Survival Of Trout Research Articles

Survival and reproduction of Myxobolus cerebralis-resistant rainbow trout introduced to the Colorado river and increased resistance of age-0 progeny.

Myxobolus cerebralis caused severe declines in rainbow trout populations across Colorado following its introduction in the 1980s. One promising approach for the recovery of Colorado’s rainbow trout populations has been the production of rainbow trout that are genetically resistant to the parasite. We introduced one of these resistant crosses, known as the GR×CRR (cross between the German Rainbow [GR] and Colorado River Rainbow [CRR] trout strains), to the upper Colorado River. The abundance, survival, and growth of the stocked GR×CRR population was examined to determine if GR×CRRs had contributed offspring to the age-0 population, and determine whether these offspring displayed increased resistance and survival characteristics compared to their wild CRR counterparts. Apparent survival of the introduced GR×CRR over the entire study period was estimated to be 0.007 (±0.001). Despite low survival of the GR×CRRs, age-0 progeny of the GR×CRR were encountered in years 2008 through 2011. Genetic assignments revealed a shift in the genetic composition of the rainbow trout fry population over time, with CRR fish comprising the entirety of the fry population in 2007, and GR-cross fish comprising nearly 80% of the fry population in 2011. A decrease in average infection severity (myxospores fish−1) was observed concurrent with the shift in the genetic composition of the rainbow trout fry population, decreasing from an average of 47,708 (±8,950) myxospores fish−1 in 2009 to 2,672 (±4,379) myxospores fish−1 in 2011. Results from this experiment suggest that the GR×CRR can survive and reproduce in rivers with a high prevalence of M. cerebralis. In addition, reduced myxospore burdens in age-0 fish indicated that stocking this cross may ultimately lead to an overall reduction in infection prevalence and severity in the salmonid populations of the upper Colorado River.

Does cortisol manipulation influence outmigration behaviour, survival and growth of sea trout? A field test of carryover effects in wild fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 496:135-144 (2014) - DOI: https://doi.org/10.3354/meps10524 Theme Section: Tracking fitness in marine vertebrates Does cortisol manipulation influence outmigration behaviour, survival and growth of sea trout? A field test of carryover effects in wild fish Jonathan D. Midwood1,*, Martin Hage Larsen2, Mikkel Boel2, Niels Jepsen2, Kim Aarestrup2, Steven J. Cooke1 1Fish Ecology and Conservation Physiology Laboratory, Department of Biology and Institute of Environmental Science, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada 2National Institute of Aquatic Resources, Freshwater Fisheries, Technical University of Denmark, Vejlsøvej 39, 8600 Silkeborg, Denmark *Corresponding author: midwoodj@gmail.com ABSTRACT: For anadromous brown trout Salmo trutta, the transition from life in freshwater to the marine environment is an inherently challenging and dangerous period characterized by high levels of mortality. As such, smoltification is a relevant life-history phase to examine how physiological state, in particular glucocorticoids, influences fitness-oriented endpoints such as migration timing and survival. We experimentally assessed the effect of cortisol by combining passive integrated transponder (PIT) telemetry with a physiologically relevant exogenous cortisol manipulation (i.e. intracoelomic injection) in juvenile sea trout in the Gudsø Stream, Denmark. Individual survival, migration behaviour (timing and speed), and growth were assessed for 4 treatment categories: control (CO), sham (SH), and low- (LW; 25 mg kg-1) and high-dose (HI; 100 mg kg-1) cortisol. There was no difference in the timing of migration among treatments, but trout in the HI treatment had lower survival rates to the lower station (41.6%) when compared to the CO (53.9%) and SH (52.3%) groups. After migration, the system was electroshocked again to contrast growth of trout that remained in the system. HI, LW and SH individuals recaptured in the stream had lower growth rates for length than the CO treatments; HI and LW also had significantly lower growth rates for mass than CO trout. Future monitoring of this population may demonstrate the long-term repercussions of chronic stress as trout return from the ocean. This study provides contributions to our understanding of the relationship between organismal condition and fitness while elucidating the potential for carryover effects, i.e. lasting effects that influence future success. KEY WORDS: Allostasis · Carryover effects · Migration · Stress Full text in pdf format PreviousNextCite this article as: Midwood JD, Larsen MH, Boel M, Jepsen N, Aarestrup K, Cooke SJ (2014) Does cortisol manipulation influence outmigration behaviour, survival and growth of sea trout? A field test of carryover effects in wild fish. Mar Ecol Prog Ser 496:135-144. https://doi.org/10.3354/meps10524 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 496. Online publication date: January 27, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Döllenmeden Sonra Farklı Zamanlarda Uygulanan, Basınç ve Sıcaklık Şoklarının Gökkuşağı Alabalıklarında (Oncorhynchus mykiss, W. 1792) Triploid Üretimine Etkileri

The objective of this study was to identify the survival and triploidy rates in rainbow trout under pressure and heat shocks induced at different times after fertilization. Fertilized eggs were exposed to a heat shock of 28°C for 10 minutes at 10, 15 and 20 minutes after fertilization. Survival rates were higher at 15 min and triploidy rates were higher at 20 min applications. Also pressure shock of 48263 kPa (7,000 psi) was applied to eggs for 4 min at 35, 40 and 45 min after fertilization, and higher survival and triploidy rates were observed at 40 min treatment. These results also show that pressure shock is more advantageous comparing with heat shock in all stages of development (embryo, eyed-stage, hatching, and first feeding) in both respect of survival and triploidy rates

Spatial variability in adult brook trout (Salvelinus fontinalis) survival within two intensively surveyed headwater stream networks

Headwater stream networks are considered heterogeneous riverscapes, but it is challenging to characterize spatial variability in demographic rates. We estimated site-scale (50 m) survival of adult (>age 1+) brook trout (Salvelinus fontinalis) within two intensively surveyed headwater stream networks by applying an open-population N-mixture approach to count data collected over two consecutive summers. The estimated annual apparent survival rate was 0.37 (95% CI: 0.28–0.46) in one network and 0.31 (95% CI: 0.15–0.45) in the other network. In both networks, trout survival was higher in stream sites characterized by more abundant pool habitats. Trout survival was negatively associated with mean depth in one network and positively associated with stream gradient in the other. Stream temperature was not related to trout survival in either network, possibly because the majority of sites were thermally suitable. A similar analytical approach can be useful for inferring survival rates when count data are available over space and time but individual tagging is not feasible.

Effects of probiotics and Fe ion on the growth and survival and body composition of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) frys

This study was carried out to investigate the effects of probiotics and Fe ion on the growth and survival of rainbow trout, Oncorhynchus mykiss frys. For this purpose, the frys were fed with dry pellets containing various ratios of probiotics and Fe for a period of 30 days after absorption of alevins' yolk sac. The growth and survival parameters were measured every 6 days. According to the results, the values of feed conversion ratio were in lowest values in fish fed by only probiotic [i.e. at the rates of 1% (T1) and 0.75% (T2) of dry pellet weight]. In contrast, weight gain percent and specific growth rate were significantly higher in fish fed with only probiotic and combination of probiotics and Fe than in other experimental treatments (P<0.05). Also, there were no significant differences between treatments in terms of survival rates (P>0.05). The body composition data showed the higher levels of ash, total protein and lower levels of moisture and lipid in the probiotic and Feriron solution-receiving treatments than control group, respectively (P<0.5). In conclusion, our results show that dry diets containing only probiotic and a combination of probiotic and Fe have more effects on the growth and survival of rainbow trout frys than dry diets containing only Feriron solution. Also, the Bio-Plus 2B has good effect on improving the carcass quality of rainbow trout frys.

Seasonal movement, growth and survival of brook trout in sympatry with brown trout in Midwestern US streams

AbstractSeasonal patterns in growth, survival and movement of brook trout Salvelinus fontinalis were monitored in two southeastern Minnesota streams divided into study reaches based on brown trout Salmo trutta abundance. We estimated survival and movement while testing for effects of stream reach and time using a multistrata Cormack–Jolly–Seber model in Program MARK. Multistrata models were analysed for three age groups (age‐0, age‐1 and age‐2+) to estimate apparent survival, capture probability and movement. Survival varied by time period, but not brown trout abundance and was lower during flood events. Age‐0 brook trout emigrated from reaches with low brown trout abundance, whereas adult brook trout emigrated from downstream brown trout‐dominated reaches. Growth was highest in spring and summer and did not differ across streams or reaches for the youngest age classes. For age‐2+ brook trout, however, growth was lower in reaches where brown trout were abundant. Interspecific interactions can be age or size dependent; our results show evidence for adult interactions, but not for age‐0. Our results suggest that brook trout can be limited by both environmental and brown trout interactions that can vary by season and life stage.

Effects of passive integrated transponder tagging methods on survival, tag retention and growth of age-0 brown trout

We evaluated the effect of 12-mm passive integrated transponder (PIT) tag implantation on age-0 brown trout Salmo trutta. The effects of implantation method (i.e. surgical incision or injection) and individual tagger on survival, tag retention and growth were assessed during a 60-day hatchery experiment. Two size classes of fish (total length) were considered: small (50–55mm) and large (56–63mm). For fish≤55mm, survival rate at 60 days was lower for tagged than for control fish (80.7 vs 91.2%, respectively), varied between taggers, but was not affected by the implantation method. For this size class injection resulted in a higher retention rate than surgical implantation (89.4 vs 69.4%, respectively); tag retention also varied among the individual taggers. The growth in length and weight of fish from this class was significantly impaired by tagging at 30 and 60 days (e.g. mean±SD length at 60 days=76.5±8.4mm for tagged fish vs 81.2±7.9mm for control), and individual specific growth rates (SGR) of tagged fish differed between taggers. In contrast, for larger fish (>55mm), neither implantation method nor tagger affected survival (mean=93.2%), tag retention (mean=86.6%), and growth rate (mean±SD specific growth rate=1.07±0.48% during the first 30 days). A slight slowdown in growth (length) appeared within 30 days post-tagging but was compensated at 60 days. Results suggest that implanting 12-mm PIT tags in salmonids smaller than 55mm (TL), by different taggers and using either surgery or injection, may have significant effects on survival, tag retention, and growth.

A bioenergetic assessment of the influence of stocking practices on rainbow trout (Oncorhynchus mykiss) growth and consumption in a New Zealand lake

Summary To investigate the carrying capacity and factors affecting growth of rainbow trout in Lake Rotoiti, we employed a bioenergetics model to assess the influence of stocking rates, timing of releases and prey abundance on growth and prey consumption. We hypothesised that stocking rates and prey abundance would affect growth and prey consumption by influencing per‐capita prey availability, and that the environmental conditions encountered by fish at the time of stocking would affect growth and consumption. Prey consumption of stocked rainbow trout was calculated with the Wisconsin bioenergetics model. We calculated growth trajectories of released trout based on data from stocked trout that were released in spring and autumn from 1993 to 2009 and then re‐captured by anglers. Diet, prey energy density, body mass lost during spawning and lake temperature were measured locally. Stocking timing had no effect on return rates to anglers or length or weight of caught fish. Although trout released in autumn were smaller than those released in spring, autumn‐released trout grew at a faster rate and had similar lengths and weights to spring cohorts after 2 years of growth in the lake. Modelled consumption parameters were negatively correlated with trout population size, suggesting that stocking rates (347–809 fish ha−1 year−1) caused density‐dependent effects on growth. Although common smelt (Retropinna retropinna) accounted for 85% of total prey consumption, no significant relationship was found between prey consumption by individual trout and adult smelt abundance, possibly because trout are targeting smaller smelt that our abundance estimate did not account for. Releasing trout in autumn appears to be advantageous for growth, possibly because (i) temperature is more suitable for growth in autumn–winter than in spring–summer and (ii) prey for small trout is abundant in autumn. Mild winter conditions appear to enhance overwinter survival and growth of rainbow trout in warm‐temperate lakes compared to higher latitudes. This implies that moderately productive warm‐temperate lake ecosystems are highly suitable for trout growth in winter, but less so in summer, when lake stratification and high nutrient levels may create conditions suitable for algal blooms and hypolimnetic deoxygenation. High growth rates of trout in warm‐temperate lakes can therefore be supported by timing releases to coincide with favourable winter conditions.

Environmental induced methylation changes associated with seawater adaptation in brown trout

Migratory trout (sea trout) and sedentary trout (freshwater trout) coexist and interbreed. However, the mechanisms underlying the development of the migrant morphotype are still unclear. At one point parr–smolt transformation is initiated and, as a result, juvenile trout are ready to leave the river and migrate to the sea. The smoltification process has been linked to various factors such as body size, growth rate and the physiological state of the fish. In addition, the process is also strongly influenced by environmental factors such as year, seasonality, water temperature and flow rate. For example, hatchery environment can depress the natural parr–smolt transformation and consequently, the success of the seawater migration of reared trout from these hatchery programmes might be adversely affected. We have investigated whether changes in DNA methylation, by means of MSAP (methylation-sensitive amplified polymorphism), could be involved in anadromy. We identified dramatic differences in genome-wide methylation patterns between hatchery reared and seawater brown trout. Furthermore, we demonstrated that salt enriched diets can trigger short-term genome-wide methylation changes in hatchery reared trout. However, these changes only lasted for a short period of time. Determining the duration of this effect could result in increased survival of hatchery-reared trout in seawater when fed on salt-enriched diets. Altogether, these results suggest that salt-induced alterations in DNA methylation patterns could play an important role in enabling fish acclimation to seawater conditions, potentially with important economic consequences for fish farming.

Survival and movement patterns of central California coast native steelhead trout (Oncorhynchus mykiss) in the Napa River

Drawing on acoustic telemetry this study identifies and describes local and regional scale survival and movement patterns of Central California Coast steelhead (Oncorhynchus mykiss), including their potential utilization of newly restored tidal marsh habitats in the Napa River system. Between April 8th and May 5th of 2010, 20 steelhead smolts ranging in fork length from 164 to 305 mm were collected, tagged with acoustic transmitters, and released in the upper Napa River (above tidal influence). We found no effect of release date (P < 0.001) or size (P < 0.005) on survival estimates based on model likelihoods. Cumulative survival from smolt release location to the Golden Gate Bridge over approximately 77 river kilometers (RKM) was 0.60 (SE = 0.16). Reach-specific survival was lowest in the initial 30 km reach (0.70 SE = 0.1). Survival was higher in San Pablo Bay (0.89 SE = 0.1) and San Francisco Bay (0.96 SE = 0.2). Sixty percent of the fish that entered the ocean were detected on a line of acoustic monitors at Point Reyes approximately 60 km north of the Golden Gate. Average movement rates of smolts were highest in San Pablo Bay (36.6 km∙d-1 SE = 3.3) and San Francisco Bay (28.9 km∙d-1 SE = 6.6). Smolts migrated more slowly in the river (9.0 km∙d-1 SE = 0.9) and ocean (4.1 km∙d-1 SE = 1.2). However, smolt movement rates in the river were dependent on location. Average movement rates of smolts were greatest shortly before their exit from the Napa River (83 km∙d-1 SE = 13.2). Fish were not detected within the recently reconnected former salt production ponds (North, Central, and South units) adjacent to the Napa River. Based on the detection patterns of fish throughout the study area, it appears that most fish were moving at relatively high rates and were not exploring off-channel habitat.

Bigger is not always better: egg size influences survival throughout incubation in brown trout (Salmo trutta)

AbstractClassical optimality models for the evolution of egg size predict a single optimal investment for females inferior to the optimal investment for offspring because of the egg size–fecundity trade‐off and the assumption that ‘bigger is better’ for offspring fitness. Such models do not satisfactorily represent observed within‐population variation in egg size. We measured the influence of maternal investment in egg size on offspring survival in brown trout. Individual measures of egg size, metabolism and survival at different temperatures throughout ontogeny were carried out. We then developed a survival model with regard to egg size, incubation temperature and observed metabolic rate. Small eggs were found to survive at higher rates than large eggs, and the egg size–survival relationship was found to differ among females in accordance with average metabolic rate measured at hatching. These results provide insights for the understanding of the evolutionary significance of egg size variations within a population.

Survival and behavior of juvenile steelhead trout (Oncorhynchus mykiss) in two estuaries in Oregon, USA

Anadromous salmonids are viewed as a prized commodity and cultural symbol throughout the Pacific coast of North America. Unfortunately, several native salmonid populations are threatened or at risk of extinction. Despite this, little is known about the behavior and survival of these fish as the juveniles transition from freshwater to the ocean. Our primary objectives were to estimate survival of juvenile steelhead migrating between trapping sites and the ocean and evaluate whether survival in the estuary varies temporally (within a year) or spatially (within and between estuaries) within the same distinct population segment. We also evaluated whether flow or fork length were correlated with survival and collected information on variables that have been demonstrated to affect smolt survival in other studies to lend insight regarding differences in survival estimates between basins. We compared run timing, migration rate, survival, condition factor, age composition and time of residence in the estuary for steelhead outmigrants from each basin and measured parasite loads in outmigrating steelhead to evaluate potential differences in parasite density and parasite community between basins. In 2009, we implanted acoustic transmitters in 139 wild steelhead smolts in two small rivers on the Oregon Coast. In general, only 40–50 % of the wild steelhead smolts tagged at upstream smolt traps were detected entering the ocean. The majority of mortality occurred in the lower estuary near the ocean. Wild steelhead smolts typically spent less than 1 day in the estuary in both basins. Using similar data from previous studies in the Nehalem and Alsea basins, we showed that survival appears to be negatively correlated with flow in most releases, and in 2009 fork length was not correlated with survival. Our observations provide baseline information on factors that could influence smolt survival through the estuary as well as smolt to adult survival in these basins, and emphasize the importance of monitoring smolt survival in the estuary.

Enhancing selective breeding for growth, slaughter traits and overall survival in rainbow trout (Oncorhynchus mykiss)

Enhancing selection using two-stage selection is normally implemented by pre-selection for tagging weight (BWT) and by final selection for ungutted harvest weight (BWH) and thermal growth coefficient from tagging to harvest (TGCTH). However, selection on harvest traits, i.e., gutted weight (GBWH), visceral percentage (VISW%), condition factor (CFH), and overall survival (SURV), can be enhanced by exploiting correlated traits. It can be hypothesized that the efficiency of two-stage selection on genetic response in BWH and TGCTH is dependent on their genetic (rg) and phenotypic (rp) correlations with BWT and therefore dependent on the time point of pre-selection. The aims of this study were, first, to estimate genetic parameters (heritability: h2, rp, and rg) for BWT (7months), BWS (weight at sorting, 9months), BWH (14months), TGCTH, GBWH, VISW%, CFH, and SURV. Second, these genetic parameters were used in two deterministic simulation studies; i) one- and two-stage selections to compare genetic responses in BWH and TGCTH, and ii) alternative selection indices using correlated traits to compare corresponding accuracy of selection (rIH) for slaughter traits, CFH, and SURV. Genetic parameters were estimated using an animal mixed model in ASReml on 2,041 fish records. The main results showed that, first, rg of BWT was 0.35 with BWH but −0.25 with TGCTH, whereas the rg of BWS was 0.72 with BWH but 0.39 with TGCTH. Pre-selection for BWS led to genetic response of 54.15g in BWH which was higher than the genetic response from pre-selection for BWT (51.90g). Similarly, pre-selection on BWS enhanced correlated genetic response in TGCTH to 0.30g(1/3)/°C*day. In contrast, pre-selection for BWT resulted in lower correlated genetic response in TGCTH of 0.20g(1/3)/°C*day. It can be concluded that genetic improvement of BWH and TGCTH can be enhanced by postponing pre-selection to a later age. However, an optimal time point for tagging and pre-selection should be found to minimize common environmental effects and rearing costs during communal rearing of full-sibs. Second, including GBWH in a selection index can reduce unfavourable selection responses in VISW%. The GBWH is highly genetically correlated with BWH and can be easily indirectly selected. TGCTH is a good predictor for selection for lower VISW%, and higher SURV, but not for higher CFH. To control genetic changes in the condition factor, it should be included to the selection index.

An experimental approach to determine esocid prey preference in replicated pond systems

Lepak JM, Fetherman ER, Pate WM, Craft CD, Gardunio EI. 2012. An experimental approach to determine esocid prey preference in replicated pond systems. Lake Reserv Manage. 28: 224–231. Competitive interactions between salmonids and white suckers (Catostomus commersonii) often result in poor salmonid growth, condition, and ultimately angler catch-per-unit-effort. Fisheries managers frequently introduce hybrid northern pike (Esox lucius) and muskellunge (E. masquinongy), known as tiger muskellunge, as biological control agents to reduce the abundance of undesirable species including white suckers, while simultaneously attempting to create viable recreational fisheries with stocked salmonids. In this study, northern pike were used to evaluate esocid prey preference between naïve, hatchery-reared rainbow trout (Oncorhynchus mykiss) and wild white suckers. Enclosures containing northern pike were stocked with rainbow trout and white suckers at 2 densities (50:50 and 20:80, respectively) to represent different ratios of forage. Weekly sampling by beach seine was used to determine rainbow trout and white sucker mortality. When the experiment was complete, enclosures were drained to determine overall survival of the forage species. Rainbow trout numbers declined precipitously to zero, while 60–75% of white suckers remained across all treatments. This study demonstrated a clear difference in survival of rainbow trout and white suckers (rainbow trout having lower survival) in the presence of northern pike under these conditions. We suggest fisheries managers consider these findings when stocking or managing for piscivores to control undesirable fish species, or to create recreational fisheries, while simultaneously stocking naïve sport fish vulnerable to predation.

Growth, survival, and tag retention of steelhead trout (Oncorhynchus mykiss) and its application to survival estimates

Steelhead trout, Oncorhynchus mykiss, are known to expel acoustic tags which can negatively bias population survival estimates. Tag burden may also affect the development and behavior of smolts, thereby impacting the results of population and behavioral studies. We monitored the growth, condition, and tag expulsion rate of steelhead trout in similar-sized individuals and used these data to adjust survival rates from an acoustic telemetry study conducted in the Sacramento River. Eighty fish were surgically implanted with tags—40 with cylindrical tags of 9 mm diameter and 21 or 24 mm length (V9, Vemco Ltd) and 40 with a 7 mm diameter and 20 mm length tag (V7, Vemco Ltd)—to examine the impact of tag size on peritoneal retention and survival rate of juvenile steelhead trout. A total of 20 % (16/80) of all tags were expelled by smolts during the 143-day study. Ten V9 tags were expelled between day 18 and day 66. Six V7 tags were expelled between day 21 and day 143. A statistical difference was found for retention rate by surgeon even though the surgeons were of equal experience and received the same training. There were no significant differences in the tag retention rate in relation to the tag/body weight ratio, or in growth (weight or fork length) among the control, V7 or V9 treatment groups over the duration of the study. All individuals survived throughout the experiment. Two methods were used to adjust the survival estimates of an acoustic telemetry data set from the Sacramento River based on the tag retention study. First, a simple individual censorship approach in Program MARK was utilized and next ATLAS, a software program designed to compensate for bias in survival estimates caused by tag failures was used. The results of the adjusted survival estimates were not significantly different from the unadjusted rates suggesting that it may be more important to focus on improving surgical techniques to reduce tag expulsion rather than adjusting survival estimates dependent on the study. The surgical techniques utilized in this study did not have significant impacts on the growth rates of either of the tag treatment groups compared to the control. However, tag retention was an issue regardless of the size and weight of the implanted tag and the size of the steelhead.

Effects of dietary vitamin B1 (thiamine) and magnesium on the survival, growth and histological indicators in lake trout (Salvelinus namaycush) juveniles

An interaction of two essential nutrients, thiamine and magnesium (Mg) has been documented in in vitro and in vivo studies in mammalian metabolism. However, the role of this association in poikilothermic vertebrates, such as fish, remains elusive. The purpose of this study was first to investigate the effects of dietary thiamine and Mg, and their interaction in lake trout and second to better understand the mechanism leading to early mortality syndrome (EMS), which is caused by a low thiamine level in embryos of many species of salmonids in the wild. Semi-purified diets (SPD) were prepared to accomplish 2×2 factorial design that were either devoid of or supplemented with thiamine mononitrate (20mg/kg diet), magnesium oxide (700mg/kg diet), or both. Lake trout alevins at the swim-up stage were fed for 10wk one of the SPD diets or a commercial diet at the same rate (2.0–1.5%) based on recorded biomass. Our results showed that the concentrations of thiamine in the trunk muscle and Mg of whole body were closely associated with the dietary level of two nutrients. The interaction of low dietary Mg and thiamine resulted in apparently worsened overt symptoms of thiamine deficiency in lake trout leading to a higher mortality of fish during the seven week long trial (P<0.05). The fish fed a thiamine-devoid and Mg-supplemented diet were presumed to survive longer (10wk) than the fish fed diets devoid of both nutrients (discontinued after 7th wk due to high mortality). However, we did not observe histopathological changes in the brain and liver corresponding to thiamine concentrations in tissues. These data suggest that Mg enhanced utilization of the thiamine remaining in the fish body and its interdependence was consistent with observations in mammals. EMS severity might be worsened when Mg is deficient in parental diets (and consequently in yolk sac) and/or first feed.

Untangling the positive genetic correlation between rainbow trout growth and survival

Explanations for positive and negative genetic correlations between growth and fitness traits are essential for life-history theory and selective breeding. Here, we test whether growth and survival display genetic trade-off. Furthermore, we assess the potential of third-party traits to explain observed genetic associations. First, we estimated genetic correlations of growth and survival of rainbow trout. We then explored whether these associations are explained by genetic correlations with health, body composition and maturity traits. Analysis included 14 traits across life stages and environments. Data were recorded from 249 166 individuals belonging to 10 year classes of a pedigreed population. The results revealed that rapid growth during grow-out was genetically associated with enhanced survival (mean rG = 0.17). This resulted because genotypes with less nematode caused cataract grew faster and were more likely to survive. Fingerling survival was not genetically related to weight or to grow-out survival. Instead, rapid fingerling growth made fish prone to deformations (rG = 0.18). Evolutionary genetics provides a theoretical framework to study variation in genetic correlations. This study demonstrates that genetic correlation patterns of growth and survival can be explained by a set of key explanatory traits recorded at different life stages and that these traits can be simultaneously improved by selective breeding.

Effects of Stocking Catchable‐Sized Hatchery Rainbow Trout on Wild Rainbow Trout Abundance, Survival, Growth, and Recruitment

AbstractThe Idaho Department of Fish and Game has proactively dealt with the potential adverse genetic effects of stocking catchable‐sized hatchery trout in waters that support native salmonids by adopting a policy in 2001 whereby only sterile rainbow trout Oncorhynchus mykiss are stocked in flowing waters; however, concerns regarding the competitive effects of introducing hatchery trout into streams and rivers supporting wild trout have not been addressed. We stocked fish in the middle 3 years of a 5‐year study to assess whether stocking hatchery rainbow trout of catchable size (hereafter, catchables) reduced the abundance, survival, growth, or recruitment of wild rainbow trout in streams. Catchables averaging 249 mm total length (TL) were stocked from 2006 to 2008 at an annual density of 4.2 fish/100 m2 into 12 treatment reaches of stream that were paired with control reaches at least 3 km apart in the same stream in which no stocking occurred. Wild rainbow trout abundance (including all fish ≥75 mm TL), recruitment, survival, and growth were determined from population estimates and recaptures of fish tagged with passive integrated transponder (PIT) tags during mark–recapture electrofishing sampling. The abundance of wild rainbow trout averaged 13.2 fish/100 m2 but varied substantially across sites and years, ranging from a low of 0.5 to a high of 131.3 fish/100 m2; similar variability was observed in recruitment to age 1. Estimates of total annual survival averaged 0.53 based on the population abundance estimates (which allowed for emigration and immigration) and 0.26 based on the PIT‐tag recaptures (which allowed for emigration but not immigration). Our paired study design demonstrated that the abundance, survival, growth, and recruitment to age 1 of wild rainbow trout were all unaffected by stocking catchables. The lack of population‐level effects from stocking catchables was not surprising considering the high short‐term mortality and the socially and physiologically naive behavior typically exhibited by hatchery catchables stocked in lotic systems.

The Interactions of Climate and Biotic Factors on Life History Characteristics and Vital Rates of Yellowstone Cutthroat Trout in Spread Creek, WY

Habitat degradation and introduction of non-native salmonids have caused substantial declines in abundance and distribution of Yellowstone cutthroat trout. Additionally, global climate change is expected to exacerbate current threats through changes to thermal regimes, hydrology, stream productivity, and distributions of non-native species. Understanding how factors such as climate and local stressors (e.g., non-native species) interact to affect Yellowstone cutthroat trout is critical for developing management strategies to enhance future persistence. However, research investigating relationships among these factors and life history characteristics and vital rates of Yellowstone cutthroat trout is lacking. To address this need, we examined the influences of temperature, streamflow, food availability, and presence of brook trout on life history characteristics of Yellowstone cutthroat trout in Spread Creek, Wyoming. We used passive integrated transponder (PIT) tags and a combination of stationary and mobile PIT tag antennae within a capture-recapture framework to monitor growth, movement, and survival of Yellowstone cutthroat trout and brook trout throughout the Spread Creek drainage. Considerable differences existed in frequencies of movements between species and among tributaries. Significant differences existed among growth rates of trout in three tributary streams. Preliminary results suggest the observed differences were driven by the complex interactions of streamflows, fish densities, and prey abundances, rather than stream temperatures. We discuss our results in the context of maintaining diversity of life-history patterns within watersheds as a means to increase metapopulation resiliency. Our findings provide critical information needed to refine climate risk assessments and to better direct limited resources to ensure the long term persistence of the subspecies.

A comparison of the behavior and survival of juvenile coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) in a small estuary system

We used radio and acoustic telemetry to study the behavior and survival of wild steelhead trout (Oncorhynchus mykiss) and hatchery coho salmon (Oncorhynchus kisutch) and steelhead outmigrants in a small coastal estuary during two years. Survival was generally low for hatchery fish but more variable, both within and between years, for wild steelhead. The rate of downstream movement in the river varied both within and between species and was generally not correlated with flow. Both hatchery and wild steelhead tended to spend less than a day in the estuary, and tended to move downstream on outgoing tides. In contrast, hatchery coho salmon spent a longer period of time in the estuary (~8d). On several occasions, coho salmon were observed moving both upstream and downstream between the upper (freshwater) and lower (saline) zones of the estuary. We also documented a high incidence of predation by avian and mammalian predators on coho outmigrants.