Determining the spatial distribution of spawning by anadromous and resident brown trout Salmo trutta L using strontium content of eggs collected from redds

Abstract – Strontium (Sr) content of eggs collected from redds were used to determine the spawning contribution of resident and anadromous female brown trout in the Taieri River, New Zealand and were analysed on the catchment and tributary scale. At the catchment scale, analysis of Sr showed differences between eggs collected above and below the Taieri River Gorge. Samples collected above the gorge all had low‐Sr concentrations similar to levels found in an entirely resident brown trout population. Samples collected below the gorge exhibited a broad range in Sr concentrations, ranging from levels comparable to the known anadromous samples to levels comparable to the known freshwater‐resident samples. This suggests that the gorge prevents upstream migration by anadromous brown trout in the Taieri River. At the tributary scale, this pattern of anadromous brown trout spawning downstream of freshwater‐resident fish was repeated in one of the two tributaries located downstream of the gorge. Energetic cost of migration is the most likely explanation for the observed patterns in catchment and tributary scale distribution of spawning by resident and anadromous brown trout. It is concluded that the use of Sr concentrations in eggs collected from redds is a cost‐effective and reliable method to investigate the spawning contribution by anadromous brown trout.     

Morphological variability of Atlantic salmon Salmo salar and brown trout Salmo trutta in different river environments

Abstract – The morphologies of sympatric juvenile Atlantic salmon Salmo salar parr and brown trout Salmo trutta parr were compared between Irish rivers with contrasting hydraulic environments – a high‐gradient and a low‐gradient tributary from the River Barrow catchment, south‐east Ireland and a high‐gradient river from the Burrishoole catchment, west of Ireland. The two catchments differ markedly in mean annual precipitation (849.0 mm year^?1 and 1370.3 mm year^?1 for the Barrow and Burrishoole catchments, respectively). Parr of both species demonstrated morphological variation between and within catchments. Changes in metrics such as pectoral fin length, body depth and body length between and within catchments suggest that hydraulic forces were a major determinant of morphological variation. Both species from the Burrishoole catchment had relatively larger pectoral fins, longer heads, larger eyes and shallower bodies than conspecifics from the Barrow catchment. In rivers subject to frequent rainfall‐driven high discharges, such as those in the Burrishoole catchment, a more fusiform body and head shape coupled with larger pectoral fins may reduce the energetic cost of maintaining position in the water column, as well as increase stability and manoeuvrability. The larger eyes in both parr species in the Burrishoole catchment could further be a response to the lower visibility of the more turbid and peat‐stained waters or to the reduced prey availability. The results of this study demonstrate that local adaptation to flow conditions can yield morphologically distinct populations and that multiple species can exhibit parallel phenotypic responses to changing environmental conditions.     

Pre-stocking acclimatisation of brown trout Salmo trutta: effects on growth and capture in a fast-flowing river

Abstract  A field experiment was carried out over two consecutive years in a fast-flowing river to evaluate the effects of a 5-day acclimation period on the subsequent growth and capture of stocked juvenile brown trout, Salmo trutta L. Post-stocking growth of both acclimated and non-acclimated fish remained very poor for at least 44 to 50 days. After this slow start, all fish grew significantly but acclimated trout performed 40.1% better than non-acclimated individuals. However, the better growth did not lead to higher capture rates. Capture success post-stocking was low, regardless of acclimation. Flooding, combined with low fitness of the stocked fish in the first weeks was considered the main reason for the unsatisfactory stocking success. It was concluded that in-stream acclimation aids rapid adaptation of stocked trout and thus imparts some growth advantages, although this does not necessarily result in higher yields.     

Migratory behaviour of brown trout, Salmo trutta L: importance of genetic and environmental influences

Lake Storvindeln in northern Sweden supports a population of fast-growing lake-run brown trout. Spawning and early rearing take place in the River Vindelälven, while most growth occurs in the lake (piscivory). A smaller tributary to the lake, Låktabäcken Creek, holds a resident, early maturing, short-lived brown trout population, although no migratory barriers have existed since 1947. To establish a lake-run trout population, fry from the migratory R. Vindelälven stock were introduced into the creek during 1985–1991. Introduced trout descended to the lake prior to maturing. As a result of the introduction, large adult trout returned from L. Storvindeln to the creek to spawn in 1991 and 1992; i. e., the introduced trout were able to complete a migratory life cycle. Genetic factors appeared to have a primary influence on the predisposition to migrate in this case, and it is suggested that migratory populations rarely develop from strictly resident ones.     

Seasonal movement patterns of Credit River brown trout (Salmo trutta)

Zimmer M, Schreer JF, Power M. Seasonal movement patterns of Credit River brown trout (Salmo trutta).
Ecology of Freshwater Fish 2010: 19: 290–299. © 2010 John Wiley & Sons A/S Abstract – Movement habits in riverine populations of brown trout vary among watersheds. Thus it is important to identify factors influencing differences in individual behaviour so as to improve the information resource base available for the design of river‐specific management strategies. Such information is particularly needed in the rapidly urbanising watersheds of eastern North America where relatively little is known about anthropogenic influences on brown trout populations. In this study, we examined the influence of water temperature on brown trout behaviour in the Credit River in south‐central Ontario, Canada with respect to seasonal movement patterns. Observed patterns of movement were also correlated with variations in river discharge and habitat quality. Forty‐three radio‐tagged, adult brown trout were tracked in a confined 39.8 km portion of the Credit River from 15 May 2002 to 28 July 2003. Fish were captured in three sections of the river that differed in distance downstream and habitat quality. Fish size had little impact on movement patterns. However, there was considerable variation in seasonal movement with upstream movements to summer positions, maintenance of summer positions, downstream and often extensive movements in fall. Also observed was maintenance of winter positions and repeated upstream movements in late spring‐early summer to previously used summer positions. The elaborate movement behaviour in the Credit River population was attributed to seasonal changes in thermal habitat quality. Fish tagged in less suitable thermal habitats moved significantly more than fish from more suitable thermal habitats.     

Effects of size and morphology on swimming performance in juvenile brown trout (Salmo trutta L.)

Abstract –  Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout ( Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size-corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade-off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size-corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage.     

Paternal variation in juvenile survival and growth of the triploid hybrid between female rainbow trout (Oncorhynchus mykiss Walbaum) and male brown trout (Salmo trutta L.)

Abstract Related sib‐groups of rainbow trout × brown trout triploid hybrid and monospecific brown trout controls were obtained from a common set of brown trout sires. On the basis of hybrid juvenile survival and growth, 10 sib‐groups were selected and the corresponding brown trouts were raised up to adult stage. Males from each group of brown trout were used to produce a second generation of hybrid progeny, the performances of which were analysed for grandpaternal variation and relation with first generation relatives. Results showed that hybrid traits were influenced by paternal and grandpaternal origin, but that there was little relation between hybrids and brown trouts, or between successive generations of hybrids.     

The effects of lakes on growth in yearling brown trout (Salmo trutta L.)

Abstract– Data from the Swedish Electrofishing Register were used to study the effects of lakes on the growth of yearling (0+) brown trout in outlet streams. It was found that growth increased close to lakes. On average, the length of the longest yearlings was 10% greater 0-100 m downstream from lakes as compared with more than 1 km downstream. Growth enhancement was most pronounced downstream from large lakes. This was exemplified with maximum yearling lengths in September in inlet streams (maximum yearlings 50-100 mm) and outlet streams (65-130 mm) of Lake Stora Le (area 200 km²), and inlet streams (50-75 mm) and outlet streams (65-95 mm) of Lake Anten (area 18 km²). It is suggested that this is a combined effect of both increased water temperature and outflow of lake seston. The growth pattern found was not correlated to population abundance or to the abundance of competitors or predators.     

Effect of sudden increase in discharge in a large river on newly emerged Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) fry

Abstract– Downstrcam displacement of salmonid fry due to flow increase, from 12–15 m³/_s to >100 m³_s, was documented in the river Suldalslåen, Western Norway. In May only fry of brown trout ( Sulmo trutta ) occurred in the drift, while from the beginning of June only newly emerged Atlantic salmon ( Sulmo sular ) were found. The maximum number of Atlantic salmon fry drifting during a single day was estimated to be 17 000 individual. Their density in the drift was higher during the night than during the day, and their appearance in the drift coincided with the predicted period of emergence. Total brown trout numbers in the drift were estimated to vary between 4000 and 16 000 per day. Fry displaced downstream from the lowermost part of the river were lost from the population. The total losses were estimated to be between 75 000 and 100 000 Atlantic salmon fry which represents between 5.6 and 11.1%) of juvenile mortality during the first year of life.     

The role of temperature in the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta)

Abstract – Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature on the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta) in a laboratory stream. Temperatures ranged between 5.7 °C and 14 °C. We found significant effects of water temperature on prey capture probability and capture manoeuvre time. The mean capture probability dropped from 96% at 14 °C to 53% at 5.7 °C. At 8 °C and higher temperatures, foraging performances did not differ much among treatments. We suggest that reduced swimming ability could be one of the most important mechanisms for the observed pattern of reduced prey capture probability at cold water temperatures, but prey detection limitations and predator avoidance may play a role. Our results will be of use for bioenergetics‐based drift‐foraging models, which to date have not incorporated a temperature‐dependent prey capture function.     

Dynamics of insulin and insulin-like growth factor-I (IGF-I) ovarian receptors during maturation in the brown trout (Salmo trutta)

In salmonid fishes, the role of insulin and insulin-like growth factor-I (IGF-I) in the regulation of ovarian function is not well understood. Recently, we reported that isolated follicular layers of the preovulatory ovarian follicle of coho salmon (Oncorhynchus kisutch) have specific receptors for insulin and IGF-I and that IGF-I modulates steroid production in the follicular layers. In the present study we have investigated the structural and functional characteristics of insulin and IGF-I receptors in the ovary of brown trout (Salmo trutta) and the changes in insulin and IGF-I binding throughout the reproductive cycle of this species. The specific binding for IGF-I was 8- to 15-fold higher than the specific binding for insulin. IGF-I receptors were also more specific than insulin receptors because unlabeled insulin displaced bound radiolabeled insulin at concentrations 40- to 80-fold lower than unlabeled IGF-I; whereas, unlabeled IGF-I displaced bound radiolabeled IGF-I at concentrations 4000- to 8000-fold lower than unlabeled insulin. Insulin and IGF-I receptors from the brown trout ovary were composed of 120 kDa -subunits and 90 kDa -subunits, which underwent autophosphorylation in a concentration-dependent manner. Receptor tyrosine kinase activity was also stimulated in a concentration-dependent manner by insulin and IGF-I. When ovarian insulin and IGF-I binding was determined from mid-vitellogenesis (March) until ovulation (November), maximal binding for both peptides was detected in mid-vitellogenesis and gradually decreased until the end of vitellogenesis (August). In the preovulatory period (October), a small increase of insulin and IGF-I binding was observed. After ovulation, insulin binding was no longer detectable and IGF-I binding was very low. These results suggest that insulin and IGF-I receptors in the salmonid ovary follow the structural pattern described in other vertebrate species and that insulin and IGF-I could be involved in the regulation of ovarian function during reproductive stages other than the preovulatory period.     

Do dams increase genetic diversity in brown trout (Salmo trutta)? Microgeographic differentiation in a fragmented river

Abstract – Local genetic differentiation may potentially arise in recently fragmented populations. Brown trout is a polytypic species exhibiting substantial genetic differentiation, which may evolve in few generations. Movement (semi‐)barriers in rivers may cause fragmentation, isolation and genetic differentiation in fish. In the Måna River (28 km) flowing from the alpine Lake Møsvatn to the boreal Lake Tinnsjø, construction of four hydropower dams during the period 1906–1957 have fragmented the previously (since last Ice Age) continuous wild resident brown trout population. Samples from the two lakes (N = 40) and six sites in the river (N = 30) isolated at different times were analysed at nine microsatellite loci. All populations showed substantial genetic variation (mean number of alleles per locus 5.3–8.9, observed heterozygosity 0.57–0.65 per population, overall F_st = 0.032). Pairwise multilocus F_st estimates indicated no significant differentiation between populations in the two lakes, and no or little differentiation in the lower river (F_st = 0.0035–0.0091). The microgeographic differentiation among wild resident trout at these sites was less than expected based on similar previous studies. However, results from the upper river, in particular the site immediately below the Lake Møsvatn outlet and dam, indicated isolation (F_st > 0.035). Calculation of genetic distances and assignment tests corroborated these results, as did a significant correlation between years of isolation (since dam construction) and F_st. The population structuring is most likely a result of fragmentation by dams, which has increased overall genetic diversity. This increased local differentiation may be caused by natural selection, but more likely by genetic drift in small, recently fragmented populations. Increased local genetic diversity by genetic drift does not justify conservation measures aiming at preserving genetic diversity.     

Does embeddedness affect growth performance in juvenile salmonids? An experimental study in brown trout,Salmo trutta L.

Abstract –  The effect of an embedded substratum on emigration and growth in juvenile brown trout was investigated in an artificial stream with sand added to produce sections of embedded or nonembedded substratum. Fish were allowed to leave the sections and were caught daily in a downstream trap. After catching and counting, fish were put back in their original section in order to keep the same amount of fish. Captures were high only on the first days after fish release. During the first 6 days after fish release, downstream-moving fish were more numerous in the embedded than in the nonembedded sections. The embedded substratum significantly decreased the final mean body weight and condition factor and increased heterogeneity in fish size. We suggest that a decrease in the habitat carrying capacity for juveniles could be the main factor explaining this result.     

Reproductive performance of cultured brown trout (Salmo trutta L.) in Chile

Data on reproductive traits in a cultured population of brown trout (Salmo trutta L.) in southern Chile were collected over three consecutive reproductive seasons: 1999, 2000 and 2001, corresponding to the first (at 3 years), second and third spawnings in females. Data were collected from individual females (n=238, 273 and 169 respectively). The reproductive season lasted mainly from June to August. The peak (July) tended to increase with each season (55.46%, 62.27% and 80.81% of total spawning fish respectively). Female body weight (470.8±102.5, 735.0±150 and 1263.9±263.4 g), total fecundity (1182±344, 1904±595 and 2744±605) and egg diameter (4.64±0.11, 4.67±0.27 and 5.24±0.12 mm) increased significantly (P<0.01) over successive reproductive seasons, particularly between the second and third spawnings. Relative fecundity, on the other hand, decreased significantly with each season (3577±471, 2591±900 and 2181±360). Following analysis of the variables over the three seasons, the correlation pattern of female body weight with total fecundity (r=0.91, n=458; P<0.001) and relative fecundity (r=?034, n=451; P<0.001) proved similar to that described in other salmonid females. Fertilization rate and survival to the eyed egg stage were also positively correlated (r=0.73, n=453; P<0.001). The systematically high values obtained for these latter variables over the seasons evaluated (consistently above 90%) are clearly greater than those we registered in other species of salmonids bred in Chile under similar conditions and suggest highly efficient biological variables that determine the gamete fertilization of this species. The brown trout is, therefore, an interesting potential aquaculture resource in Chile.     

Effects of the protein/carbohydrate ratio of extruded diets on protein synthesis, protein growth and body composition in juvenile brown trout (Salmo trutta)

High levels of protein in fish feeds result in higher costs and nitrogen waste. Therefore, studies focused on protein substitution by alternative energy sources are necessary. Here we examine whether the protein:carbohydrate ratio in extruded diets affects protein-turnover parameters and the main tissue components in brown trout. Juvenile fish were adapted to two extruded diets: one higher in protein and lower in carbohydrate, C: 45/28 and the other higher in carbohydrate and lower in protein, HC: 37/40. Gross energy was 19 MJ kg⁻¹ DM in both diets. Protein and lipid digestibility were high and similar in both groups (≈90%), whereas total and carbohydrate digestibility and digestible energy were lower in the HC-fed group than in the C-fed group. Consequently, when fish were adapted to the diets, plasma levels of glucose and insulin differed between diets. HC-group presented higher plasma glucose levels and lower plasma insulin levels than C-group. Protein synthesis rates in white muscle, liver and whole body did not differ significantly between diets. In contrast, protein accretion rate of white muscle and whole body were significantly lower in the HC group, indicating an increase of protein degradation in these tissues and a decrease of synthesis retention efficiency. In spite of the daily protein intake of HC group was lower than C-group, the anabolic stimulation efficiency was increased by 34% in HC group. Protein and lipid contents in white muscle and liver were stable throughout the experiment. No hepatomegalia or increased fat deposition was observed in fish fed HC. Differences in specific growth rates (C: 0.88%; HC: 0.77%) were associated more with the lower protein consumption rate and the lower level of digestible energy in fish fed HC than with the higher dietary carbohydrate content of the diet.     

Fillet texture and muscle structure in brown trout (Salmo trutta) subjected to long-term exercise

Brown trout (Salmo trutta) (2.7 g initial mean weight) were reared in freshwater for 8 months at water velocities of <0.1 (control group), 1 or 2 body lengths per second (BL s^?1) (exercise groups). Growth (body weight, body length and body width), muscle structure (muscle fibre diameter and width of myosepta) and flesh quality parameters (dry matter, muscle pH, collagen content and solubility, instrumental evaluation of texture) were measured at the end of the experiment. The body weight of fish at 1 BL s^?1 was 22% higher than the control group. Muscle development was stimulated at 1 and 2 BL s^?1, leading to a higher condition factor, greater body height and width, and muscle fibre hypertrophy (55 vs. 59.5 μm fibre diameter in the control and 2 BL s^?1 groups respectively). Connective tissue and collagen were only slightly affected by exercise (no difference in collagen solubility, but a greater proportion of γ trimer and fewer α chains in the control compared with the exercised group). Flesh quality was affected, with greater dry matter content and lower post‐mortem pH in the 1 BL s^?1 group compared with the control and 2 BL s^?1 groups. The mechanical resistance of the raw fillets was slightly but significantly increased by exercise. The exercise‐related changes in muscle structure and texture are discussed.     

Dietary soybean phosphatidylcholine affects growth performance and lipolytic enzyme activity in Caspian brown trout (Salmo trutta Caspius) alevin

The effects of supplemental dietary phosphatidylcholine (PtCho) on the growth performance, survival and digestive enzyme activity of Caspian brown trout (Salmo trutta caspius Kessler 1877) alevins were investigated in this study. Alevin (initial weight 0.8 ± 0.12 g) was fed for 5 weeks with an isoproteic‐ and isolipidic‐formulated diet with increased levels of PtCho from 0 to 60 g kg^?1 dry matter and decreasing levels of soybean oil. The increase in dietary PtCho up to 4% led to an increase in alevin final weight, suggesting that moderate PtCho levels are needed during this stage of Caspian brown trout. Survival was not affected by the dietary PtCho level. Phosphatidylcholine incorporation into the diet caused higher phospholipase A2‐specific activity. Phosphatidylcholine did not show a beneficial effect on the specific activity of amylase and protease. Lipase‐specific activity was significantly higher in the PtCho groups compared with the control group. The hepatosomatic index (HSI) was significantly influenced by the dietary PtCho level. The results of the present study indicated that the dietary supplementation of PtCho in the diet of Caspian brown trout alevin improved growth and lipolytic enzyme activity.     

Swimming performance of wild and F1-hatchery-reared Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts

Abstract –  The swimming performance of wild and hatchery-reared smolts of two salmonid species was investigated. Wild Atlantic salmon smolts (WS) and brown trout smolts (WT) of equal size were caught in fish traps during migration. Hatchery-reared smolts of both species (HS and HT for salmon and trout respectively) were first generation offspring from wild broodstock. The swimming performance of individual smolts from the four groups (WS, HS, WT, HT) was tested three consecutive times using a swimming flume with water flowing at a start rate of 0.16 m·s⁻¹ and a constant acceleration rate of 0.167 cm·s⁻² (10 cm·s⁻¹·min⁻¹). Wild caught smolts of both species performed significantly better than those reared in hatchery conditions. The WS group were observed to maintain an average swimming speed ( U _burst) that was 30% faster than the HS group, whereas the wild trout smolts were superior to HT by approximately 25%. Repeated measures revealed species-specific exhaustion patterns. Brown trout smolts maintained consecutive U _burst indicating significant stamina compared with Atlantic salmon smolts that were found to be exhausted by the initial trial.     

Density-dependence of growth characteristics and maturation in stream-dwelling resident brown trout, Salmo trutta, in Serbia

Abstract  Breakpoints in both length and weight that represent the onset of first maturation, revealed that growth and maturation were correlated with density-related parameters in stream-dwelling resident brown trout, Salmo trutta L., from nine different rivers in Serbia. The determination of density dependence of growth is not simple, as both river width and depth, as single variables of habitat and relative biomass, and density were not significantly correlated with breakpoints. The significant relationship between breakpoints and the mean weight of brown trout ( x _p) suggests that differences in breakpoints were inversely related to brown trout density. The implications of density dependence for management of streams holding resident brown trout are discussed.