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.     

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.     

Historical record of an alligator gar,Atractosteus spatula (Lacépède, 1803), captured on the floodplain of the Middle Mississippi River at Columbia,Illinois, USA

Historical photographs, newspapers, and interviews can provide useful information on the abundance, distribution, and habitat use of rare fish species and can be useful in the development of conservation and management plans for target species. We report on the historical occurrence of Atractosteus spatula (alligator gar) on the Middle Mississippi River (MMR) floodplain near Columbia, Illinois (Monroe County), approximately 280.5 river kilometers above the Ohio River (River Mile 168) during the spring of 1937. Based on measurements taken from a photograph of a captured specimen and Mr. Paul Lopinot's recollection of the specimen's weight, the alligator gar was approximately 2.0 m total length and weighed 60 kg. An additional 25–30 large alligator gar were observed on the floodplain approximately 3.6 km from the river. The loss of seasonally inundated floodplain habitat due to construction of an extensive agricultural levee system on the MMR may be a contributing factor to the decline of the alligator gar in the northern portion of its range.     

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.     

Critical thermal maxima of juvenile alligator gar (Atractosteus spatula,Lacépède, 1803) from three Mississippi‐drainage populations acclimated to three temperatures

Local adaptation may cause thermal tolerance to vary between nearby but distinct populations of a species. During the summer of 2013, alligator gar Atractosteus spatula spawned from broodstock collected from three populations within the Mississippi River drainage separated by a 5° latitudinal gradient were acclimated to three temperatures (25, 30, and 35°C). Ten fish from each population were acclimated at each temperature. CT_Max was determined at each temperature for each population, using five fish for each population‐acclimation temperature pairing. CT_Max for each population‐acclimation temperature pairing was compared using two‐factor anova . CT_Max increased significantly with acclimation temperature (F_2,40 = 600.5, P < 0.001) but population had no significant effect (F_2,40 = 1.882, P = 0.166). Temperature tolerance appears to be consistent across populations of alligator gar, with no evidence of local adaptation.     

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.     

Population prediction and viability model for pallid sturgeon (Scaphirhynchus albus,Forbes and Richardson, ) in the lower Missouri River

Long‐term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River were evaluated via a discrete and stochastic age‐structure population viability model. The intent of this model was to (i) estimate the local pallid sturgeon population size, (ii) quantify the contribution of hatchery‐reared fish to the overall population, (iii) predict the level of natural production needed to create a self‐sustaining population, and (iv) determine the parameters that produce the largest model sensitivity. The model estimated that the wild, adult population size was approximately 6000 fish that remained in the lower Missouri River in 2012 compared to approximately 42 000 hatchery‐reared pallid sturgeon. Under the assumption of no natural recruitment, the population size will continue to decline at approximately 8% annually, with an annual egg to age‐1 survival rate of 0.00011 predicted to maintain a stable population. The model was most sensitive to survival rates of fish ≥ age‐1 and less sensitive to age‐0 survival rates and fecundity. Decreasing or increasing the female spawning interval by 1 year had minimal effect on the overall population trajectory. Recovery management planning for a species such as pallid sturgeon, which is slow‐growing, late‐maturing, and has intermittent spawning would require several years to access recovery potential and management decisions. Barring any unforeseen natural catastrophe, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be far from viable and self‐sustaining.     

Growth and contribution of stocked channel catfish,Ictalurus punctatus (Rafinesque, 1818): the importance of measuring post‐stocking performance

In this study it was sought to quantify post‐stocking growth, survival, and contribution of advanced size (178 mm total length [TL]) channel catfish Ictalurus punctatus fingerlings, something rarely done. Channel catfish populations were evaluated before (May 2010) and after (May to August 2011 and 2012) stocking. Relative abundance, stocking contribution, and growth were different (P < 0.05) in the two study impoundments (lakes Lone Chimney and Greenleaf, Oklahoma). For fish stocked in Lake Lone Chimney, stocking contribution was lower (3–35%), and average length and weight of stocked fish by age‐2 reached 230 mm TL and 85 g, whereas the stocking contribution (84–98%) and growth in length (340 mm TL) and weight (280 g) were higher by age‐2 in Lake Greenleaf. Given these unambiguous differences of post‐stocking performance, benchmark metrics that represent population‐level information such as relative abundance and average length and weight of the sample masked these significant differences, highlighting the importance of marking hatchery‐fish and then following them through time to determine the effectiveness of stocking. These results suggest that stock enhancement programmes would benefit from studies that quantify post‐stocking performance of hatchery fish.     

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.     

Validation of annulus in otolith and estimation of growth rate for Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> in tropical southern Taiwan

The age of Japanese eels (Anguilla japonica) is often estimated from otoliths, but this method has not been fully validated, particularly in tropical areas where the annulus in otolith is considered to be less distinct than in temperate areas. To validate the annuli in Japanese eel otoliths from southern Taiwan, known-age (2 year-old) cultured eels from an eel farm and wild eels from Kao-Ping River were collected. It was found that 26 out of 31 cultured eels (83.9%) showed two clear annuli and the remained 5 eels showed either one or three annuli. The mean (± SD) age of the cultured eels was 1.97 ± 0.4 years. Meanwhile, a clear peak in the mean monthly marginal increment ratio of the otolith in wild yellow and silver eels occurred once a year during winter (November to March). The annual deposition of presumed annuli in otoliths of Japanese eel was validated and the age and growth rate estimation for Japanese eels in the tropical southern Taiwan is deemed feasible. The growth rate of cultured eels was significantly faster than that of wild eels, but it did not differ significantly between sexes for wild silver, yellow or cultured eels. The von Bertalanffy Growth Function parameters (K, and t ₀ ) of the wild eels were estimated as 0.114 ± 0.028 year⁻¹, 1178 ± 171 mm and −0.8 ± 0.2 years, respectively.     

Growth and morphological development of laboratory-reared larval and juvenile three-spot gourami <Emphasis Type="Italic">Trichogaster trichopterus</Emphasis>

Morphological development, including the body proportions, fins, pigmentation and labyrinth organ, in laboratory-hatched larval and juvenile three-spot gourami Trichogaster trichopterus was described. In addition, some wild larval and juvenile specimens were observed for comparison. Body lengths of larvae and juveniles were 2.5 ± 0.1 mm just after hatching (day 0) and 9.2 ± 1.4 mm on day 22, reaching 20.4 ± 5.0 mm on day 40. Aggregate fin ray numbers attained their full complements in juveniles >11.9 mm BL. Preflexion larvae started feeding on day 3 following upper and lower jaw formation, the yolk being completely absorbed by day 11. Subsequently, oblong conical teeth appeared in postflexion larvae >6.4 mm BL (day 13). Melanophores on the body increased with growth, and a large spot started forming at the caudal margin of the body in flexion postlarvae >6.7 mm BL, followed by a second large spot positioned posteriorly on the midline in postflexion larvae >8.6 mm BL. The labyrinth organ differentiated in postflexion larvae >7.9 mm BL (day 19). For eye diameter and the first soft fin ray of pelvic fin length, the proportions in laboratory-reared specimens were smaller than those in wild specimens in 18.5–24.5 mm BL. The pigmentation pattern of laboratory-reared fish did not distinctively differ from that in the wild ones. Comparisons with larval and juvenile morphology of a congener T. pectoralis revealed several distinct differences, particularly in the numbers of myomeres, pigmentations and the proportional length of the first soft fin ray of the pelvic fin.     

Gonadosomatic index and fecundity of Lower Missouri and Middle Mississippi River endangered pallid sturgeon estimated using minimally invasive techniques

Minimally invasive, non‐lethal methods of ultrasonography were used to assess sex, egg diameter, fecundity, gonad volume, and gonadosomatic index, as well as endoscopy to visually assess the reproductive stage of Scaphirhynchus albus. Estimated mean egg diameters of 2.202 ± 0.187 mm and mean fecundity of 44 531 ± 23 940 eggs were similar to previous studies using invasive techniques. Mean S. albus gonadosomatic indices (GSI) for reproductive and non‐reproductive females were 16.16 and 1.26%, respectively, while reproductive and non‐reproductive male GSI were 2.00 and 0.43%, respectively. There was no relationship between hybrid status or capture location and GSI. Mean fecundity was 48.5% higher than hatchery spawn estimates. Fecundity increased as fork length increased but did so more dramatically in the upper river kilometers of the Missouri River. By examining multiple fish over multiple years, the reproductive cycle periodicity for hatchery female S. albus was found to be 2–4 years and river dwelling males 1–4 years. The use of ultrasonic and endoscopic methods in combination was shown to be helpful in tracking individual gonad characteristics over multi‐year reproductive cycles.     

Seasonal growth differences of larval Hyporhamphus picarti (Hemiramphidae) in the Sine Saloum estuary,Senegal

The African halfbeak Hyporhamphus picarti (Hemiramphidae) is one of the most abundant species within the ichthyoplankton community of the Sine Saloum estuary (Senegal). A year‐round occurrence of larvae suggests that the Sine Saloum is an important spawning habitat for this species. Annual fluctuations in water temperature, however, can have severe impacts on the survival probabilities of marine fish larvae. To determine whether temperature has an effect on the growth of H. picarti during its larval development, larval age at length and somatic growth rates were investigated for two contrasting spawning seasons in 2014: February (cold season, 20.8°C) and June (warm season, 26.4°C). In both months H. picarti larvae were sampled at the mouth of the Saloum River using neuston nets. Sagittal otoliths’ increments were counted to estimate the larva age at a given standard length (SL). The age of larvae ranged between 2 and 22 days, with SL of 3.86–21.68 mm, respectively. In order to describe larval age at length during the contrasting spawning seasons, two distinctive Gompertz functions were applied. Accordingly, specimens sampled in June (0.94 ± 0.17 mm per day) exhibited significantly higher somatic growth rates than those sampled in February (0.60 ± 0.06 mm per day). These findings suggest that water temperature is an important factor influencing larval growth in H. picarti. Information concerning the early life stages of H. picarti are scarce and the results of the present study may contribute to a better understanding of the species’ biology and ecology.     

Validation of daily increment formation in otoliths for Gymnocypris selincuoensis in the Tibetan Plateau,China

Daily increment validation in fish otolith is fundamental to studies on fish otolith microstructure, age determination and life history traits, and thus is critical for species conservation and fishery management. However, it has never been done for Schizothoracine fish, which is the dominant component of fish fauna in the Tibetan Plateau. This study validated the daily increment formation of Gymnocypris selincuoensis, as a representative of Schizothoracine fish, by monitoring the growth of hatchery‐reared larvae group and wild‐caught post‐yolk‐sac larvae group under controlled experiments. The results from monitoring the hatchery‐reared larvae group showed that sagittae and lapilli were found in yolk‐sac larvae, and formed 5–7 days before hatching, but asterisci were not found until 11 days post‐hatching. The first increment in sagittae and lapilli was formed in the first day after hatching. The daily periodicity of increment formation was examined and confirmed in sagittae and lapilli of both larvae groups. However, sagittae were better for age determination than lapilli for larvae at earlier days. For larval G. selincuoensis older than 50 days, lapilli were the only otolith pair suitable for larvae daily age determination. This study validated the daily increment formation in Schizothoracine fish for the first time has primary implications to other fishes from this subfamily.     

Reproductive ecology and movement of pallid sturgeon in the upper Missouri River,Montana

Successful recruitment of endangered pallid sturgeon has not been documented in the upper Missouri River basin for decades, and research on the reproductive ecology of pallid sturgeon has been hindered by low sample size. A conservation propagation program was initiated in the 1990s, and the oldest age class of hatchery‐origin pallid sturgeon are becoming sexually mature increasing the number of reproductively‐active fish in the system. However, it is currently unknown how the reproductive ecology of hatchery‐origin pallid sturgeon relates to the few remaining wild fish. Following spring reproductive assessments, weekly relocations were recorded for each individual from late‐May to mid‐July to facilitate comparisons of spawning season movements among reproductive classifications and between spring hydrographs (2015 and 2016) for male pallid sturgeon. Mean total movement distances (±SE) were 104.5 km (18.9) for reproductively‐active wild males, 116.0 km (18.1) for reproductively‐active 1997‐year class males, and 20.6 km (3.0) for non‐reproductively‐active fish of unconfirmed sex. Movement characteristics of reproductively‐active males did not differ between 2015 and 2016 despite a difference of eight days in the timing of peak discharge and a difference of 79 m³/s (16.7%) in magnitude. Male aggregations were observed on the descending limb of the hydrograph in 2016 during temperatures suitable for spawning, but female pallid sturgeon underwent follicular atresia, similar to the other years of the study. Hatchery‐origin pallid sturgeon from the conservation propagation program appear to have retained reproductive characteristics from the wild broodstock, a key finding for a population where local extirpation of the wild stock is imminent.     

Larval competition for food between wild and hatchery-reared ayu, Plecoglossm altivelis Temminck et Schlegel, in culture ponds

To examine the larval competition between wild and hatchery ayu in the culture ponds, mixed rearing of 580 000 wild and 520 000 hatchery larvae was carried out in two 25-m³ ponds for 3 months, in contrast to the control in which 860 000 wild larvae were reared in another pond.
The number of wild larvae in the mixed-rearing treatments decreased rapidly 20 days after the start of mixed rearing, in contrast to hatchery larvae. Mortality of wild larvae was almost 100% at the end of the experiment (3 months), while the hatchery larvae showed the usual survival rate of 15–16%. In the control pond, however, 16% of the wild larvae survived. The wild larvae grew much slower (0.10mmday ^-1) than the hatchery larvae (0·26 mm day ^-1) in the mixed-rearing ponds, whereas the wild larvae in the control pond showed almost the same growth rate (0·24 mm day ^-1) as hatchery larvae. On day 6 the gut fullness of wild larvae was only 30% of that of the hatchery larvae in the mixed-rearing experiments. On day 46 the wild larvae occurred deeper in the mixed-rearing ponds than the hatchery larvae. This depth difference in vertical distribution appeared to cause a disadvantage for the wild larvae in the competition with hatchery larvae, since the food was supplied at the surface. Thus, the wild larvae starved and died.     

Effect of water temperature on activity of wintering age‐0 Acipenser transmontanus and A. brevirostrum: An artificial stream study

The effect of water temperature on behaviour and life history of wintering age‐0 = young‐of‐the‐year (YOY) northern sturgeons (populations using winter refuge habitat) is poorly understood. Using artificial stream tanks, we observed the effect of water temperature on 1) day‐time activity of cultured YOY Kootenai River white sturgeon, Acipenser transmontanus, during two winters (2008 and 2009–2010), and 2) observed day‐time activity of cultured YOY Connecticut River shortnose sturgeon, A. brevirostrum, in the winter, 2009–2010. Activity of YOY was measured every 2 to 7 days by visual or video observations on each fish to determine the mean number of 10 cm² square gridlines on the tank bottom crossed by all fish in each replicate tank (two replicate tanks, 10 fish in each tank). Daily water temperature was recorded by a logger in one tank every 20 min, 24 hr per day. In 2008, YOY A. transmontanus activity was positively related to decreasing mean daily temperature (R² = 0.96, p < 0.01) with 0 to 5 gridlines (range) crossed by all fish during observation periods at the coldest temperature (≤3°C). During the winter of 2009–2010, activity of both species was significantly related to decreasing temperature, and again, a mean of 0 to 5 gridlines (range) were crossed by fish at ≤3°C. We accept the hypothesis that YOY of both species are mostly inactive in the day when winter water temperature decreases to ≤3°C. Using the daytime inactivity temperature threshold of 3°C for YOY, and recent temperatures in river reaches where wild wintering YOY likely occur, we predict (a) wild wintering YOY A. transmontanus are moderately active in the day, may be energy challenged due to elevated temperatures from the warm river discharge by Libby Dam, and have poor survival in the regulated Kootenay River, and (b) wintering YOY Connecticut River A. brevirostrum are moderately active most winter months due to elevated natural river temperatures and may be energy challenged. More research is needed on YOY wintering activity and energetics relative to temperature to insure management of river temperature includes conservation of sturgeons.     

A genetically distinct wild redband trout (<Emphasis Type="Italic">Oncorhynchus mykiss gairdneri</Emphasis>) population in Crane Prairie Reservoir,Oregon, persists despite extensive stocking of hatchery rainbow trout (<Emphasis Type="Italic">O. m. irideus</Emphasis>)

Crane Prairie Reservoir in the upper Deschutes River Basin has historically supported a wild population of migratory Deschutes River redband trout. Owing to its status as a premier destination for recreational angling in Oregon, the reservoir has been stocked with domesticated hatchery rainbow trout since 1955. In recent years the wild redband trout population has experienced a substantial decline. Effects on productivity related to genetic interaction with naturally spawning hatchery-origin fish (fitness risks) have not been determined. The species Oncorhynchus mykiss has been characterized with substantial genetic diversity throughout the Deschutes River Basin that further heightens the challenge of identifying specific conservation needs of wild populations. A conservation plan for Crane Prairie wild redband trout requires a better understanding of the natural reproductive success of out-of-basin hatchery trout in the reservoir tributaries, and the similarity between Crane Prairie redband trout with other extant redband trout populations in the basin. Using a suite of 17 microsatellite nuclear DNA markers, we evaluated the genetic structure among Crane Prairie Reservoir redband trout, hatchery rainbow trout, and two adjacent populations of redband trout from within the Upper Deschutes River Basin. We observed significant heterogeneity between the hatchery and wild Crane Prairie populations that may reflect differences in life histories, differential productivity and assortative mating. The genetic distinctions observed among the three redband trout populations suggest restricted gene flow and genetic drift within the upper basin. Temporally stratified sampling and larger numbers of samples will be necessary to confirm these conclusions.     

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.     

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.