Assessment of Fish Embryo Survival and Growth by In Situ Incubation in Acidic Boreal Streams Undergoing Biomining Effluents.

The applicability of an in situ incubation method in monitoring the effects of metal mining on early life stages of fish was evaluated by investigating the impacts of a biomining technology utilizing mine on the mortality, growth, and yolk consumption of brown trout (Salmo trutta) and whitefish (Coregonus lavaretus) embryos. Newly fertilized eggs were incubated from autumn 2014 to spring 2015 in six streams under the influence of the mine located in North-Eastern Finland and in six reference streams. Although the impacted streams clearly had elevated concentrations of several metals and sulfate, the embryonic mortality of the two species did not differ between the impacted and the reference streams. Instead, particle accumulation to some cylinders had a significant impact on the embryonic mortality of both species. In clean cylinders, mortality was higher in streams with lower minimum pH. However, low pH levels were evident in both the reference and the mine-impacted groups. The embryonic growth of neither species was impacted by the mining activities, and the growth and yolk consumption of the embryos was mainly regulated by water temperature. Surprisingly, whitefish embryos incubated in streams with lower minimum pH had larger body size. In general, the applied in situ method is applicable in boreal streams for environmental assessment and monitoring, although in our study, we did not observe a specific mining impact differing from the effects of other environmental factors related to catchment characteristics.

The male handicap: male-biased mortality explains skewed sex ratios in brown trout embryos.

Juvenile sex ratios are often assumed to be equal for many species with genetic sex determination, but this has rarely been tested in fish embryos due to their small size and absence of sex-specific markers. We artificially crossed three populations of brown trout and used a recently developed genetic marker for sexing the offspring of both pure and hybrid crosses. Sex ratios (SR = proportion of males) varied widely one month after hatching ranging from 0.15 to 0.90 (mean = 0.39 ± 0.03). Families with high survival tended to produce balanced or male-biased sex ratios, but SR was significantly female-biased when survival was low, suggesting that males sustain higher mortality during development. No difference in SR was found between pure and hybrid families, but the existence of sire × dam interactions suggests that genetic incompatibility may play a role in determining sex ratios. Our findings have implications for animal breeding and conservation because skewed sex ratios will tend to reduce effective population size and bias selection estimates.

Higher temperature exacerbates the impact of sediments on embryo performances in a salmonid.

In a warming climate, higher temperatures are likely to modulate positively or negatively the effect of other environmental factors on biota, although such interactions are poorly documented. Here, we explore under controlled conditions the combined effects of two common stressors in freshwater ecosystems, higher temperature and sediment load, on the embryonic development of arctic charr (Salvelinus alpinus L.). In the warm treatment, embryos had a lower survival, a longer incubation period and a smaller body size with a bigger yolk sac volume. Our data show a significant interaction between temperature and sediment load with temperature increasing dramatically the negative effects of sediment load on fitness-related traits. In the climate change context, these findings highlight the importance of taking into account different thermal scenarios when examining the effect of environmental or anthropogenic stressors.

Miniature circulatory systems: A new exposure system for ecotoxicological effect assessments in riverine organisms.

Long-term effect assessments in ecotoxicological investigations are important, yet there is a lack of suitable exposure systems for these experiments that can be used for riverine species. A cost-efficient miniature circulatory system was developed that was evaluated for its applicability in long-term exposures in 2 stream-dwelling species: brown trout (Salmo trutta) and an amphipod (Gammarus roeseli). In an egg-to-fry exposure of S. trutta, the toxicity of 2 reverse osmosis concentrates was investigated as examples. Control hatching rate of yolk sac fry was 75 ± 7% and thus complies with the Organisation for Economic Co-operation and Development validity criterion (≥66%). The reverse osmosis concentrates did not impair the hatching rate in any tested concentration. In G. roeseli, mortality rates remained below 20% during a 21-d cultivation, fulfilling the common validity criterion in ecotoxicological testing. Mortality was significantly lower when the species was fed with conditioned alder leaves instead of an artificial shrimp food. Finally, a toxicity test on G. roeseli using copper as the test substance revealed median lethal concentration (LC50) values of 156 µg/L after 96 h and 99 µg/L after 264 h, which is in line with literature findings using other accepted exposure units. In conclusion, the miniature circulatory system provides a novel and cost-efficient exposure system for long-term investigations on riverine species that may also be applicable for other species of fishes and macroinvertebrates. Environ Toxicol Chem 2016;35:2827-2833. © 2016 SETAC.

Transient exposure to environmental estrogen affects embryonic development of brown trout (Salmo trutta fario).

Transient exposure of brown trout embryos from fertilization until hatch (70 days) to 17ß-estradiol (E2) was investigated. Embryos were exposed to 3.8 and 38.0 ng/L E2 for 2h, respectively, under four scenarios: (A) exposure once at the day of fertilization (0 days post-fertilization, dpf), (B) once at eyeing stage (38 dpf), (C) weekly exposure until hatch or (D) bi-weekly exposure until hatch. Endpoints to assess estrogen impact on embryo development were fertilization success, chronological sequence of developmental events, hatching process, larval malformations, heart rate, body length and mortality. Concentration-dependent acceleration of development until median hatch was observed in all exposure scenarios with the strongest effect observed for embryos exposed once at 0 dpf. In addition, the hatching period was significantly prolonged by 4-5 days in groups receiving single estrogen exposures (scenarios A and B). Heart rate on hatching day was significantly depressed with increasing E2 concentrations, with the strongest effect observed for embryos exposed at eyeing stage. Estrogenic exposure at 0 dpf significantly reduced body length at hatch, not depending on whether this was a single exposure or the first of a series (scenarios A and D). The key finding is that even a single, transient E2 exposure during embryogenesis had significant effects on brown trout development. Median hatch, hatching period, heart rate and body length at hatch were found to be highly sensitive biomarkers responsive to estrogenic exposure during embryogenesis. Treatment effects were observable only at the post-hatch stage.

Patterns of miRNA expression in Arctic charr development.

Micro-RNAs (miRNAs) are now recognized as a major class of developmental regulators. Sequences of many miRNAs are highly conserved, yet they often exhibit temporal and spatial heterogeneity in expression among species and have been proposed as an important reservoir for adaptive evolution and divergence. With this in mind we studied miRNA expression during embryonic development of offspring from two contrasting morphs of the highly polymorphic salmonid Arctic charr (Salvelinus alpinus), a small benthic morph from Lake Thingvallavatn (SB) and an aquaculture stock (AC). These morphs differ extensively in morphology and adult body size. We established offspring groups of the two morphs and sampled at several time points during development. Four time points (3 embryonic and one just before first feeding) were selected for high-throughput small-RNA sequencing. We identified a total of 326 conserved and 427 novel miRNA candidates in Arctic charr, of which 51 conserved and 6 novel miRNA candidates were differentially expressed among developmental stages. Furthermore, 53 known and 19 novel miRNAs showed significantly different levels of expression in the two contrasting morphs. Hierarchical clustering of the 53 conserved miRNAs revealed that the expression differences are confined to the embryonic stages, where miRNAs such as sal-miR-130, 30, 451, 133, 26 and 199a were highly expressed in AC, whereas sal-miR-146, 183, 206 and 196a were highly expressed in SB embryos. The majority of these miRNAs have previously been found to be involved in key developmental processes in other species such as development of brain and sensory epithelia, skeletogenesis and myogenesis. Four of the novel miRNA candidates were only detected in either AC or SB. miRNA candidates identified in this study will be combined with available mRNA expression data to identify potential targets and involvement in developmental regulation.

Early fish myoseptal cells: insights from the trout and relationships with amniote axial tenocytes.

The trunk muscle in fish is organized as longitudinal series of myomeres which are separated by sheets of connective tissue called myoseptum to which myofibers attach. In this study we show in the trout that the myoseptum separating two somites is initially acellular and composed of matricial components such as fibronectin, laminin and collagen I. However, myoseptal cells forming a continuum with skeletogenic cells surrounding axial structures are observed between adjacent myotomes after the completion of somitogenesis. The myoseptal cells do not express myogenic markers such as Pax3, Pax7 and myogenin but express several tendon-associated collagens including col1a1, col5a2 and col12a1 and angiopoietin-like 7, which is a secreted molecule involved in matrix remodelling. Using col1a1 as a marker gene, we observed in developing trout embryo an initial labelling in disseminating cells ventral to the myotome. Later, labelled cells were found more dorsally encircling the notochord or invading the intermyotomal space. This opens the possibility that the sclerotome gives rise not only to skeletogenic mesenchymal cells, as previously reported, but also to myoseptal cells. We furthermore show that myoseptal cells differ from skeletogenic cells found around the notochord by the specific expression of Scleraxis, a distinctive marker of tendon cells in amniotes. In conclusion, the location, the molecular signature and the possible sclerotomal origin of the myoseptal cells suggest that the fish myoseptal cells are homologous to the axial tenocytes in amniotes.

Validation of reference genes for expression studies during craniofacial development in arctic charr.

Arctic charr (Salvelinus alpinus) is a highly polymorphic species and in Lake Thingvallavatn, Iceland, four phenotypic morphs have evolved. These differences in morphology, especially in craniofacial structures are already apparent during embryonic development, indicating that genes important in the formation of the craniofacial features are expressed differentially between the morphs. In order to generate tools to examine these expression differences in Arctic charr, the aim of the present study was to identify reference genes for quantitative real-time PCR (qPCR). The specific aim was to select reference genes which are able to detect very small expression differences among different morphs. We selected twelve candidate reference genes from the literature, identified corresponding charr sequences using data derived from transcriptome sequencing (RNA-seq) and examined their expression using qPCR. Many of the candidate reference genes were found to be stably expressed, yet their quality-rank as reference genes varied considerably depending on the type of analysis used. In addition to commonly used software for reference gene validation, we used classical statistics to evaluate expression profiles avoiding a bias for reference genes with similar expression patterns (co-regulation). Based on these analyses we chose three reference genes, ACTB, UB2L3 and IF5A1 for further evaluation. Their consistency was assessed in an expression study of three known craniofacially expressed genes, sparc (or osteonectin), matrix metalloprotease 2 (mmp2) and sox9 (sex-determining region Y box 9 protein) using qPCR in embryo heads derived from four charr groups at three developmental time points. The three reference genes were found to be very suitable for studying expression differences between the morphotypes, enabling robust detection of small relative expression changes during charr development. Further, the results showed that sparc and mmp2 are differentially expressed in embryos of different Arctic charr morphotypes.

Parental influences on pathogen resistance in brown trout embryos and effects of outcrossing within a river network.

Phenotypic plasticity can increase tolerance to heterogeneous environments but the elevations and slopes of reaction norms are often population specific. Disruption of locally adapted reaction norms through outcrossing can lower individual viability. Here, we sampled five genetically distinct populations of brown trout (Salmo trutta) from within a river network, crossed them in a full-factorial design, and challenged the embryos with the opportunistic pathogen Pseudomonas fluorescens. By virtue of our design, we were able to disentangle effects of genetic crossing distance from sire and dam effects on early life-history traits. While pathogen infection did not increase mortality, it was associated with delayed hatching of smaller larvae with reduced yolk sac reserves. We found no evidence of a relationship between genetic distance (W, FST) and the expression of early-life history traits. Moreover, hybrids did not differ in phenotypic means or reaction norms in comparison to offspring from within-population crosses. Heritable variation in early life-history traits was found to remain stable across the control and pathogen environments. Our findings show that outcrossing within a rather narrow geographical scale can have neutral effects on F1 hybrid viability at the embryonic stage, i.e. at a stage when environmental and genetic effects on phenotypes are usually large.

Linking transcriptomic and genomic variation to growth in brook charr hybrids (Salvelinus fontinalis, Mitchill).

Hybridization can lead to phenotypic differences arising from changes in gene expression patterns or new allele combinations. Variation in gene expression is thought to be controlled by differences in transcription regulation of parental alleles, either through cis- or trans-regulatory elements. A previous study among brook charr hybrids from different populations (Rupert, Laval, and domestic) showing distinct length at age during early life stages also revealed different patterns in transcription regulation inheritance of transcript abundance. In the present study, transcript abundance using RNA-sequencing and quantitative real-time PCR, single-nucleotide polymorphism (SNP) genotypes and allelic imbalance were assessed in order to understand the molecular mechanisms underlying the observed transcriptomic and differences in length at age among domestic × Rupert hybrids and Laval × domestic hybrids. We found 198 differentially expressed genes between the two hybrid crosses, and allelic imbalance could be analyzed for 69 of them. Among these 69 genes, 36 genes exhibited cis-acting regulatory effects in both of the two crosses, thus confirming the prevalent role of cis-acting regulatory elements in the regulation of differentially expressed genes among intraspecific hybrids. In addition, we detected a significant association between SNP genotypes of three genes and length at age. Our study is thus one of the few that have highlighted some of the molecular mechanisms potentially involved in the differential phenotypic expression in intraspecific hybrids for nonmodel species.

The influence of parental effects on transcriptomic landscape during early development in brook charr (Salvelinus fontinalis, Mitchill).

Parental effects represent an important source of variation in offspring phenotypes. Depending on the specific mechanisms involved, parental effects may be caused to different degrees by either the maternal or the paternal parent, and these effects may in turn act at different stages of development. To detect parental effects acting on gene transcription regulation and length phenotype during ontogeny, the transcriptomic profiles of two reciprocal hybrids from Laval × Rupert and Laval × Domestic populations of brook charr were compared at hatching, yolk sac resorption and 15 weeks after exogenous feeding. Using a salmonid cDNA microarray, our results show that parental effects modulated gene expression among reciprocal hybrids only at the yolk sac resorption stage. In addition, Laval × Domestic and Laval × Rupert reciprocal hybrids differed in the magnitude of theses parental effects, with 199 and 630 differentially expressed transcripts, respectively. This corresponds to a maximum of 18.5% of the analyzed transcripts. These transcripts are functionally related to cell cycle, nucleic acid metabolism and intracellular protein traffic, which is consistent with observed differences associated with embryonic development and growth differences in other fish species. Our results thus illustrate how parental effects on patterns of gene transcription seem dependent on the genetic architecture of the parents. In addition, in absence of transcriptional differences, non-transcript deposits in the yolk sac could contribute to the observed length differences among the reciprocal hybrids before yolk sac resorption.

Testing for local adaptation in brown trout using reciprocal transplants.

BACKGROUND: Local adaptation can drive the divergence of populations but identification of the traits under selection remains a major challenge in evolutionary biology. Reciprocal transplant experiments are ideal tests of local adaptation, yet rarely used for higher vertebrates because of the mobility and potential invasiveness of non-native organisms. Here, we reciprocally transplanted 2500 brown trout (Salmo trutta) embryos from five populations to investigate local adaptation in early life history traits. Embryos were bred in a full-factorial design and raised in natural riverbeds until emergence. Customized egg capsules were used to simulate the natural redd environment and allowed tracking the fate of every individual until retrieval. We predicted that 1) within sites, native populations would outperform non-natives, and 2) across sites, populations would show higher performance at 'home' compared to 'away' sites. RESULTS: There was no evidence for local adaptation but we found large differences in survival and hatching rates between sites, indicative of considerable variation in habitat quality. Survival was generally high across all populations (55% ± 3%), but ranged from 4% to 89% between sites. Average hatching rate was 25% ± 3% across populations ranging from 0% to 62% between sites. CONCLUSION: This study provides rare empirical data on variation in early life history traits in a population network of a salmonid, and large-scale breeding and transplantation experiments like ours provide powerful tests for local adaptation. Despite the recently reported genetic and morphological differences between the populations in our study area, local adaptation at the embryo level is small, non-existent, or confined to ecological conditions that our experiment could not capture.

Altered gene transcription and telomere length in trout embryo and larvae obtained with DNA cryodamaged sperm.

Sperm cryopreservation could entail DNA damage, promoting base oxidization and strand breaks. In a previous work we showed that trout DNA damaged sperm is able to fertilize leading to embryo loss when the repair system of the oocyte is inhibited. Here we have analysed the later effects on embryo and larvae of fertilizing trout oocytes with cryopreserved DNA-damaged spermatozoa. Fish have weak sperm selection mechanisms, are very prolific and have external embryo development, being convenient models for this type of study. We cryopreserved rainbow trout semen using extenders containing egg yolk or their low density lipoprotein fraction to obtain samples with different degrees of DNA damage. DNA fragmentation was evaluated using the Comet assay and telomere length using quantitative-PCR. Fertilization trials were performed and the transcription at different developmental stages of telomerase reverse transcriptase (Tert) and eight genes related with embryo growth and development (Igf1, Igf2, Igfr1a, Igfr1b, Gh1, Gh2, Ins1 and Ins2) were analyzed using quantitative-PCR in surviving embryos and larvae. Results showed an increase in sperm DNA fragmentation after both cryopreservation procedures as well as a decrease in sperm telomere length. Larvae obtained with damaged sperm showed longer telomeres and Tert overexpression. The transcription of the analyzed genes in these embryos and larvae was also modified with respect to the control, most of them as an increase at hatch. We conclude that fertilization with cryopreserved DNA-damaged spermatozoa significantly affects offspring performance, detectable as an increase in telomere length as well as some alterations in gene expression in surviving embryo and larvae.

Reproduction impairment following paternal genotoxin exposure in brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus).

This work describes some consequences of paternal germ cell DNA damage on the reproduction success in two fish species. Male brown trout (n=31) and male Arctic charr (n=28) were exposed to the model genotoxicant MMS at the end of spermatogenesis to generate a significant DNA damage level in mature spermatozoa (28% and 25% tail DNA in trout and charr sperm, respectively, evaluated through the comet assay). Sperm from each MMS exposed and control fish was then used to fertilize in vitro an aliquot of a single pool of eggs collected from 4 unexposed females for each species. Each batch of fertilized eggs was monitored individually in the hatchery to follow embryonic and larval abnormalities during the fry development. Paternal exposure did not influence fertilization rate or survival rate at hatching in either species. However, MMS paternal treatment resulted in a large array of morphological abnormalities during embryonic and larval development. At the eyed stage, malformations exhibited a 8 fold increase in trout and a 2 fold increase in charr for larvae stemming from MMS treated males as compared with controls. At the end of yolk sac resorption, an increase in the gross morphological abnormality incidence was found in trout larvae originating from MMS exposed males (2.10% vs. 0.93% in control, p<0.05). When looking more in detail at bony structures after Alizarin red S staining, a 20% incidence of skeletal defects was recorded at the swimming stage. A positive correlation was found between the paternal sperm DNA damage level and the skeletal abnormality incidence of its progeny. During the next 2 months of development, mortality in trout originating from DNA damaged sperm was 3 times higher than in control. After one year, no effect of paternal treatment was found on growth traits (length and weight) but the gross morphological abnormality incidence was still very high in the treated group (27% malformation incidence vs. 0.5% in control). These results demonstrate ecologically relevant consequences of fish spermatozoa DNA damage and stress the value of using this parameter as a biomarker signaling potential long term effects of environmental genotoxins in aquatic systems.

Effects of different mating scenarios on embryo viability in brown trout.

Mating with attractive or dominant males is often predicted to offer indirect genetic benefits to females, but it is still largely unclear how important such non-random mating can be with regard to embryo viability. We sampled a natural population of adult migratory brown trout (Salmo trutta), bred them in vitro in a half-sib breeding design to separate genetic from maternal environmental effects, raised 2098 embryos singly until hatching, and exposed them experimentally to different levels of pathogen stress at a late embryonic stage. We found that the embryos' tolerance to the induced pathogen stress was linked to the major histocompatibility complex (MHC) of their parents, i.e. certain MHC genotypes appeared to provide better protection against infection than others. We also found significant additive genetic variance for stress tolerance. Melanin-based dark skin patterns revealed males with 'good genes', i.e. embryos fathered by dark coloured males had a high tolerance to infection. Mating with large and dominant males would, however, not improve embryo viability when compared to random mating. We used simulations to provide estimates of how mate choice based on MHC or melanin-based skin patterns would influence embryos' tolerance to the experimentally induced pathogen stress.

Parental effects on embryonic viability and growth in Arctic charr Salvelinus alpinus at two incubation temperatures.

The parental influences on three progeny traits (survival to eyed-embryo stage, post-hatching body length and yolk-sac volume) of Arctic charr Salvelinus alpinus were studied under two thermal conditions (2 and 7 degrees C) using a factorial mating design. The higher temperature resulted in elevated mortality rates and less advanced development at hatching. Survival was mostly attributable to maternal effects at both temperatures, but the variation among families was dependent on egg size only at the low temperature. No additive genetic variation (or pure sire effect) could be observed, whereas the non-additive genetic effects (parental combination) contributed to offspring viability at 2 degrees C. In contrast, any observable genetic variance in survival was lost at 7 degrees C, most likely due to the increased environmental variance. Irrespective of temperature, dam and sire-dam interaction contributed significantly to the phenotypic variation in both larval length and yolk size. A significant proportion of the variation in larval length was also due to the sire effect at 2 degrees C. Maternal effects were mediated partly through egg size, but as a whole, they decreased in importance at the high temperature, enabling a concomitant increase in non-additive genetic effects. For larval length, however, the additive component, like maternal effects, decreased at 7 degrees C. The present results suggest that an exposure to thermal stress during incubation can modify the genetic architecture of early developmental traits in S. alpinus and presumably constrain their short-term adaptive potential and evolvability by increasing the amount of environmentally induced variation.

Conspecific presence affects the physiology and behaviour of developing trout.

Interactions between conspecifics during embryonic development have the potential to influence phenotypic traits of individuals, with social interaction being particularly important for the realisation of normal behaviours. Here, the effect of increasing numbers of conspecifics (from isolation to groups of 20, 50, 100 and 200) on the physiology and behaviour of developing trout was investigated with the hypothesis that a) conspecific presence would alter physiological processes and b) that development in the absence of conspecifics would affect subsequent behavioural performance. During development, mass, oxygen consumption, sodium uptake and ammonia excretion rates were measured at a variety of time points from fertilisation to after hatching. After first feeding, behaviour of individuals raised in social isolation was compared to behaviour of juvenile fish raised in social groups. Embryos and larvae raised in social isolation had lower oxygen consumption rates, lower sodium uptake rates and higher ammonia excretion rates compared to those raised in groups. Social isolation delayed the response of a juvenile fish to its own mirror image but did not affect the probability of it winning a paired encounter with an individual raised in a social environment. In conclusion, the presence of conspecifics alters physiological processes during trout embryo and larval development and subsequent social behaviours of juveniles.

Effects of vitamin B1 (thiamine) deficiency in lake trout (Salvelinus namaycush) alevins at hatching stage.

The objectives of this study were to examine the relationship between thiamine concentrations in unfertilized eggs and yolksac individuals of lake trout (Salvelinus namaycush), along with any associated histopathological changes in the tissues of alevins at the hatching stage. We address these questions in a lake trout population from different spawning grounds of Lake Michigan (North and South), known for compromised survival due to early mortality syndrome (EMS). However, a dichotomous forage base of lake trout spawning stocks, with a dietary thiaminase-rich alewife in the North, and dietary low-thiaminase round goby in the South, provides the basis for the assumption that different diets may lead to differences in severity of EMS between different stocks. Lake trout eggs of 18 females were collected and fertilized individually with the sperm of several males. The eggs, eyed embryos and newly-hatched alevins were sampled to examine thiamine utilization during embryogenesis. Progenies of females with low (< 0.73 nmol/g) and high (> 0.85 nmol/g) levels of thiamine were chosen for histological studies. The obtained results showed that total thiamine levels in the body and yolk of eyed embryos and alevins at hatching were influenced by thiamine levels of unfertilized eggs and it decreased during embryogenesis (to 51% in eyed embryos and 28% in newly-hatched alevins in comparison to unfertilized eggs). The survival of lake trout until hatching stage does not correlate with the thiamine level, however it was affected by collection site and was significantly higher in fish from the South site (Julian's Reef). At the hatching stage, no pathological changes were observed in the brain, olfactory lobe, retina or liver in embryos regardless of thiamine concentrations in unfertilized eggs. It has been concluded that an enhanced thiamine requirement for the fast muscle mass growth near the swim-up stage is responsible for overt and histopathological signs of EMS. Current study confirms earlier findings that lake trout suffering from EMS can be successfully treated by immersion in thiamine solution as late as at the swim-up stage.

Effect of temperature on heart rate in diploid and triploid brook charr, Salvelinus fontinalis, embryos and larvae.

Increased cell size in triploid fish likely affects rates of respiratory gas exchange. Respiratory deficiencies can be addressed in fish by adjustments in cardiac output, through changes in heart rate and stroke volume. The aim of this study was to determine whether heart rate differs between triploid and control (diploid) brook charr, Salvelinus fontinalis, at embryo-larval stages, when the heart is easily visible and the fish are relatively inactive. Heart rate was measured at 6, 9 and 12 degrees C at three developmental stages: eyed-egg, hatch and yolk absorption. Heart rate was unaffected by ploidy, but increased with temperature and age from a low of 43.4+/-2.2 beats/min (6 degrees C, eyed egg) to a high of 73.3+/-1.5 beats/min (12 degrees C, yolk absorption). The Q(10) for heart rate was unaffected by ploidy and age, but decreased with temperature from 1.99+/-0.28 at 6-9 degrees C to 1.72+/-0.17 at 9-12 degrees C. Triploid brook charr thus do not use adjustments in heart rate as a mechanism to deal with the physiological consequences of altered haematology at embryo-larval stages.

A review of the likely effects of climate change on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta, with particular reference to water temperature and flow.

The present paper reviews the effects of water temperature and flow on migrations, embryonic development, hatching, emergence, growth and life-history traits in light of the ongoing climate change with emphasis on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta. The expected climate change in the Atlantic is for milder and wetter winters, with more precipitation falling as rain and less as snow, decrease in ice-covered periods and frequent periods with extreme weather. Overall, thermal limits for salmonids are species specific. Scope for activity and growth and optimal temperature for growth increase with temperature to an optimal point before constrain by the oxygen content of the water. The optimal temperature for growth decreases with increasing fish size and varies little among populations within species, whereas the growth efficiency may be locally adapted to the temperature conditions of the home stream during the growth season. Indirectly, temperature influences age and size at smolting through its effect on growth. Time of spawning, egg hatching and emergence of the larvae vary with temperature and selective effects on time of first feeding. Traits such as age at first maturity, longevity and fecundity decrease with increasing temperature whilst egg size increases with temperature. Water flow influences the accessibility of rivers for returning adults and speed of both upstream and downstream migration. Extremes in water flow and temperature can decrease recruitment and survival. There is reason to expect a northward movement of the thermal niche of anadromous salmonids with decreased production and population extinction in the southern part of the distribution areas, migrations earlier in the season, later spawning, younger age at smolting and sexual maturity and increased disease susceptibility and mortality. Future research challenges are summarized at the end of the paper.