Ecological Forms of Black Sea Brown Trout (<Emphasis Type="Italic">Salmo trutta labrax</Emphasis>) in the Mzymta River as Manifestation of Ontogenetic Plasticity

Populations of brown trout in the Mzymta River and its tributaries include anadromous (mainly female) and resident (mainly males) fish. Some resident males in the basin of the Mzymty River attain sexual maturity at the age 1+, and resident females mature at the age 2+ or 3+. The maximum age of resident fish is 4+ in the samples studied. Migrations of anadromous brown trout to the sea occur at the ages 1+, 2+, or 3+. Future spawners spend from 1 to 4 years at feeding grounds in the sea. Smolts of the population are characterized by performing not only spring but also autumn migrations to the sea. One smolt specimen has been detected upstream from the dam in the river where spawners of anadromous brown trout do not migrate; this means that the capability for sea migrations persists long in the population represented only by resident specimens of brown trout. The diversity of life cycles and ecological forms in populations of brown trout is not lower than in populations of brown trout in Northern and Western Europe. The comparison of the data obtained with published data makes it possible to come to the conclusion about the high plasticity of ontogenesis of Black Sea brown trout.     

亚东鲑幼鱼饲料中适宜淀粉种类与水平的研究

为考察淀粉种类与水平对亚东鲑(Salmo trutta)幼鱼生长性能、饲料利用、消化酶活性、肝脏生化指标和组织学的影响, 实验采用2×3双因素设计, 选取玉米淀粉和木薯淀粉, 分别以5%、10%和15%水平添加, 共配制6种等氮等脂饲料, 饲喂初始体重为(0.50±0.03) g的亚东鲑幼鱼84d。结果表明, 随着饲料中玉米淀粉和木薯淀粉水平的提高, 增重率呈现先上升后下降的趋势, 饲料系数则先下降后上升(P<0.05), 其中10%木薯淀粉组增重率最高(518.8%), 饲料系数最低(1.32)。各组成活率、脏体比、肥满度和全鱼水分、粗蛋白质、粗脂肪和粗灰分含量均没有显著差异(P>0.05), 粗蛋白沉积率随淀粉水平的提高呈下降趋势, 其中15%水平组显著低于其他水平组(P<0.05), 而脂肪沉积率则随着淀粉水平的升高先上升后下降, 且10%木薯淀粉组显著高于玉米淀粉组(P<0.05); 淀粉种类和水平对胃蛋白酶和胃淀粉酶无显著影响(P>0.05), 15%淀粉水平组肠淀粉酶和肠蛋白酶活性显著高于其他水平组(P<0.05)。饲料中淀粉种类和水平对肝脏谷丙转氨酶、谷草转氨酶、总胆固醇和甘油三酯均无显著影响(P>0.05), 15%淀粉组的肝糖原含量显著高于其他水平组(P<0.05)。在肝脏组织学方面, 15%水平组较其余两个水平组表现出明显的细胞核移位和细胞空泡化现象。上述结果表明, 在实验条件下, 亚东鲑幼鱼饲料中淀粉的适宜添加水平为10%, 木薯淀粉的效果优于玉米淀粉。     

Lipid status of fingerlings of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis> from different microbiotopes of the Varzuga River

Mechanisms of formation of phenotypic groups of fingerlings of the Atlantic salmon are investigated, related to diversity of embryos and subsequent start possibilities of dispersion of larvae to microbiotopes differing in their life conditions. The fingerlings of salmon, which after hatching and dissolution of the yolk sac moved from the mainstream of the Varzuga River to mouths of its tributaries, had an increased level of triacylglycerols and a higher growth rate than the juveniles remaining in the coastal zone of the river. The revealed differences between the compared groups of fingerlings by the spectrum of stock and structural lipids are mainly connected with distinctions of feeding of juveniles of the same age. The found stable differences by lipid spectra in fingerlings of salmon from the investigated biotopes of the Varzuga in July, August, and October are considered as biochemical prerequisites of the origin of different phenotypic groups of juveniles. Subdivision of fingerlings into phenotypic groups may further on influence the oncoming of the smoltification time of juveniles at the age 2+, 3+, and 4+. Accordingly, this is reflected in formation of the complex age structure (by the number of years spent in the river and in the sea) of the Varzuga population of Atlantic salmon.     

Growth and nutrient utilization by 0 + and 1 + triploid rainbow trout, Oncorhynchus my kiss

Growth performance, protein and energy utilization in triploid rainbow trout juveniles of two yearclasses, 0 + and 1 +, were compared to diploid control groups. Growth rate, food conversion and protein efficiency ratios of triploid rainbow trout did not differ (0 + juveniles) or were slightly lower (1 + juveniles) than the diploid control. Proximate body composition was also not affected by ploidy.
Apparent digestibility coefficients (ADC) ofprotein and ofenergy, oxygen uptake, and ammonia excretion rates were not different between the two groups. Nitrogen and energy balance studies showed that digestive and metabolic utilization of the diets did not differ in triploid and diploid rainbow trout juveniles.     

A comparison of the effect of long-term starvation on responses to low-temperature stress by juvenile rainbow (Oncorhynchus mykiss) and brown (Salmo trutta) trout reveal different responses in the two species

Biometric parameters and oxidative stress indicators were measured in liver and muscle samples from rainbow trout and brown trout juveniles exposed to a 45-day starvation period at low water temperature. As a general tendency, hepatic antioxidant enzyme activities in both species increased with fasting to eliminate the harmful effects of reactive oxygen species (ROS). However, the metabolic response to food deprivation in the muscle of each species was different. Lipid peroxidation levels in both species increased with starvation. We concluded that (1) low water temperature enhances ROS production in salmonids because of increased polyunsaturated fatty acid content in the cell membrane; (2) starvation significantly impaired the growth parameters of brown trout, yet the reverse was found for rainbow trout; and (3) despite this negative interaction, brown trout juveniles can physiologically tolerate oxidative stress caused by starvation and can therefore be cultivated under stressful conditions even in their early life stages.     

Genetic verification of native brown trout from the Persian Gulf (Catak Cay River, Tigris basin)

Analysis of the mtDNA control region in six individual brown trout Salmo trutta from the Catak Cay River (Tigris basin) revealed a single, new, haplotype, 1·0 to 1·5% divergent from five other Da lineage haplotypes analysed, that groups with the Danubian clade with low bootstrap support. This highly divergent haplotype combined with unique phenotypic characteristics underscores the novelty and native status of this population, which has probably been isolated from other brown trout lineages for at least several hundred thousand years.     

Interspecific association of brown trout (Salmo trutta) with non‐native brook trout (Salvelinus fontinalis) at the fry stage

The introduction of non‐native brook trout (Salvelinus fontinalis) in Europe has led to displacement and decreasing populations of native brown trout (Salmo trutta). Some studies have found that brown trout shift to a diet niche similar to brook trout when the two species live in sympatry, which conflicts with the competitive exclusion principle. A change in feeding niche may be a sign of early interspecific association and social learning, leading to behavioral changes. As a first step to address this possibility, it is essential to assess the interspecific association between the species during the early ontogenetic life stages. In this study, we therefore assess whether juvenile brown trout associate with non‐native juvenile brook trout to the same extent as with conspecifics by setting up two experiments: (i) a binomial choice test allowing visual and chemical cues to estimate the species specificity of group preference, and (ii) an association test without physical barriers to estimate the degree of association of a focal brown trout with a group of either conspecifics or heterospecifics. In experiment (1), we found that focal juvenile brown trout preferred to associate with the stimuli groups and did not discriminate either against conspecific or heterospecific groups. Furthermore, more active individuals showed stronger preference for the stimuli group than less active ones, regardless of species. In experiment (2), we found that brook trout groups had a tighter group structure than brown trout groups, and that focal brown trout showed stronger association with brook trout than with brown trout. These results indicate that brown trout may associate with brook trout at an early life stage, which would allow for interspecific social learning to occur. Future studies should look closer into causes and consequences of interspecific association and social learning, including potential effects on the phenotype selection in brown trout populations.     

Comparative Analysis of the Fatty Acid Profiles of Smolts of the Brown Trout <Emphasis Type="Italic">Salmo trutta</Emphasis> L. and Atlantic Salmon <Emphasis Type="Italic">Salmo salar</Emphasis> L. during Smoltification (Indera River,White Sea Basin)

The fatty acid status of the total lipids was studied in smolts of the brown trout and the Atlantic salmon collected in summer in the Indera River (White Sea basin). Higher 18:3ω-3/18:2ω-6, ω-3/ω-6, and 20:4ω-6/18:2ω-6 ratios were found in smolts of the Atlantic salmon in comparison to smolts of the brown trout. A higher amount of essential fatty acid 18:2ω-6 and an increased ratio of the sum of polyunsaturated fatty acids to the sum of saturated fatty acids in smolts of brown trout were observed. We have registered the differences in the ratios of the fatty acids, including physiologically active ones, which indicated species-specific physiological and biochemical processes during smoltification.     

An experimental study of ontogenetic and seasonal changes in the temperature preferences of unfed and fed brown trout,Salmo trutta

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Seasonal and regional infestation characteristics of three ectoparasites of whiting, Merlangim merlangus L., in the North Sea

The colonization by both resident and migrating spawner populations of brown trout and the characteristics of resident and migrating juveniles derived from the two populations have been studied in a brook and its tributary over 4 years. Resident trout spawns mainly in the upstream part of the brook and migrating trout in the downstream part. There are density and growth variations for the two age classes (0+ and 1 +) of juveniles in autumn according to the year and the environment. In the brook, the population of 0 + fish increases from downstream to upstream while the density of other age classes decreases. The migrating juvenile population of the brook changes annually and consists mainly of 1 s (one summer) individuals coming from the upper part. These individuals migrate generally in autumn and winter while young trout produced in the middle and downstream parts of the brook migrate mainly in the spring. The emigration process of the 0 + population decreases markedly from upstream to downstream and appears to be independent of the autumn length and sex ratio. In the tributary, most trout are 0+ years old, the population structure is different, and no migrating fish is observed. The results are discussed and a colonization strategy of the brown trout population in this brook is suggested.     

Intra- and Interspecific Competition in Hatchery Landlocked Salmon and Brown Trout in Semi-Natural Streams

I studied inter- and intraspecific competition in two hatchery stocks: landlocked salmon with long-hatchery background and a heterogenic brown trout stock. These species are potential competitors in the natural environment when landlocked salmon is being restored to wild by stocking hatchery juveniles. Behavioural responses were studied in four indoor laboratory flumes (400 cm long and 37 cm wide) and habitat use in six semi-natural outdoor streams (26 m long and 1.5 m long). Video recordings were used to monitor fish behaviour and electrofishing for fish positioning in the outdoor channels. The study design included five treatments: two densities of brown trout and salmon in solitary and both species together. The results of the study demonstrated that juvenile brown trout changed their behaviour in laboratory streams in response to presence of the landlocked salmon and the density of the conspecifics also tended to alter the habitat use by brown trout in semi-natural streams. Landlocked salmon juveniles showed no response to treatments. I conclude that possible poor adaptive ability to conditions outside hatchery by the hatchery salmon together and more competitive brown trout stocks may limit the success of management action in restoring landlocked salmon back to their natural streams of stocking.     

Static habitat partitioning and dynamic selection by sympatric young Atlantic salmon and brown trout in south-west England streams

Direct underwater observation of micro‐habitat use by 1838 young Atlantic salmon Salmo salar [mean L_T 7·9 ± 3.1(s.d.) cm, range 3·19] and 1227 brown trout Salmo trutta (L_T 10·9 ± 5·0 cm, range 3·56) showed both species were selective in habitat use, with differences between species and fish size. Atlantic salmon and brown trout selected relatively narrow ranges for the two micro‐habitat variables snout water velocity and height above bottom, but with differences between size‐classes. The smaller fishes <7 cm held positions in slower water closer to the bottom. On a larger scale, the Atlantic salmon more often used shallower stream areas, compared with brown trout. The larger parr preferred the deeper stream areas. Atlantic salmon used higher and slightly more variable mean water velocities than brown trout. Substrata used by the two species were similar. Finer substrata, although variable, were selected at the snout position, and differences were pronounced between size‐classes. On a meso‐habitat scale, brown trout were more frequently observed in slow pool‐glide habitats, while young Atlantic salmon favoured the faster high‐gradient meso‐habitats. Small juveniles <7 cm of both species were observed most frequently in riffle‐chute habitats. Atlantic salmon and brown trout segregated with respect to use of habitat, but considerable niche overlap between species indicated competitive interactions. In particular, for small fishes <7 cm of the two species, there was almost complete niche overlap for use of water depth, while they segregated with respect to water velocity. Habitat suitability indices developed for both species for mean water velocity and water depth, tended to have their optimum at lower values compared with previous studies in larger streams, with Atlantic salmon parr in the small streams occupying the same habitat as favoured by brown trout in larger streams. The data indicate both species may be flexible in their habitat selection depending on habitat availability. Species‐specific habitat overlap between streams may be complete. However, between‐species habitat partitioning remains similar.     

Genetic differences between wild and hatchery‐bred brown trout (Salmo trutta L.) in single nucleotide polymorphisms linked to selective traits

To study effects from natural selection acting on brown trout in a natural stream habitat compared with a hatchery environment, 3,781 single nucleotide polymorphism (SNP) markers were analyzed in three closely related groups of brown trout (Salmo trutta L.). Autumn (W/0+, n = 48) and consecutive spring (W/1+, n = 47) samples of brown trout individuals belonging to the same cohort and stream were retrieved using electrofishing. A third group (H/1+, n = 48) comprised hatchery‐reared individuals, bred from a mixture of wild parents of the strain of the two former groups and from a neighboring stream. Pairwise analysis of F_ST outliers and analysis under a hierarchical model by means of ARLEQUIN software detected 421 (10.8%) candidates of selection, before multitest correction. BAYESCAN software detected 10 candidate loci, all of which were included among the ARLEQUIN candidate loci. Body length was significantly different across genotypes at 10 candidate loci in the W/0+, at 34 candidate loci in the W/1+ and at 21 candidate loci in the H/1+ group. The W/1+ sample was tested for genotype‐specific body length at all loci, and significant differences were found in 10.6% of all loci, and of these, 14.2% had higher frequency of the largest genotype in the W/1+ sample than in W/0+. The corresponding proportion among the candidate loci of W/1+ was 22.7% with genotype‐specific body length, and 88.2% of these had increased frequency of the largest genotype from W/0+ to W/1+, indicating a linkage between these loci and traits affecting growth and survival under this stream's environmental conditions. Bayesian structuring of all loci, and of the noncandidate loci suggested two (K = 2), alternatively four clusters (K = 4). This differed from the candidate SNPs, which suggested only two clusters. In both cases, the hatchery fish dominated one cluster, and body length of W/1+ fish was positively correlated with membership of one cluster both from the K = 2 and the K = 4 structure. Our analysis demonstrates profound genetic differentiation that can be linked to differential selection on a fitness‐related trait (individual growth) in brown trout living under natural vs. hatchery conditions. Candidate SNP loci linked to genes affecting individual growth were identified and provide important inputs into future mapping of the genetic basis of brown trout body size selection.     

Differences in the sensitivity of brown trout, Salmo trutta L., and rainbow trout, Salmo gairdneri Richardson, to physiological doses of cortisol

Interspecific differences in the stress response of fish may be due, in part, to differences in the sensitivity of target tissues to cortisol. The relative response of brown and rainbow trout to a standardized dose of cortisol was assessed by monitoring condition (K factor), the number of circulating lymphocytes and mortality due to disease, following cortisol treatment. Cortisol implantation resulted in a significant decline in K factor and number of circulating lymphocytes in immature brown trout, but not in immature rainbow trout, despite plasma cortisol levels being similar in both cases. Cortisol implantation in mature brown and rainbow trout significantly increased the mortality rate due to bacterial and fungal infection compared with control fish. Furthermore, the mortality rate due to disease was significantly greater in brown trout than rainbow trout, despite both groups receiving similar doses of steroid.     

Higher growth variability and stronger responses to temperature changes in wild than hatchery‐reared sea trout (Salmo trutta L.)

Each year, millions of hatchery‐reared sea‐run brown trout Salmo trutta L. (the sea trout) juveniles are released into the natural environment in the Atlantic region. The aim of this work was to investigate the growth responses of sea trout to changing temperature conditions and to compare the growth plasticity between wild and hatchery‐reared fish. Scales were collected from sea trout in a selected river flowing into the southern Baltic Sea. We analyzed the scale increment widths as a proxy of somatic growth and investigated the interannual variabilities and differences in growth between fish groups (wild and hatchery‐reared). We used mixed‐effects Bayesian modeling and ascribed the variances in growth to different sources. Furthermore, we developed indices of interannual (2003–2015) growth variation in the marine and freshwater phases of the life cycle of the fish and analyzed the relationships between trout growth and temperature. Temperature positively affects fish growth, regardless of the origin of the fish. We observed stronger relationships between fish growth and temperature conditions in the marine phase than in the freshwater phase. Additionally, wild sea trout are characterized by stronger responses to temperature variability and higher phenotypic plasticity of growth than those of the hatchery‐reared individuals. Therefore, wild sea trout might be better suited to changing environmental conditions than hatchery‐reared sea trout. This knowledge identifies possible threats in management actions for sea trout with an emphasis on ongoing climate change.     

The viscosity and glycoprotein biochemistry of salmonid mucus varies with species,salinity and the presence of amoebic gill disease

Fish mucus has previously been reported to change in appearance and composition among species and in response to changes in salinity and disease status. This study reports on the mucus viscosity and glycoprotein biochemistry of Atlantic salmon (Salmo salar L.), brown trout (Salmo trutta L.) and rainbow trout (Oncorhynchus mykiss Walbaum) in freshwater and seawater, both naïve to and affected by amoebic gill disease (AGD). Cutaneous mucus viscosity was measured over a range of shear rates (11.5, 23, 46 and 115 s^–1), and non-Newtonian behaviour was demonstrated for all three species. Mucus viscosity was significantly greater in seawater than in freshwater for all species, and significantly lower in AGD-affected Atlantic salmon and brown trout. Mucus glucose, total protein and osmolality data indicated that differences in viscosity due to salinity were mostly attributed to changes in mucus hydration, while differences due to disease were mostly attributed to changes in mucus composition. Trends in gill mucus cell histochemistry included shifts in glycoproteins from neutral mucins in freshwater to acidic mucins in seawater, and shifts towards neutral mucins, with an increase in mucus cell numbers, in response to AGD. Results suggested that Atlantic salmon and brown trout are more similar to one another in their mucus profile than to rainbow trout. Atlantic salmon and brown trout both exhibited a whole-body mucus response to AGD, whereas rainbow trout exhibited only a local gill response. Findings hold implications for fish physiology and pathology, and indicate that future fish-disease management strategies should be species and condition specific.Communicated by I.D. HumeThe word mucus has been used in its noun form throughout the paper for clarity

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An erratum to this article can be found at .     

Maintenance of a small anadromous subpopulation of brown trout (Salmo trutta L.) by straying

1. Microsatellite and isozyme loci variation were used to study structure and dynamics of a brown trout (Salmo trutta) population heavily affected by damming. The downstream area accessible for spawning was drastically reduced to a stream 1 km long influenced by regulated discharge. 2. Stocking of hatchery‐reared juveniles failed and the population is entirely supported by anadromous adults from neighbouring populations. 3. Temporal genetic stability is reported here. Some punctual between‐river genetic differences are likely because of different contribution from each neighbouring river through years. 4. High anadromy‐mediated gene flow produces a lack of genetic substructure in the region. The role of anadromous brown trout on maintenance of endangered small populations is emphasised.     

Phylogeography,genetic structure,and conservation of the endangered Caspian brown trout, <Emphasis Type="Italic">Salmo trutta caspius</Emphasis> (Kessler, 1877), from Iran

The Caspian Sea, the largest inland closed water body in the world, has numerous endemic species. The Caspian brown trout (Salmo trutta caspius) is considered as endangered according to IUCN criteria. Information on phylogeography and genetic structure is crucial for appropriate management of genetic resources. In spite of the huge number of studies carried out in the Salmo trutta species complex across its distribution range, very few data are available on these issues for S. trutta within the Caspian Sea. Mitochondrial (mtDNA control region) and nuclear (major ribosomal DNA internal transcribed spacer 1, ITS-1, and ten microsatellite loci) molecular markers were used to study the phylogeography, genetic structure, and current captive breeding strategies for reinforcement of Caspian trout in North Iranian rivers. Our results confirmed the presence of Salmo trutta caspius in this region. Phylogenetic analysis demonstrated its membership to the brown trout Danubian (DA) lineage. Genetic diversity of Caspian brown trout in Iranian Rivers is comparable to the levels usually observed in sustainable anadromous European brown trout populations. Microsatellite data suggested two main clusters connected by gene flow among river basins likely by anadromous fish. No genetic differences were detected between the hatchery sample and the remaining wild populations. While the current hatchery program has not produced detectable genetic changes in the wild populations, conservation strategies prioritizing habitat improvement and recovering natural spawning areas for enhancing wild populations are emphasized.     

Observational and experimental studies on the acquisition of Anisakis sp. larvae (nematoda: Ascaridida) by trout in fresh water

In the enclosed fresh-water environmsnt of Hanningfield Reservoir, Essex, England, Anisakis sp. larvae (parasites of marine fish) were found in 55 per cent of 40 brown trout and in 26·2 per cent of 61 rainbow trout. Experimental infection by intubating larvae into the stomach was more successful in brown trout (50·6 per cent recovery rate) than in rainbow trout (27 per cent recovery rate). Some larvae reached the body-cavity as early as 2 h after infection. They penetrated the region between the oesophagus and intestine immediately posterior to the caecal openings. Fewer larvae successfully penetrated the gut wall of brown trout within 24 h at 8°C than at 15 ± 1°C. It appears that the reservoir trout acquired Anisakis by being fed as juveniles on untreated marine fish offal containing live larvae.     

Among-sibling differences in the phenotypes of juvenile fish depend on their location within the egg mass and maternal dominance rank

We investigated whether among-sibling differences in the phenotypes of juvenile fish were systematically related to the position in the egg mass where each individual developed during oogenesis. We sampled eggs from the front, middle and rear thirds of the egg mass in female brown trout of known dominance rank. In the resulting juveniles, we then measured traits that are related to individual fitness: body size, social status and standard metabolic rate (SMR). When controlling for differences among females in mean egg size, siblings from dominant mothers were initially larger (and had a lower mass-corrected SMR) if they developed from eggs at the rear of the egg mass. However, heterogeneity in the size of siblings from different positions in the egg mass diminished in lower-ranking females. Location of the egg within the egg mass also affected the social dominance of the resulting juvenile fish, although the direction of this effect varied with developmental age. This study provides the first evidence of a systematic basis for among-sibling differences in the phenotypes of offspring in a highly fecund organism.