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Critical thermal maximum (CT max ) is widely used to measure upper thermal tolerance in fish but is rarely examined in embryos. Upper thermal limits generally depend on an individual's thermal history, which molds plasticity. We examined how thermal acclimation affects thermal tolerance of brook trout (Salvelinus fontinalis) embryos using a novel method to assess CT max in embryos incubated under three thermal regimes. Warm acclimation was associated with an increase in embryonic upper thermal tolerance. However, CT max variability was markedly higher than is typical for juvenile or adult salmonids., (© 2023 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Background: The salmon parasite Gyrodactylus salaris Malmberg, 1957 has caused high mortalities in many Atlantic salmon, Salmo salar, populations, mainly in Norway. The parasite is also present in several countries across mainland Europe, principally on rainbow trout, Oncorhynchus mykiss, where infections do not seem to result in mortalities. There are still European countries where there are potential salmonid hosts for G. salaris but where the occurrence of G. salaris is unknown, mainly due to lack of investigations and surveillance. Gyrodactylus salaris is frequently present on rainbow trout in low numbers and pose a risk of infection to local salmonid populations if these fish are subsequently translocated to new localities., Methods: Farmed rainbow trout Oncorhynchus mykiss (n = 340), brook trout, Salvelinus fontinalis (n = 186), and brown trout, Salmo trutta (n = 7), and wild brown trout (n = 10) from one river in Romania were sampled in 2008 and examined for the presence of Gyrodactylus spp. Alltogether 187 specimens of Gyrodactylus spp. were recovered from the fish. A subsample of 76 specimens representing the different fish species and localities were subjected to species identification and genetic characterization through sequencing of the ribosomal internal transcribed spacer 2 (ITS2) and mitochondrial cytochrome c oxidase subunit 1 (cox1)., Results: Two species of Gyrodactylus were found, G. salaris and G. truttae Gläser, 1974. This is the first time G. salaris is diagnosed in Romania. Gyrodactylus salaris was found to infect rainbow trout, brown trout and brook trout in eight of the 12 farms examined. The prevalence and intensity of infections were generally low in all farms. Gyrodactylus truttae was present on brook trout in one farm and on wild brown trout in the river studied. This also represents the first record of this parasite in Romania. Analyses of sequences of the cox1 gene of G. salaris from Romania revealed four haplotypes, all previously undescribed. While it is not unlikely that the infections in Romanian fish farms originate directly from imported rainbow trout, the current data is not sufficient to conclude on this and does not exclude that the infections can originate from hosts in the local water systems. The study shows that there are still unknown populations and variants (haplotypes) of G. salaris present in European rainbow trout aquaculture, all or many of them with unknown biological characteristics such as host specificity and virulence. As some strains might be pathogenic to Atlantic salmon, the importance of carrying out surveillance and keeping a high focus on control with import and export of live fish for aquaculture purposes is important., Conclusions: Gyrodactylus salaris and G. truttae are for the first time found on salmonids in Romania. All mitochondrial haplotypes recovered were previously undescribed and this indicates that there is still an unknown diversity of this parasite present in localities not previously examined. The virulence of the haplotypes found in Romania is unknown and requires establishing.

In many freshwater ecosystems, carbon dioxide (CO2) is increasing. Unknown are the risks that high CO2 poses for freshwater organisms, especially fish. The objective of this study was to determine how CO2 may influence the growth rate, metabolic rate, feeding rate, and volitional behaviour of young-of-year Arctic charr (Salvelinus alpinus (Linnaeus, 1758)), brook charr (Salvelinus fontinalis (Mitchill, 1814)), and rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). For this study, fish stayed in control (1100 microatmospheres (µatm)) or elevated (5236 µatm) CO2 levels for 15 days. During this time, metabolic rate and behavioural tests were conducted on alternating days for each treatment. Weight and length of each fish were taken on days 0, 7, and 15. There was no evidence that elevated CO2 affected the growth rate, feeding rate, or behaviour in any of these species. The standard metabolic rate in Arctic charr differed based on CO2 exposure. Therefore, salmonids can withstand short periods of elevated CO2 under these conditions. By comparing closely related species, the implications of this work are more ecologically relevant and will also help industry quantify the effects of high CO2 on young salmonids. [ABSTRACT FROM AUTHOR]

Indicators of the condition factor, growth rate, and quality of the final products of cultivated objects are important parameters for the effective management of cold-water fish farming. These indicators are also used as a way to control the impact of environmental factors on fish, which requires constant research in the context of intensification of the aquaculture sector. The research is aimed at determining the condition factor and the amino acid composition of muscle tissues of Salmo trutta fario (Linnaeus, 1758), Oncorhynchus mykiss (Walbaum, 1792) and Salvelinus fontinalis (Mitchill, 1814) under the conditions of the western region of Ukraine. The results of the condition factor showed that, S. fontinalis had the highest value with 1.52±0.0340, and O. mykiss and S. trutta showed the lowest value with 1.33±0.0361 and 1.26±0.0181, respectively. Food conversion ratios were similar for S. fontinalis and O. mykiss (1.0), whereas S. trutta showed higher values (1.4). The specific growth rate was higher for rainbow trout (1.4) compared to the brook trout (1.32) and brown trout (1.28). The maximum content of protein, total amino acids (TAA), total essential amino acids (TEAA) and nonessential amino acids (TNEAA) were recorded in the brook trout. The muscle tissue of the investigated fish species is a well-balanced source of the nutrition energy in terms of the ratio of total essential to total nonessential amino acids (TEAA:TNEAA ratio). [ABSTRACT FROM AUTHOR]

Hematological parameters of fish are useful for diagnosing pathophysiological conditions associated with metabolic perturbations in fish and therefore act as a non-specific biomarker of acute and chronic stress in the natural habitat and in aquaculture. Salmonid fish are of great importance in aquaculture; however, hematological studies of these species are scarce. This study presents the first set of data for the complete hematological profile of brook trout (Salvelinus fontinalis, Salmonidae). In total, seven blood cell types were identified and their characterization, range, size/surface area, and the leukocyte differential count are presented. Large numbers of immature erythrocytes and two subtypes of thrombocytes (round and prolate) were present in blood. Lymphocytes were the dominant leukocytes, followed by segmented neutrophils. Total leukocyte and segmented neutrophil counts were higher in the blood of male than female fish (P < 0.05). Here we describe, for the first time, basophilic cells in salmonid fish species. Blood cell types present in brook trout were similar to mammalian blood cells, but their morphology, number, size, and subtypes were unique to this fish species. The established reference model indicates differences in comparison with the cyprinid fish. The hematological profile described in this study will serve as an important model for examining comparative physiology of blood cells in other salmonid fish and will provide useful diagnostic criteria in aquaculture for the detection and mitigation of different pathological outcomes. [ABSTRACT FROM AUTHOR]

Manual removal of non-native brown trout (Salmo trutta) led to increased abundance and improved size structure of a native brook trout (Salvelinus fontinalis) population. Reproductive dynamics of brook trout in response to release from this competitor were quantified using 14 microsatellite DNA loci to estimate effective population sizes, family sizes, and parentage across five cohorts. We hypothesized that brown trout removal allowed more brook trout to reproduce and distribute reproductive success more evenly among individuals, thereby increasing generational effective population size (Ne) and cohort effective number of breeders (Nb). However, N ^ e varied little (27–32), but was estimated for only one generation before and after removals began. Similarly, N ^ b differed little between pre-removal (21–25) and post-removal (19–23) cohorts, because increased numbers of reproductively successful adults were offset by highly skewed family sizes. Variance in family size increased following brown trout removal, but was uncorrelated with brook trout abundance across all years. Although most individuals matured at a small size, reproductive success increased with length. Increased abundance of adult brook trout has not increased N ^ b and N ^ e remains low. Managers should consider moving adults from nearby populations to increase genetic diversity of this isolated population. [ABSTRACT FROM AUTHOR]

We used direct observation via snorkeling surveys to quantify microhabitat use by native brook (Salvelinus fontinalis) and non‐native brown (Salmo trutta) and rainbow (Onchorynchus mykiss) trout occupying natural and restored pool habitats within a large, high‐elevation Appalachian river, United States. Permutational multivariate analysis of variance (PERMANOVA) and subsequent two‐way analysis of variance (ANOVA) indicated a significant difference in microhabitat use by brook and non‐native trout within restored pools. We also detected a significant difference in microhabitat use by brook trout occupying pools in allopatry versus those occupying pools in sympatry with non‐native trout—a pattern that appears to be modulated by size. Smaller brook trout often occupied pools in the absence of non‐native species, where they used shallower and faster focal habitats. Larger brook trout occupied pools with, and utilized similar focal habitats (i.e. deeper, slower velocity) as, non‐native trout. Non‐native trout consistently occupied more thermally suitable microhabitats closer to cover as compared to brook trout, including the use of thermal refugia (i.e. ambient–focal temperature >2°C). These results suggest that non‐native trout influence brook trout use of restored habitats by: (1) displacing smaller brook trout from restored pools, and (2) displacing small and large brook trout from optimal microhabitats (cooler, deeper, and lower velocity). Consequently, benefits of habitat restoration in large rivers may only be fully realized by brook trout in the absence of non‐native species. Future research within this and other large river systems should characterize brook trout response to stream restoration following removal of non‐native species. [ABSTRACT FROM AUTHOR]

Host-parasite interactions may play a significant role in biological invasions: for example, an invader may benefit from lower infectivity by native parasites in competition against the native hosts ('enemy release hypothesis')., The invasive North American brook trout ( Salvelinus fontinalis) is replacing the native salmonid hosts of the freshwater pearl mussel (FPM, Margaritifera margaritifera) in northern Europe, but the suitability of brook trout as a host for FPM is poorly known. In this study its suitability was investigated using an array of laboratory and field experiments, and several FPM populations from a catchment in northern Finland. The occurrence of brook trout in FPM rivers in the area was also studied., There were differences with respect to numbers and size of FPM larvae among the fish exposed to FPM, but generally brook trout was an unsuitable host or was clearly a poorer host for FPM than the native European salmonids, brown trout ( Salmo trutta) or Atlantic salmon ( Salmo salar). However, in one river a few FPM glochidia remained encysted in wild brook trout for at least 9 months, suggesting successful development - the first observation of its kind in Europe., A tendency was found for higher occurrence of brook trout in brown trout rivers with FPM than in brown trout rivers without FPM, being consistent with the enemy release hypothesis: as FPM infection is costly to the host, a higher glochidial load in brown trout may offer a competitive advantage to brook trout in FPM rivers., Generally, these results indicate that northern European FPM populations cannot typically use brook trout as their host fish. Therefore, the invasion and dispersal of brook trout, potentially leading to the disappearance of native salmonids, should also be considered as a potential threat to the endangered FPM populations., Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background. Salmonid spermatozoa are characterised by a very short time of activity in the water, therefore sudden water pollution in the form of increased salinity on the spawning grounds may have a negative effect on the sperm motility parameters, thus affecting the subsequent egg fertilisation and, consequently, the number of hatched individuals of the species. The aim of this study was to determine the effect of water salinity on the motility parameters of spermatozoa of brook trout, Salvelinus fontinalis (Mitchill, 1814). Material and methods. Sperm motility was monitored with a camera (Basler A312fc) coupled with Nikon Eclipse 50i light microscope from the moment of their activation (contact with water) until the cessation of movement. The following water-salinity treatments were tested: 1.0‰, 3.0‰, 5.0‰, and 10.0‰. The motility parameters: VCL, VSL, VAP, ALH, BCF, LIN, STR, WOB, and MOT, were analysed with Computer Assisted Sperm Analysis (CASA). Results. The mean values of the studied motility parameters of the brook trout spermatozoa (obtained within 30 s), whose activation took place in the water of 0.35‰ salinity and in water of 1.0‰ and 3.0‰ salinity, did not differ significantly. The highest mean values of motility parameters were recorded for the water of 5.0‰ salinity. The 10.0‰ treatment caused a distinct decrease in the values of all the studied parameters. The percentage of MOT was the highest (37.5%) in the sample activated in the water used for fi sh rearing (0.35‰). In the remaining samples the MOT was lower, and in the water of 10.0‰ salinity it was only 9.1%. No spermatozoa movement of any kind was recorded in the 35th second of the experiment. Conclusion. The values of the motility parameters as well as the percentage of motile spermatozoa (MOT) in the semen decrease with increasing salinity of the water used for activation, and with increasing time of exposure. [ABSTRACT FROM AUTHOR]

Les introductions de Salmonidés ont été importantes au cours des 60 dernières années dans les lacs et ruisseaux d'altitude des Hautes-Pyrénées. Six espèces de Salmonidés ont été introduites dans des milieux qui, pour la plupart, étaient vierges de populations piscicoles : la truite commune (Salmo trutta L.), la truite arc-en-ciel (Oncorhynchus mykiss Walbaum), l'omble de fontaine (Salvelinus fontinalis Mitchill), l'omble chevalier (Salvelinus alpinus L.), le cristivomer (Salvelinus namaycush Walbaum) et le splake (Salvelinus fontinalis x Salvelinus namaycush). Dans de très nombreux cas, ces introductions ont abouti à des acclimatations. En revanche, les naturalisations sont beaucoup plus rares. Seules les espèces lacustres (cristivomer et omble chevalier) se sont naturalisées dans la majorité des lacs où elles ont été introduites. Les conditions de reproduction constituent le facteur clé permettant d'expliquer la naturalisation des espèces. En ruisseau, il faut y ajouter la compétition avec l'espèce indigène (la truite commune), la pression halieutique ainsi que les conditions hivernales très rigoureuses. Les incidences écologiques des introductions sur les populations de truites communes indigènes sont faibles. En revanche, elles ne sont pas négligeables pour les populations de batraciens. Cette politique d'introduction a largement participé au développement de l'halieutisme dans ces milieux d'altitude. En cela, les introductions ont parfaitement répondu aux objectifs halieutiques qu'on leur avait fixés. L'acquisition de connaissances sur l'ensemble de la chaîne pyrénéenne constitue aujourd'hui une étape incontournable pour une politique de gestion globale des introductions.

Abstract: Distributions of species, animals or plants, terrestrial or aquatic, are influenced by numerous factors such as physical and biogeographical gradients. Dominant wind and current directions cause the appearance of gradients in physical conditions whereas biogeographical gradients can be the result of historical events (e.g. glaciations). No spatial modelling technique has been developed to this day that considers the direction of an asymmetric process controlling species distributions along a gradient or network. This paper presents a new method that can model species spatial distributions generated by a hypothesized asymmetric, directional physical process. This method is an eigenfunction-based spatial filtering technique that offers as much flexibility as the Moran''s eigenvector maps (MEM) framework; it is called asymmetric eigenvector maps (AEM) modelling. Information needed to construct eigenfunctions through the AEM framework are the spatial coordinates of the sampling or experimental sites, a connexion diagram linking the sites to one another, prior information about the direction of the hypothesized asymmetric process influencing the response variable(s), and optionally, weights attached to the edges (links). To illustrate how this new method works, AEM is compared to MEM analysis through simulations and in the analysis of an ecological example where a known asymmetric forcing is present. The ecological example reanalyses the dietary habits of brook trout (Salvelinus fontinalis) sampled in 42 lakes of the Mastigouche Reserve, Québec. [Copyright &y& Elsevier]

In this study, we repeatedly observed individually marked Brook Trout in a field setting to determine if the bimodal variation in foraging tactics previously observed in young salmonid populations (without distinct morphological differences) is generated by individuals specializing at different foraging tactics. We found significant but low repeatability in several foraging movement parameters. This indicated that while individuals did have tendencies to be sedentary versus highly active, there was considerable variation in foraging activity within individuals. These results suggest that relatively consistent differences among individuals may facilitate selection for specialized morphology and that there may be a heritable component to activity. [ABSTRACT FROM AUTHOR]

Recently emerged brook charr foraging in still-water pools along the sides of streams tend to be either sedentary, feeding from the lower portion of the water column (a sit-and-wait tactic) near the stream bank, or very active, feeding from the upper portion of the water column (an active search tactic) away from the bank. We tested whether the search tactics used by charr in the field represent behavioural syndromes related to activity and space use. After quantifying the behaviour of fish in the field, focal individuals were captured and their behaviour quantified in novel environment experiments in the laboratory. In an aquarium, individuals that used an active search tactic in the field spent a higher proportion of time moving, spent less time near the aquarium bottom, and took less time to find their way out of an erect glass jar, on average, than did individuals that used a sit-and-wait tactic in the field. When presented with near-bank and open-water conditions over 6 days in the laboratory, individuals that used an active search tactic in the field remained active and altered their activity less, on average, than individuals that used a sit-and-wait tactic in the field. Immediate responses to a pebble dropped in the aquarium (simulated risk from above) were not correlated with field behaviour. The search tactics used by brook charr in the field reflect part of a behavioural syndrome related to general activity and space use, but not to startle responses. These initial, individual differences in behaviour provide important raw material for the initial stages of resource polymorphism. [Copyright &y& Elsevier]

The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty-seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis. [ABSTRACT FROM AUTHOR]

In this study, data on the incubation of eggs, survival rates and development of brook trout (Salvelinus fontinalis, Mitchill 1814) larvae and alevins were evaluated. Durations of eyeing, hatching and swim-up were 245, 415 and 675 degree-days at a temperature range of 4-12 °C, while survival rates from fertilisation to hatching and from fertilisation to swim-up stage were 56.5% ± 24.28 and 52.0% ± 23.67, respectively. Alevin weight exhibited a positive relationship with egg size (r = 0.945, P < 0.01). [ABSTRACT FROM AUTHOR]

Abstract To examine constraints on evolution of larger body size in two stunted populations of brook charr (Salvelinus fontinalis ) from a single river in Cape Race, Newfoundland, Canada, we measured viability selection acting on length-at-age traits, and estimated quantitative genetic parameters in situ (following reconstruction of pedigree information from microsatellite data). Furthermore we tested for phenotypic differentiation between the populations, and for association of high juvenile growth with early maturity that is predicted by life history theory. Within each population, selection differentials and estimates of heritabilities for length-at-age traits suggested that evolution of larger size is prevented by both selective and genetic constraints. Between the populations, phenotypic differentiation was found in length-at-age and age of maturation traits, whereas early maturation was associated with increased juvenile growth (relative to adult growth) both within and between populations. The results suggest an adaptive plastic response in age of maturation to juvenile growth rates that have a largely environmental basis of determination. [ABSTRACT FROM AUTHOR]

Habitat assessments are often based on the premise that spatial variation in population density arises from, and accurately reflects, underlying differences in quality among habitats. Nonetheless, this premise has been criticized on both theoretical and empirical grounds. Habitat quality perhaps is best evaluated by examining behavioural processes which directly influence habitat use. We present an approach based on the assumption that measures of local movement, such as habitat-specific immigration and loss rates, provide useful indicators of habitat quality. A dynamic turnover model was used in conjunction with mark-recapture techniques to estimate movement parameters for brook charr, Salvelinus fontinalis, and Atlantic salmon, Salmo salar, in different stream habitats during the summer. Immigration and loss rates were derived from mark-recapture experiments covering short periods of time (6 days). Movement-based rankings of habitat quality for both charr (pools ≥ glides > riffles) and salmon (riffles > glides > pools) were in agreement with results from earlier studies. Over evaluation periods of up to 65 days, observed abundances were highly variable in time and fluctuated about the equilibrium abundances calculated from movement parameters in the short-term experiments, suggesting that movement-based parameters may be more stable than measures of abundance for evaluating salmonid habitat. Because the approach based on movement behaviour focuses on immigration and loss, two processes that directly generate density differentials between habitats, it provides a more reliable mechanistic basis for understanding habitat selection than do traditional approaches based on density–quality relationships. [ABSTRACT FROM AUTHOR]

Simple Summary: There has been intensive research addressing the positive effects of different prolonged photoperiods on wide spectrum of aspects of salmonids aquaculture. The present study was an attempt to assess non-circadian photoperiod regimens on growth and puberty onset of brook trout. We found regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light to be remarkably effective on the delay of gonad development and onset of puberty, enabling fish farmers to fight with negative aspects related to brook trout puberty. The aim of the present study was to assess the effects of a prolonged photoperiod on growth rate and sexual maturation in brook trout Salvelinus fontinalis. The task of the experiment was to determine the most effective light regimen capable to minimizing the effects of puberty, including impairment of somatic growth and further general characteristics. In this regard, the studied fish were reared under three photoperiod regimens in which fish were exposed to 24 h continuous light alternating with 24 or 48 h under the ambient photoperiod or 48 h continuous light alternating with a 24 h ambient photoperiod. A control group was reared under the natural ambient photoperiod. Four-hundred and fifty fish with an average initial body weight of 101.3 ± 1.2 g were used for each experimental group (three replicates of each treatment plus control). A statistically lower growth rate showed control groups in both sexes. At the end of the study, control males had an average body weight of 226.6 ± 39.8 g and control females a body weight of 199.8 ± 12.2 g. At the same period, a significantly higher average body weight was found in groups reared 24 h under ambient photoperiod alternating with a 48 h continuous light regime (2CP:1AP) in both sexes (296.56 ± 62.5 g—males, and 239.9 ± 19.2 g—females, respectively). A significantly higher percentage of sexually mature fish was observed in the control group (80% of males and 29% of females, respectively). We found significantly fewer sexually mature females compared to males. The lowest survival was observed in group 2CP:1AP at 92%. It was concluded that regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light (1CP:2AP) lead to the successful delay of gonad development and onset of puberty and increased somatic growth in both sexes. [ABSTRACT FROM AUTHOR]