Growth Of Brown Trout Research Articles

Effects of kinship on growth and movements of brown trout in field enclosures

Abstract – The effect of kinship on growth and use of space by individually PIT‐tagged 1+ brown trout was studied for 11 weeks in eight stream enclosures. Each enclosure consisted of two sections, separated by a region containing PIT‐detecting antennae, which enabled us to measure use of sections by all individuals. Two types of sibling groups were tested, a single sibling group, F1, consisting of four individuals that were reared together in hatchery tank ‘a’ (F1a) plus four additional siblings of the same family but raised in hatchery tank ‘b’ (F1b), and a mixed sibling group, consisting of four F1a individuals plus four siblings from a second family, F2. Based on kin theory and earlier laboratory studies, we expected that growth of the F1a individuals in the single sibling group to be greater than that of F1a individuals in the mixed family sibling group, but instead we found just the opposite. The variance of growth did not differ between treatments. Nor was there a difference in time F1a individuals spent together when they were in mixed versus single sibling groups. We did find that F1a individuals changed habitat more frequently than F2 individuals in the mixed sibling group but less frequently than F1b in the single sibling groups. Thus, our predictions based on kin theory for growth and behavior of brown trout were not supported by our data, and we suggest that the role of kin recognition for the ecology of salmonids deserves further attention.

Density‐dependent growth in brown trout: effects of introducing wild and hatchery fish

SummaryAlthough it is not clear to what extent density dependence acts on the survival, emigration or growth of organisms, experiments testing alternative explanations are rare. A field experiment on 1‐year‐old brown trout (Salmo truttaL.) was undertaken to address the following questions: are the mortality, movement and growth of wild stream‐living trout affected by population density? If so, are the density‐dependent effects of released hatchery trout different from the effects of wild fish?In each of two small streams, two replicate treatment blocks were used, each with four treatments assigned to stream sections 50–70 m in length: (1) control, no fish was introduced and population density was kept at its original level. (2) Trout biomass was doubled by introducing additional wild fish. (3) Trout biomass was doubled by introducing additional hatchery fish. (4) Hatchery trout were introduced, but biomass was kept at its original level by the removal of some resident wild fish.We found no treatment effects on the recapture rates of resident trout, which suggests that survival was not strongly affected by competition. They were also remarkably stationary, regardless of treatment. However, trout growth rate was reduced to the same extent in both treatments with increased density, suggesting that growth was negatively density‐dependent, and that the density‐dependent effects of hatchery trout and introduced wild fish were similar.Wild resident fish grew faster than introduced wild trout, which in turn grew faster than hatchery trout. Hatchery fish and introduced wild fish moved more than wild resident fish.The results show that population density affected growth in trout parr. We conclude that competition is not limited to the underyearlings, as has previously been suggested, and that density‐dependent growth is the main density‐dependent response in yearling trout. Furthermore, this effect was the same for wild and hatchery‐reared competitors, suggesting that stocking of hatchery fish may affect natural populations negatively through density dependence.

Relationship between Spring Snow Depth and Growth of Brown Trout, Salmo trutta, in an Alpine Lake: Predicting Consequences of Climate Change

Growth of brown trout in the alpine lake Litlosvatn, 1172 m a.s.l. on the Hardangervidda mountain plateau in western Norway, has been studied in relation to annual variations in accumulated spring snow and date of ice-breaks during the period 1991–1998. The annual growth was negatively correlated with the spring snow depth. During the years 1992–1995, a period with mean spring snow depth at 275 cm, the observed average annual growth of the age-classes 6–8 was 3.5 cm, or a reduction of about 50% compared to years with much less snow in spring (1991 and 1996). Average spring snow depth during the period 1990–1999 was 220 cm, while the average for the period 1930–1979 was 169 cm. A further increase in winter precipitation, resulting in even more accumulated spring snow compared to the 1990–1999 level, would result in further reduction in growth of brown trout in the lake. Thus, the present catchable size of brown trout would probably not be reached, due to increased population density and an additional density dependent growth. A climate change, resulting in more snowfall in the whole alpine region of West Norway, as predicted by climate models, may therefore have an important negative effect on fish production and fisheries in a whole region.

Relationship between Spring Snow Depth and Growth of Brown Trout, Salmo trutta, in an Alpine Lake: Predicting Consequences of Climate Change

Growth of brown trout in the alpine lake Litlosvatn, 1172 m a.s.l. on the Hardangervidda mountain plateau in western Norway, has been studied in relation to annual variations in accumulated spring snow and date of ice-breaks during the period 1991–1998. The annual growth was negatively correlated with the spring snow depth. During the years 1992–1995, a period with mean spring snow depth at 275 cm, the observed average annual growth of the age-classes 6–8 was 3.5 cm, or a reduction of about 50% compared to years with much less snow in spring (1991 and 1996). Average spring snow depth during the period 1990–1999 was 220 cm, while the average for the period 1930–1979 was 169 cm. A further increase in winter precipitation, resulting in even more accumulated spring snow compared to the 1990–1999 level, would result in further reduction in growth of brown trout in the lake. Thus, the present catchable size of brown trout would probably not be reached, due to increased population density and an additional density dependent growth. A climate change, resulting in more snowfall in the whole alpine region of West Norway, as predicted by climate models, may therefore have an important negative effect on fish production and fisheries in a whole region.

Intercohort competition effects on survival, movement, and growth of brown trout (Salmo trutta) in Swedish streams

The effects of density-dependent intercohort competition on growth and mortality in stream-resident brown trout (Salmo trutta) were tested by experimentally reducing the densities of age-1 fish and fish older than age 1 in six small streams. When densities of age-1 fish were reduced, abundance of age-0 and age-1 fish increased the following year, while age-1 fish experienced a reduced mean size. Reduced densities of fish older than age 1 resulted in increased apparent survival of age-0, age-1, and age-2 fish in the subsequent year. Mean size of age-2 fish increased as well. Many older immigrants (age >2) were found in the treatment sections where densities previously had been reduced. Data from the Swedish Electrofishing RegiSter (SERS) showed that mean body size of age-0 brown trout was negatively related to both age-0 and age >0 densities. The database also verified the inverse relationship between age-0 abundance and abundance of older cohorts. Our results indicate that intercohort competition regulates territorial fish populations, even when simple single populations in restricted environments are considered.

Modelling growth of brown trout,Salmo trutta, in terms of weight and energy units

1. The chief objectives were: (i) to compare two growth models, one based on weight and the other on energy, using the same data set for the analyses; (ii) to discover if weight and energy units can be simply interchanged for growth assessment. The data set was for 183 brown trout,Salmo trutta(live weight 1–300 g), fed to satiation on shrimps,Gammarus pulex, and grown individually over 42 days at constant temperatures (range 3.8–20.4 °C).2. Rates of change in weight or energy content, and final weight or energy content at the end of 42 days growth, were estimated from the models and were excellent fits to the experimental data (P < 0.001). The shape of the temperature relationship for rates of change or final values was triangular for the weight model and curvilinear for the energetics model. Optimum temperatures for growth according to the weight and energetics models were 13.1 and 13.9 °C, respectively, for rates of change and 13.1 and 13.5 °C, respectively, for final values. When the growth period was extended to 100 and then 300 days, the triangular relationship and optimum temperature remained the same for the weight model, but the curvilinear relationship became more triangular for the energetics model and the optimum temperature identical to that in the weight model. The relationship between gross efficiency and temperature also differed in shape between the two models but maximum efficiencies occurred at a similar value of 9 ± 0.1 °C (18 and 32% for weight and energetics models). As fish weight increased, gross efficiency remained constant in terms of energy units, but decreased markedly in terms of weight.3. These comparisons showed that different conclusions can be drawn from the two models, even if the same data set was analysed. There was a close relationship between initial wet weight and energy content for stock trout used in the experiments, but the relationship was not so close at the end of the experiments, and interchangeability of units could no longer be assumed. A variable error, often as high as 10–12%, would occur if the relationship for initial values was used to predict one unit from the other. Therefore, weight and energy units cannot be simply interchanged for growth assessment, especially in comparisons for trout of different sizes.

Individual variation in habitat use and growth of male and female brown trout

We examined variation in growth and habitat use of individually PIT‐tagged brown trout Salmo trutta in three stream enclosures, each divided into a fine substrate, deep pool habitat and a coarse substrate, shallow habitat. Habitat use and movements of individual fish were monitored continually by placing PIT detectors between habitats. All fish were measured and weighed biweekly over a three month period. There was no significant relationship between habitat use and initial body size, nor was there a consistent relationship between habitat use and densities of benthic macroinvertebrates or abundance of drifting invertebrates in the two habitats. Most habitat changes occurred at night, with activity peaks just prior to sunrise and after sunset. Trout used pools more at night than during the day. Within any given day, diurnal and nocturnal habitat use of individual fish varied little, with variation greater at night than during the day. Partial habitat segregation by sex was observed; only males used pools extensively during daytime, whereas males and females used riffles. Growth rate was positively related to use of pools during daytime but not at night. Growth rate was also affected by enclosure, with growth rates being highest in the most downstream enclosure, which had the deepest pool (mean of 42 cm) and lowest in the most upstream enclosure, which had the shallowest pool (mean of 28 cm). A complete exchange of trout between the most upstream and downstream enclosure indicated that the enclosure effect was due to physical differences and not to individual fish differences between enclosures. The effect appears to have been caused by differences in depth as daytime use of pools was correlated with the area of the pool ≥35 cm deep, and production of trout biomass per enclosure was directly related to mean pool depth. Our results suggest that there is a relationship between habitat use and growth of individuals that is independent of body size, but that this relationship is influenced by sex of the fish and by the physical characteristics of the environment. Further, the data indicate that short‐term behavioral decisions on habitat use by brown trout have a potential effect on longer‐term individual fitness through growth rates.

Thermal sensitivity of growth, food intake and activity of juvenile brown trout

Growth rate, food intake and activity of juvenile brown trout ( Salmo trutta L.) were studied at 10 constant temperatures (2.6–22.3°C) and using eight full-sib families. We found between-family differences in growth rate but not significant temperature×family interaction. The effects of temperature were well described by polynomial regressions that allowed the calculation of optima, performance breadths and thermal limits. The obtained values were noticeably higher and the performance breadth wider, than previously reported data for the species.

Selection for growth of brown trout ( Salmo trutta) affects feed intake but not feed efficiency

Brown trout ( Salmo trutta) were selected for growth for 4 generations. We tested the effects of selection on voluntary feed intake measured by self-feeders, feed efficiency and size variability. The specific effects of a slight feed restriction and of food deprivation were also investigated. Fish were issued from groups of eggs of selected females fertilised with sperm of selected (S group) or control males (S 1 2 group). According to the growth rates expected for the selected and control lines, the S 1 2 group was fertilised 12 days before the S group, so that all the fish reached 8 g at the same time. At 8 g, they were allotted to 8 tanks (500 fish per group) and 3 experimental periods followed. Fish were accustomed to self-feeders during a 28 days pre-experimental period. Then, half of the groups were fed ad libitum, and half were restricted (80% of the expected ad libitum level) for 171 days; growth and feed intake were recorded regularly and any uneaten food was weighed. Then followed a 56 days starvation period. At the end of the pre-experimental, feeding and starvation periods, individual weights and lengths were measured on 50 trout per tank. The response to selection at the end of the feeding period varied with the feeding level. In ad libitum fed groups, the mean final body weight of S was +6.1% higher than that of S 1 2 and feed efficiency was similar (1.10 for S and S 1 2 ). The higher growth of S compared to S 1 2 was related to a higher feed intake of the S groups (+5.3%). When fish were restricted, the final body weight was lower in S (117.1 ± 2.1 g) than in S 1 2 groups (123.8 ± 1.7 g). This was mainly related to a slightly lower feed efficiency of S compared to S 1 2 at the beginning of the feeding period. Neither the group nor the feeding level affected the size variability of the fish. At the end of the starvation period, the relative loss of weight was equivalent for all the groups, and the variability of the weight was higher for S than for S 1 2 . The results highlight the fact that genetic gain can only be expressed when brown trout are fed ad libitum.

Intercohort competition effects on survival, movement, and growth of brown trout (<i>Salmo trutta</i>) in Swedish streams

Intercohort competition effects on survival, movement, and growth of brown trout (<i>Salmo trutta</i>) in Swedish streams

Latitudinal variation in growth of young brown trout Salmo trutta

Summary 1. A new laboratory‐based growth model for brown trout (Salmo trutta) was used to explore latitudinal variation in growth among natural populations. The model included the effects of differences in ambient temperatures and fish size among populations. Annual growth rates of anadromous brown trout parr from 22 Norwegian populations at 61–70 °N were compared with predictions from the growth model. Published field data from one Spanish, 15 British and four Danish populations at 44–58 °N were included in the analysis to increase the latitudinal range. 2. Among the Norwegian populations, the ratio between observed and predicted growth rates was not significantly different from 1·00 in eight rivers, but was significantly higher in eight, and was significantly lower in six. Observed growth was highest, relative to predicted growth, in the coldest rivers. In Spanish, British and Danish rivers, observed growth did not exceed predicted growth. 3. The ratio between observed and predicted annual growth rate decreased significantly with increasing annual mean temperature. Observed annual growth was higher than predicted growth only in rivers with an annual mean temperature lower than 5·1 °C, and this indicates that some kind of thermal adaptation may occur in trout populations in the coldest rivers. 4. Regression analyses showed that besides the direct effects of temperature and body size predicted by the growth model, annual growth rates were significantly related to annual mean temperature, densities of juvenile salmonids, duration of twilight (average for May–August) and latitude. Adding these variables to the original model increased the explanatory power from 73·9 to 80·6%.

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 Dalalven, Sweden was scrutinised. In a mirror image stimulation (MIS) experiment, and in a 35 000 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.

Daily energy intake and growth of piscivorous brown trout,Salmo trutta

1. The chief objectives were to determine the daily energy intake and growth of piscivorous brown trout (Salmo trutta), and to compare the observed values with those expected from models developed previously for brown trout feeding on freshwater invertebrates. Energy budgets for individual fish were obtained from experiments with 40 trout (initial live weight 250-318 g) bred from wild parents, and kept at five constant temperatures (5, 10, 13, 15, 18 °C) and 100% oxygen saturation. Each trout was fed to satiation on freshly killed sticklebacks (Gasterosteus aculeatus) over a period of 42 days. 2. Energy intake (C IN cal day -1 ) and growth (C G cal day -1 ) were measured directly and energy losses (C Q cal day -1 ) were estimated by difference (C Q = C IN - C G ). All three variables increased with temperature. A model previously used to predict the daily energy intake (C IN(INV) ) of trout feeding to satiation on invertebrates was adapted, by changing only one parameter, to provide an excellent model (R 2 = 0.998) for predicting the mean daily energy intake (C IN(ST) ) for the piscivorous trout. Values of C IN(ST) were 58% (range 48-67%) higher than those for C IN(INV) . A simple model was also developed to estimate mean daily energy losses for piscivorous trout (R 2 = 0.999). Both models were combined to provide excellent estimates of the daily energy gain (growth) of the piscivorous trout, and this was about three times that for trout feeding on invertebrates. The optimum temperature for maximum growth in energy terms increased from 13.9 °C for trout feeding on invertebrates to 17.0 °C (range 16.6-17.4 °C) for piscivorous trout. 3. The models are basically an extension of those developed for trout feeding on invertebrates. They show clearly how energy intake, growth, and the optimum temperature for growth increase markedly when trout change their diet from invertebrates to fish. The implications of this are discussed and it is shown that, in theory, these increases should continue if a more energy-rich diet was utilised by the trout.

Phenotypic Correlation of Juvenile Growth Rate between Different Consecutive foraging Environments in a Salmonid fish: A Field Experiment

Many organisms occupy considerably different environments during individual's lifespan. We are interested in how the phenotypic characteristics that are favourable in the earlier environment predict fitness in the later environment. High predictability of fitness between the two consecutive environments suggests that the either the same traits are favored in both environments, or that the favourable traits are genetically correlated. In this study, we ask how similarity of consecutive foraging environments affects the phenotypic correlation of juvenile brown trout growth rate. More specifically, we used a genetically narrow stock of hatchery-bred fish to contrast individual growth rates between high and low density hatchery environments, and thereafter between hatchery and natural lake environment. As expected, growth rate was highly dependent on the environment, and the fish showed considerable phenotypic plasticity. Furthermore, we found a strong positive correlation in growth rate between similar foraging environments, for example, between high and low density hatchery stocks, and between hatchery and a lake with small fish as main prey. However, hatchery growth did not predict growth rate in lakes where fish had to forage on bottom-dwelling invertebrates. Our results suggest that when the consecutive environments differed dramatically with respect to traits that fish use for foraging, relative performance of individual fish changed, earlier performance not being an accurate predictor of performance in the new environment. In this case, fitness of the fish was determined by an environment-specific set of traits that were not the same between the two consecutive environments. The result indicates that assessment of individual performance may be highly environment specific in trout.

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.

Response of resident brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), to the stocking of hatchery-reared brown trout

Two strains of hatchery-reared adult brown trout, Salmo trutta L., [208–334 mm total length (TL); n= 591] were individually marked and released into a limestone stream. The estimated survival after one month (86%; n= 508) was comparable to that for resident brown trout and rainbow trout, Oncorhynchus mykiss (Walbaum), (89%; n= 771), but declined to 14% (n= 83) after 8 months compared with 52% (n= 451) for resident trout. The movement of resident trout out of stocked stretches was higher (14%) than from control sites (5%), but the population size in both individual sites and the overall study area were unaffected. The growth of resident brown trout was unaffected by stocking, but rainbow trout showed lower growth rates in stocked versus unstocked stretches both one and 8 months after stocking (P < 0.002).

Effects of Population Density on Individual Growth of Brown Trout in Streams

Effects of Population Density on Individual Growth of Brown Trout in Streams

Effect of habitat type on growth and diet of brown trout, Salmo trutta L., in stream enclosures

AbstractThe effect of habitat on the growth and diet of brown trout, Salmo trutta L., stocked at the same densities in nine stream enclosures, comprising three habitat types of different quality, were tested. The habitats, which were created based on microhabitat preference data, were a shallow water habitat lacking cobbles (habitat 1), a deeper, mixed cobble‐bottomed (128‐384 mm diameter) habitat (habitat 2) and a large cobble‐bottomed (256‐384 mm) habitat of intermediate depth (habitat 3). Brown trout were found to have greater increases in total biomass in habitats 2 and 3 than in habitat 1. The pattern for length did not follow that of biomass as trout had greater increases in total length in habitat 2 than in the other two habitats. Biomass of food in trout diets reflected habitat‐specific fish biomass changes, with a greater total biomass of prey as well a greater biomass of the leech, Erpobdella, in habitats 2 and 3 than in habitat 1. There were no habitat‐specific differences in the biomass of benthic or drifting invertebrates in the enclosures, with the exception of a tendency for an effect of habitat on the biomass of Erpobdella. Although there may have been habitat‐specific differences in food resources that were not detected, it is believed that the higher biomass growth in habitats 2 and 3 may have reflected differences in cover afforded by the deeper water and coarser substrates and/or improved foraging opportunities facilitated by the larger volumes of water in the deeper habitats in which the trout could search for prey.

Feeding time, feed intake and growth of baltic salmon, Salmo salar, and brown trout, Salmo trutta, reared in monoculture and duoculture at constant low temperature

It has previously been reported that the growth of salmonids is improved when they are reared in duoculture, possibly due to reductions in the levels of intraspecific aggression. These claims were examined in more detail by studying the time of feeding, feed intake and growth in Baltic salmon, Salmo salar, and brown trout, Salmo trutta, held at constant low temperature (2.7–3°C) and reared in monoculture or duoculture for 3 months. Rates of feed intake and growth were initially low, but increased during the course of the experiment, this being particularly evident for the salmon. At the same time, interindividual variations in feed intake and growth tended to decrease, and group feed intakes were negatively correlated with interindividual variations in feed intake. Rates of growth of brown trout did not differ significantly between groups reared in monoculture and duoculture. By contrast, rates of feed intake and growth of Baltic salmon were depressed when they were held together with brown trout. Baltic salmon, held together with brown trout, had a significantly greater incidence of fin damage than those held in monoculture, possibly indicating that they were subject to aggression from the trout. Fish of both species tended to feed during the hours of daylight, and there was no evidence of an increase in nocturnal feeding activity amongst fish of either species when held in duoculture.

Effect of prolonged feed restriction on size variation, feed consumption, body composition, growth and smolting of brown trout, Salmo trutta

1+ brown trout ( Salmo trutta) were reared under three different feeding frequencies from the end of May until the beginning of November. Those groups fed only twice a week for 4 h (TW) or once a day for 30 min (OD) were significantly smaller than the control fish (fed 4 h in the morning and 4 h in the evening) at the end of the feed restriction period. All the groups were fed in excess. After 2 months an increase in growth rate was observed in the TW groups. Decreased feeding frequency did not affect the size variation within a group, even though the feed was divided more evenly between the individuals in feed restricted than in control groups. At the beginning of November all the groups were switched to 4 h day −1 ad libitum feeding. That switch did not cause any compensatory growth during the winter. The decrease of the growth opportunity between the end of May and the beginning of November did not markedly affect smolting behaviour or hypo-osmoregulatory capacity during the following spring.