Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus).

The diversity of functional feeding anatomy is particularly impressive in fishes and correlates with various interspecific ecological specializations. Intraspecific polymorphism can manifest in divergent feeding morphology and ecology, often along a benthic-pelagic axis. Arctic charr (Salvelinus alpinus) is a freshwater salmonid known for morphological variation and sympatric polymorphism and in Lake Þingvallavatn, Iceland, four morphs of charr coexist that differ in preferred prey, behaviour, habitat use, and external feeding morphology. We studied variation in six upper and lower jaw bones in adults of these four morphs using geometric morphometrics and univariate statistics. We tested for allometric differences in bone size and shape among morphs, morph effects on bone size and shape, and divergence along the benthic-pelagic axis. We also examined the degree of integration between bone pairs. We found differences in bone size between pelagic and benthic morphs for two bones (dentary and premaxilla). There was clear bone shape divergence along a benthic-pelagic axis in four bones (dentary, articular-angular, premaxilla and maxilla), as well as allometric shape differences between morphs in the dentary. Notably for the dentary, morph explained more shape variation than bone size. Comparatively, benthic morphs possess a compact and taller dentary, with shorter dentary palate, consistent with visible (but less prominent) differences in external morphology. As these morphs emerged in the last 10,000 years, these results indicate rapid functional evolution of specific feeding structures in arctic charr. This sets the stage for studies of the genetics and development of rapid and parallel craniofacial evolution.

Genetic and correlative light and electron microscopy evidence for the unique differentiation pathway of erythrophores in brown trout skin.

Based on their cell ultrastructure, two types of erythrophores in the spotted skin regions of brown trout (Salmo trutta) were previously described. To test the hypothesis regarding the origin of a new cell type following genome duplication, we analysed the gene and paralogue gene expression patterns of erythrophores in brown trout skin. In addition, the ultrastructure of both erythrophore types was precisely examined using transmission electron microscopy (TEM) and correlative light microscopy and electron microscopy (CLEM). Ultrastructural differences between the sizes of erythrophore inclusions were confirmed; however, the overlapping inclusion sizes blur the distinction between erythrophore types, which we have instead defined as cell subtypes. Nevertheless, the red spots of brown trout skin with subtype 2 erythrophores, exhibited unique gene expression patterns. Many of the upregulated genes are involved in melanogenesis or xanthophore differentiation. In addition, sox10, related to progenitor cells, was also upregulated in the red spots. The expressions of paralogues derived from two genome duplication events were also analysed. Multiple paralogues were overexpressed in the red spots compared with other skin regions, suggesting that the duplicated gene copies adopted new functions and contributed to the origin of a new cell subtype that is characteristic for red spot. Possible mechanisms regarding erythrophore origin are proposed and discussed. To the best of our knowledge, this is the first study to evaluate pigment cell types in the black and red spots of brown trout skin using the advanced CLEM approach together with gene expression profiling.

Temporal analysis shows relaxed genetic erosion following improved stocking practices in a subarctic transnational brown trout population.

Maintaining standing genetic variation is a challenge in human-dominated landscapes. We used genetic (i.e., 16 short tandem repeats) and morphological (i.e., length and weight) measurements of 593 contemporary and historical brown trout (Salmo trutta) samples to study fine-scale and short-term impacts of different management practices. These had changed from traditional breeding practices, using the same broodstock for several years, to modern breeding practices, including annual broodstock replacement, in the transnational subarctic Pasvik River. Using population genetic structure analyses (i.e., Bayesian assignment tests, DAPCs, and PCAs), four historical genetic clusters (E2001A-D), likely representing family lineages resulting from different crosses, were found in zone E. These groups were characterized by consistently lower genetic diversity, higher within-group relatedness, lower effective population size, and significantly smaller body size than contemporary stocked (E2001E) and wild fish (E2001F). However, even current breeding practices are insufficient to prevent genetic diversity loss and morphological changes as demonstrated by on average smaller body sizes and recent genetic bottleneck signatures in the modern breeding stock compared to wild fish. Conservation management must evaluate breeding protocols for stocking programs and assess if these can preserve remaining natural genetic diversity and morphology in brown trout for long-term preservation of freshwater fauna.

A new species of trout from the northern drainages of Euphrates River, Turkey (Salmoniformes: Salmonidae).

Salmo fahrettini, a new species, is distributed in the northern tributaries of the Euphrates River. It differs from other Salmo species in adjacent waters by a combination of the following characters: a greyish body; one black spot behind the eye and on the cheek; three to six black spots on the opercle; numerous black spots on the back (missing on the predorsal area), flank and middle part of body, surrounded by a roundish white ring; red spots in the median part of the body, surrounded by a roundish white ring; short and narrow maxilla; increase in the number of black and red spots with an increase in size; adipose fin medium size, no or rarely one red spot at its posterior edge; 109-116 lateral line scales; 27-30 scale rows between dorsal-fin origin and lateral line; 20-23 scale rows between the lateral line and anal-fin origin; maxilla length 8.8-10.0% standard length in males, 8.8-9.6 in females.

Heritable morphological differentiation in salmonids from two distinct stream types.

We tested for phenotype-to-habitat associations in brown trout Salmo trutta populations from two ecologically different habitat types; i.e., groundwater and surface-water-fed streams. Additionally, we raised captive offspring from two such populations under standardised conditions to test whether potential phenotypic differentiation would be passed on to offspring. We found analogous differentiation by habitat in multiple wild populations. Some of these morphological differences were at least partially inherited by offspring. We suggest that this could have implications for both scientists and fisheries authorities studying or managing trout populations.

Effect of dietary soybean lecithin on fish performance, hemato-immunological parameters, lipid biochemistry, antioxidant status, digestive enzymes activity and intestinal histomorphometry of pre-spawning Caspian brown trout (Salmo trutta caspius).

A feeding experiment was conducted to evaluate the effects of dietary soybean lecithin (SBL) supplementation on performance, hemato-immunological parameters, lipid biochemistry, antioxidant status, digestive enzymes activity and intestinal histomorphometry of Caspian brown trout, Salmo trutta caspius in the pre-spawning stage. The basal diet was supplemented with 0% (control), 3%, 6%, 9% and 12% of SBL to obtain five experimental diets. Fish with an average weight of 350 ±â€¯10 g were randomly distributed among five experimental groups and fed for 90 days. Dietary SBL resulted in better performance including specific growth rate (SGR), weight gain (WG) and feed conversion ratio (FCR) (p < 0.05). Among the different hemato-immunological parameters, white blood cell counts (WBC), lysozyme, alternative complement activity (ACH50) and total immunoglobulin (IgM) content of serum were significantly increased with dietary SBL inclusion (p < 0.05). For antioxidant enzymes, glutathione S-transferase (GST) and catalase (CAT) showed significant differences among various experimental diets (p < 0.05). Furthermore, digestive enzymes activity including alkaline protease, lipase and amylase were increased in those fish received SBL supplemented diets (p < 0.05). Our results revealed that the dietary SBL improved some physiological responses of the fish and indicate 6-9% dietary SBL supplementation would improve the physiological competence of the pre-spawning Caspian brown trout breeders.

Subtle temperature increase can interact with individual size and social context in shaping phenotypic traits of a coldwater fish.

Temperature and individual egg size have been long studied in the development of fishes because of their direct effects on individual fitness. Here we studied the combined effects of three important factors for fish development, i.e. egg size, social environment and water temperature. Arctic charr (Salvelinus alpinus), a coldwater fish known to be phenotypically plastic, was used to investigate how these factors may affect growth and foraging behaviour of juvenile fish in a benign environment. We accounted for the social environment during early development by comparing fish raised in groups and in isolation. We examined the effect of egg size and a 2 °C difference on foraging behaviour, activity and growth a few weeks after first feeding. Growth trajectories of fish originating from large and small eggs were similar within each temperature: larger fish coming large eggs were at all time larger than smaller fish. There was no indication that small fish raised at a higher temperature grew faster than larger fish raised at a lower temperature. A 2 °C difference in temperature affected the behaviour of fish differently according to body size and/or social context. The foraging probability difference between fish raised in groups and fish briefly isolated was higher at 4.5 °C than at 6.5 °C for both size fish. Finally, there was no repeatability in foraging behaviour and mobility for isolated individuals. These results highlight the importance of small changes in temperature when evaluating growth and behaviour of fishes, and reveal the importance of considering the interaction of temperature with other factors, e.g. individual size and social environment, especially at early stages of development in fishes. We discuss these findings in the context of rapid changes in temperature and how temperature and its interaction with other factors may affect the phenotypes, ecology and evolution of coldwater fishes.

Body shape and robustness response to water flow during development of brown trout Salmo trutta parr.

Domesticated brown trout Salmo trutta parr were subjected to increased, variable flow under controlled experimental conditions. Using geometric morphometric analyses, K¯ (a mass-length index) and caudal fin area-body length ratio, this study assessed morphological responses in lateral body depth, growth and robustness and propulsive potential, respectively, of parr over the course of 32 weeks. Geometric morphometric analyses did not reveal an effect of exercise on either lateral body depth or caudal fin area. However, improved overall robustness and growth trajectories in exercised parr showed a positive adaptive response to the enriched habitat. Exercise and habitat heterogeneity thus have the potential to improve survivability of domesticated salmonids in the wild.

Pontoon trap for salmon and trout equipped with a seal exclusion device catches larger salmons.

The growing seal populations of the Baltic have led to more frequent interactions with coastal fisheries. The motivation for seals to interact with fishing gear is high. It provides high densities of fish. A successful means of mitigating the conflict is the pontoon trap. Seal visits here have been frequent. Seals have access to most parts of the trap system including the middle chamber, which is an overhead environment. Concerns have been raised about seals possible entanglement in this specific part of the trap. As a means of keeping seals from entering the middle chamber, two different Seal Exclusion Devices (SEDs) were tested. A diamond mesh SED and a square mesh SED, which was rotated 45°. The aim was to compare the functionality of the different SEDs with respect to seal deterrent abilities and catch composition. The hypothesis tested were (i) that seals would not be able to enter the middle chamber, (ii) that the catch would increase and (iii) that the SED would deter larger fish from swimming into the middle chamber. Catch data and underwater film were collected. Larger salmons were caught in traps equipped with SEDs. The SEDs did not affect the number of caught fish or the total catch per soak day.

Introgressive hybridization between wild and domestic individuals and its relationship with parasitism in brook charr Salvelinus fontinalis.

The effects of introgression on parasitism in brook charr Salvelinus fontinalis were investigated in 28 lakes with various levels of stocking in Québec, Canada. No effect of genetic background on parasitism was found at the individual level. Body length seemed to explain most of the variation observed at this level, with largest fish being more infected. However, lakes with the greater average domestic genetic background were found to display significantly lower parasite prevalence and diversity. Since our results indicate no effect of domestic genes at the individual level, the negative association with introgression found at the population level may be mainly attributed to differences in intrinsic environmental quality of lakes (e.g. fishing pressure, availability of food resources, abiotic characteristics).

Natural selection for body shape in resource polymorphic Icelandic Arctic charr.

Resource polymorphisms exhibit remarkable intraspecific diversity and in many cases are expected to be maintained by diversifying selection. Phenotypic trade-offs can constrain morphologically intermediate individuals from effectively exploiting both alternate resources, resulting in ecological barriers to gene flow. Determining if and how phenotypic trade-offs cause fitness variation in the wild is challenging because of phenotypic and environmental correlations associated with alternative resource strategies. We investigated multiple pathways through which morphology could affect organismal performance, as measured by growth rate, and whether these effects generate diversifying selection in polymorphic Icelandic Arctic charr (Salvelinus alpinus) populations. We considered direct effects of morphology on growth and indirect effects via trophic resource use, estimated by stable isotopic signatures, and via parasitism associated with trophic resources. We sampled over 3 years in (lakes) Thingvallavatn and Vatnshlíðarvatn using the extended selection gradient path analytical approach and estimating size-dependent mortality. We found evidence for diversifying selection only in Thingvallavatn: more streamlined and terminally mouthed planktivore charr experienced greater growth, with the opposite pattern in small benthic charr. However, this effect was mediated by parasitism and nontrophic pathways, rather than trophic performance as often expected. Detection of between-morph differences in the presence (Vatnshlíðarvatn) and direction (Thingvallavatn) of size-dependent mortality, together with nontrophic effects of shape, suggests that a morphological trophic performance explanation for polymorphism is insufficient. This rare insight into selection during early diversification suggests that a complex of interacting local factors must be considered to understand how phenotype influences fitness, despite morphological variation reflecting intuitive trade-off explanations.

Pressure shock triploidization of Salmo trutta f. lacustris and Salvelinus umbla eggs and its impact on fish development.

The study tested the efficiency of hydrostatic pressure triploidization methods for Salmo trutta f. lacustris and Salvelinus umbla and investigated the effects on survival rate, skeletal malformation, and on morphometrics and cellular composition of gills, spleen, liver, kidney, intestine, and blood. In Salmo trutta f. lacustris a 100% triploidy rate in combination with high larvae survival rate (80% in comparison to control) was obtained when treating eggs with a pressure of 66 × 103 kPa 360 °C temperature minutes (CTM) post fertilization for 5 min, in Salvelinus umbla with a similar pressure after 270 CTM. Juvenile triploid Salmo trutta f. lacustris and Salvelinus umbla (145 days post hatch) had neither an increased rate of mortality, nor an increased rate of malformations. In triploid Salmo trutta f. lacustris and Salvelinus umbla the erythrocyte volume was 50% higher and the erythrocyte concentration in peripheral blood 25-35% lower relative to diploids. In triploids also the erythrocytes surface area: volume ratio was reduced. Gills of triploid Salmo trutta f. lacustris and Salvelinus umbla had increased width of primary lamellae and increased length of secondary lamellae which might compensate for unfavorable erythrocytes surface area: volume ratio. Length of the digestive tract and histology of kidney, liver, spleen, and gills were only investigated in Salmo trutta f. lacustris. In triploids the hematopoietic tissue of the kidney was decreased by 12%, the spleen index by 53%, and the erythroblast concentrations of the spleen by 42% relative to diploids, possibly indicating reduced erythropoiesis. Length of the digestive tract and cellular arrangement of intestine, liver, and gills were not affected. In summary, the used triploidization procedure seems a reliable method not counteracting the principles of animal welfare.

Temperature-related parasite infection dynamics: the case of proliferative kidney disease of brown trout.

Climate change, in particular rising temperature, is suspected to be a major driver for the emergence of many wildlife diseases. Proliferative kidney disease of salmonids, caused by the myxozoan Tetracapsuloides bryosalmonae, was used to evaluate how temperature dependence of host-parasite interactions modulates disease emergence. Brown trout (Salmo trutta fario) kept at 12 and 15 °C, were experimentally infected with T. bryosalmonae. Parasite development in the fish host and release of spores were quantified simultaneously to unravel parasite transmission potential from the vertebrate to the invertebrate host. A change to a stable plateau in infection intensity of the kidney coincided with a threshold at which spore shedding commenced. This onset of parasite release was delayed at the low temperature in accordance with reaching this infection intensity threshold, but the amount of spores released was irrespective of temperature. The production of parasite transmission stages declined with time. In conclusion, elevated temperature modifies the parasite transmission opportunities by increasing the duration of transmission stage production, which may affect the spread and establishment of the parasite in a wider range of rivers.

Flank spot number and its significance for systematics, taxonomy and conservation of the near-threatened Mediterranean trout Salmo cettii: evidence from a genetically pure population.

The number of spots on the flank of the Mediterranean trout Salmo cettii population from Tellesimo Stream in Sicily, Italy, varied between seven and 37, with a median and mode of 21, numbers much lower than those reported in the literature and different from those of other Italian trout populations. This finding could be ascribed to the phenotypic plasticity of the species or, alternatively, could provide evidence to support the different origin of Sicilian autochthonous trout. Given the ease of use of this character for the identification of native fish, it could be particularly important for conservation and management purposes.

Morphological, physiological and dietary covariation in migratory and resident adult brown trout (Salmo trutta).

The causes and consequences of trait relationships within and among the categories of physiology, morphology, and life-history remain poorly studied. Few studies cross the boundaries of these categories, and recent reviews have pointed out not only the dearth of evidence for among-category correlations but that trait relationships may change depending on the ecological conditions a population faces. We examined changes in mean values and correlations between traits in a partially migrant population of brown trout when migrant sea-run and resident stream forms were breeding sympatrically. Within each sex and life-history strategy group, we used carbon and nitrogen stable isotopes to assess trophic level and habitat use; assessed morphology which reflects swimming and foraging ability; measured circulating cortisol as it is released in response to stressors and is involved in the transition from salt to freshwater; and determined oxidative status by measuring oxidative stress and antioxidants. We found that sea-run trout were larger and had higher values of stable isotopes, cortisol and oxidative stress compared to residents. Most groups showed some correlations between morphology and diet, indicating individual resource specialization was occurring, and we found consistent correlations between morphology and cortisol. Additionally, relationships differed between the sexes (cortisol and oxidative status were related in females but not males) and between life-history strategies (habitat use was related to oxidative status in male sea-run trout but not in either sex of residents). The differing patterns of covariation between the two life-history strategies and between the sexes suggest that the relationships among phenotypic traits are subjected to different selection pressures, illustrating the importance of integrating multiple phenotypic measures across different trait categories and contrasting life-history strategies.

Occurrence of sympatric charr groups, Salvelinus, Salmonidae, in the lakes of Kamchatka: a legacy of the last glaciations.

Six postglacial lakes were studied along both sides of the Kamchatka central mountain range, Russia. Pairs of local morphotypes of species of Arctic charrs, Salvelinus spp., have previously been described from the southernmost lakes while the fish fauna of the four northernmost lakes was studied here for the first time. Phenotypic data support the division of Kamchatkan lacustrine charrs into two groups according to the number of gill rakers and pyloric caeca, as well as snout-dorsal and snout-ventral distances (MANOVA, P < 0·001). These groups respectively correspond to phenotypes commonly referred to as Salvelinus malma and Salvelinus taranetzi. To clarify the identity of these groups, D-loop and cytochrome b (cytb) region sequences were analysed. Haplotype network analysis of mtDNA shows the salmonids inhabiting four lakes on the south and north are phylogenetically close to either Beringian S. malma or to S. taranetzi from the Chukotka and Kolyma River basins (the mean ± s.e. pairwise per cent sequence divergence is 0·006 ± 0·001). Phenotype-genotype discordance suggests that mitochondrial introgression between species has occurred in the two smallest lakes (<0·5 km2 ) in the central part of the peninsula. Identical haplotypes of D-loop and cytb regions were found for the populations of S. taranetzi from the most distant southern and northern lakes, indicating all lakes were colonized by both species simultaneously after the last glacial maximum. Salvelinus taranetzi may have colonized the Kamchatka peninsula from one or both of two different source regions: the Arctic Beringia and the northern coast of the Okhotsk Sea.

Novel insights into cardiac remodelling revealed by proteomic analysis of the trout heart during exercise training.

The changes in the cardiac proteome of rainbow trout (Oncorhynchus mykiss) were quantified during the early phases (4, 7, and 14d) of a typical exercise-training regime to provide a comprehensive overview of the cellular changes responsible for developing a trained heart phenotype. Enhanced somatic growth during the 14d experiment was paralleled by cardiac growth to maintain relative ventricular mass. This was reflected in the cardiac proteome by the increased abundance of contractile proteins and cellular integrity proteins as early as Day 4, including a pronounced and sustained increase in blood vessel epicardial substance - an intercellular adhesion protein expressed in the vertebrate heart. An unexpected finding was that proteins involved in energy pathways, including glycolysis, ß-oxidation, the TCA cycle, and the electron transport chain, were generally present at lower levels relative to Day 0 levels, suggesting a reduced investment in the maintenance of energy production pathways. However, as the fish demonstrated somatic and cardiac growth during the exercise-training program, this change did not appear to influence cardiac function. The in-depth analysis of temporal changes in the cardiac proteome of trout during the early stages of exercise training reveals novel insights into cardiac remodelling in an important model species. BIOLOGICAL SIGNIFICANCE: Rainbow trout hearts have a remarkable ability for molecular, structural, and functional plasticity, and the inherent athleticism of these fish makes them ideal models for studies in comparative exercise physiology. Indeed, several decades of research using exercise-trained trout has shown both conserved and unique aspects of cardiac plasticity induced by a sustained increase in the workload of the heart. Despite a strong appreciation for the outcome of exercise training, however, the temporal events that generate this phenotype are not known. This study interrogates the early stages of exercise training using in-depth proteomic analysis to understand the molecular pathways of cardiac remodelling. Two major and novel findings emerge: (1) structural remodelling is initiated very early in training, as evidenced by a general increase in proteins associated with muscle contraction and integrity at Day 4, and (2) the abundance of proteins directly involved in energy production are decreased during 14d of exercise training, which contrasts the general acceptance of an exercise-induced increase in aerobic capacity of muscle, and suggests that regulation of energy pathways occurs at a different biological level than protein abundance.

Seasonal and Morphological Variations of Brown Trout (Salmo trutta f. fario) Kidney Peroxisomes: A Stereological Study.

Literature about fish kidney peroxisomes is scarce. To tackle this caveat, a stereological approach on renal peroxisome morphological parameters was performed for the first time in a fish, establishing correlations with maturation stages as it was previously done in brown trout liver. Three-year-old brown trout males and females were collected at the major seasons of their reproductive cycle. Trunk kidney was fixed and processed for catalase cytochemistry. Classical stereological methods were applied to electromicrographs to quantitate morphological parameters. Different seasonal variation patterns were observed between genders, and between renal proximal tubule segments I and II. In males, peroxisomes from proximal tubule segment II had a relatively higher volume and number in May, being individually bigger in February. Females presented similar trends, though with less marked variations. Overall, males and females did not show exactly the same seasonal patterns for most peroxisomal parameters, and no correlations were found between the latter and the gonado-somatic index (GSI). Hence, and despite the variations, the morphology of renal peroxisomes is not strictly correlated with gonad maturation kinetics, therefore suggesting that kidney peroxisome morphology is not seasonally modulated by sex steroids, like estradiol, as it seems to happen in liver peroxisomes.

Predictors of pesticide concentrations in freshwater trout - The role of life history.

Concentrations of halogenated pesticides in freshwater fish can be affected by age, size, trophic position, and exposure history. Exposure history may vary for individual fish caught at a single location due to different life histories, e.g. they may have hatched in different tributaries before migrating to a specific lake. We evaluated correlations of pesticide concentrations in freshwater brown trout (Salmo trutta) from the Clutha River, New Zealand, with potential predictors including capture site, age, length, trophic level, and life history. Life history was determined from otolith (fish ear bone) strontium isotope signatures, which vary among tributaries in the region of our study. Variability in pesticide concentrations between individual fish was not well explained by capture site, age, length, or trophic level. However, hexachlorobenzene (HCB) and chlorpyrifos concentrations were distinct in lake-based trout with different life histories. Additionally, one of the riverine life histories was associated with relatively high concentrations of total endosulfans. Linear models that included all potential predictor variables were evaluated and the resulting best models for HCB, chlorpyrifos, and total endosulfans included life history. These findings show that in cases where otolith isotope signatures vary geographically, they can be used to help explain contaminant concentration variations in fish caught from a single location.

Occurrence of intersex in wild freshwater fish in Slovenian rivers: a histological evaluation.

The aim of this preliminary research was to establish if there are intersex occurrences in wild freshwater fish in Slovenian rivers and streams. In the first study we evaluated all fish species of both sexes obtained from the river Ljubljanica from its source to mouth. In the second study we focused on the rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta m. fario) males from 30 rivers and streams in different parts of Slovenia. The male gonads were histologically assessed for the presence of oocytes to determine the frequency and degree of intersex. Oocytes were found in the testicular tissue of a single grayling (Thymallus thymallus) and in the adipose tissue adjacent to the testis of a single common barbel (Barbus barbus), both from the Ljubljanica. Several cyst-like structures that resemble degenerated presumptive oocytes were also present in several trout testes. This preliminary report is the first of its kind in Slovenia. To gain a better insight into the intersex issue in Slovenia, we plan to regularly biomonitor freshwater pollution by histologically examining fish gonads and, if possible, by determining vitellogenin plasma levels in fish.