Objective
We developed a novel, simple approach to summarize variation in quantile regression estimates of weight at length across multiple levels of grouping factors (locations or years) and ...demonstrate its utility for comparing fish condition using Arctic Grayling Thymallus arcticus data. We compared condition among 28 geographic locations of Arctic Grayling populations and among 12 and 25 years for two populations.
Methods
We summarized variation among locations and among years within locations using percentiles (maximum, 75th, 50th, 25th, and minimum) of predicted quantiles of weight at length, allowing us to simplify the distributions of predicted quantiles of weight into highest to lowest fourths (quartiles) across locations or years. One part of this summary information, 75th percentiles of median (0.50 quantile) predicted weights at length across populations, is identical to summary statistics used to develop standard weight equations for computing relative weights. However, our approach avoids biases inherent in fitting a single standard weight equation and can accommodate among‐fish variation in weight at length via multiple quantiles when developing reference standards for comparative or diagnostic purposes. A selected new weight at length can be compared with the distribution of quantile predictions among locations in terms of weights or as proportionate weights similar to relative weight.
Result
Arctic Grayling in 28 geographic locations, from the southern limit of their distribution in Montana and Wyoming north through Canada and Alaska to the Arctic coast, had considerable variation in allometric exponents in weight–length relationships and in predicted weights at length. Predicted weights of Arctic Grayling for heavier fish (0.90 quantiles) in populations with less (lower quartiles) to greater (upper quartiles) weights were 127–194 g and 336–510 g at total lengths = 250 and 350 mm, respectively. Lighter fish (0.10 quantiles) in populations with less to greater weights were 100–133 g and 259–364 g, at the same total lengths, respectively. We provide statistical code and tabled values that can be used as reference standards as a replacement for standard weight equations for comparing new samples of fishes. We also quantified annual variation in condition within two intensively sampled populations, the Kuparuk River in Alaska (25 years, 1985–2012) and Red Rock Creek, Montana (12 years, 1994–2016). Annual distributions of weights at length were greater for Arctic Grayling in Red Rock Creek than those in the Kuparuk River. Variation in predicted distributions of weights at length among years was also greater for Red Rock Creek, although fish from both locations exhibited substantial among‐year variation that exceeded half the variation estimated among geographic locations.
Conclusion
Our estimates indicated that there was substantial spatial and temporal variation in condition of Arctic Grayling that might be investigated further to help understand constraints on populations to aid conservation and management of the species. Our summary approach can be easily extended to other investigations of fish weight at length relationships where multiple quantile estimates are made across many levels of grouping factors.
Impact statement
Fish condition based on measures of their weight and length is commonly used to assess the health and status of fish populations and response to management actions. Our new approach summarizing across percentiles of weight at length allows fisheries biologists to better understand variation in lighter to heavier fish at a given length within and among populations to aid our understanding about factors that impact condition.
Objective
Arctic Grayling Thymallus arcticus are Holarctically distributed, with a single native population in the conterminous United States occurring in the Big Hole River, Montana, where water ...temperatures can fluctuate throughout the year from 8°C to 18°C. A gradual increase in mean water temperature has been reported in this river over the past 20 years due to riparian habitat changes and climate change effects. We hypothesized that exposing Arctic Grayling to higher temperatures would result in lower survival, decreased growth, and increased stress responses.
Methods
Over a 144‐day trial, Arctic Grayling juveniles were subjected to water temperatures ranging from 8°C to 26°C to measure the effects on growth, survival, gene expression, and antioxidant enzyme activity.
Result
Fish growth increased with increasing water temperature up to 18°C, beyond which survival was reduced. Fish did not survive at temperatures above 22°C. In response to temperatures above 16°C, 3.0‐fold and 1.5‐fold increases in gene expression were observed for superoxide dismutase (SOD) and glutathione peroxidase (GPx), respectively, but no changes were seen in the gene expression ratio of heat shock protein 70 to heat shock protein 90. Activities of the SOD and GPx enzymes also rose at temperatures above 16°C, indicating heightened oxidative stress. Catalase gene expression and enzyme activity decreased with rising temperatures, suggesting a preference for the GPx pathway, as GPx could also be providing help with lipid peroxidation. An increase in thiobarbituric acid reactive substances was also recorded, which corresponded with rising temperatures.
Conclusion
Our findings thus underscore the vulnerability of Arctic Grayling to minor changes in water temperature. Further increases in mean water temperature could significantly compromise the survival of Arctic Grayling in the Big Hole River.
Impact statement
The Big Hole River, Montana, contains the only remaining native population of Arctic Grayling in the lower 48 states. This laboratory study shows that higher average water temperatures that accompany climate change and other environmental pertubations will adversely affect the stress and future survival of this population.
In fish with the XX/XY sex determination system, the production of all-female offspring within one generation was achieved by gynogenesis. Successful induction of gynogenesis in the European grayling ...(Thymallus thymallus) (Salmonidae) included egg activation with UV-irradiated homologous (996 J/m2) and heterologous (rainbow trout) sperm (1370 J/m2) followed by exposure of the inseminated eggs to a high hydrostatic pressure (HHP) shock (9000 psi for 5 min) 20 min after their activation. The survival rates of the gynogenotic larvae at the swim-up stage exhibited a huge inter-clutch variability that ranged from 1.12 ± 0.53% to 14.15 ± 1.27% and from 0.96 ± 0.33% to 60.57 ± 1.85% when the eggs were activated by UV-irradiated homologous and heterologous sperm, respectively. Maternal inheritance was only confirmed in the gynogenotes that hatched from eggs inseminated by inactivated heterologous sperm, whereas an admixture of the paternal DNA was detected among screened individuals that originated from eggs activated by homologous sperm. All the examined gynogenotes produced using heterologous sperm were confirmed to be genetically females. In the case of fish with an admixture of the paternal DNA, male genotypes and phenotypes were observed. One of the genetic males had well developed testes. Differences in the ratio of deformed larvae that hatched from eggs activated by UV-irradiated homologous and heterologous sperm were nonsignificant. Based on the obtained results, it has to be stated that the activation of grayling eggs with UV-irradiated rainbow trout sperm followed by HHP shock is a reliable and fast method for the production of all-female grayling stocks.
•UV-irradiated rainbow trout sperm induced gynogenetic development of the European grayling.•Diploidization was achieved by pressure shock (9000 psi/5 min) applied 20 min post fertilization.•Gynogenetic grayling hatched from eggs activated by UV-treated trout sperm were all females.•Gynogenetic grayling exhibited increased ratio of body deformations.
Objective
Some graylings Thymallus spp. possess an elongated dorsal fin and other morphological traits that can be sexually dimorphic, as demonstrated in the European Grayling T. thymallus. North ...American Arctic Grayling T. arcticus are assumed to follow these trends, but decisive evidence is lacking. This study aimed to determine whether sexually dimorphic characteristics, including posterior dorsal height, can be used to accurately predict the sex of Arctic Grayling in Interior Alaska.
Methods
We used computer imaging software to measure 22 morphometrics on 97 Arctic Grayling of known sex from streams in Interior Alaska, and we developed a set of binomial models to evaluate the validity of morphometrics as predictors of Arctic Grayling sex.
Result
Posterior dorsal height was a reasonably accurate predictor of sex (~90% accurate at fork lengths ≥300 mm), although models containing additional morphometrics were more accurate (100% accuracy at fork lengths ≥250 mm).
Conclusion
This study presents an affordable, noninvasive, and replicable method for nonlethal determination of Arctic Grayling sex by using digital images from the field, with potential application to other salmonids.
Impact statement
Precise image analysis software and binomial regression models are feasible methods to measure and predict sex in fishes that exhibit sexual dimorphism.
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•ddRAD dataset of the complex genus Thymallus (Salmonidae) was used for this study.•Nuclear and mitochondrial phylogenies show few but important incongruencies.•Rare cases of ...introgression are reported in two of the four contact zones.•Past introgression events are congruent with the hypothesis of Asian dispersal.•Combining markers helps uncover evolutionary histories in non-model organisms.
Hybridization and introgression are very common among freshwater fishes due to the dynamic nature of hydrological landscapes. Cyclic patterns of allopatry and secondary contact provide numerous opportunities for interspecific gene flow, which can lead to discordant paths of evolution for mitochondrial and nuclear genomes. Here, we used double digest restriction-site associated DNA sequencing (ddRADseq) to obtain a genome-wide single nucleotide polymorphism (SNP) dataset comprehensive for allThymallus (Salmonidae)species to infer phylogenetic relationships and evaluate potential recent and historical gene flow among species. The newly obtained nuclear phylogeny was largely concordant with a previously published mitogenome-based topology but revealed a few cyto-nuclear discordances. These incongruencies primarily involved the placement of internal nodes rather than the resolution of species, except for one European species where anthropogenic stock transfers are thought to be responsible for the observed pattern. The analysis of four contact zones where multiple species are found revealed a few cases of mitochondrial capture and limited signals of nuclear introgression. Interestingly, the mechanisms restricting interspecific gene flow might be distinct; while in zones of secondary contact, small-scale physical habitat separation appeared as a limiting factor, biologically based reinforcement mechanisms are presumed to be operative in areas where species presumably evolved in sympatry. Signals of historical introgression were largely congruent with the routes of species dispersal previously inferred from mitogenome data. Overall, the ddRADseq dataset provided a robust phylogenetic reconstruction of the genus Thymallus including new insights into historical hybridization and introgression, opening up new questions concerning their evolutionary history.
•Gonadal steroids concentration did change in European grayling during the examined all reproductive stages.•Relative working fecundity of two-year-old females was 15 % higher than three-year-old.•In ...both of experimental age groups, very low levels of embryo survival to the eyed-egg stage were noted.
The initial experiment of this study was conducted to determine whether sex steroid concentrations varied before, during and after the reproductive season of European grayling (Thymallus thymallus L.) farmed broodstock confined in a recirculation aquaculture system (RAS). The results indicated that the plasma sex steroid (testosterone - T, progesterone - P4 and estradiol - E2) concentrations varied (P < 0.05) during these reproductive periods. There were greater concentrations of T, P4 and E2 before and during the grayling reproductive season indicating there are important functions of these steroid hormones associated with gonadal maturation, gamete production and reproductive behavior during the spawning period. In the second experiment of this study, the effectiveness of European grayling controlled reproduction treatment regimens was analyzed and there were 34.69 % and 68.18 % having ovulations in the 2 and 3-year-old broodfish, respectively. Of the embryos developing to the eyed-egg stage, there were 3.70 % and 6.87 % derived from eggs of 2- and 3-year-old grayling females, respectively. Proportions of embryos developing from the eyed-egg stage to hatching were 38.1 % and 52.1 % from eggs of 2- and 3-year-old grayling females, respectively, when there was culturing in a RAS. The results indicate that with grayling broodfish there is greater efficacy in induction of reproduction when there is imposing of the controlled reproduction treatment regimen on 3- rather than 2-year-old broodfish.
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