First marine record of marble trout Salmo marmoratus

A specimen of marble trout Salmo marmoratus, of 955 mm total length (L_T) and weighing 10 220 g, was caught on 26 December 2008 by a commercial fisherman near the coast of Igrane (eastern Adriatic Sea). This represents the first marine record of this species.     

Thermoregulatory behavior of brown trout,Salmo trutta

Brown trout, Salmo trutta, were allowed to thermoregulate individually in an electronic shuttlebox. Pooled data for 6 fish showed a diel pattern of preferred temperature, with a diurnal minimum of 10.3°C, an early nocturnal maximum of 13.7°C, a less pronounced mid-scotophase minimum of 11.7°C, and a secondary dawn maximum of 12.8°C, in a somewhat crepuscular pattern. The 24-hour mean preferendum was 12.2°C.     

Associations between epidermal thionin-positive cells and skin parasitic infections in brown trout Salmo trutta

The dynamics of the densities of epidermal thionin-positive cells (putative mast cells) in the skin of brown trout fry were investigated during experimental infections with the skin parasites Ichthyophthirius multifiliis (Ciliophora) and Gyrodactylus derjavini (Monogenea). It was shown that the metachromatic thionin-stained cells were extremely sensitive to parasite exposure, as the density of cells in the skin of trout decreased markedly after exposure to the pathogens. As early as 7 d post infection the cell counts were significantly reduced and almost totally depleted following 9 d infection, which suggests that degranulation of the cells occurs following parasite exposure. No recruitment of new cells was seen during the study period. Some reduction in uninfected control groups indicates that the putative mast cells are sensitive to stress as well. A notable variation in densities of thionin-stained cells between different fins was found and the corneal surface was devoid of these cells. The possible implications of these cells in host-parasite interactions are suggested and discussed.     

Allozyme variability in brown trout Salmo trutta in Chile

1. Brown trout ova were imported during the last century from different locations in Europe to establish populations in Chilean rivers (South America). The rivers are currently occupied by naturalized populations that have adapted to very different environmental conditions, such as areas of semi-desert in the north, or rainy and cold areas in the south.
2. In this first study in this geographical area, electrophoretic variability of proteins encoded by twenty-five loci was screened in seven populations from northern to southern Chile.
3. The results show significant heterogeneity of allelic frequencies between populations in seven of eleven polymorphic loci detected. The estimated value of genetic diversity 0.1274 ( H _T) is higher than that observed in populations from areas of natural distribution of this species. However, only 12.64% of this genetic diversity was found between samples ( G _ST), indicating a low genetic divergence among Chilean populations. The observed associations among the Chilean and 'modern' group of European populations suggests the probable origin of the new populations.     

Sexual size dimorphism in anadromous brown trout Salmo trutta

Anadromous trout Salmo trutta exhibits sexual size dimorphism (S_SD); females were larger than males in populations where male mean total length (L_T) at maturity was below 49 cm and females were smaller than males when mean male L_T was above 49 cm, the slope of the regression of female on male L_T was 0·59. In streams with mean annual discharge below 41 m³ s^?1, flow added significantly to a model with S_SD as the dependent variable and male mean L_T at maturity as the first predictor variable. There was a slight increase in S_SD with increasing latitude, which may result from an increase in male size with increasing latitude.     

Morphological variability among seven populations of brown trout, Salmo trutta L., in Greece

Morphological variation in five meristic and 21 morphometric characters was examined in the brown trout, Salmo trutta L., from seven distinct streams and rivers from N and NW Greece. Variation within each sample, estimated as the multivariate generalization of the coefficient of variation, did not vary substantially among the populations. The phenetic relationships of these populations were examined using the stepwise discriminant analysis. The taxonomic implications of these results are discussed.     

Environmental stress and the survival of brown trout, Salmo trutta

SUMMARY. 1. The hypothalamic-pituitary-interrenal axis of the brown trout, Salmo trutta , is activated in response to most forms of environmental stress. This results in an elevation of blood cortisol levels.
2. Experimental elevation of blood cortisol levels in otherwise unstressed brown trout caused a dose-dependent increase in mortality rate due to disease. In our studies., Saprolegnia-infection , furunculosis and bacterial fin-rot were the principal diseases.
3. Chronic cortisol elevation also suppressed several of the endocrine processes controlling sexual maturation, resulting in a significant reduction in the size of the gonad in both male and female fish.
4. It is argued that many of the deleterious effects of sublethal pollution (including acidification) on natural trout populations can be attributed to chronically-elevated blood cortisol levels and that a knowledge of such physiological changes would allow an assessment of the impact of pollution events and act as an early warning of potential disease and recruitment problems.     

Haemolytic activity in the serum of brown trout, Salmo trutta

Brown trout serum contains a natural, spontaneous, antibody-independent lytic activity and a haemolysin antibody complement-mediated lytic activity against unsensitized and trout antibody-sensitized sheep erythrocytes, respectively. The use of various activators and inactivators of the mammalian complement system demonstrated that trout serum possesses complement or complement-like components similar in activity to those present in the classical and alternative pathways found in mammals. A single injection of trout with sheep erythrocytes stimulated the production of antibody-secreting cells in lymphoid organs and increased the levels of natural haemolysins. A second injection of sheep erythrocytes further raised the haemolysin values and antibody-secreting cell counts. Serum complement from homologous or closely related fish species was more effective for use in the haemolysin and antibody-secreting cell assays than that from heterologous sources, except guinea pig. Based on physico-chemical properties, gel filtration and immunoelectrophoretic studies, natural and induced anti-sheep erythrocyte haemolysins were found to be similar molecules and are possibly high molecular weight IgM antibodies.     

Activity cycles in the brown trout (Salmo trutta Lin.)

Summary The annual and diurnal activity cycle for four naturally feeding brown trout separately confined in netting cages on the bed of Windermere is described. All the fish showed a similar annual cycle of maximum activity during May and June, one fish showing a second activity peak during the autumn. The fish also showed a similar diurnal activity rhythm of low activity during the night and increased activity during the day with a pronounced increase at dawn.The possible influence of light and temperature on the fishes activity is briefly discussed.     

The immune response of the brown trout Salmo trutta to lipopolysaccharide

Brown trout produced high molecular weight, thermostable, dithiothreitol sensitive, non-precipitating, complement-fixing antibodies and agglutinins to lipopolysaccharides after intramuscular injection with adjuvant. Antibodies were first detected on Day 14 and reached maximum titres after 56 to 63 days when a single injection was given. When either a second or a third injection was administered maximum titres occurred 34 to 40 days after the injection. After each injection the titres increased significantly, and the protein concentration of the sera was significantly decreased. In cellulose acetate electrophoresis experiments those bands which migrated in the β- to γ-globulin regions were increased.
Antibody-secreting and antigen-binding cells were detected on Days 8 and 4 respectively and maxima were reached between Day 16 and Day 18. The number of cells per 10⁶ lymphoid cells was higher in the spleen than in the kidney.     

Aggressiveness and kinship in brown trout (Salmo trutta) parr

In a series of experiments, kin-biased behavior of young browntrout (Salmo trutta) was observed. The aggressiveness shownby groups of familiar siblings (siblings reared together sincefertilization) and groups of unfamiliar siblings (siblings rearedapart since fertilization) was significantly lower comparedto that of mixed groups of two unrelated sibling groups (offspringof two different pairs of parents). The evolution of kin-biasedbehavior, as shown by a reduction in aggressiveness, is assumedto have evolved through a kin-selective mechanism.[Behav Ecol7: 445-450 (1996)]     

Migration of anadromous brown trout Salmo trutta in a Norwegian river

1. Upstream and downstream migrating anadromous brown trout Salmo trutta were monitored daily in fish traps in the River Imsa in south-western Norway for 24 years, from 1976 to 1999. One-third of the fish descended to sea during spring (February–June) and two-thirds during autumn (September–January).
2. In spring, high water temperature appeared to influence the downstream descent. Large brown trout (> 30 cm, chiefly two or more sea sojourns) descended earlier and appeared less dependent on high water temperature than smaller and younger fish. The spring water flow was generally low and of little importance for the descent.
3. In autumn, the daily number of descending brown trout correlated positively with flow and negatively with water temperature.
4. Brown trout ascended from the sea between April and December, but more than 70% ascended between August and October. The number of ascending trout increased significantly with both decreasing temperature and flow during the autumn. This response to flow appeared to be the result of the autumn discharge which is generally high and most fish ascended at an intermediate flow of 7.5–10 m³ s⁻¹ (which is low for the season).
5. In a river like the Imsa with low spring and high autumn flows, water temperature appears to be the main environmental factor influencing the timing and rate of spring descent, while both water temperature and flow seemed to influence the timing and rate of the autumn descent and ascent. These relationships make sea trout migrations susceptible to variation in climate and human impacts of the flow regime in rivers.     

Rates of gastric evacuation in piscivorous brown trout, Salmo trutta

SUMMARY. 1. The dry weight of food remaining in the stomachs of piscivorous trout decreased exponentially with time. Gastric evacuation rates increased exponentially with increasing temperature but were unaffected by predator size, meal size or type of fish prey.
2. Mathematical models were developed to estimate both the rate and time for the gastric evacuation of different meal sizes (expressed as dry weight), and were applicable to piscivorous trout of different sizes (length range 10–32 cm) feeding on trout fry or sticklebacks at different temperatures (range 5–18°C).
3. The wet weight of food in the stomachs also decreased exponentially with time, but evacuation rates both increased with temperature and decreased with increasing meal size; the latter relationship occurred because relative rates of water loss from a meal also decreased with increasing meal size. Use of wet or dry weights can therefore lead to different conclusions about the effect of meal size on evacuation rates.
4. When piscivorous trout were fed three consecutive meals of varying size, the models predicted the total dry weight of food left in the stomach, but not the weight remaining for each individual meal. Interactions between meals led to an increase in evacuation rates for meals consumed early in the series and a decrease in evacuation rates for later meals.
5. Evacuation rates for piscivorous trout were compared with those for trout feeding on invertebrates in an earlier study, and were close to those for caddis larvae as prey, higher than those for mealworms and lower than those for a variety of invertebrate prey. Although a great deal is now known about the daily food intake and growth rates of trout feeding on invertebrates, there is little comparable information for piscivorous trout.     

Spatial association of nest construction by brown trout Salmo trutta

Spawning patterns in female brown trout Salmo trutta were examined by documenting the construction of nests in a small stream and later excavating them to recover progeny. The maternal provenance of nests was determined by genetic typing of embryos using microsatellite markers. Seventy-two nests, for which position and date of construction were known, were made by 59 individuals. Position and date of construction were known for a further 35 nests, comprising 11 Atlantic salmon Salmo salar nests and 24 nests which contained few or no progeny. Salmo trutta showed a behavioural preference for spawning near (≤ 1 m) prior nests; nests made by different individuals tended to accumulate in a spatial sequence that progressed upstream. The directionality of the association between prior and new nests suggests that later spawners use the residual depressions created by previous spawners as the first element of their own nests.     

Early-age changes in oxidative stress in brown trout,Salmo trutta

Fish are often used as models for studies investigating the ability of xenobiotics to induce oxidative stress, though age or developmental stage of the individuals studied has been given little attention. Oxidative stress in other organisms is associated with aging as well as with periods of rapid growth, which occurs in young brown trout. We measured protein carbonyls, 20S proteosome activity and glutathione (GSH) levels in farmed Salmo trutta in four different age groups from 5 months to 3 years. We found an increase in protein carbonyls and a decrease in 20S proteosome activity in both brain and liver tissues of the fish with increasing size and age. Total GSH levels in liver tissue declined as fish aged and the GSSG:GSH ratio increased. Five month and 1 year old trout were treated with paraquat (PQ) to induce oxidative stress. Five month old fish showed no changes in the measured parameters while 1 year old fish had both an increase in protein carbonylation in liver tissue and a decrease in 20S proteosome activity in brain tissue. These results indicate that oxidative stress biomarkers are affected by age or rapid growth in brown trout, and that individuals of different ages respond differently to oxidative stress induced by PQ.     

Morphology of the pronephros of the juvenile brown trout, Salmo trutta

The pronephros in juvenile brown trout (Salmo trutta) consists of a large ovoid renal corpuscle and a pair of tubules. The corpuscle is retained for 11 months, after which the glomerulus regresses. The glomerular arteries come directly from the dorsal aorta. The interstitium is permeated with venous blood vessels that arise from the anterior cardinal veins and are closely apposed to the tubules. Two distinct segments of the pronephric tubular system are distinguished by the histological and ultrastructural features of their component cells: 1) a short, transitional neck in which cells change from capsular epithelium to columnar epithelium, typical of tubules; 2) the convoluted segment composed of cells similar to first proximal tubular cells of the opisthonephros with well-formed brush borders, apical vesicles that vary in size and number along this segment, and lysosomes. Pinocytosis and exocytosis are also evident in this segment. The tubular system increases in length and in its convolutions until about week 9, when the opisthonephros develops. Distally each tubule connects with a Wolffian duct, with cells marked by the absence of apical inclusions and the presence of a uniform brush border, numerous mitochondria, and elaborate infolding of the basalar membrane. Nephrostomes, which are often characteristic of pronephroi, are not present. Cells with long cilia are found throughout the tubular system but are most characteristic of the neck and Wolffian-duct segments.     

Morphological organ alterations and infectious diseases in brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss exposed to polluted river water

Poor water quality is discussed as a major factor causing a decline of brown trout populations in Swiss rivers. For our study we have chosen a river in the Swiss midlands, where the brown trout population has decreased dramatically during the last 10 yr and where feral fish have shown distinctive pathological alterations. The objective of our study was to investigate whether river water may be responsible for impaired fish health leading to an increased mortality in the river. In an active monitoring program, groups of brown and rainbow trout were exposed to polluted river water for 24 mo. Fish held in tap water served as a reference. Mortality, macroscopic and histopathologic changes, and infectious agents were investigated. Compared with the reference group, high mortality rates and severe pathological alterations of the inner organs were observed in fish held in river water. Especially gills, liver and kidney of these fish showed significantly higher changes than fish from tap water. These changes were dominated by degenerative and inflammatory reactions. Additionally, several infectious agents were diagnosed in fish exposed to river water. The most important findings were furunculosis and proliferative kidney disease. Brown trout seemed to be more sensitive than rainbow trout to environmental stress and infectious agents.     

The ecology of brown trout Salmo trutta in English chalk streams

SUMMARY. .1. Chalkstream trout are fast-growing, short-lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.
2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.
3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro-habitat distributions between fish species.
4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly-emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.
5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearling trout.     

Seasonal adaptations in oxygen transport in brown trout Salmo trutta fario

• 1.1. Blood parameters determining oxygen capacity and oxygen affinity were measured in brown trout at different times of the year.
• 2.2. Haematological data indicate a slight decrease in blood oxygen capacity during the warm seasons. 3. Oxygen affinity increases significantly during summer and decreases in winter.
• 3.4. The changes in P₅₀ exhibited a positive correlation with the amount of anodic haemoglobin components, and a negative correlation with the amount of cathodic haemoglobin components.
• 4.5. The changes observed in the [ATP]/[Hb] molar ratio were not correlated with oxygen affinity and gave values near one.
• 5.6. We conclude that the oxygen affinity increase could be a physiological adaptation to oxygen transport during the wanner period. A possible mechanism is discussed.