Young Brown Trout Research Articles

Using qPCR to Identify Potential Effects of Thermal Conditions during Embryogenesis on Mitochondrial DNA Copy Number in Juvenile Brown Trout Salmo trutta

Changes in the number, structure, and function of mitochondria during the early life stages of animals can play an important role for an organism’s metabolic rate, growth, and health. Previous studies have shown that juvenile brown trout (Salmo trutta) subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduced metabolic rate. The aim of this study was to explore if embryonic temperature affects the mitochondria content of young brown trout and as such explains the previously found differences in metabolic rates. Here, we optimize a quantitative PCR (qPCR) method for the mitochondria cytochrome c oxidase subunit I gene, and then use the method as a proxy for mitochondrial DNA content. We hypothesize that young trout subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduced mitochondrial DNA content. To test this hypothesis, we subjected brown trout to either control ambient (4.4 ± 1.5 °C) or elevated temperatures (7.1 ± 0.6 °C) during embryogenesis. Subsequently, we extracted DNA from liver and white muscle tissue of juvenile brown trout from the two different incubation temperature treatments and successively optimized qPCR for mitochondrial DNA. We found that the amount of mitochondria DNA in liver tissue was 18 times higher than in white muscle tissue, but there was no significant difference in mitochondria content in liver or muscle tissue between brown trout exposed to elevated and ambient control temperatures during embryogenesis. We conclude that reduced metabolic rate is not likely associated with mitochondria DNA content. We also suggest that qPCR is a simple and cost-effective method to quantify mitochondria DNA in frozen and partly degraded tissue from different treatment groups and a useful proxy for identification of differences in mitochondria number.

Egg incubation temperature influences the population-specific outmigration rate of juvenile brown trout Salmo trutta.

The present experiment tested if temperature during embryogenesis and parental heritage affected the migratory behaviour of young brown trout Salmo trutta. Two parental forms were used, a freshwater resident form and an anadromous form, both from the same river system but geographically isolated since 1993–95. Four groups of young S. trutta were produced and reared from (a) freshwater resident parents spawning in a tributary to the River Imsa, Norway, (b) anadromous parents spawning in the main stem of the same river system, (c) resident male × anadromous female parents and (d) resident female × anadromous male parents. The eggs were incubated until first exogenous feeding in River Imsa water, either unheated or heated c. 2.7°C above ambient temperature. Thereafter, all fish experienced the same ambient river temperature until release. Groups were released below an impassable waterfall 900 m upstream of the mouth of the River Imsa, either as age‐0 in October 2019 or as age‐1 in May 2020. About 7.5% of the released fish moved downstream and were captured in a trap at the outlet. For any given body size, the proportion of warm incubated trout that moved downstream was greater than the proportion of cold incubated trout. It was also found that most emigrants of the October‐released S. trutta were caught within a month of release. Also, most May‐released S. trutta emigrated in October. The offspring of the freshwater resident parents emigrated to a larger extent than offspring of anadromous parents. Thus, the difference in emigration with regard to embryonic temperature was phenotypically plastic and may be associated with an epigenetic effect of the thermal conditions during early development. The effect of parental origin suggests there may be genetic divergence between the geographically isolated populations.

Long-Term Influence of Surfagon Injection on the Cytological Condition of the Gonads and Level of Thyroid and Sexual Steroid Hormones in Young Brown Trout Salmo trutta

The long-term effect of the injection of a synthetic analogue of gonadotropin releasing hormone—Surfagon—on the reproductive system of juvenile brown trout Salmo trutta has been studied. The concentration of thyroid hormones in the blood, the rate of gametogenesis, and physiological adaptation of individuals to external conditions increased over five months after injection. The changes identified predetermine the formation of a predominantly resident fish of the brown trout population. Based on the patterns found, the interrelation of the hormonal status, puberty, and the formation of life strategies in salmon species has been analyzed.

Surfagon Effect on Rheoreaction of Young Brown Trout Salmo trutta

The effect of surfagon injection (synthetic analog of gonadotropic-releasing hormone) on the kind and time of rheoreaction change in juvenile brown trout Salmo trutta is studied. In spite of the fact that the increase of gonadotropins in the organism after surfagon injection is recorded just during several hours, the action of this preparation on the rheoreaction is discovered only at the 25th day, continues for 19 days, and is seen as the increase of the part of fish swimming upstream. The long-term effect of surfagon is found later – 5 months after the injection. This effect is present only in starving specimens and is the stabilization of their behavior in the water flow.

Macrozoobenthos in tributaries of the lower reaches of the ponoy river (Kola peninsula, Russia) in the habitats of young atlantic salmon (Salmo Salar L.) and brown trout (Salmo Trutta L.)

Macrozoobenthos in tributaries of the lower reaches of the ponoy river (Kola peninsula, Russia) in the habitats of young atlantic salmon (Salmo Salar L.) and brown trout (Salmo Trutta L.)

Feeding of juvenile Atlantic Salmon Salmo salar L. and its trophic relations with other fish species in rivers of the Barents and White sea drainage basins (Kola peninsula)

The feeding patterns of the young Atlantic salmon (salmon) and its trophic relations with members of the resident fish fauna – brown trout, grayling, perch, pike and mature min66 now were investigated in a variety of their shared habitats in rivers of theKola Peninsula. At the same time, the food resources were studied, the hydrological characteristics of selected areas were assessed, and the overall fish distribution density was determined. The species and age compositions of the fish fauna were found to vary among habitats. Underyearlings of Atlantic salmon and brown trout, as well as of the minnow prefer to aggregate (in a mosaic pattern) in large numbers in shallow water areas with low current. Juvenile salmon, brown trout and grayling of older age classes occupy the deeper and fast-flowing part of the watercourse, with a differentiation among horizons – trout and salmon closer to the bottom, and grayling in the pelagic layer. The greatest similarity of the feeding spectra was observed between young Atlantic salmon and brown trout. No cases of competition for food or predation on juvenile salmon by brown trout, perch and pike have been observed. The division of food items, owing to rheophilic species preferring to live separately in relatively isolated hydrological niches, can be considered as a manifestation of adaptation aimed at a more complete exploitation of the food resource in a situation where several species coexist at fairly high densities

Fatty Acid Status of Freshwater Resident and Anadromous Forms of Young Brown Trout (Salmo trutta L.)

No qualitative or quantitative differences in the profiles of fatty acids (FAs) belonging to the main classes have been found between freshwater resident (Orzega River, Onega Lake Basin) and anadromous (Indera River, White Sea Basin) forms of young brown trout. Differences have been registered in the conversion rate of the food-derived 18:2ω-6 and 18:3ω-3 FAs into long-chain and physiologically active FAs: 20:4ω-6 (arachidonic) and 22:6ω-3 (docosahexaenoic). Freshwater residential form of young brown trout (parr, at 3+-age) from the Orzega River are distinguished by a higher index of 20:4ω-6/18:2ω-6. Anadromous form of young of brown trout (smolts, at 4+-age) from the Indera River have a higher ratio of essential FAs 22:6ω-3/18:3ω-3 and ω-3/ω-6 polyunsaturated FAs; the last index correlates with higher weight–length characteristics of the studied individuals.

Fatty Acid Status of Freshwater Resident and Anadromous Forms of Young Brown Trout (Salmo trutta L.)

Fatty Acid Status of Freshwater Resident and Anadromous Forms of Young Brown Trout (Salmo trutta L.)

Mitigation of acidified salmon rivers - effects of liming on young brown trout Salmo trutta.

In southern Norway, 22 acidified rivers supporting anadromous salmonids were mitigated with lime to improve water quality and restore fish populations. In 13 of these rivers, effects on Salmo trutta and Salmo salar densities were monitored over 10-12 years, grouped into age 0 and age ≥ 1 year fish. These rivers had a mean annual discharge of between 4·9 and 85·5 m3 s-1 , and six of them were regulated for hydro-power production. Salmo salar were lost in six of these rivers prior to liming, and highly reduced in the remaining seven rivers. Post-liming, S. salar became re-established in all six rivers with lost populations, and recovered in the seven other rivers. Salmo trutta occurred in all 13 study rivers prior to liming. Despite the improved water quality, both age 0 and age ≥ 1 year S. trutta densities decreased as S. salar density increased, with an average reduction of >50% after 10 years of liming. For age 0 year S. trutta this effect was less strong in rivers where S. salar were present prior to liming. In contrast, densities of S. trutta increased in unlimed streams above the anadromous stretches in two of the rivers following improved water quality due to natural recovery. Density increases of both age 0 and age ≥ 1 year S. salar showed a positive effect of river discharge. The results suggest that the decline in S. trutta density after liming is related to interspecific resource competition due to the recovery of S. salar. Thus, improved water quality through liming may not only sustain susceptible species, but can have a negative effect on species that are more tolerant prior to the treatment, such as S. trutta.

Highly dilute water chemistry during late snowmelt period affects recruitment of brown trout (Salmo trutta) in River Sira, southwestern Norway

During the past two-three decades the water chemistry in southern Norway has recovered considerably from acidification. The biological response, however, has been more variable. Thus, it has become increasingly apparent that decades of acidification may have masked other restrictors to fish populations in this area. The current study compiles data on young brown trout ( Salmo trutta ) density and water chemistry from 16 sites in River Sira in southwestern Norway during 2003–2014. The water chemistry during late snowmelt period was highly dilute, having a median conductivity and Ca of 10.5 μS/cm and 0.42 mg/l, respectively (n = 208). The corresponding minimum values were 5.0 μS/cm and 0.15 mg/l. With a pH median value of 5.89, the water was only slightly acidic. No effect of pH on the density of young brown trout was found, suggesting that acidification is no longer a limiting factor. However, both conductivity in year n-1 and Ca in year n correlated significantly with the density of 1+ brown trout. Al in year n , and surprisingly Ca in year n-1 , correlated negatively on their densities. We conclude that very dilute water chemistry during late snowmelt is a limiting factor for the recruitment of brown trout in the study river. This effect has probably existed in the past as well, but has been less apparent due to decades of severe acidification.

State-dependent behavior and alternative behavioral strategies in brown trout (Salmo trutta L.) fry.

Animals generally adjust their behavior in response to bodily state (e.g., size and energy reserves) to optimize energy intake in relation to mortality risk, weighing predation probability against the risk of starvation. Here, we investigated whether brown trout Salmo trutta adjust their behavior in relation to energetic status and body size during a major early-life selection bottleneck, when fast growth is important. Over two consecutive time periods (P1 and P2; 12 and 23 days, respectively), food availability was manipulated, using four different combinations of high (H) and low (L) rations (i.e., HH, HL, LH, and LL; first and second letter denoting ration during P1 and P2, respectively). Social effects were excluded through individual isolation. Following the treatment periods, fish in the HL treatment were on average 15–21 % more active than the other groups in a forced open-field test, but large within-treatment variation provided only weak statistical support for this effect. Furthermore, fish on L-ration during P2 tended to be more actively aggressive towards their mirror image than fish on H-ration. Body size was related to behavioral expression, with larger fish being more active and aggressive. Swimming activity and active aggression were positively correlated, forming a behavioral syndrome in the studied population. Based on these behavioral traits, we could also distinguish two behavioral clusters: one consisting of more active and aggressive individuals and the other consisting of less active and aggressive individuals. This indicates that brown trout fry adopt distinct behavioral strategies early in life.Significance statementThis paper provides information on the state-dependence of behavior in animals, in particular young brown trout. On the one hand, our data suggest a weak energetic state feedback where activity and aggression is increased as a response to short term food restriction. This suggests a limited scope for behavioral alterations in the face of starvation. On the other hand, body size is linked to higher activity and aggression, likely as a positive feedback between size and dominance.The experiment was carried out during the main population survival bottleneck, and the results indicate that growth is important during this stage, as 1) behavioral compensation to increase growth is limited, and 2) growth likely increases the competitive ability. However, our data also suggests that the population separates into two clusters, based on combined scores of activity and aggression (which are positively linked within individuals). Thus, apart from an active and aggressive strategy, there seems to be another more passive behavioral strategy.Electronic supplementary materialThe online version of this article (doi:10.1007/s00265-016-2215-y) contains supplementary material, which is available to authorized users.

Recovery of young brown trout (Salmo trutta) in acidified streams: What are the critical values for acid-neutralizing capacity?

The recovery of young allopatric brown trout (Salmo trutta) grouped into YoY (age 0+) and older parr (age ≥1+) fish, was studied in acid-sensitive streams in a Norwegian watershed during a 24-year-period (1987–2010). Their abundance was assessed by electrofishing. Most sites typically had 5.0–5.5 in pH, 0.4–0.7 mg L−1 Ca, 10–20 μg L−1 inorganic toxic aluminum (Ali) and acid-neutralizing capacity adjusted for organic acids (ANCOAA) of - 15 to +25 μeq L−1. Densities of both YoY and older parr increased significantly during the study period. Water quality also improved in recent years with respect to pH (5.8–6.0), Ali (5–15 μg L−1) and ANCOAA (10–20 μeq L−1). However, some negative trends in both fish density and water chemistry were found during both the first (1987–1993) and last years (2004–2008) of the study. Initially, YoY densities remained at about 16–20 specimens 100 m−2 (1987–1990), declined to 10–15 specimens 100 m−2 in the early/mid 1990s, and rosed to 30–50 specimens 100 m−2 in recent years (1997–2010). Their densities correlated significantly with ANCOAA, and at least three stages in the recovery process were recognised: (i) Low density with 10–20 specimens 100 m−2 at −18 to −5 μeq L−1, (ii) medium and unstable density with 20–30 specimens 100 m−2 at −5 to 10 μeq L−1, and (iii) increasing density to 40–50 specimens 100 m−2 at 10–25 μeq L−1. The decline in brown trout density in the early-mid 1990s coincided with high sea salt depositions, which caused increased acidification. Component 1 in a PCA explained 51% of the variation in fish densities, including conductivity, Mg, Ca, Na, alkalinity and TOC. Component 2 explained an additional 31% of the variation, including pH, Ali and ANCOAA. Multiple regression analysis coefficients showed that the two components explained 41% of the variance in total fish density. Young brown trout suffered a high mortality during the initial phase of the study in spite of relative low levels of Ali. This is probabaly because the study streams have very diluted water. The densities of young brown trout have levelled off in recent years, indicating a development towards reaching carrying capacity and hence full recovery. However, still some annual fluctuations in density are recorded, which may be related to an unstable water chemistry.

Re‐building brown trout populations in dredged boreal forest streams: in‐stream restoration combined with stocking of young trout

Summary1. Rivers in boreal forested areas were often dredged to facilitate the transport of timber resulting in channels with simplified bed structure and flow fields and reduced habitat suitability for stream organisms, especially lotic fishes. Currently, many streams are being restored to improve their physical habitat, by replacing boulders and gravel and removing constraining embankments. The most compelling justification behind stream restoration of former floatways has been the enhancement of native fish populations, specifically salmonids.2. We examined the success of a stream management programme aimed at re‐building diminished brown trout (Salmo trutta) populations by monitoring densities of young‐of‐year and older trout in 18 managed and three reference streams during 2000–2005. Rehabilitation included in‐stream restoration combined with a 5‐year post‐restoration period of stocking young brown trout. Our space‐for‐time substitution design comprised four pre‐management, four under‐management, 10 post‐management and three reference streams.3. Densities of young‐of‐year brown trout, indicating population establishment, were significantly higher in post‐ compared with pre‐management streams. However, density of young‐of‐year brown trout in post‐management streams was significantly lower compared with near‐pristine reference streams. Furthermore, success of managed brown trout population re‐building varied, indicating stream‐specific responses to management measures. Density of burbot (Lota lota), a native generalist predator, was associated with low recruitment of brown trout.4. Stream‐specific responses imply that rehabilitation of brown trout populations cannot be precisely predicted thereby limiting application. Our findings support the importance of adaptive stream restoration and management, with focus on identifying factor(s) limiting the establishment of target fish populations.

Repeatability of standard metabolic rate, active metabolic rate and aerobic scope in young brown trout during a period of moderate food availability

Standard metabolic rate (SMR) and active metabolic rate (AMR) are two fundamental physiological parameters providing the floor and ceiling in aerobic energy metabolism. The total amount of energy available within these two parameters confines constitutes the absolute aerobic scope (AAS). Previous studies on fish have found SMR to closely correlate with dominance and position in the social hierarchy, and to be highly repeatable over time when fish were provided an ad libitum diet. In this study we tested the temporal repeatability of individual SMR, AMR and AAS, as well as repeatability of body mass, in young brown trout (Salmo trutta L.) fed a moderately restricted diet (0.5-0.7% fish mass day⁻¹). Metabolism was estimated from measurements of oxygen consumption rate (M(.)(O₂)) and repeatability was evaluated four times across a 15-week period. Individual body mass was highly repeatable across the entire 15 week experimental period whereas residual body-mass-corrected SMR, AMR and AAS showed a gradual loss of repeatability over time. Individual residual SMR, AMR and AAS were significantly repeatable in the short term (5 weeks), gradually declined across the medium term (10 weeks) and completely disappeared in the long term (15 weeks). We suggest that this gradual decline in repeatability was due to the slightly restricted feeding regime. This is discussed in the context of phenotypic plasticity, natural selection and ecology.

First feeding diet of young brown trout fry in a temperate area: disentangling constraints and food selection

Diet composition of newly emerged brown trout fry in natural areas remains poorly known, and foraging abilities at this early stage, although presumably reduced, are still under discussion. We have studied gut content composition of brown trout fry in a temperate area (Galicia, NW Spain) and compared it to the benthic macroinvertebrate community. Small prey such as chironomid larvae and baetid nymphs were the most important food items for newborns, some of them still presenting yolk remnants. However, the positive selection observed for Polycentropodidae and Simuliidae and the rejection of Elmidae and Leuctricidae suggest that other factors apart from size, such as locomotor abilities of fish or accessibility and antipredator behaviour of prey play an important role in feeding behaviour. Additionally, analysis of diet changes on the studied fry suggests a dramatic shift in niche breadth at the moment of complete yolk absorption, which might be related to the improvement of swimming and handling ability of fry for capturing and ingesting prey. The presence of aerial imagoes only in the stomachs of fry with no yolk provides further support to this hypothesis. Planning of restoration works on spawning grounds should then allow enough time for complete recolonization by benthic macroinvertebrates, including first instars, as searching for food in newborns is limited to the nest area due to mobility constraints.

Evaluación del lavado gástrico como herramienta para el análisis de la dieta en trucha común

Evaluation of the gastric lavage as a tool for the analysis of the brown trout diet The efcacy of the method of extracting stomach content, by means of the procedure of stomach washing through a pump, based on Seaburg's original model (1957), has been studied. The effectiveness of the method is not related to the size of thesh, but rather to the prey's own morphological characteristics, the degree of repletion of the stomach and the extent of digestion of the food. Thus, the effectiveness of the method is inversely related to the degree of repletion. Furthermore, bigger prey having rigid structures, such as Aeshnidae and Caddisies with cases are more difcult to expel. However, the observed differences in the effectiveness of expulsion between preys with similar characteristics are due to the extent of their digestion. Nevertheless, the average effectiveness of the method is high and in excess of 80 %. It is therefore a relatively simple and effective methodology and the reason why its use is appropriate for obtaining stomach content samples in young and adult brown trout.

Within-reach spatial variability of snails and molluscivory by brown trout

Linking habitat distributions of prey to the probability of predation is important to understanding consumptive effects of predators on prey populations. This study reports how within-reach spatial variability of two snails, the hydrobiid Potamopyrgus antipodarum and the physid Physella acuta, was linked to habitat-based predation risk by young brown trout (Salmo trutta) of different age classes. Potamopyrgus is endemic to New Zealand streams and lakes, where it commonly co-exists with the invader P. acuta, but both snails are worldwide invaders to many freshwater systems. Examination of egested snails revealed Potamopyrgus and Physella were consumed in similar numbers within age classes. However, 10-month-old trout consumed, on average, fewer snails than 20-month-old trout, and 8-month-old trout ate essentially no snails, suggesting snails were a more important prey item for larger age-1 fish than smaller age-0 fish. No Physella were egested alive by any trout age class. However, 38% and 16% of the Potamopyrgus consumed were egested alive by 10- and 20-month-old trout, respectively, with some passing live after ~70 h in digestive tracts. Physella and the spiny-shell form of Potamopyrgus were significantly denser on macrophytes than on stony sediments in midchannel, and these habitat distributions affected their odds of consumption. Risk of consumption by trout was ~10 times greater for Physella than Potamopyrgus on stones, but their risk was similar in protective macrophytes. Odds of consumption were similar for spiny and smooth shell forms of Potamopyrgus on stones, suggesting spines do not provide protection from large predators like trout. My results suggest that brown trout can potentially exert stronger population regulatory effects on Physella than on Potamopyrgus and that these effects are partly mediated by macrophyte cover.

Diet overlap between introduced European minnow (Phoxinus phoxinus) and young brown trout (Salmo trutta) in the lake, Øvre Heimdalsvatn: a result of abundant resources or forced niche overlap?

A study of the diet of native brown trout (Salmo trutta) parr and introduced European minnow (Phoxinus phoxinus) in the subalpine lake, Ovre Heimdalsvatn, showed that the two species had considerable dietary overlap, both in the littoral zone and in the outlet of the lake. Chironomidae constituted a substantial proportion of the diet of the two species in both habitats. The results indicated that both zooplankton (Cladocera) and large macroinvertebrates (EPT-species) made up a higher proportion of the minnow diet in the early phase of the minnow establishment (1975–1977) than later, and that the significance of small macroinvertebrates (Chironomidae) as prey has increased during the same period. Dietary analysis of the sympatric brown trout and minnow population in Ovre Heimdalsvatn does not provide a definitive conclusion about the degree of competition between the two species. However, together with the findings in other studies in Ovre Heimdalsvatn that have documented reduced recruitment and individual growth of brown trout, decreased individual growth of minnows and a marked decline in the density of large crustaceans (Lepidurus arcticus and Gammarus lacustris) in the shallow littoral of the lake during the last decades indicates that competitive interactions between the two species are likely. This is probably an example of the competition between two fish species with a high degree of dietary overlap when living in sympatry, most likely caused by absence of alternative prey and alternative habitats due to the high predation risk for both brown trout parr and minnows in deeper parts and in the open waters of the lake.

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.

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.