Post‐release growth and dispersal of pond and hatchery‐reared European grayling Thymallus thymallus compared with their wild conspecifics in a small stream

The growth, and dispersal of stocked European grayling Thymallus thymallus, reared in a hatchery (fed dry food pellets) or in a pond (fed natural food), compared with their wild conspecifics was assessed from the recapture of individually tagged fish 168 days after their release into the Blanice River, Czech Republic. Recapture rates and site fidelity were higher for wild T. thymallus than for artificially reared fish. Specific growth rate and upstream or downstream dispersal did not significantly differ between any of the groups of fish. An influence of rearing conditions (pond v. hatchery) on the overall performance of stocked fish was not demonstrated. Initially, lower condition factors of reared T. thymallus were equal to wild fish after recapture, suggesting adaptation of artificially reared fish that remained in the sections studied.     

Recapture rate and growth of hatchery‐reared brown trout (Salmo trutta v. fario,L.) in Blanice River and the effect of stocking on wild brown trout and grayling (Thymallus thymallus,L.)

Hatchery‐reared adult brown trout, Salmo trutta v. fario L., [215–335 mm standard length (L_S), n = 82] were individually tagged and released into three sections of the Blanice River in May 2007. Wild populations of brown trout and grayling, Thymallus thymallus, L., in these sections and three non‐stocked control sections were also tagged. The recapture rate of hatchery‐reared adult brown trout after 6 months (18%, n = 15) was comparable to that of wild adult brown trout in stocked (15%, n = 14) and control (14%, n = 11) sections. The recapture rates of wild brown trout and grayling after 6 months were higher in control sections than in stocked sections, but the differences were not significant. The movement of recaptured large juvenile wild brown trout from stocked sections was significantly higher (36%) than from control sections (9%). Wild brown trout growth and grayling growth were unaffected by stocking with adult hatchery‐reared brown trout.     

Effects of hatchery rearing on Florida largemouth bass Micropterus floridanus resource allocation and performance under semi‐natural conditions

This study examined the growth, activity, metabolism and post‐release survival of three groups of Florida largemouth bass Micropterus floridanus: wild‐caught fish, hatchery fish reared according to standard practice (hatchery standard) and hatchery fish reared under reduced and unpredictable food provisioning (hatchery manipulated). Hatchery‐standard fish differed from wild‐caught fish in all measured variables, including survival in semi‐natural ponds. Hatchery‐standard and hatchery‐manipulated fish showed higher activity levels, faster growth and lower standard metabolic rates than wild‐caught fish in the hatchery. Fish reared under the manipulated feeding regime showed increased metabolic rates and increased post‐release growth, similar to wild‐caught fish. Their activity levels and post‐release survival, however, remained similar to those of hatchery‐standard fish. Activity was negatively correlated with post‐release survival and failure of the feed manipulation to reduce activity may have contributed to its failure to improve post‐release survival. Activity and post‐release survival may be influenced by characteristics of the rearing environment other than the feeding regime, such as stock density or water flow rates.     

Effect of hatchery environment on cranial morphology and developmental stability of Atlantic salmon (Salmo salar L.) from North‐West Russia

The study addresses the effect of hatchery rearing on morphological variation and developmental stability of Atlantic salmon parr from North‐West Russia. Totally, we collected nine samples. Four wild samples were collected from each of the rivers Kola, Umba, Keret’ and Shuia. Five samples of hatchery‐reared parr were the first‐generation progeny of wild adults from these rivers reared separately at the four hatcheries (one hatchery was represented by two samples). Ten meristic and 48 morphometric cranial characters were analysed. We studied the morphological divergence between wild and hatchery fishes of the same river of origin. To analyze developmental stability we used fluctuating asymmetry (random deviations from perfect bilateral symmetry). It was found that hatchery‐reared parr significantly differ from wild parr in both meristic characters and the shape of cranial bones. Different hatcheries caused similar effect on morphological variation in all populations. Fluctuating asymmetry in morphometric characters was significantly higher in hatchery fish than in wild from the Shuia River, indicating a higher level of developmental instability. However, wild parr from the Keret’ River had significantly higher fluctuating asymmetry than cultivated parr of the same origin, possible due to a high infection pressure of the parasite Gyrodactylus salaris Malmberg which has led to significant decline of the wild salmon population in this river, or from genetic changes caused by cultivation. The obtained results indicate a notable effect of hatchery environment on Atlantic salmon’s phenotype.     

Daily age estimation reveals rapid growth of age‐0 alligator gar in the wild

We estimated the daily age and growth of wild age‐0 alligator gar (Atractosteus spatula) from Choke Canyon Reservoir and the Guadalupe and Trinity rivers, Texas, USA. Growth rates of wild age‐0 alligator gar were compared across systems, as well as to alligator gar reared in a Texas hatchery. Estimated ages of alligator gar ranged from 7 to 80 days in Choke Canyon Reservoir (n = 140), 11–73 days in the Guadalupe River (n = 16), and 4–115 days in the Trinity River samples (n = 245). Alligator gar growth was faster in the Trinity and Guadalupe rivers than growth in Choke Canyon Reservoir. Growth of alligator gar in Choke Canyon Reservoir (3.60 ± 0.08 mm/day), the Guadalupe River (4.76 ± 0.35 mm/day), and the Trinity River (5.13 ± 0.07 mm/day) was faster than growth of hatchery reared fish (3.41 ± 0.08 mm/day). This study represents the first account of early growth of age‐0 alligator gar in the wild, and documents some of the fastest growth of age‐0 fish among freshwater fishes. We attribute the rapid growth of wild alligator gar to their quick transition to piscivory at early stages, and their effective use of habitat and resources on inundated floodplains during flood pulses. Future studies should explore the effects of environmental factors on the hatching success, growth, and survival of age‐0 alligator gar.     

Impact of live food on survival and growth of hatchery‐reared sea trout (Salmo trutta trutta L.) parr in the wild

Survival rates and growth parameters of hatchery‐reared sea trout (Salmo trutta trutta L.) fry were determined after stocking in the wild. The larvae were hatchery‐reared for 12 weeks in two groups: fry were fed either on live zooplankton and live chironomidae larvae (LFG), or fed a pellet diet (PFG). The survival rate and specific growth rates were higher in the LFG than in the PFG group. Most effective for hatchery‐reared fish intended for stocking was the natural, live feed. The mean number of chironomid larvae found in the stomachs of fish that were initially captured in the wild was significantly higher in the LFG than in the PFG group. The live diet supplied in the rearing period had a positive impact on the foraging skills of the sea trout fry and their survival in the wild after their release on 24 April 2010.     

Validation of scale‐age determination in European grayling Thymallus thymallus using tag‐recapture analysis

To validate age determination from scales in European grayling Thymallus thymallus, the scale‐read age of fish was compared with the true age obtained by tag‐recapture analysis. A total of 3997 individuals were tagged with visible implant tags and passive integrated transponder (PIT) tags in the River Wylye, south‐west England during 1999–2007. Annual repeat surveys were undertaken and collected scales read without prior knowledge of tag‐recapture age. Accuracy of fish ageing by scales was highest in 1 and 2 year‐old fish but decreased in older fish. In later life stages (>4 years old), underestimation of age occurred and the error in reading scales rose to 51·9% in 5 year‐old fish. Age assigned from scales underestimated the tag‐recapture assigned age by as much as 3 years. This study suggests that use of scales is an appropriate method to age a short‐lived population of T. thymallus inhabiting productive lotic systems. The underestimation of age in older fish, however, needs to be considered in the management of fish stocks because it may lead to undesirable exploitation of population.     

Updated assessment of hatchery‐reared pallid sturgeon (Forbes & Richardson, 1905) survival in the lower Missouri River

As pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905), natural reproduction and recruitment remains very minimal in the lower Missouri River from Gavins Point Dam (river kilometer [rkm] 1305.2) to the confluence with the Mississippi River (rkm 0.0), hatchery supplementation and river‐wide monitoring efforts have continued. Annual survival estimates of hatchery‐reared pallid sturgeon stocked in the lower Missouri River were previously estimated during 1994–2008. Low recapture rates prior to 2006 limited the data available to estimate survival, which resulted in considerable uncertainty for the estimate of annual survival of age‐1 fish. Therefore, the objective was to provide more precise estimates of annual survival of pallid sturgeon using five additional years of stocking and sampling. The Cormack‐Jolly‐Seber model structure provided in program MARK was used to estimate the age‐specific survival estimates. Over 135 000 hatchery‐reared pallid sturgeon were released during 1994–2011 and recaptured at a rate of 1.9%, whereby estimates for the annual survival of age‐0 (Ø = 0.048) and >age‐1 (Ø = 0.931) were similar to those previously reported, but the age‐1 (Ø = 0.403) survival estimate was 52% lower. Post hoc analysis using time‐specific survival estimates indicated lower survival for age‐1 fish post‐2003 year classes, relative to the pre‐2002 year classes. An analysis confirms that hatchery‐reared pallid sturgeon continue to survive in the wild. However, low survival during the first 2 years of life is a management concern as efforts are aimed at maximizing genetic diversity and population growth. A follow‐up analysis also demonstrated the variability of capture rates and survival over time, which reinforces the need to continue to monitor and evaluate mark‐recapture data. The mark‐recapture efforts have provided demographic parameter estimates that remain a critical component for species recovery as these data are incorporated into population models.     

Do stocked hatchery‐reared juveniles ecologically suppress wild juveniles in Salvelinus leucomaenis?

The dominancy of semi‐wild and hatchery‐reared white‐spotted charr Salvelinus leucomaenis juveniles was evaluated using pair‐wise enclosure tests and field stocking tests. The semi‐wild S. leucomaenis originated in a hatchery, being stocked into the test stream as eyed‐eggs. In the pair‐wise enclosure test, the semi‐wild S. leucomaenis dominated the hatchery S. leucomaenis that were of a similar standard length (L_S). The semi‐wild S. leucomaenis were subordinate to hatchery S. leucomaenis that were > 11% larger in L_S. In the field stocking test, the abundance and growth of semi‐wild S. leucomaenis was decreased in the presence of larger hatchery S. leucomaenis (14% larger L_S). Taken together, these results suggest that larger hatchery S. leucomaenis ecologically suppress the smaller semi‐wild S. leucomaenis. Salvelinus leucomaenis juveniles that are stocked with the intention of supplementing natural populations should be < 10% larger than their wild counterparts at the time of stocking to minimize their competitive advantage. The semi‐wild and hatchery S. leucomaenis used in both tests were genetically similar individuals, suggesting that the differences are due to the early rearing environment of either a natural stream or hatchery. The hatchery S. leucomaenis have lower levels of aggression as a result of selection in the hatchery rearing environment. Rearing in a natural stream from the eyed‐egg stage is likely to increase their lowered aggression.     

Supportive breeding boosts natural population abundance with minimal negative impacts on fitness of a wild population of Chinook salmon

While supportive breeding programmes strive to minimize negative genetic impacts to populations, case studies have found evidence for reduced fitness of artificially produced individuals when they reproduce in the wild. Pedigrees of two complete generations were tracked with molecular markers to investigate differences in reproductive success (RS) of wild and hatchery‐reared Chinook salmon spawning in the natural environment to address questions regarding the demographic and genetic impacts of supplementation to a natural population. Results show a demographic boost to the population from supplementation. On average, fish taken into the hatchery produced 4.7 times more adult offspring, and 1.3 times more adult grand‐offspring than naturally reproducing fish. Of the wild and hatchery fish that successfully reproduced, we found no significant differences in RS between any comparisons, but hatchery‐reared males typically had lower RS values than wild males. Mean relative reproductive success (RRS) for hatchery F₁ females and males was 1.11 (P = 0.84) and 0.89 (P = 0.56), respectively. RRS of hatchery‐reared fish (H) that mated in the wild with either hatchery or wild‐origin (W) fish was generally equivalent to W × W matings. Mean RRS of H × W and H × H matings was 1.07 (P = 0.92) and 0.94 (P = 0.95), respectively. We conclude that fish chosen for hatchery rearing did not have a detectable negative impact on the fitness of wild fish by mating with them for a single generation. Results suggest that supplementation following similar management practices (e.g. 100% local, wild‐origin brood stock) can successfully boost population size with minimal impacts on the fitness of salmon in the wild.     

Population characteristics of pallid sturgeon (Scaphirhynchus albus (Forbes & Richardson, )) in the Lower Missouri River

Population characteristics of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. Therefore, data collected from the Nebraska Game and Parks Commission Pallid Sturgeon Population Assessment Program was synthesized to (i) document the population structure of pallid sturgeon by origin (hatchery‐reared or wild), gender, and reproductive readiness, (ii) document the minimum size and age‐at‐maturity by gender, and (iii) document the fecundity rates of the fish that were successfully spawned in the hatchery. During this 4‐year study (2008–2011), relative abundance for wild and hatchery‐reared pallid sturgeon collected with gill nets did not significantly change whereas relative abundance for wild fish using trot lines declined significantly. The proportion of hatchery‐reared pallid sturgeon increased annually, with the population being composed primarily of hatchery‐reared fish. The proportion of reproductively ready females to non‐reproductively ready females was 1 : 2.0, compared to male ratios at 1 : 0.9. Minimum fork length‐at‐maturity was estimated for females at 788 mm and for males at 798 mm. Minimum age‐at‐maturity for hatchery‐reared released fish was age‐9 for females and age‐7 for males. Highest relative fecundity, based on the ovosomatic index, was 10% with an overall mean of 7%. The number of eggs per ml (egg size) was not correlated with fork length (P = 0.0615) or weight (P = 0.0957). Relative condition factor (Kn) for females was significantly different by reproductive condition (P = 0.0014) and Kn for males did not differ between reproductive conditions (P = 0.2634). Detecting shifts in population characteristics are essential not only to understand population dynamics since hatchery inputs and natural perturbations continue to change the population structure but also to assess species recovery efforts to ensure long‐term species sustainability.     

The post‐release process of establishing stable home ranges and diel movement patterns of hatchery‐reared black‐spot tuskfish Choerodon schoenleinii

Post‐release change of home ranges and diel movement patterns of hatchery‐reared black‐spot tuskfish Choerodon schoenleinii were examined using ultrasonic telemetry. Nine hatchery‐reared C. schoenleinii were released in Urasoko Bay, Ishigaki Island, Okinawa, Japan and monitored using ultrasonic telemetry. The fish gradually increased home ranges for c. 3 months before establishing stable home ranges. This pattern of home‐range change might have been associated with the learning process of natural environments and intraspecific and interspecific competition. The fish also showed strong diurnal movement patterns: moving horizontally and vertically during the day and staying in the same place at night. The behaviour observed in this study is highly valuable to determine when, where and how to release the fish as well as how to increase the fitness of the fish before releasing.     

The genetic structure of endangered indigenous populations of the amago salmon, <Emphasis Type="Italic">Oncorhynchus</Emphasis><Emphasis Type="Italic">masou</Emphasis><Emphasis Type="Italic">ishikawae</Emphasis>, in Japan

The amago salmon, Oncorhynchus masou ishikawae, is an endemic subspecies of O. masou in Japan. Owing to the extensive stocking of hatchery fish throughout Japan, indigenous populations of O. m. ishikawae are now on the verge of extinction. We examined the genetic effects of stocking hatchery fish on wild populations in the River Koza, Japan, using microsatellite and mitochondrial DNA (mtDNA) markers. For mtDNA, haplotype mt1, which is common in wild populations, was present exclusively in isolated wild populations assumed to be unaffected by previous stocking, while it was never observed in hatchery fish. Genetic diversity was much higher in wild populations in the stocked area, which shared many mtDNA haplotypes with hatchery fish, than in isolated wild populations with haplotype mt1. Pairwise F _ST estimates based on microsatellites showed significant differentiation among the isolated populations with many microsatellite loci monomorphic. Significant deviation from Hardy–Weinberg equilibrium was observed in wild populations in the area subject to stocking, where a Bayesian-based assignment test showed a high level of introgression with hatchery fish. These results suggest that wild populations with haplotype mt1, which became isolated through anthropogenic environmental change in the 1950–1960s, represent indigenous populations of O. m. ishikawae in the River Koza. They have low genetic diversity, most likely caused by genetic bottlenecks following damming and environmental deterioration, while stocking of hatchery fish over the past 30 years apparently had a large impact on the genetic structure of wild populations in the main channel of the River Koza.     

Passing a seawater challenge test is not indicative of hatchery‐reared Atlantic salmon Salmo salar smolts performing as well at sea as their naturally produced conspecifics

Despite satisfactory reactions to seawater challenge tests indicative of appropriate physiological state, hatchery‐reared Atlantic salmon Salmo salar smolts stocked in the Eira River in Norway between 2001 and 2011 performed less well at sea in terms of growth, age at maturity and survival than smolts of natural origin. The mean rates of return to the river for hatchery‐reared and naturally produced S. salar were 0·98 and 2·35%. In the Eira River, c. 50 000 hatchery‐reared S. salar smolts of local origin were stocked annually to compensate for reduced natural smolt production following regulation for hydroelectric purposes, while a mean of 17 262 smolts were produced naturally in the river. This study demonstrates that, although captive S. salar perform well in seawater challenge tests, hatchery‐reared smolts are not necessarily as adaptable to marine life as their naturally produced counterparts. These findings suggest that production of hatchery‐reared smolts more similar to naturally produced individuals in morphology, physiology and behaviour will be necessary to improve success of hatchery releases. Where possible, supplementary or alternative measures, including habitat restoration, could be implemented to ensure the long‐term viability of wild stocks.     

Maternal effects in vulnerability to eye‐parasites and correlations between behavior and parasitism in juvenile Arctic charr

Hatchery‐reared fish show high mortalities after release to the wild environment. Explanations for this include potentially predetermined genetics, behavioral, and physiological acclimation to fish farm environments, and increased vulnerability to predation and parasitism in the wild. We studied vulnerability to Diplostomum spp. parasites (load of eye flukes in the lenses), immune defense (relative spleen size) and antipredator behaviors (approaches toward predator odor, freezing, and swimming activity) in hatchery‐reared juvenile Arctic charr (Salvelinus alpinus) using a nested mating design. Fish were exposed to eye‐fluke larvae via the incoming water at the hatchery. Fish size was positively associated with parasite load, but we did not find any relationship between relative spleen size and parasitism. The offspring of different females showed significant variation in their parasite load within sires, implying a dam effect in the vulnerability to parasites. However, the family background did not have any effect on spleen size. In the mean sire level over dams, the fish from the bolder (actively swimming) families in the predator trials suffered higher loads of eye flukes than those from more cautiously behaving families. Thus, the results indicate potentially maternally inherited differences in vulnerability to eye‐fluke parasites, and that the vulnerability to parasites and behavioral activity are positively associated with each other at the sire level. This could lead to artificial and unintentional selection for increased vulnerability to both parasitism and predation if these traits are favored in fish farm environments.     

Effects of Hatchery Rearing on Brain Structures of Rainbow Trout, Oncorhynchus mykiss

In this study, we contrast brain morphology from hatchery and wild reared stocks to examine the hypothesis that in salmonid fishes, captive rearing produces changes in brain development. Using rainbow trout, Oncorhynchus mykiss, as a model, we measured eight regions of the salmonid brain to examine differences between wild and hatchery reared fish. We find using multiple analysis of covariance (MANCOVA), analysis of covariance (ANCOVA) and discriminant function analysis (DFA) that the brains of hatchery reared fish are relatively smaller in several critical measures than their wild counterparts. Our work may suggest a mechanistic basis for the observed vulnerability of hatchery fish to predation and their general low survival upon release into the wild. Our results are the first to highlight the effects of hatchery rearing on changes in brain development inbreak fishes.     

Maladaptation and phenotypic mismatch in hatchery‐reared Atlantic salmon Salmo salar released in the wild

Changes in body shape, fluctuating asymmetry (FA) and crypsis were compared among Atlantic salmon Salmo salar fry kept as controls in captivity and those released and subsequently recaptured in the wild according to a before‐after‐control‐impact (BACI) design. Hatchery fish that survived in the wild became more cryptic and displayed a much lower incidence of fin erosion and of asymmetric individuals than control fish kept in captivity. Significant differences in body shape were also apparent, and survivors had longer heads, thicker caudal peduncles and a more streamlined body shape than hatchery controls as early as 20 days following stocking, most likely as a result of phenotypic plasticity and non‐random, selective mortality of maladapted phenotypes. Hatchery‐reared fish typically perform poorly in the wild and the results of this study indicate that this may be due to phenotypic mismatch, i.e. because hatcheries generate fish that are phenotypically mismatched to the natural environment.     

Influence of immune‐relevant genotype on the reproductive success of a salmonid alternative mating strategy

Major histocompatibility complex (MHC) and immune‐relevant gene markers were used to evaluate differences in reproductive success (RS) among naturally spawning coho salmon Oncorhynchus kisutch mate pairs involving an alternative male reproductive phenotype, known as jacks. These mate pairs included both hatchery‐reared and wild origin fish such that three classes were evaluated in two consecutive years (2005 and 2006) using a previously constructed multigenerational genetic pedigree: wild × wild (W × W), hatchery × hatchery (H × H) and wild × hatchery (W × H). Oncorhynchus kisutch jack mate pairs mated randomly based on immune‐relevant genotype in both years; a result consistent with the opportunistic mating strategy of jacks. An association between greater number of alleles shared at three immune‐relevant gene markers and increased RS was found for: W × H mate pairs in 2005 (BHMS429), W × H pairs in 2006 (SsalR016TKU) and W × W pairs in 2006 (OMM3085). No correlation between immune gene diversity and RS was found for H × H pairs in either year. The results suggest that the influence of immune‐relevant genotype on mating success may be different for jacks when compared with previous studies of large adult male O. kisutch.     

Adoption of alternative migratory tactics: a view from the ultimate mechanism and threshold trait changes in a salmonid fish

Partial migration, in which a portion of the population migrates while the rest of the population remains as residents, is a common form of migration. Alternative migratory tactics (AMTs) of partial migration are often determined by polygenic threshold traits. However, the ultimate mechanisms that drive inter‐population variations in threshold traits are not well understood. We present a simple schematic model to explain how the threshold trait changes with fitness consequences under opposing natural and artificial selection forces. We conducted a field test to evaluate the effects of migration difficulty (as a natural selective force) and selective captive breeding (as an artificial selective force) on threshold traits of a partially migratory fish. Male masu salmon Oncorhynchus masou in the Shari River system have AMTs divided into three population categories of hatchery, wild/above the waterfall, and wild/below the waterfall (control). The wild/above the waterfall salmon live in a high‐migration‐cost situation, and the threshold trait changed in a direction that promoted residency. In hatchery salmon, which are produced by migrant‐selective captive breeding, the threshold trait changed in a direction that promoted migration. In contrast, Dolly Varden charr Salvelinus malma displayed only resident tactics, and the threshold trait did not differ between the populations above and below the waterfall, indicating that environment did not explain the variation in the threshold trait. Our results support the model and suggest that opposing natural and artificial selection forces drive variations in the threshold traits and migratory patterns in the studied species. Our conceptual framework for the ultimate mechanism may help to better understand adoption of AMTs and production of diverse intraspecific traits in migratory animals.     

First maturity and spawning periodicity of hatchery‐origin pallid sturgeon in the upper Missouri River above Fort Peck Reservoir,Montana

The pallid sturgeon Scaphirhynchus albus conservation propagation program has augmented declining wild populations since the 1990s and the older age classes of hatchery‐origin fish are beginning to reach sexual maturity in the wild. Currently, the majority of the information available on the age and size at first maturity and spawning periodicity for pallid sturgeon in the upper basin is from captive hatchery‐origin pallid sturgeon (i.e. age and size at first maturity and spawning periodicity) or from wild pallid sturgeon artificially spawned in the propagation program (i.e. spawning periodicity). The purpose of this study was to document age and size at first maturity and spawning periodicity of known age hatchery‐origin pallid sturgeon that have reached maturity in the wild. Radio‐tagged pallid sturgeon in the upper Missouri River upstream of Fort Peck Reservoir were serially sampled in the early‐spring over multiple years and assigned to reproductive classifications each year based on sex‐steroid concentrations. The youngest reproductively‐active male hatchery‐origin pallid sturgeon sampled was 14.5 years old and the youngest female was 18. Hatchery‐origin males were observed having annual (N = 3) and biennial (N = 2) reproductive cycles. The observed spawning periodicity was similar to what has been reported elsewhere for the species. The youngest mature fish in this study are older and larger than what has been reported for those retained in captivity, indicating that body size alone is not a reliable predictor of maturity for pallid sturgeon.