Timing of spawning in cultured and wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in the River Vosso, Norway

Spawning time and size of wild and nonnative cultured female Atlantic salmon (Salmo salar L.) were studied in the River Vosso, Norway. Cultured immigrants were smaller, and peak spawning occurred 21 and 26 days earlier relative to wild salmon in 1991 and 1992, respectively. It was calculated that hatching and initial feeding of offspring of cultured females peaked 12 and 9 days earlier in spring 1992 and 19 and 8 days earlier in spring 1993 relative to offspring of wild females. Spawning time of the cultured salmon is similar to most Norwegian salmon populations and to cultured fish in other streams. In the River Vosso it also overlaps with that of brown trout (Salmo trutta L.), which may increase hybridization. The early time of breeding in nonnative fish indicates local adaptation in this trait in wild salmon. The consequences of early breeding of cultured fish are unpredictable in relation to spring temperatures but probably reduce their relative breeding success. The smaller size may also reduce the success of cultured females.     

Survival and growth of hatchery and wild brown trout (Salmo trutta) parr in three Austrian headwater streams

Brown trout populations of three headwater streams in the Northern Limestone Alps of Austria were supplemented by three‐month‐old hatchery‐reared parr from a wild and locally adapted strain and a nonresident domesticated hatchery strain. Growth and survival were monitored with three surveys over a period of 16 months after stocking. Fish descending from the wild reared origin strain demonstrated higher survival rates than the hatchery strain. Differences in growth were found among the investigated streams but not among the investigated strains. The differing temperature regimes of the streams were considered as the primary factor causing those disparities. We conclude that stocking measures had little or no additive effect on successful natural reproduction, as the resident wild brown trout performed significantly better than the stocked fish.     

River temperature and adult anadromous Atlantic salmon,Salmo salar,and brown trout,Salmo trutta

Abstract In terms of the spawning migration of adult salmon, Salmo salar L., water flow is often considered the primary factor controlling river entry and fluctuations in flow controlling when the fish subsequently migrate upstream. However, water temperature has also been suggested to modify the spawning migration of salmon, particularly their movements within estuaries and the timing of freshwater entry. Freshwater temperature is more likely to impact salmonid biology than flow, particularly in relation to temperature dependant metabolic costs, time of spawning and fecundity. Therefore, temperature may be more of a factor regulating salmonid populations in fresh water than flow itself. This study focuses on two aspects of the impact of temperature on salmonids in fresh water: first, how salmon may modify their behaviour to adapt to changes in temperature and second the potential relationship between temperature, environmental conditions (e.g. water quality) and physiology (e.g. maturation and olfaction) in regulating adult migration.     

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.     

The effects of ration size on migration by hatchery‐raised Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Abstract – The possibility to increase the proportion of migrating hatchery‐reared smolts by reducing their food ration was studied. Lake‐migrating, hatchery‐reared salmon (Salmo salar) and trout (Salmo trutta) smolts were either fed normal rations, based on recommendations from the fish‐farming industry, or reduced (15–20%) rations. They were released into the River Klarälven, western Sweden, and followed as they swam downstream to Lake Vänern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.     

The relationship between the snowmelt flood and the establishment of non‐native brown trout (Salmo trutta) in streams of the Chitose River,Hokkaido, northern Japan

Flow regime is one of the major determinants of establishment success for non‐native aquatic organisms. Here, we examine the influence of flow variability associated with snowmelt flood on the establishment success of non‐native brown trout in 10 streams in northern Japan. We regarded the presence of Age‐0 brown trout as the index of the successful establishment. The emergence of Age‐0 brown trout in our study region begins in May, a time that overlaps with the occurrence of snowmelt flood. The presence of Age‐0 brown trout was negatively associated with flow variability, and it was also negatively associated with summer water temperature. Our results indicate that the non‐native brown trout tends to establish in the streams with smaller snowmelt floods and lower summer water temperatures. Brown trout is an invasive, non‐native species that is problematic all over the world, and effective management strategies for preventing their further expansion are urgently needed. This study suggests that river managers should recognise that stable streams such as spring‐fed streams (i.e., low flow and summer water temperature) and flow‐regulated streams, have a higher potential risk of brown trout invasion.     

Competition between hatchery‐raised and wild brown trout Salmo trutta in enclosures – do hatchery releases have negative effects on wild populations?

Abstract –  We compared the growth and prey consumption of juvenile hatchery and wild brown trout of similar genetic origin in 12 wire mesh cages in a natural river in North-Eastern Finland. Wild trout started feeding shortly after the start of the experiment, and clearly earlier than novel hatchery trout, but ate less in the presence of hatchery trout. When accompanied with wild trout, novel hatchery trout started to feed earlier, consumed more live prey, and lost less weight than when in allopatry. Hatchery trout grew more slowly than wild trout. To our knowledge, this is the first study to show that hatchery trout benefit from the presence of wild, experienced trout in a complex semi-natural environment. However, our results also indicate that the benefits to hatchery fish are not transferred to wild fish, and ultimately that care should be exercised in management actions when using hatchery trout to supplement wild populations. On the other hand survival potential of the novel hatchery brown trout could be better in the wild when also undomesticated trout are present.     

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.     

Lake survival of hatchery and pre-stocked pond brown trout, Salmo trutta L.

Abstract. A comparison was made of lake survival, after 2 years, of hatchery and pre-stocked pond brown trout, Salmo trutta L., (age 0+) in two small mountain lakes in south-central Norway, one which contained a resident population of brown trout. There was a significantly higher recapture of pond fish in both lakes. The mortality rate for the stocked fish was significantly higher in the lake which contained a resident population of brown trout. The competitiveness of the stocked fish is discussed in relation to foraging success, predation and stress.     

Selective segregation in intraspecific competition between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Interactive segregation has been suggested as the ruling competition mechanism determining niche and niche segregation between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Results from allopatry–sympatry observations of habitat use in both nature and in experiments were contrary to predictions derived from the interactive segregation hypothesis. Habitat use parameters under natural conditions such as distance to shore for Atlantic salmon parr were nearly identical in allopatric (mean ± SD; 3.2 ± 1.4 m) and sympatric (3.3 ± 1.4 m) situations. Occupied water depths largely reflected available water, but water depths <15 cm were avoided by salmon parr. Under experimental conditions, habitat use of allopatric salmon was density independent and salmon size had only minor effects, with smaller fish being more likely to occur in the shallow. Habitat use of salmon in sympatry with trout did not differ from allopatric salmon habitat use, and only salmon size had minor effects on depth choice – occurrence of trout or fish density had no effect. Allopatric trout was in general more frequent in the shallow habitat than salmon. Habitat use of sympatric trout was affected by the occurrence of salmon and trout size, resulting in a higher use of the shallow habitats for small trout. To conclude, selective segregation has a dominant role in salmon habitat use (not affected by trout occurrence), whereas a mixed situation occurs in trout habitat use with elements of interactive segregation when competing with Atlantic salmon (affected by salmon occurrence).     

Piscine reovirus (PRV) in wild Atlantic salmon,Salmo salar L., and sea‐trout,Salmo trutta L., in Norway

This is the first comprehensive study on the occurrence and distribution of piscine reovirus (PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation (HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross‐sectional survey based on real‐time RT‐PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea‐trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea‐trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV‐positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI‐related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI.     

Triploidization of brown trout (Salmo trutta) by heat shocks

This study was made to optimize heat shock conditions for producing triploidy in the brown trout, Salmo trutta. Heat shock at 29°C for 10 min duration, initiated between 5 and 45 min after insemination, gave high frequencies of triploid embryos (77–91%) as assessed by chromosome observation. Shocks initiated between 90 and 260 min following insemination had no effect on polyploidization. Other groups heat shocked at 29°C for 5–15 min duration initiated 10 min after insemination resulted in moderate rates of triploidy (50–63%). A high temperature shock of 32°C for 6 min duration gave 100% triploidy but a lower temperature shock of 26°C, even for 30 min duration, had only a moderate effect (57%). Rates of hatching were generally decreased in the groups giving moderate to high frequencies of triploidy. In most treated lots haploid embryos were observed and were considered to be a cause of decreased survival.     

Feeding by hatchery-reared and wild brown trout, Salmo trutta L., in a Norwegian stream

Abstract. Hatchery-reared brown trout, Salmo trutta L., yearlings were captured shortly (3h to one week) after their release in a Norwegian stream. The feeding of recaptured hatchery fish was compared with that of wild brown trout. The investigations were carried out during three different periods (May, July and October). Investigations of drift fauna indicated that food availability was best in May. Most hatchery-reared brown trout started feeding shortly after their release in all three periods. Hatchery fish went through a learning process with respect to feeding. This was most clearly demonstrated by the amounts of plant fragments in their stomachs, which were always greater in hatchery fish than in wild fish but which decreased with time after release in hatchery fish stomachs in all three periods. By about a week after release, hatchery trout appeared to be feeding on wild prey nearly as well as did wild fish, but they achieved this better in May than in October.     

Comparison of population dynamics of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in a small tributary of the River Scorff (Brittany, France)

The population dynamics of Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) were compared in a small tributary of the River Scorff (Brittany, France) from spawning time to the beginning of the third growing season. The spawning and fry emergence of the two species took place at approximately the same time. In the first autumn, the densityof 0+ juveniles and settling rate from the egg stage were much higher in trout than in salmon. The emigration rate from 0+ population was much higher in trout than in salmon. The size of resident and migrating fish was always smaller in salmon than in trout, whatever the age. The low level of salmon production in the brook, compared with trout, was the result of low survival from egg to 0+ stage in autumn, combined with the small proportion of juveniles migrating after the first growing season. This was not compensated by a high number of migrants the next year. The role of physical habitat, inter-and intraspecific competition, predation and migration dependence on size and early sexual maturity is discussed. Indications are that small tributaries of the type studied are of great value for recruitment in trout but not very productive for juvenile salmon.     

No difference in survival, growth and morphology between offspring of wild-born, hatchery and hybrid brown trout (Salmo trutta)

Abstract –  We studied survival, growth and morphological characters in the offspring of native hatchery and wild-born anadromous brown trout ( Salmo trutta ) and their hybrids (wild-born female × hatchery male and wild-born male × hatchery female) in a 1-year field experiment. We also conducted laboratory studies where we examined social interactions between the offspring of the same hatchery and wild-born trout. All offspring were raised in a hatchery and nose tagged before being released into the stream. In total, 1125 individuals were released into the stream (1999) and a total of 614 individuals were recovered (2000). We found no differences in growth and survival between the offspring of hatchery, wild-born and hybrid trout. Morphology was also similar among groups, where only 38% females and 36% males were classified into the right category, which were only 12% better than random classification. In the laboratory experiment, we compared only the offspring of hatchery and wild-born trout with respect to growth, dominance, aggressiveness, feeding and activity. We found small differences between the offspring of hatchery and wild-born fish with respect to growth but this effect was not found in the field experiment. Our result suggests that the offspring of hatchery trout and hybrids between hatchery and wild-born trout performed equally well to the offspring of wild-born trout.     

River modification reduces climate resilience of brown trout (Salmo trutta) populations in Ireland

This study investigated interactions between eco‐hydromorphological state, riparian vegetation cover, water temperature and fish community composition in lowland rivers in Ireland. Physical habitat modification of study sites corresponded with degraded eco‐hydromorphological state (degree of ecological and physical modification) and reduced thermal buffering capacity (greater temperature fluctuation and increased frequency of extreme temperature events). This impact was reflected in the fish community, with a shift from a brown trout‐dominated (Salmo trutta L.) fish assemblage to predominance of the more thermally plastic minnow, Phoxinus phoxinus (L.), and stone loach, Barbatula barbatula (L.). Eco‐hydromorphological state may be a central factor affecting the ability of temperate rivers to resist temperature change in a warming climate and to maintain suitable conditions for salmonids and other cold‐water biota. Strategies aimed at climate change proofing of temperate rivers should focus on preserving or re‐establishing the eco‐hydromorphological processes that create habitat complexity and buffer stream temperature.     

Metabolic characteristics of early life history stages of native marble trout (Salmo marmoratus) and introduced brown trout (Salmo trutta) and their hybrids in the Soča River

Metabolic potential and respiration rate have been measured in the early life stages of native marble trout Salmo marmoratus (MT), introduced brown trout Salmo trutta (BT) and their hybrids (MH = female of MT × male of BT and BH = female of BT × male of MT) to examine the differences in their metabolic characteristics. Metabolic potential and respiration rate were lowest in each developmental stage in MT, followed by MH, BT and BH. The ratio between metabolic potential and respiration rate (ETS/R) in larvae was also lowest for MT (1.0) and MH (1.1), followed by BT (1.4) and BH (1.6), indicating more intensive exploitation of metabolic potential for actual respiration in MT (100%) and MH (~90%) than in BT (~70%) and BH (~60%). Lower ETS/R means a disadvantage in the case of enhanced metabolic activity due to insufficient enzyme machinery needed for energy production. Thus, potential and actual metabolic activity and ETS/R ratio could account for the different competitive abilities among pure trout species and their hybrids in a particular environment. This is the first report on biochemical and physiological differences between pure MT and their hybrids. The combination of metabolic and respiration rate measurements appears to be a useful tool for estimating the metabolic properties in the early developmental stages of fish.     

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.     

Genetic effects of introduced hatchery stocks on indigenous brown trout (Salmo trutta L.) populations in Spain

Abstract– To assess the levels of gene introgression from cultured to wild brown trout populations, four officially stocked locations and four nonstocked locations were sampled for one to three consecutive years and compared to the hatchery strain used for stocking. Allozyme analysis for 25 loci included those previously described as providing allelic markers distinguishing hatchery stocks and native populations. Different levels of hybridization and introgression with hatchery índividuals were detected in stocked drainages as well as in protected locations. These findings indicate that new policies for stocking and monitoring hatchery fish are needed if gene pools of wild Spanish brown trout populations are to be preserved.