Growth Of Brown Trout Research Articles

Growth of brown trout in the wild predicted by embryo stress reaction in the laboratory.

Laboratory studies on embryos of salmonids, such as the brown trout (Salmo trutta), have been extensively used to study environmental stress and how responses vary within and between natural populations. These studies are based on the implicit assumption that early life-history traits are relevant for stress tolerance in the wild. Here we test this assumption by combining two data sets from studies on the same 60 families. These families had been experimentally produced from wild breeders to determine, in separate samples, (1) stress tolerances of singly kept embryos in the laboratory and (2) growth of juveniles during 6 months in the wild. We found that growth in the wild was well predicted by the larval size of their full sibs in the laboratory, especially if these siblings had been experimentally exposed to a pathogen. Exposure to the pathogen had not caused elevated mortality among the embryos but induced early hatching. The strength of this stress-induced change of life history was a significant predictor of juvenile growth in the wild: the stronger the response in the laboratory, the slower the growth in the wild. We conclude that embryo performance in controlled environments can be a useful predictor of juvenile performance in the wild.

Annual growth of brown trout in alpine lakes is highly influenced by spring snow depth and ice-out day

Growth of annular zones in otoliths of brown trout from the alpine lakes Litlosvatn and Kollsvatn on western part of the Hardangervidda mountain plateau have been studied during the period 2004–2021, concurrent with recordings of accumulated snow in spring and dates of ice-out. Unlike the conditions in lowland areas, years with much accumulated snow have not decreased during the last decades, and years with delayed ice break-up are still frequent, opposite the trend observed elsewhere in Europe and in North America. The annual growth of the brown trout otoliths is significantly reduced in years with much snow in April and late ice-out dates, irrespective of age of the fish, indicating that somatic growth of brown trout is considerably reduced in such years. Accumulated snow in spring and ice-out day may thus be useful parameters in predictions of fish production and potential yield in such alpine lakes.

Growth and mortality of sympatric Atlantic salmon and brown trout fry in fluctuating and stable flows

AbstractSub‐daily fluctuations in streamflow may have adverse effects on the biota downstream of dams in hydropeaking‐regulated rivers. Although the stranding of salmonid fry is one documented effect of hydropeaking, little is known about the species‐specific behavioural and subsequent growth effects of sub‐daily flow fluctuations. We investigated the effects of sub‐daily flow fluctuation on growth, mortality and behaviour of sympatric Atlantic salmon (Salmo salar) and brown trout (S. trutta) fry (29–34 mm) in a laboratory experiment. The fluctuating flow treatment negatively affected growth and increased mortality for trout but not for salmon. The level of aggressive behaviour was similar in the fluctuating‐ and stable‐flow treatments. Within the fluctuating flow treatment, there was a trend that more fishes were visibly active above the substrate during low than high flow. These findings suggest that hydropeaking‐induced flow fluctuations may affect fry of different salmonid species in different ways and that brown trout fry may be more vulnerable to hydropeaking effects than Atlantic salmon fry. It can therefore be important to consider the possibility of divergent reactions by different fish species under hydropeaking situations and to incorporate species‐specific strategies to conserve culturally and economically relevant riverine fish species.

In situ management options to improve crucian carp (Carassius carassius, L.) and brown trout (Salmo trutta, L.) population status in Central Europe: A case study from the Czech Republic.

The crucian carp (Carassius carassius, L.) and the brown trout (Salmo trutta, L.) are vanishing from freshwater ecosystems of central Europe. To conserve both species, tailor‐made conservation management of habitats and populations of both species was implemented and tested in the Czech Republic (central Europe). This management was adjusted to reflect the ecological needs of both species. This study aimed to describe the results of a tested in situ management and to analyze the population growth of brown trout and crucian carp under ideal conditions. An experiment was performed at 14 small gravel pit lakes. Seven of them were adjusted to fit the crucian carp habitat requirements while the other seven were treated as a control group. The same experiment was done on 14 smaller streams and with brown trout. The occurrence and growth of crucian carp and brown trout were surveyed over 2 years. A significantly faster growth of both crucian carp and brown trout was observed on the adjusted lakes and streams in comparison to the control group ones. Trout and carp prospered on small streams and gravel pit lakes (respectively) that were free of angling, fish stocking, pollution, piscivorous predators, and competition with hybridizing species like Prussian carp (Carassius auratus, L.) or hatchery‐reared brown trout.

Low impact of first-time spawners on population growth in a brown trout population

For species with individual variation in reproductive success, experience in breeding and the distribution of different breeders is important for population productivity and viability. Human impacts, such as climate change and harvesting, can alter this distribution and thus population dynamics. Here, we investigated the effect of spawning experience on population growth in a population of migratory brown troutSalmo truttasubject to stressors including migration barriers, harvesting, and climate change. We described the population dynamics with a structured integral projection model that differentiates between first-time and repeat spawners. We then took a scenario-based approach to test to which extent spawning experience has a positive effect on the population growth of brown trout by running 3 different model simulations: a baseline scenario with no changes to the reproductive output of the population, a non-selective scenario in which the reproductive output of all spawners was reduced, and a selective scenario where the reproductive output of only first-time spawners was reduced. We found that the reproductive output of repeat spawners is more important than that of first-time spawners for population growth, in line with other studies. Moreover, the contribution of first-time spawners to the population growth through their own survival is more important than their contribution to growth through reproduction. To ensure the continued existence of the study population, survival of first-time spawners and reproductive success of repeat spawners should be prioritised. More generally, including breeding experience adds more mechanistic detail, which ultimately can aid management and conservation efforts.

Effects of Density Reduction on Age‐Specific Growth of Stream‐Dwelling Brown Trout

AbstractDensity‐dependent growth has been well documented among stream‐dwelling Brown Trout Salmo trutta populations. In Spearfish Creek, South Dakota, biomass of adult Brown Trout (>200 mm) is about three times greater than that reported for similar Black Hills streams, whereas the mean length of adult fish is about 30% less. Here, we evaluate density reduction as a management tool for improving the growth rate of stream‐dwelling Brown Trout. We compared age‐specific growth of wild Brown Trout in stream sections receiving 50% reductions in fish abundance (removal sections) to that of fish in sections containing natural densities (control sections). Annual growth in length and weight of older Brown Trout (age > 2) was greater in removal sections compared to control sections, particularly among fish between 230 and 280 mm TL (ages 3–4). We attribute the growth response to constraints imposed by food availability and the strong feeding hierarchies, characteristic of larger (older) Brown Trout. Data collected from PIT‐tagged fish that were recaptured 2 years after fish removal efforts revealed that growth responses owing to density reduction likely did not extend beyond 1 year. Nonetheless, among cohorts that showed improved growth after the first year, we found that their growth advantage was sustained into the second year. At removal sections, age‐3 and older Brown Trout that experienced greater growth after 1 year were larger than fish from control sections 2 years later at age 5 and older. Identification of cohort(s) for which density‐dependent growth is most pronounced could help to focus efforts on targeted reduction of specific fish sizes/ages that minimize the cost–benefit ratio of fish removal efforts.

Increasing connectivity of Great Lakes tributaries: Interspecific and intraspecific effects on resident brook trout and brown trout populations

AbstractUnderstanding resident fish population responses to restored connectivity would enhance decision‐making on dam removal and fish passage. Since such evaluations are limited in the Great Lakes region of North America, we compared abundance, survival, and growth of resident brook trout and brown trout between sets of Michigan streams where populations were or were not interacting with salmonid species that might be present if connectivity existed. We analysed data from 34 electrofishing index sites to compare resident trout populations between streams without versus with Great Lakes access (and migratory Pacific salmonids), and brook trout populations in Great Lakes inaccessible (land‐locked) streams where brown trout were present versus absent. Great Lakes accessibility effects on fish density became increasingly positive for older age groups of brown trout while generally negative for all age classes of brook trout. Brown trout had consistently negative effects on brook trout density in land‐locked streams. Increased connectivity had significant effects on annual survival for only one of seven trout age classes modelled, while intraspecific density‐dependent effects on survival were significant in six models. Significant intraspecific effects on resident trout growth occurred for seven of eleven age classes examined. Negative interspecific effects of Great Lakes access on resident trout growth were most noticeable for age‐0 and age‐1 resident trout, age classes that likely compete with juvenile Pacific salmonids. Our findings provide a more robust understanding of how Great Lakes connectivity affects resident trout populations, highlighting negative influences of brown trout on brook trout and intraspecific density‐dependent effects.

The Effects of starvation and refeeding on growth and digestive enzymes activity in Caspian brown trout (Salmo caspius Kessler, 1877) fingerlings

240 Caspian brown trout (Salmo caspius) fingerlings with initial weight of 13.74±0.63 g were stored in 300 L tanks to investigate the effect of starvationand refeeding on compensatory growth and digestive enzymes activity. The fish were introduced to four different periods of starvationduring 10 weeks including control (with no starvation: C), 2 weeks (S2), 4 weeks (S4) and 6 weeks (S6) and then fed to satiation during the refeeding period. Sampling for growth and enzymes activity measurements was conducted three times: day 1 (T1), after starvation(T2), after 2 weeks (R2) and 4 weeks [X1] (R4) of refeeding. Results have indicated a significant decrease in growth performance after starvation(p 0.05). Generally, results declared that Caspian brown trout fingerlings could recover digestive capacity after 2 weeks of starvationby appropriate refeeding with no negative impact on growth performance.

Modelling effects of climate change on Michigan brown trout and rainbow trout: Precipitation and groundwater as key predictors

AbstractUnderstanding how changes in stream temperature affect survival and growth of coldwater fishes, including brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss), is important for conserving coldwater stream fisheries in a changing climate. However, some contemporary stream temperature models assume spatially uniform (i.e. unrealistic) air–stream temperature relationships or demand hydrometeorological predictors (e.g. solar radiation and convection) that are expensive and often impractical for fisheries managers to measure. As such, we produced a relatively cost‐effective, management‐relevant modelling approach for predicting effects of changes in air temperature, precipitation and groundwater inputs on stream temperature and, consequently, the survival and growth of brown trout and rainbow trout in Michigan, USA. We found that precipitation‐ and groundwater‐corrected stream temperature models (mean adjusted R2 = .77, range = 0.65–0.88) performed better than linear air–stream temperature models (mean adjusted R2 = .59, range = 0.21–0.80). Stream temperature was projected to increase by 0.07–3.88°C (1%–22%) with simulated changes in air temperature, precipitation and groundwater inputs. The greatest warming was predicted for surface runoff‐dominated sites with limited groundwater‐driven thermal buffering, where thermal habitat suitability for salmonid survival and growth declined 20%–40%. However, groundwater‐dominated sites may not be immune to temperature warming, especially if groundwater temperature increases or groundwater inputs decline in a changing climate. Our modelling approach provides a reliable, cost‐effective method for predicting effects of climate change on brown trout and rainbow trout survival and growth, allowing for strategic management actions to increase the thermal resilience and sustainability of salmonid populations (e.g. groundwater conservation and riparian/watershed rehabilitation).

Determination of resident brown trout Salmo trutta features by their habitat characteristics in streams of Serbia

Streams’ order, their width and depth, as well as the water temperature, conductivity, dissolved oxygen contents and pH reaction were recorded for 18 streams of the Danube River basin in Serbia that home brown trout Salmo trutta. For each of them, the number of fish species was recorded, and for brown trout in them the number of cohorts, age-structure, productivity (biomass, annual production and average weight) and growth (von Betalanffy’s growth parameters L∞, t0, K and ø’) were calculated. They were examined in relation to stream’s habitat features. Stepwise multiple regression revealed strong interdependence between habitat variables. Size, i.e., width and depth of streams increased and their oxygen content dropped with increase in their order and rise of the water temperature, and water conductivity was strongly interrelated with order and depth of streams. Increase in streams’ order and their water’s temperature were accompanied with the increase of species number in them, number of brown trout cohorts raised with the water conductivity and dropped with the increase of the alkaline pH value of streams, whereas growth of brown trout was determined by width of streams and their water’s conductivity. However, when analyzed one at a time, very few of habitat and population traits, e.g., stream depth and L∞, varied clearly in streams of either various orders, or conductivity classes, respectively. The notable, but not yet significant variability of almost all other characters implicates their strong and complex acting in concert to determining number of fish species in syntopy, brown trout population, productivity and growth features.

Fine stream wood decreases growth of juvenile brown trout (Salmo trutta L.)

In this study, the growth rate, gut fullness, diet composition and spatial distribution of brown trout was compared between artificial channels with and without fine wood (FW). Access to FW resulted in significantly lower brown trout growth rates over the study period from late summer to early winter as water temperatures declined from 17 °C to 1 °C. Access to FW resulted in minor differences in occurrence of the most common taxa found in brown trout diets, except for chironomid larvae which were found in c. 60% of the brown trout guts from control treatments but in only 30% of the guts from FW treatments in early winter. Diet consisted primarily of case-bearing and free-living Trichoptera larvae, Asellus, chironomid and Ephemeroptera larvae. Brown trout gut fullness was not significantly affected by access to FW bundles. Brown trout aggregated among FW but were more evenly distributed in channels lacking it. Our results suggest that juvenile brown trout use FW as a shelter at a wide range of water temperatures, and that this behaviour may result in reduced growth rates during their first fall and the onset of their first winter. We also show that prey availability and the composition of brown trout diet changes from late summer to early winter and that FW has a small but significant effect on brown trout diet composition.

Predation on wild and hatchery salmon by non‐native brown trout (Salmo trutta) in the Trinity River, California

AbstractNon‐native predators may interfere with conservation efforts for native species. For example, fisheries managers have recently become concerned that non‐native brown trout may impede efforts to restore native salmon and trout in California's Trinity River. However, the extent of brown trout predation on these species is unknown. We quantified brown trout predation on wild and hatchery‐produced salmon and trout in the Trinity River in 2015. We first estimated the total biomass of prey consumed annually by brown trout using a bioenergetics model and measurements of brown trout growth and abundance over a 64‐km study reach. Then, we used stable isotope analysis and gastric lavage to allocate total consumption to specific prey taxa. Although hatchery‐produced fish are primarily released in the spring, hatchery fish accounted for most of the annual consumption by large, piscivorous brown trout (>40 cm long). In all, the 1579 (95% CI 1,279–1,878) brown trout >20 cm long in the study reach ate 5,930 kg (95% CI 3,800–8,805 kg) of hatchery fish in 2015. Brown trout predation on hatchery fish was ca. 7% of the total biomass released from the hatchery. Brown trout only ate 924 kg (95% CI 60–3,526 kg) of wild fish in 2015, but this was potentially a large proportion of wild salmon production because wild fish were relatively small. As large brown trout rely heavily on hatchery‐produced fish, modifying hatchery practices to minimise predation may enhance survival of hatchery fish and potentially reduce the abundance of predatory brown trout.

Effect of spirulinaSpirulina platensisas a complementary ingredient to reduce dietary fish meal on the growth performance, whole‐body composition, fatty acid and amino acid profiles, and pigmentation of Caspian brown trout (Salmo trutta caspius) juveniles

Spirulina has been highlighted as a valuable complementary ingredient in aquafeeds due to its high protein and vitamin content, in addition to other nutritional benefits. To evaluate the effect of dietary spirulina inclusion in fish meal sparing (FMS) on juvenile Caspian brown trout as a slow‐growth fish, a complete randomized experimental design was developed with five treatments: 0% (control), 2% FMS (13.2 g/kg spirulina in diet), 4% FMS (26.4 g/kg spirulina in diet), 6% FMS (39.6 g/kg spirulina in diet) and 8% FMS (52.8 g/kg spirulina in diet). Six hundred juveniles (11.0 ± 1.0 g) were assigned to 15 experimental tanks. Although this fish is sensitive to diet composition, fish fed the 6% FMS and 8% FMS diets had a significantly higher weight gain rate (239.51% and 231.27%) and specific growth rate (1.74% bw per day and 1.71% bw per day) compared with those fed the control diet. Furthermore, 6% FMS and 8% FMS treatments had statistically higher protein efficiency (0.76 and 0.78), lipid efficiency (1.89 and 1.94) and statistically lower feed conversion ratio (2.47 and 2.41) compared with other treatments, respectively (p < 0.05). In terms of whole‐body composition, the higher amount of protein and lower content of lipid were observed in fish fed the 8% FMS diets as compared to control. Although no significant differences in ash and moisture content were observed, the highest protein deposition (157.3 g/kg) and the lowest lipid content (77 g/kg) in whole body were reported in fish fed 8% FMS diet. Based on the fillet fatty acid outcome, fish fed the 8% FMS diet had significantly higher saturated fatty acids (SFAs), C20:3n‐6, C18:3n‐3, polyunsaturated fatty acids (PUFAs) and total n‐3 fatty acids as compared to those fed the control diet (p < 0.05). Accordingly, increasing dietary spirulina content significantly enhanced the amount of these fatty acids in fish fillet. As regards of whole‐body amino acid profile, arginine and lysine in fish fed 6% FMS and 8% FMS diets were higher and lower than in those fed the control diet, respectively (p < 0.05). Fillet and skin colour parameters, such as luminosity, redness and yellowness, significantly increased with spirulina supplementation with the 8% FMS treatment displaying higher values than the control. In summary, according to our results, 8% FMS (52.8 g/kg spirulina in diet) treatment improved juvenile Caspian brown trout growth, carcass composition and pigmentation.

Hierarchical variance decomposition of fish scale growth and age to investigate the relative contributions of readers and scales

Correct estimation of interindividual variability is of primary importance in models aiming to quantify population dynamics. In a fisheries context, individual information such as age and growth is often extracted using scales; however, the rationale for using a given scalimetric method (i.e. number of scales per individual and number of readers) is rarely discussed, but different sources of variance may affect the results. As a case study, we used scale growth and age of brown trout (Salmo trutta) caught in the Kerguelen Islands. Based on a nested design (readings of four scales per fish by two independent readers), we decomposed variance in growth and age according to fish (interindividual level), scales (intraindividual level) and readers by using repeatability analysis. The results highlight that most variation is attributable to fish. Readers and scales contribute little to interindividual variance, suggesting that inference was insensitive to intraorganism biological variation. Using additional scales or readers was an inefficient use of sampling resources. We argue that variance decomposition should be widely used for studies aimed at modelling natural variability in life history traits. This would improve our knowledge of the implications of measurement error, helping rationalise and define appropriate sampling strategies.

Advantages and insights from a hierarchical Bayesian growth and dynamics model based on salmonid electrofishing removal data

Growth is a fundamental ecological process of stream-dwelling salmonids which is strongly interrelated to critical life history events (emergence, mortality, sexual maturity, smolting, spawning). The ability to accurately model growth becomes critical when making population predictions over large temporal (multi-decadal) and spatial (meso) scales, e.g., investigating the effect of global change. Body length collection by removal sampling is a widely-used practice for monitoring fish populations over such large scales. Such data can be efficiently integrated into a Hierarchical Bayesian Model (HBM) and lead to interesting findings on fish dynamics. We illustrate this approach by presenting an integrated HBM of brown trout (Salmo trutta) growth, population dynamics, and removal sampling data collection processes using large temporal and spatial scales data (20 years; 48 sites placed along a 100 km latitudinal gradient). Growth and population dynamics are modelled by ordinary differential equations with parameters bound together in a hierarchical structure. The observation process is modelled with a combination of a Poisson error, a binomial error, and a mixture of Gaussian distributions. Absolute fit is measured using posterior predictive checks, those results indicate that our model fits the data well. Results indicate that growth rate is positively correlated to catchment area. This result corroborates those of other studies (laboratory, exploratory) that identified factors besides water temperature that are related to daily ration and have a significant effect on stream-dwelling salmonid growth at a large scale. Our study also illustrates the value of integrated HBM and electrofishing removal sampling data to study in situ fish populations over large scales.

Wood addition in the hatchery and river environments affects post‐release performance of overwintering brown trout

Abstract Habitat structural complexity affects the behaviour and physiology of individuals, and responses to the environment can be immediate or influence performance later in life through delayed effects. Here, we investigated how structural enrichment, both pre‐release in the hatchery rearing environment and post‐release in the wild, influenced winter growth and site fidelity of brown trout stocked into side channels of a regulated river. Experiencing structural enrichment in the rearing environment during 3 months in autumn had no pre‐release effect on growth, but a delayed positive effect after release during the subsequent winter. Moreover, trout recaptured in wood‐treated sections of the side channels had grown more than trout recaptured in control sections. Wood enrichment in the side channels also increased overwinter site fidelity. These results show that adding structure during a relatively short period may alter growth trajectories, and adding wood to side channels is a cost‐effective method to enhance winter habitat carrying capacity for juvenile salmonids in regulated rivers.

Assessment of Fish Embryo Survival and Growth by In Situ Incubation in Acidic Boreal Streams Undergoing Biomining Effluents.

The applicability of an in situ incubation method in monitoring the effects of metal mining on early life stages of fish was evaluated by investigating the impacts of a biomining technology utilizing mine on the mortality, growth, and yolk consumption of brown trout (Salmo trutta) and whitefish (Coregonus lavaretus) embryos. Newly fertilized eggs were incubated from autumn 2014 to spring 2015 in six streams under the influence of the mine located in North-Eastern Finland and in six reference streams. Although the impacted streams clearly had elevated concentrations of several metals and sulfate, the embryonic mortality of the two species did not differ between the impacted and the reference streams. Instead, particle accumulation to some cylinders had a significant impact on the embryonic mortality of both species. In clean cylinders, mortality was higher in streams with lower minimum pH. However, low pH levels were evident in both the reference and the mine-impacted groups. The embryonic growth of neither species was impacted by the mining activities, and the growth and yolk consumption of the embryos was mainly regulated by water temperature. Surprisingly, whitefish embryos incubated in streams with lower minimum pH had larger body size. In general, the applied in situ method is applicable in boreal streams for environmental assessment and monitoring, although in our study, we did not observe a specific mining impact differing from the effects of other environmental factors related to catchment characteristics.

Effects of dietary protein at two lipid levels on growth, gonadal development, body composition and liver metabolic enzymes of brown trout (Salmo trutta fario) broodstock

Effects of dietary protein at two lipid levels on growth, gonadal development, body composition and liver metabolic enzymes of brown trout (<i>Salmo trutta fario</i>) broodstock

Rearing Performance of Juvenile Brown Trout (&amp;lt;i&amp;gt;Salmo trutta&amp;lt;/i&amp;gt;) Subjected to Exercise and Dietary Bioprocessed Soybean Meal

This 121-day experiment evaluated the rearing performance of brown trout Salmo trutta fed one of two isonitrogenous and isocaloric diets and reared at velocities of either 2.8 or 16.1 cm/s. Fishmeal was the primary protein source for the reference diet, and bioprocessed soybean meal replaced approximately 67% of the fishmeal in the experimental diet. At the end of the experiment, there were no significant differences in gain, percent gain, feed conversion rates, or specific growth rates between the dietary treatments. There were also no significant differences in intestinal morphology, splenosomatic, hepatosomatic, and viscerosomatic indices related to diet composition. However, gain, percent gain, feed fed, and specific growth rate were all significantly greater in brown trout reared at the higher velocity. No significant differences in any of the other variables measured were observed between the velocity treatments. There were no significant interactions between diet and velocity in any of the variables. Based on the results of this study, bioprocessed soybean meal can replace at least 67% of the fishmeal in brown trout diets, regardless of the rearing velocities used in this study. However, higher rearing velocities are recommended to maximize juvenile brown trout growth rates.

Justification for retention of the catch-and-release in the wild brown trout Salmo cf. trutta fishery

Total catch-and-release (C&R) is a regulatory measure implemented for maintaining the self-sustainability of stocks encountering strong fishing pressure. The River Đetinja is a tailwater with very strong fishing pressure, managed for more than a decade by C&R. That fishing regime was questioned by a new fishery manager, without the justification provided. The only available data for examining the brown trout growth were those from catches of two fly fishermen over five consecutive years. Only in one year did the average catch of one fisherman slightly surpass the legal limit for taking brown trout, and in none of years was the average size of pooled catches close to it. Survival data were similar, suggesting the stability of the brown trout stock through the period of investigation. Asymptotic length L∞ gradually increased and coincided with the growth speed ϕ and maximal yield length Lopt values. In spite of that, the high fishing pressure and low proportion of brown trout above both the legal taking limit of ≥25 cm SL and Lopt values in catches strongly support the retention of C&R as a regulatory measure on the River Đetinja.