Embryonic development of the endangered Caspian brown trout,Salmo trutta caspius (Kessler, 1877)

The Caspian brown trout, Salmo trutta caspius is an endangered species of economic value and better knowledge of its biology will contribute to conservation measures. In the present study we characterized its early development to identify critical embryonic stages, by observing embryos and larvae from a broodstock maintained in captivity incubated at 9 ± 1°C. Morphological analysis of landmark stages of embryonic development revealed that first cleavage occurred at 189 degree‐h, a many‐celled blastoderm formed at 62 degree‐days (dd), a germ ring at 72 dd, the neural keel stage at 88 dd, the blastopore closed at 137 dd, the eye became pigmented at 188 dd and the larvae hatched at 373 dd. The detailed timing of these landmark features will help development of strategies aiming at increased aquaculture production of this species.     

The Effects of a Synbiotic Mixture of Galacto-Oligosaccharides and Bacillus Strains in Caspian Salmon,Salmo trutta caspius Fingerlings

The effect of dietary supplementation with a synbiotic mixture of galacto-oligosaccharides (GOS) and Bacillus spp. was examined in Caspian salmon, Salmo trutta caspius (Kessler, 1877) fingerlings. Caspian salmon fed with the synbiotic diet had significantly higher weight gain rate, protein efficiency ratio, and survival rate, as well as lower feed conversion ratio, compared to the control group (P < 0.05). The serum protein, albumin, globulin, and lactate dehydrogenase levels of the fish fed with the synbiotic diet were significantly higher than the control group (P < 0.05), while the serum alkaline phosphatase levels were significantly lower (P < 0.05). The activities of the innate immune response parameters, including lysozyme, superoxide dismutase, and catalase were significantly higher in the Caspian salmon fed with the synbiotic diet (P < 0.05). The gut microbiota of the Caspian salmon fed with the synbiotic diet contained significantly elevated total viable aerobic bacterial counts (TVABCs), lactic acid bacteria (LAB) levels, and LAB/TVABCs ratio (P < 0.05). Additionally, the gut activities of amylase, trypsin, and chymotrypsin in the gut, as well as the trypsin/chymotrypsin ratio, were significantly increased in the fish that received the synbiotic diet (P < 0.05). In conclusion, the combined GOS and Bacillus spp. supplement positively affected the growth, survival rate, immunobiochemical parameters, digestive activity, and beneficial microbial density in the gut of Caspian salmon fingerlings.

     

Invasion Dynamics of a Fish-Free Landscape by Brown Trout (Salmo trutta)

Metapopulation dynamics over the course of an invasion are usually difficult to grasp because they require large and reliable data collection, often unavailable. The invasion of the fish-free freshwater ecosystems of the remote sub-Antarctic Kerguelen Islands following man-made introductions of brown trout (Salmo trutta) in the 1950''s is an exception to this rule. Benefiting from a full long term environmental research monitoring of the invasion, we built a Bayesian dynamic metapopulation model to analyze the invasion dynamics of 85 river systems over 51 years. The model accounted for patch size (river length and connections to lakes), alternative dispersal pathways between rivers, temporal trends in dynamics, and uncertainty in colonization date. The results show that the model correctly represents the observed pattern of invasion, especially if we assume a coastal dispersal pathway between patches. Landscape attributes such as patch size influenced the colonization function, but had no effect on propagule pressure. Independently from patch size and distance between patches, propagule pressure and colonization function were not constant through time. Propagule pressure increased over the course of colonization, whereas the colonization function decreased, conditional on propagule pressure. The resulting pattern of this antagonistic interplay is an initial rapid invasion phase followed by a strong decrease in the invasion rate. These temporal trends may be due to either adaptive processes or environmental gradients encountered along the colonization front. It was not possible to distinguish these two hypotheses. Because invasibility of Kerguelen Is. freshwater ecosystems is very high due to the lack of a pre-existing fish fauna and minimal human interference, our estimates of invasion dynamics represent a blueprint for the potential of brown trout invasiveness in pristine environments. Our conclusions shed light on the future of polar regions where, because of climate change, fish-free ecosystems become increasingly accessible to invasion by fish species.     

Growth hormone-induced effects on mortality, energy status and growth: a field study on Brown Trout (Salmo trutta)

1. Growth hormone (GH) treatment increases the growth rate and competitive ability of salmonids under laboratory conditions. Since fast growth should increase fitness, why is endogenous secretion of GH not higher in wild fish? To address this question, three hypotheses were suggested. H₁: high GH levels reduce antipredator responses and may therefore increase mortality from predation. H₂: high GH levels reduce long-term (e.g. over winter) survival by reducing allocation to critical energy reserves. H₃: GH is not beneficial for growth under natural conditions.
2. To test these hypotheses, the performance of GH-treated juvenile Brown Trout ( Salmo trutta ) and control (placebo) trout was compared in an enclosed stream section subjected to natural predation. Four experiments were conducted during winter, spring, summer and autumn, respectively.
3. Mortality rates were not significantly different between GH-treated and control trout in any of the four experiments so H₁ was not supported. Energy reserves were generally lower in GH-treated fish, which is consistent with H₂, whereas growth rates in mass were higher in GH-treated fish than in controls so H₃ was not supported. This suggests that GH promotes growth at the expense of investment in maintenance.
4. Judging from growth and mortality rates, the fitness of GH-treated and control trout appeared similar. Thus, escaped GH-manipulated fish may compete successfully with wild fish.
5. Hatchery-raised trout with higher initial condition index suffered higher mortality rates than more slender fish. This novel finding may be explained by reduced escape ability related to body morphology, reduced behavioural responses towards predators by high-condition trout, or predator preferences for high-condition fish.     

Limestone Treatment of Whetstone Brook, Massachusetts. II. Changes in the Brown Trout (Salmo trutta)and Brook Trout (Salvelinus fontinalis)Fishery

Density, age structure, and growth rates of wild brook trout (Salvelinus fontinalis)and brown trout (Salmo trutta)in Whetstone Brook in northcentral Massachusetts were monitored for 4 years before and 3 years during limestone treatment to mitigate acidic conditions. The population density of brook trout increased significantly during treatment. Liming did not have any significant effects on the growth rates of brook trout or brown trout. Actual survival rates of brook trout and brown trout were not calculated due to the low density of both species, but more older individuals of both species were captured during the treatment period. Fulton condition factors (an index of fish condition) increased significantly for both brook trout and brown trout during treatment. Seven-day in situ bioassays of brown trout and rainbow trout demonstrated that liming improved the chemical environment for fish in Whetstone Brook. During a pretreatment bioassay in 1987, 100% rainbow trout mortality was observed at both the control and treatment stations in Whetstone Brook. Brown trout mortality was 67% in the control station and 70% in the treatment station. The pH during the 1987 bioassay averaged 4.90 in the control station and 4.99 in the treated station. During a bioassay conducted in 1990 after treatment began, rainbow trout mortality was 100% in the control station and 0% in the treatment station. Brown trout mortality was 17% in the control station and 0% in the treatment station. The pH during the 1990 bioassay averaged 5.23 in the control station and 6.60 in the treatment station. Analysis of total aluminum in the gills of fish from the 1990 bioassay revealed higher levels in fish from the control station than in those from the treatment station.     

Genetic Structure of Brown Trout (Salmo trutta) Populations from Turkey Based on Microsatellite Data

This present study investigated micro- and macro-geographic microsatellite DNA variations using five polymorphic microsatellite loci from 27 brown trout populations in Turkey. Average number of alleles and average observed heterozygosity were 7.4 and 0.254, respectively. Even populations from the same sea basin and river system (the so called micro-geographic regions) had unique alleles. Genetic variation among the populations from macro-geographic regions (different sea basins and river systems) was 45.78%. The mtDNA lineages of brown trout that have previously been identified by mtDNA analyses were supported by the analysis of the microsatellite DNA data in general. The Çatak population, which belongs to the Tigris lineage, was clustered together with the Euphrates populations within the Adriatic mtDNA lineage, based on microsatellite data. Both mitochondrial and microsatellite DNA analyses have made it possible to determine a secondary contact between Adriatic and Tigris lineages.     

Combined Assessment of Genetic Variability in Populations of Brown Trout (Salmo trutta L.) Based on Allozymes, Microsatellites, and RAPD Markers

Genetic variability within and among four Spanish natural populations of Salmo trutta L. was evaluated on the basis of 25 enzyme loci, 3 microsatellite loci, and 9 randomly amplified polymorphic DNAs (RAPDs). A total of 21 allelic markers were found, 12 of which were reported by microsatellites, whereas enzyme and RAPD accounted only for 6 and 3, respectively. Genetic variation within samples was significantly higher for microsatellites and RAPD than for enzyme loci. Although all methods reported a high degree of allelic heterogeneity among samples, also revealing a high degree of gene diversity, genetic relationships depicted by UPGMA dendrograms closely agreed for all kinds of data. Microsatellite loci appeared to be the most feasible technique when searching for specific alleles for a population or an area, owing to the higher number of allelic variants found. Received July 1, 1998; accepted January 14, 1999     

The functional relationship between peak spring floods and survival and growth of juvenile Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta)

1. The effects of high spring floods on survival and growth of juvenile Atlantic Salmon, Salmo salar, and Brown Trout, Salmo trutta , are explored, using data from a long-term study in the River Saltdalselv, northern Norway. The flow regime in this river is typical for northern rivers.
2. There was considerable variation in year class strength of both species.
3. Mortality of Atlantic Salmon increased significantly in years with high discharge during the alevin stage as well as the first week after emergence. High discharge during the egg stage and more than 1 week after emergence seemed to be of minor importance. Water temperature at emergence was rather high (average 10·5 °C) and did not significantly affect year class strength.
4. Brown Trout emerged earlier than Atlantic Salmon at an average water temperature of 8·2 °C. Highest mortality was observed in years with low water temperatures at emergence as well as high discharge during the alevin stage.
5. For 1-year-old fish or older, the size of the spring peak flood did not influence mortality significantly.
6. Growth of Atlantic Salmon parr was diminished in years with a high peak spring flood. A similar effect on Brown Trout was not detected.     

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.     

Discrimination against Water Containing Unrelated Conspecifics and a Marginal Effect of Relatedness on Spacing Behaviour and Growth in Juvenile Brown Trout, Salmo trutta L.

In this study, we assessed whether juvenile brown trout are able to discriminate between, and swim towards, water containing unrelated conspecifics and blank stream water. In a second stage we investigated the behavioural response to sibling-scented vs. nonsibling conspecific-scented water, and how the social environment could affect growth. All the six families (full sibs) tested showed an overall preference to blank water instead of water scented by unfamiliar fish of similar age and size. This result reveals that juvenile brown trout are able to detect chemical water components released by conspecifics, and show a biased behaviour based on this ability. When trout were given the choice between water scented by sibs and unfamiliar nonsibs, results were variable, some families spent more time in the sibling-scented water channel (only significant for one of six families) while others showed the opposite trend. Large within-family variation was also observed in the responses of individual fish towards water scented by siblings and nonsiblings. When fish from three of the families were reared with either siblings or nonsiblings, we obtained results that were only partially consistent with the hypothesis that fish growth could be enhanced in the preferred social environment (which had been predicted from the results of the choice tests).     

And the Last Shall Be First: Heterochrony and Compensatory Marine Growth in Sea Trout (Salmo trutta)

Early juvenile growth is a good indicator of growth later in life in many species because larger than average juveniles tend to have a competitive advantage. However, for migratory species the relationship between juvenile and adult growth remains obscure. We used scale analysis to reconstruct growth trajectories of migratory sea trout (Salmo trutta) from six neighbouring populations, and compared the size individuals attained in freshwater (before migration) with their subsequent growth at sea (after migration). We also calculated the coefficient of variation (CV) to examine how much body size varied across populations and life stages. Specifically, we tested the hypothesis that the CV on body size would differ between freshwater and marine environment, perhaps reflecting different trade-offs during ontogeny. Neighbouring sea trout populations differed significantly in time spent at sea and in age-adjusted size of returning adults, but not on size of seaward migration, which was surprisingly uniform and may be indicative of strong selection pressures. The CV on body size decreased significantly over time and was highest during the first 8 months of life (when juvenile mortality is highest) and lowest during the marine phase. Size attained in freshwater was negatively related to growth during the first marine growing season, suggesting the existence of compensatory growth, whereby individuals that grow poorly in freshwater are able to catch up later at sea. Analysis of 61 datasets indicates that negative or no associations between pre- and post-migratory growth are common amongst migratory salmonids. We suggest that despite a widespread selective advantage of large body size in freshwater, freshwater growth is a poor predictor of final body size amongst migratory fish because selection may favour growth heterochrony during transitions to a novel environment, and marine compensatory growth may negate any initial size advantage acquired in freshwater.     

Organization of the Cone Cells in the Retinae of Salmon (Salmo salar) and Trout (Salmo trutta trutta) in Relation to Their Feeding Habits

Regional variations of cone density, cone types and cone mosaic were investigated by light microscopy in yolk sac fry, parr and adults of salmon (Salmo salar) and trout (Salmo trutta trutta) and related to the feeding habits of different stages. The retinal organization of the two species is similar, as are their feeding habits. In parr and adults of both species a region with high cone density was found in the ventro-temporal part of the retina. The lowest values of cone density were found centrally in the dorsal half of the retina. An increase in cone density towards the ora serrata was noted in all retinae investigated. There is a good agreement between the density distribution of the cones in parr of salmon and trout and their feeding habits. The parr feed to a great extent on the invertebrate drift. Facing the current, the parr search the water region in front and above themselves for food organisms, thereby probably making use of the ventro-temporal area of high cone density. The connection between the cone density distribution and the feeding habits is less clear in adult salmon and trout, but the high cone density region is probably used when they feed on surface organisms and schooling prey. The ecological significance of cone types and cone mosaics is discussed. During growth there was a change of the cone mosaic from a regular square pattern in the fry towards a less regular square or row pattern in the adults. The position of regions with high and low cone density did not change during development in each species and had a similar distribution in the two species. On the other hand, the range of cone density values becomes relatively greater as the animal grows older. The cone density distribution seems to be more homogeneous in parr than in adults. Differences in the relative density distribution of the cones are influenced by recruitment at the retinal periphery and by spreading out of existing cells. In addition to the ora serrata, mitoses were also observed in more central parts of the retina having well-differentiated receptors and a cone mosaic. Mitoses were noted in all three nuclear layers but were most frequent in the outer nuclear layer, in which the resulting cells probably differentiate into rods. Undifferentiated zones similar to the peripheral growth zone of the retina were found on both sides of the falciform process in fry. In parr and adults an undifferentiated zone persisted only on the temporal side. It probably contributes to the high cone density in the ventro-temporal part of the retina by a delivery of new cells.     

Effects of Fish-farm Activity on the Limnetic Community Structure of Brown Trout, Salmo trutta, and Arctic Charr, Salvelinus alpinus

Establishment of four fish-farms during the period 1971 to 1994 in the oligotrophic lake Skogseidvatnet affected Arctic charr, Salvelinus alpinus, but not brown trout, Salmo trutta. From 1971 to 1987, an increase in mean individual size of Arctic charr was recorded, while the mean individual size of brown trout remained stable. Arctic charr were found to use deeper benthic areas than brown trout. Approximately 8% of the Arctic charr population (>26cm), were found to switch to waste food from fish-farms, resulting in a novel feeding habitat for the species. They were, however, found in gillnets distant from the fish farm cages, indicating high mobility. The habitat segregation between the two species can most likely be explained by selective differences and asymmetric competition with brown trout as the dominant species. Based on the present results, changes in the Arctic charr population may be due to increased food availability and due to a new habitat use as a waste food feeder. The reason for the brown trout population to have remained stable with respect to mean size, growth pattern and habitat use, may be due to a different diet choice than Arctic charr in this lake. Brown trout were found to feed mainly on terrestrial insects, while Arctic charr fed mainly on zooplankton and on waste food.     

Environmental dependence of manganese and zinc in the scales of Atlantic salmon, Salmo salar (L) and Brown trout, Salmo trutta (L)

Analysis of manganese and zinc concentrations in the scales of salmon and trout from a number of sites showed significant dependence of the levels of these metals in the scales on the levels in the environment. There is some evidence to suggest that in trout scales there is a minimum concentration of zinc above which there is a direct proportion between environmental and scale concentration. It is also possible that the response of trout to environmental zinc differs from that of salmon.     

The Diet of the Brown Trout Salmo trutta (L.) during the Reproductive Period: Size‐Related and Sexual Effects

We investigated the autumnal diet of the brown trout Salmo trutta, in a Prepyrenean stream (NW Iberian Peninsula) focusing on intraspecific dietary differences related to size and sex. The diet of trout included 18 types of prey, with Plecoptera and Ephemeroptera nymphs and Diptera larvae as the most consumed taxa. Large trout ate larger prey, than did small trout, and also increased the consumption of terrestrial‐surface prey with respect to aquatic‐benthic prey. As terrestrial‐surface preys were larger than aquatic‐benthic prey, the size‐related differences in the diet of trout were related to gape‐limitations. Although male and female trout did not differ in size, we found that males foraged on a more diverse type of prey than females, probably owing to male territoriality during the reproductive period. This study provides new evidence of dietary plasticity in the brown trout and confirms the importance of local dietary studies to better understand factors which drive trophic ecology of predators. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diel Periodicity and Environmental Influence on the Smolt Migration of Arctic charr, Salvelinus alpinus, Atlantic salmon, Salmo salar, and Brown Trout, Salmo trutta, in Northern Norway

We caught smolts of Arctic charr, Salvelinus alpinus (L.), Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a trap situated at the mouth of the river Halselva (70° N 23° E), northern Norway during a 5-year period. Salmon and charr were the first to leave freshwater at the end of May, while most trout left freshwater about 14 days later. Whereas the midnight sun shines continuously during the downstream migration period, the light intensity has a diel intensity pattern. The majority of the descending migrants were recorded during the night. The number of descending fish was relatively low at water temperatures below 3°C. The increase in water level was largely caused by snowmelt and thus correlated with lower water temperatures. The number of migrants of all three species increased with increasing water level and decreased with increasing water temperature, with the exception of trout, which increased with water temperature. Notably, the increase in number of migrants was also correlated with the increase in water level the following day, indicating that fish movements represent an early response to a later spate. There was no significant relationship between the number of migrants and the daily change in water level or temperature. The three species were highly synchronised in their daily number of migrants. The strongest synchronisation was found between Arctic charr and Atlantic salmon, followed by Arctic charr and brown trout.     

Both Contest and Scramble Competition Affect the Growth Performance of Brown Trout, Salmo Trutta, Parr of Wild and of Sea-ranched Origins

The effect of contest and scramble competition on the growth performance of wild and sea-ranched juvenile (0+) brown trout, Salmo trutta, originating from the River Dalälven, Sweden was scrutinised. In a mirror image stimulation (MIS) experiment, and in a 35000 1 stream-water aquarium the trout was studied for three weeks (20 individuals in each of four replicates). Activity in MIS was correlated with swimming activity in the stream-water aquarium. The MIS results could not be used for predicting any social behaviour patterns or the growth performance of a fish. No behavioural differences between the two strains were noted. However, the sea-ranched strain grew faster than the wild one, both in regard to the RNA/DNA ratio and the weight-specific growth rate. Because the strains had the same genetic background and prior to the experiments were raised under similar hatchery condition, the results of this study suggest that the sea-ranching process selects for faster juvenile growth in brown trout. The ultimate mechanisms underlying the faster growth by the domesticated strain probably involves both contest and scramble competition.