance Important for Arctic charr and Nile tilapia feed development. [ABSTRACT FROM AUTHOR]

To address the problem of high maturity at 2 years of age among Salvelinus alpinus (Labrador strain), PIT-tagged yearlings (ca. 110 g) were reared for 18 weeks overwinter (Nov. 16 to Apr. 1) under six treatments (90 fish per treatment) that combined three factors: photoperiod (natural day length, LDN or 24 h light, LL), temperature (10 or 5 °C), and food (fed daily or no food). On April 1 all fish were returned to LDN, 10 °C and fed daily for a further six months. In November, the maturity rate was very high among fish reared the previous winter under LDN and fed daily at both 10 °C (♀ 94%, ♂ 43%) and 5 °C (♀ 87%, ♂ 45%). Replacing LDN with LL overwinter, at 10 °C halved the maturity rate (♀ 49%, ♂ 19%), and at 5 °C eliminated maturity among females, and male maturity was 6%. Food deprivation for 18 weeks posed no health problems, and combined with LL also was highly effective at preventing maturation, both at 10 °C (♀ 0%, ♂ 2%) and 5 °C (♀ 0%, ♂ 7%). Compensatory growth following the suppression of growth overwinter indicates this approach to reducing maturity can be a commercially viable means to produce 1 kg immature product around 2 years old. A new two-step gating mechanism is proposed to explain the photoperiod prevention of maturation, one independent of somatic growth, the other dependent. Statement of relevance This study shows that the combination of LL, reduced temperature and food deprivation can significantly reduce the incidence of maturation and improve the productivity among diploid Arctic charr. This combination approach can potentially be applied to other farmed salmonids and non-salmonids to improve the efficacy of controlling sexual maturation. [ABSTRACT FROM AUTHOR]

The bacterium Aeromonas salmonicida ssp. achromogenes (Asa) causes atypical furunculosis in salmonids that may lead to extensive financial losses in intensive fish farming. The commercially available vaccine commonly used against the ssp. achromogenes in the production of Arctic charr in Iceland has been developed for Atlantic salmon (Salmon salar) against the subspecies salmonicida which causes typical furunculosis, but it has insufficient efficacy in Arctic charr. In response to this, a novel vaccine against Asa in Arctic charr was developed in cooperation with Spanish vaccine company; HIPRA, and the antibody response of Arctic charr against Asa investigated using enzyme-linked immunosorbent assay. Fish used for testing were vaccinated using the novel, monovalent autogenous experimental vaccine and a commercially available vaccine Alpha Ject® 3000 developed for Atlantic salmon that was used as a comparison. The study was conducted in commercial production units where the fish were continually exposed to natural outbreaks of atypical furunculosis. Blood samples were collected from the fish prior to vaccination and thereafter at approximately ten-week intervals in each production unit throughout the production period until the fish reached harvesting size. Fish growth and mortality was recorded throughout the study. The results indicated that both vaccines induced antibody response in fish against Asa antigens and that antibody titers obtained during the first weeks following vaccination were maintained throughout the production period. However, significantly higher antibody titers were observed in fish vaccinated with the experimental novel vaccine and fish mortality was significantly lower in production units containing fish vaccinated with the novel vaccine in comparison to the Alpha Ject 3000® vaccine. These results suggest that the novel vaccine may be a promising candidate for protective immunity against atypical furunculosis caused by Asa in Arctic charr. • The specific antibody responses in Arctic charr against Aeromonas salmonicida ssp. achromogenes were analyzed using ELISA. • A novel experimental vaccine developed for Arctic charr and a commercial vaccine developed for Atlantic salmon were compared. • The novel experimental vaccine induced a higher specific antibody response and with more extended duration. • Significantly reduced fish mortality was observed in the group vaccinated using the experimental vaccine. [ABSTRACT FROM AUTHOR]

The Swedish breeding programme for Arctic charr aims to improve traits that are important for farming. Selection has been ongoing since the 1980s, and the aim of this study was to re-estimate the genetic parameters in the selected population. In addition, the genetics of skin pigmentation was studied, as previous work indicated a relationship between pigmentation and the ability to cope with stress. One hundred twenty-five full sib families of Arctic charr were hatched and reared separately until they were individually tagged (n = 12,266). In connection with the tagging, three replicates were formed, which were subsequently reared at different sites. The genetic relationships were known from a seven-generation pedigree. Body weight and length were at one site measured at six occasions until 27 months old, and these measurements were used to estimate the DGC (daily growth coefficient) and condition factor. At a second site fish were measured at 21 and 27 months age and at a third site at 27 months age. Skin pigmentation was measured using image analysis. The final weight at 27 months of age varied widely between rearing sites, ranging from 529 g to 1443 g. Weight heritability differed among the sites, at 0.45, 0.11, and 0.07. At one of the sites, where growth was followed closely, weight heritability varied among growth periods, ranging from 0.01 to 0.25, and similar results were obtained for the DGC. In contrast, condition factor heritability did not show such pronounced variations within and among sites. The magnitude of the differences in heritability of weight and growth among different sites that was observed here was not observed previously with this charr population. In particular, the low heritability among the fastest growing fish is unprecedented. Skin pigmentation showed a high heritability of 0.76, indicating a strong additive genetic component. At most ages, pigmentation showed a weak positive genetic correlation with growth. The genotype environment interaction (GEI) was estimated using genetic correlations among sites. For the final weight, genetic correlations were high, indicating weak GEI, although the presence of GEI was suggested from the DGC data. Statement of relevance The ms will impact charr breeding for commercial farming. [ABSTRACT FROM AUTHOR]

Abstract: The present study aims to analyze several biological and environmental variables to explain the unpredictable reproductive success at the main aquaculture facility involved in the Swedish Arctic charr breeding program. Data from 540 egg batches, collected from the years 2000 to 2011, were analyzed for the effects of factors such as temperature conditions, female age and egg size on egg viability (% of eyed eggs). An exploratory factor analysis (EFA) reduced 12 variables into 4 factors. Factor 1 mainly explains the negative relationship between high temperature in summer and egg viability. Factor 2 mainly explains a significant relationship between increasing temperatures in autumn (September to November) and decreased egg viability. Factor 3 explains that an early stripping date and increased temperature during stripping and egg incubation together have a negative, although not statistically significant, relationship to egg viability. Factor 4 explains a significant positive relationship between female age and egg size on the proportion of eyed eggs. The most relevant factors in explaining egg viability identified by the EFA analysis were evaluated further, indicating how farming conditions need to be improved. The broodstocks have been subjected to critically high water temperatures during July and August, resulting in decreased egg viability. Access to sufficiently cool water during summer is crucial. Based on the negative correlations found between incubation temperature and egg survival we suggest that a more moderate water heating may be beneficial. Most females were used as broodfish for several years. By applying individual tagging, data on the individual reproductive performance of females for up to 5 consecutive years could be analyzed. In this analysis, both egg size and the proportion of eyed eggs increased with the mean female age. There was also a strong age-unrelated positive correlation between egg size and survival. [Copyright &y& Elsevier]

Abstract: The short and long term effects of short photoperiods on growth and maturity were investigated in 240 individually tagged juvenile Arctic charr (Salvelinus alpinus). The Arctic charr were reared at constant temperature (12°C) and on four different light regimes; one group on continuous light (LD24:0) as control and three groups experienced a period of short day (LD8:16) on a three subsequent 6week periods i.e. 24th September–6thNovember (LD8:16Sep–Nov), 6th November–19th December (LD8:16Nov–Dec), 19th December-29th January (LD8:16Dec–Jan). Before and after the short photoperiod treatment the groups were reared at continuous light. The growth of the fish was monitored over a period of 11months. At the termination of the experiment in September 2009, the body mass of the three groups receiving a short day period (LD8:16 Sep–Nov, LD8:16 Nov–Dec and LD8:16 Dec–Jan) was significantly higher (13.9%, 12.9% and 10.7% respectively) than that of the group reared at continuous light (LD24:0). The three groups receiving the short photoperiod did not differ in weight at the end of the trial so the time of the year at which the short photoperiod was applied did not seem to be of importance regarding the growth enhancement. The maturation rate did not appear to be affected by the photoperiod treatments. The improved growth was mainly a result of a higher feed intake and improved feed conversion efficiency for the period following transfer of the charr from a short photoperiod to the continuous light. Application of such a winter photoperiod during the juvenile phase can, therefore, be used as a tool to increase the biomass and growth rate in Arctic charr farming. [Copyright &y& Elsevier]

Abstract: Groups of Arctic charr (Salvelinus alpinus) were reared in duplicate tanks supplied with freshwater, and subjected to two different ration levels, 100% (full ration) and 50% (half ration) in two six week periods during autumn (Sept.–Nov.) and winter (Dec.–Feb.). In between the restricted ration periods and from February onwards, all fish were fed full ration. After the first and second 42day restricted feed periods, the 50% had lower mean weight than the 100% group in both sexes, but this size difference diminished as the trial progressed, and full final size compensation was seen for both males and females in the 50% group. Specific growth rates for both sexes were higher in the 100% group during the two reduced feeding periods, whereas growth was higher in the 50% group in the subsequent periods after feed restriction. No differences in growth were seen from May onwards. Feed conversion efficiency was higher in the 50% group during, and after, feed restriction, and daily feeding rate (F%) was higher in the 50% group in the periods subsequent to feeding restriction. In the following summer and autumn signs of lower maturation were seen for females in the feed restricted group. No differences were found in fillet water- and fat content in the experimental groups. The present findings indicate that intermittent feeding during autumn and winter could be a cost-effective strategy for Arctic charr farmers. [Copyright &y& Elsevier]

Abstract: This study evaluated the survival and growth of juvenile Arctic charr in comparison to their diploid siblings. Eight triploid full-sib families were produced by hydrostatic pressure treatment of eggs (5 min at 65.5×103 kPa) beginning 210 °C-min post-fertilization. Diploid siblings came from the same eight families, but without pressure treatment. Mean survival from eyed-egg to first size-grading (at 1980 °C-days post-hatch) was 70% for triploids and 84% for diploids. In two growth studies using 4 m3 tanks containing 100 juveniles per ploidy level of each family, triploidization resulted in higher levels of phenotypic variance for growth traits. Specifically, triploids consistently had smaller mean body weight and fork length than their diploid siblings. Juveniles were first measured at 850 °C-dph and again every four weeks over a 24 week period. The proportion of the overall variance in weight was due to ploidy level in the first tank experiment whereas this variance was due to the effect of family in the second tank experiment. Mean specific growth rates of triploids and diploids were 2.01 and 2.09% for weight and 0.64 and 0.66% for length, respectively, which was not significant. The condition factor of triploids was less than that of diploids at every sampling date, except for the initial assessment. After transfer to a commercial site following completion of the tank trials, the same families were grown until market size (1 kg) and were measured again nine and 11 months after the conclusion of the growth studies. The condition factor of triploids improved at the commercial site and was not different from that of diploids. The difference in weight of triploid and diploid populations was significant at the conclusion of the study. These results indicate that as juveniles, triploids have reduced performance in important aquaculture traits. However, because triploid performance was reduced in a predictable fashion in comparison to sibling diploids, triploids of some full-sib families outperformed diploids of others. Any overall advantage of triploids may not be realized until the diploids begin to mature. [Copyright &y& Elsevier]

Abstract: This study investigates how simulation of condensed winter light conditions effects the growth of wild caught Arctic charr (Salvelinus alpinus L.) held in culture. After capturing from Altevatn, Northern Norway, juvenile Arctic charr were cultivated and subsequently individually divided into two groups. The fish were held under identical conditions from May to October including continuous light. Starting from week 41 after capture (October) one group was subjected to a winter light regime of 6 h light and 18 h dark per day (Winter Light group—WL), while light regimes in the second group remained continuous (Light group). After an eight weeks treatment period the WL-group was reverted to the continuous light regime until the experiment ended in May 2007. Results revealed no pre-treatment differences in growth between the two groups. However, starting from two months after the short day treatment, fishes from the WL group had significant higher growth rates compared to L group fish. At the end of the experiment, e.g. five months after the light treatment, fishes from WL group had increased their average body weight by 353 g as compared to 252 g in the L group. Consequently, results show that simulation of winter light conditions can increase the productivity of land-based Arctic charr (Salvelinus alpinus L.) cultivation by 25 to 30%. Thus, management of wild caught charr farming, great care should be taken as to what light regimes the fish are exposed to. [Copyright &y& Elsevier]

The general objective of this study was to establish a standardized procedure for the cryopreservation of Arctic charr milt and its use in the production of 'sparctic' hybrids. The specific objectives of this study were to determine: (i) the optimal final sperm concentration as well as (ii) the final glucose concentration, (iii) the effect of post-thaw storage time on sperm motility characteristics, and (iv) the fertilization ability of cryopreserved Arctic charr milt at 0 and 60 min after thawing at sperm:egg ratios of 500,000:1 and 1,000,000:1. We observed high post-thaw sperm motility (49–57%) at final sperm concentrations ranging from 0.5 to 2.0 × 109 spermatozoa ml−1 in straw. We determined that a final glucose concentration of 0.15–0.19 M in 7.5% methanol was optimal (post-thaw sperm motility 48–60%). Milt cryopreserved at optimal conditions (final concentrations: 0.17 M of glucose, 7.5% methanol and 1.5 × 109 spermatozoa ml−1) could be stored for up to 15 min after thawing without the loss of sperm motility. The ability of cryopreserved milt to fertilize brook trout eggs was high (68–72%) and did not differ between the tested sperm:egg ratios (500,000:1 and 1,000,000:1) when milt was used immediately after thawing or after 60 min of post-thaw storage. The milt used in this study was obtained from two hatcheries and was characterized by significantly different values of sperm concentrations. In conclusion, a standardized and efficient cryopreservation method for Arctic charr milt has been developed and used for the production of 'sparctic' hybrids. Species-specific requirements for final sperm and glucose concentrations and the post-thaw storage time were determined. The hatchery of origin of Arctic charr should be taken into consideration, as high variability in sperm characteristics may be expected. The development of this method and the positive results of the fertilization trials indicate promising potential for the implementation of cryopreserved milt in hatchery practice. • Glucose from 0.15 to 0.19 M and sperm concentration from 0.5 to 2.0 × 109 spermatozoa ml−1 resulted in high sperm motility. • High fertilization rates were obtained both at sperm:egg ratios (500,000:1 and 1,000,000:1) and at 0 or 60 min after thawing. • Post-thaw sperm motility was negatively affected by time of storage. [ABSTRACT FROM AUTHOR]