Influence of growth rate on white muscle dynamics in rainbow trout and brook trout

In trout, fast growth stimulated white muscle fibre hypertrophy ( P 0·001) and hyperplasia ( P <0·01) in outer fibres but not in deep fibres. Glycogen was most prevalent in outer fibres ( P <0·01) and in brook trout ( P <0·01) that on average had three to four times larger fibres than rainbow trout.     

Variation in brook and brown trout survival within and among seasons, species, and age classes

The Program MARK was used to generate and test a plausible set of survival models for brook trout Salvelinus fontinalis and brown trout Salmo trutta to determine whether survival differed by season, species or age class. Apparent survival varied with time and age, but not by species. For the older (1999) age class, survival was lowest during the autumn of their age 1+ year whereas survival was lowest for the younger (2000) age class during the early summer of their age 1+ year. Additionally, estimates of survival for the younger age class exceeded those of the older age class in all but one interval (early summer 2001) but significant differences were observed in only one of these intervals (autumn 2000). To determine whether the observed seasonal differences in survival were related to seasonal differences in movement rates, multi‐strata spatial models were used within Program MARK to determine the probability of moving for each interval. In‐site movement rates were found to be low regardless of season (average for all cohorts combined was 5%). The ability of the multi‐strata modelling approach to detect temporal variability in movement, however, was potentially limited by spatial scale of the study reach ( c . 1 km). Differences in survival between different aged fishes could lead to selection acting on age at maturity or reproductive effort at a given age.     

Experimental test of genetic rescue in isolated populations of brook trout

Genetic rescue is an increasingly considered conservation measure to address genetic erosion associated with habitat loss and fragmentation. The resulting gene flow from facilitating migration may improve fitness and adaptive potential, but is not without risks (e.g., outbreeding depression). Here, we conducted a test of genetic rescue by translocating ten (five of each sex) brook trout (Salvelinus fontinalis) from a single source to four nearby and isolated stream populations. To control for the demographic contribution of translocated individuals, ten resident individuals (five of each sex) were removed from each recipient population. Prior to the introduction of translocated individuals, the two smallest above‐barrier populations had substantially lower genetic diversity, and all populations had reduced effective number of breeders relative to adjacent below‐barrier populations. In the first reproductive bout following translocation, 31 of 40 (78%) translocated individuals reproduced successfully. Translocated individuals contributed to more families than expected under random mating and generally produced larger full‐sibling families. We observed relatively high (>20%) introgression in three of the four recipient populations. The translocations increased genetic diversity of recipient populations by 45% in allelic richness and 25% in expected heterozygosity. Additionally, strong evidence of hybrid vigour was observed through significantly larger body sizes of hybrid offspring relative to resident offspring in all recipient populations. Continued monitoring of these populations will test for negative fitness effects beyond the first generation. However, these results provide much‐needed experimental data to inform the potential effectiveness of genetic rescue‐motivated translocations.     

Seasonal influence of brook trout and mottled sculpin on lower trophic levels in an Appalachian stream

1. In some situations fish have strong top‐down effects in stream communities while in others they seem to be relatively unimportant. Differences in the impact of fish may depend on a variety of factors including the foraging mode of the fish, interactions among fish species and temporal variation in environmental conditions and species interactions. 2. We investigated the effect of brook trout (Salvelinus fontinalis) and mottled sculpin (Cottus bairdi) on lower trophic levels in Appalachian streams and whether or not interactions between these fish changed their influence. Mesocosms were placed in a headwater stream in a randomized complete block design. Within blocks, mesocosms were randomly assigned to one of the following treatments: (i) no fish; (ii) sculpin only; (iii) trout only and (iv) both sculpin and trout. Fish biomass was the same in all three fish treatments. Invertebrate density and algal biomass in mesocosms were determined after 3 weeks. We repeated the experiment in the autumn, spring and summer to test for seasonality of fish effects. 3. The effect of fish on invertebrate assemblages was seasonal and depended on prey identity. Sculpin strongly suppressed grazer abundance in spring while trout had little effect on grazers in any season. The influence of both fish on insect predators was similar and relatively constant across seasons. We found little evidence of an interaction between sculpin and trout that strongly influenced their effect on prey across seasons. 4. None of the fish treatments influenced algal biomass during any of the seasons. Algal growth was also seasonal, with a two‐ to four‐fold increase in algal biomass in spring compared to autumn and summer. 5. Our results indicate that benthic and drift feeding fish differ in their effects on some, but not all prey. Furthermore, fish effects on prey were strongly seasonal for some, but not all prey types. While the temporal context is not commonly considered, our results indicate seasonality can be an important component of predator–prey interactions in streams.     

Importance of terrestrial subsidies for native brook trout in Appalachian intermittent streams

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Genetic variation,inheritance, and quaternary structure of malic enzyme in brook trout (Salvelinus fontinalis)

Electrophoretic variation is described for malic enzyme (ME) for the first time in brook trout (Salvelinus fontinalis). Since the quaternary structure of ME was not clear from examination of banding patterns in brook trout alone, ME phenotypes in rainbow trout (Salmo gairdneri) × brook trout hybrids as well as in esocid species demonstrated that ME is tetrameric. A model of two duplicated loci is proposed to account for the observed variation. One locus (ME-2) is fixed and one locus (ME-1) is variable with three electrophoretically distinct alleles; the protein products of ME-1 are reduced in activity relative to the protein products of ME-2. Joint segregation was examined between ME-1 and ten other biochemical loci in brook trout, and between ME-1, ME-2, and nine other biochemical loci in a splake—lake trout (Salvelinus namaycush) × brook trout hybrid—backcross. All pairwise examinations showed random assortment except ME-2 with an isocitrate dehydrogenase locus (IDH-3), which showed complete linkage in the splake backcross. This may be due to a chromosomal aberration.Authorized for publication as Paper No. 5599 in the Journal Series of The Pennsylvania Agricultural Experiment Station, University Park, Pennsylvania, in cooperation with the Benner Spring Fish Research Station, The Pennsylvania Fish Commission, Bellefonte, Pennsylvania. M.S. was supported by an NSF Graduate Fellowship.     

Effects of river flow fluctuations on groundwater discharge through brook trout,Salvelinus fontinalis,spawning and incubation habitats

The effects of short-term fluctuations in river discharge simulating a hydroelectricity peaking regime on the hydrogeological environment of the brook trout's reproductive habitats were examined. Fluctuating river levels altered shallow ( 2.5 m) groundwater pathways, chemistry, and flow potentials within the river bed at spawning and incubation sites. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow, particular in an offshore direction. The character of the river water — groundwater interaction appeared to be related to the hydrogeological nature of the river channel and adjacent catchment which varied among sites. The observations suggested hydroelectricity peaking regimes have potential negative impacts on brook trout reproduction.     

Endurance of simulated winter conditions by age-0 walleye pollock: effects of body size, water temperature and energy stores

Survival of age-0 walleye pollock Theragra chalcogramma in the absence of food followed simple bioenergetic models, with large body size, high initial condition, and cold temperatures all increasing survival rates. High survival after >200 days at cold temperatures (<3·0° C) indicated extended tolerance of extreme cold, as long as sufficient body size and condition are attained during the summer growth period. Analysis of body constituents demonstrated a substantial increase in tissue water and depletion of lipid during starvation. Survivors had significantly higher lipid stores than mortalities, and larger fish had higher levels of lipid than smaller fish among experimental survivors, laboratory fish that were never starved, and wild fish. Fish returned to warm temperatures and high rations following 205 days of food deprivation displayed nearly complete recovery, with rapid increases in length, weight, and condition and minimal mortality (6·8%) during the subsequent 3 months. Age-0 walleye pollock collected in September in the Bering Sea were substantially smaller and generally had lower lipid levels than fish used in laboratory starvation experiments, suggesting they are susceptible to size- and condition-dependent mortality during the winter. The results are interpreted with respect to field distributions of age-0 walleye pollock, overwinter survival, and synergistic effects of food and temperature under varying models of climate change.     

Comparison of brook trout reproductive success and recruitment in an acidic adirondack lake following whole lake liming and watershed liming

Limestone applications to the catchment of one tributary to Woods Lake were highly effective in reducing stream acidity and stabilizing seasonal fluctuations in pH. The resulting improvement in stream water quality also led to a dramatic shift in reproductive strategy of the Woods Lake brook trout population. Prior to catchment liming, brook trout in Woods Lake were restricted to spawning on poor quality near shore substrate with limited ground water seepage. Reproductive success was limited by high mortality of eggs and larvae and recruitment from in lake spawning was not successful. Spawning brook trout did not utilize the tributary for spawning prior to watershed liming. Mitigation of acidity in the tributary, by catchment liming, effectively extended the spawning habitat available to the Woods Lake brook trout population and one year following treatment brook trout spawned successfully in the tributary for the first time in 6 years of observation. Significant recruitment of young trout into the lake population occurred from 1991 through 1993, although the absolute number of fish captured was relatively small. In the fall of 1993, four year classes of naturally spawned brook trout were present in the lake. Although reproductive success was enhanced by improving tributary spawning habitat in the Woods Lake basin, self maintenance of the population may be limited by low recruitment rates of young trout, due to high levels of summer mortality resulting from predation. Mitigation of this constraint would require substantially higher levels of fry production than were observed in Woods Lake and/or enhanced refugia for young trout. The results of this experiment suggest that re-establishment of tributary spawning populations of brook trout may be possible, with future reductions in acidic deposition, in acidic Adirondack lakes with limited in-lake spawning habitat.     

Context‐specific influence of water temperature on brook trout growth rates in the field

1. Modelling the effects of climate change on freshwater fishes requires robust field‐based estimates accounting for interactions among multiple factors. 2. We used data from an 8‐year individual‐based study of a wild brook trout (Salvelinus fontinalis) population to test the influence of water temperature on season‐specific growth in the context of variation in other environmental (i.e. season, stream flow) or biotic factors (local brook trout biomass density and fish age and size) in West Brook, a third‐order stream in western Massachusetts, U.S.A. 3. Changes in ambient temperature influenced individual growth rates. In general, higher temperatures were associated with higher growth rates in winter and spring and lower growth rates in summer and autumn. However, the effect of temperature on growth was strongly context‐dependent, differing in both magnitude and direction as a function of season, stream flow and fish biomass density. 4. We found that stream flow and temperature had strong and complex interactive effects on trout growth. At the coldest temperatures (in winter), high stream flows were associated with reduced trout growth rates. During spring and autumn and in typical summers (when water temperatures were close to growth optima), higher flows were associated with increased growth rates. In addition, the effect of flow at a given temperature (the flow‐temperature interaction) differed among seasons. 5. Trout density negatively affected growth rate and had strong interactions with temperature in two of four seasons (i.e. spring and summer) with greater negative effects at high temperatures. 6. Our study provided robust, integrative field‐based estimates of the effects of temperature on growth rates for a species which serves as a model organism for cold‐water adapted ectotherms facing the consequences of environmental change. Results of the study strongly suggest that failure to derive season‐specific estimates, or to explicitly consider interactions with flow regime and fish density, will seriously compromise our ability to predict the effects of climate change on stream fish growth rates. Further, the concordance we found between empirical observations and likely energetic mechanisms suggests that our general results should be relevant at broader spatial and temporal scales.     

Food partitioning between coexisting Atlantic salmon and brook trout in the Sainte‐Marguerite River ecosystem, Quebec

Food resource partitioning between similar‐sized, sympatric Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis was examined as a possible mechanism enabling their coexistence in a stream (Allaire) of the Sainte‐Marguerite River ecosystem, Quebec, Canada. Fish stomach contents and invertebrate drift were collected concurrently during three diel cycles in August to September 1996. The food and feeding habits of an allopatric brook trout population in a nearby stream (Epinette) were studied for comparison. The diel feeding rhythms of the two coexisting fish species were similar. The composition of their diet, however, showed significant differences. Atlantic salmon predominantly (60–90%) fed on aquatic insects, mainly Ephemeroptera (35–60% of the diet). The brook trout mostly (50–80%) fed upon the allochthonous terrestrial insects (mainly adults of Coleoptera, Hymenoptera and Diptera) which comprised 5–40% of the stream drift. The allopatric brook trout fed opportunistically on the more abundant aquatic insects and terrestrial insects rarely formed 25% of its diet. The allopatric trout fed nearly twice as much as the sympatric brook trout during a day. The results suggest that the differences in feeding by brook trout in the two streams (with and without Atlantic salmon) are the result of inter‐specific interaction with Atlantic salmon and are not related to the differences in food availability between the two streams. Food resource partitioning between Atlantic salmon and brook trout may be viewed as an adaptive response resulting in a greater exploitation of available resources and coexistence.     

Stoneflies (Plecoptera) in the diet of brook trout (Salvelinus fontinalis Mitchell) in Libby Creek,Wyoming, USA

The stonefly component of a naturally reproducing population of brook trout ( Salvelinus fontinalis) was studied by analyzing 216 stomach pump samples collected between May 15 and August 10, 1991 and 1992, from Libby Creek, an alpine stream in the Medicine Bow National Forest in Wyoming. Stoneflies constituted 10.3% of the total items recovered and were the second most abundant order in the samples. Nineteen species of Plecoptera representing five families were identified. Approximately 43% of all stoneflies were Sweltsa lamba; the next most prevalent species was Zapada haysi (12%). The other prevalent insect orders in the samples were Diptera (57.2%), Ephemeroptera (8.4%) and Trichoptera (6.1%). Terrestrial Coleoptera, Hymenoptera, and Hemiptera were most common in July and August. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sex expression,sex change and fruiting habit in anAcer rufinerve population

Three hundred and thirty-eight plants ofAcer rufinerve Sieb. et Zucc. were monitored in a secondary deciduous forest for 5 years in terms of their sex expression and fruiting habit. Two types of flowers, functionally male and female, were recognized. The adult population consisted of constant males, inconstants and constant females. Constant males, plants that bore exclusively male flowers throughout the study period, accounted for 87% of the adult population. Thirty-four inconstant plants (11%) changed their sex in various ways. Constant females which accounted for only 2% of the population, were significantly smaller plants than the other two morphs, and suffered greater mortality. Fruit set was consistent and generally high for plants bearing female flowers. Thirteen juvenile plants out of 17 began reproduction during the 5 years, and all became male. For inconstant plants, fluctuation in sex expression tended to be more frequent and/or greater in magnitude for smaller plants. However, there was no evidence of the directional sex transition predicted by the size advantage hypothesis. Plant health and the successional stage of the stand should be taken into account as well as resource allocation problems to explain the proximate mechanisms of sex expression.     

Individual behaviour and resource use of thermally stressed brook trout Salvelinus fontinalis portend the conservation potential of thermal refugia

Individual aggression and thermal refuge use were monitored in brook trout Salvelinus fontinalis in a controlled laboratory to determine how fish size and personality influence time spent in forage and thermal habitat patches during periods of thermal stress. On average, larger and more exploratory fish initiated more aggressive interactions and across all fish there was decreased aggression at warmer temperatures. Individual personality did not explain changes in aggression or habitat use with increased temperature; however, larger individuals initiated comparatively fewer aggressive interactions at warmer temperatures. Occupancy of forage patches generally declined as ambient stream temperatures approached critical maximum and fish increased thermal refuge use, with a steeper decline in forage patch occupancy observed in larger fish. These findings suggest that larger individuals may be more vulnerable to stream temperature rise. Importantly, even at thermally stressful temperatures, all fish periodically left the thermal refuge to forage. This indicates that the success of refugia at increasing population survival during periods of stream temperature rise may depend on the location of thermal refugia relative to forage locations within the larger habitat mosaic. These results provide insights into the potential for thermal refugia to improve population survival and can be used to inform predictions of population vulnerability to climate change.     

Alien invasions in aquatic ecosystems: Toward an understanding of brook trout invasions and potential impacts on inland cutthroat trout in western North America

Experience from case studies of biologicalinvasions in aquatic ecosystems has motivated aset of proposed empirical rules forunderstanding patterns of invasion and impactson native species. Further evidence is neededto better understand these patterns, andperhaps contribute to a useful predictivetheory of invasions. We reviewed the case ofbrook trout (Salvelinus fontinalis)invasions in the western United States andtheir impacts on native cutthroat trout (Oncorhynchus clarki). Unlike many biologicalinvasions, a considerable body of empiricalresearch on brook trout and cutthroat trout isavailable. We reviewed life histories of eachspecies, brook trout invasions, their impactson cutthroat trout, and patterns and causes ofsegregation between brook trout and cutthroattrout. We considered four stages of theinvasion process: transport, establishment,spread, and impacts to native species. Most ofthe research we found focused on impacts. Interspecific interactions, especiallycompetition, were commonly investigated andcited as impacts of brook trout. In many casesit is not clear if brook trout invasions have ameasurable impact. Studies of speciesdistributions in the field and a variety ofexperiments suggest invasion success of brooktrout is associated with environmental factors,including temperature, landscape structure,habitat size, stream flow, and humaninfluences. Research on earlier stages ofbrook trout invasions (transport,establishment, and spread) is relativelylimited, but has provided promising insights. Management alternatives for controllingbrook trout invasions are limited, and actions tocontrol brook trout focus on direct removal,which is variably successful and can haveadverse effects on native species. Themanagement applicability of research has beenconfounded by the complexity of the problem andby a focus on understanding processes atsmaller scales, but not on predicting patternsat larger scales. In the short-term, animproved predictive understanding of brooktrout invasions could prove to be most useful,even if processes are incompletely understood. A stronger connection between research andmanagement is needed to identify more effectivealternatives for controlling brook troutinvasions and for identifying managementpriorities.     

Critical thermal maxima of diploid and triploid brook charr, Salvelinus fontinalis

The purpose of this experiment was to determine whether diploid and triploid brook charr, Salvelinus fontinalis, differ in their critical thermal maxima (CTM). Two age classes were tested (underyearlings, having average weight of 25 g, and yearlings, having average weight of 668 g) at two rates of temperature increase (2° C h^-1 and 15° C h^-1). No effect of ploidy on CTM was found. Fish exposed to the faster rate of temperature increase had higher CTM values than those exposed to the slower rate (underyearlings: 29.5 ± 0.1° C versus 29.1 ± 0.1° C in one trial and 29.8 ± 0.1° C versus 28.3 ± 0.1° C in a second trial; yearlings: 29.3 ± 0.1° C versus 27.7 ± 0.1° C in two trials, p < 0.001 in all cases). Underyearlings had higher CTM values than yearlings (29.2 ± 0.1° C versus 28.5 ± 0.1° C, p < 0.05). Female yearlings, which were immature, had higher CTM values than males, which had previously matured as one-year-olds (28.8 ± 0.1° C versus 28.3 ± 0.1° C, p < 0.001).     

Husbandry,overwinter care,and reproduction of captive striped skunks (Mephitis mephitis)

The striped skunk (Mephitis mephitis) is the focus of research interest for a variety of reasons, including its roles as a rabies reservoir, urban pest, predator of bird eggs, and parasite host. Some research programmes may require husbandry and breeding of captive animals, and because skunks are inactive in the winter in northern environments, special methods are needed to maintain the animals over winter. We report on the establishment of a colony of striped skunks kept in captivity in the northern part of their range. Our goals were to develop simple and effective methods to keep skunks in captivity over winter, and successfully breed skunks in a manner that resembles conditions in the wild. In the spring of 2002, three wild‐caught, pregnant females gave birth in captivity (mean litter size=7). During the first year, 11 of 12 females kept in captivity over winter reproduced successfully in the spring of 2003, with a mean litter size of 5.5 (range=4–8, n=11). In the summer of 2003, 91 of 93 juveniles (97.9%) survived >60 days past weaning. Our high survival and reproduction rates testify to the success of this program, and provide insights into the husbandry of a species that is inactive during winter. Zoo Biol 24:83–91, 2005. © 2005 Wiley‐Liss, Inc.     

Influences of logging history and riparian forest characteristics on macroinvertebrates and brook trout (Salvelinus fontinalis) in headwater streams (New Hampshire, U.S.A.)

1. Logging can strongly affect stream macroinvertebrate communities, but the direction and magnitude of these effects and their implications for trout abundance are frequently region‐specific and difficult to predict. 2. In first‐order streams in northern New England (U.S.A.) representing a chronosequence of logging history (<2 to >80 years since logging), we measured riparian forest conditions, stream macroinvertebrate community characteristics and brook trout (Salvelinus fontinalis) abundance. Principal component analysis was used to collapse forest data into two independent variables representing variation in logging history, riparian forest structure and canopy cover. We used these data to test whether logging history and associated forest conditions were significant predictors of macroinvertebrate abundance and functional feeding group composition, and whether brook trout abundance was related to logging‐associated variation in invertebrate communities. 3. Catchments with high PC1 scores (recently logged, high‐density stands with low mean tree diameter) and low PC2 scores (low canopy cover) had significantly higher total macroinvertebrate abundance, particularly with respect to chironomid larvae (low PC2 scores) and invertebrates in the grazer functional feeding group (high PC1 scores). In contrast, proportional representation of macroinvertebrates in the shredder functional feeding group increased with time since logging and canopy cover (high PC2 scores). Brook trout density and biomass was significantly greater in young, recently logged stands (high PC1 scores) and was positively related to overall macroinvertebrate abundance. In addition, three variables – trout density, invertebrate abundance and shredder abundance – successfully discriminated between streams that were less‐impacted versus more‐impacted by forestry. 4. These results indicate that timber harvest in northern New England headwater streams may shift shredder‐dominated macroinvertebrate communities supporting low trout abundance to a grazer/chironomid‐dominated macroinvertebrate community supporting higher trout abundance. However, while local effects on brook trout abundance may be positive, these benefits may be outweighed by negative effects of brook trout on co‐occurring species, as well as impairment of habitat quality downstream. Research testing the generality of these patterns will improve understanding of how aquatic ecosystems respond to anthropogenic and natural trajectories of forest change.     

Identification of sex chromosome molecular markers using RAPDs and fluorescent in situ hybridization in rainbow trout

The goal of this work is to identify molecular markers associated with the sex chromosomes in rainbow trout to study the mode of sex determination mechanisms in this species. Using the RAPD assay and bulked segregant analysis, two markers were identified that generated polymorphic bands amplifying preferentially in males of the Mount Lassen and Scottish strains of rainbow trout. Chromosomal localization using fluorescent in situ hybridization of a 900 bp probe developed from one of these markers revealed a brightly defined signal on a chromosome that could morphologically be classified as the Y chromosome. This revised version was published online in July 2006 with corrections to the Cover Date.